oulu 2018 d 1478 university of oulu p.o. box 8000 fi-90014...
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UNIVERSITY OF OULU P .O. Box 8000 F I -90014 UNIVERSITY OF OULU FINLAND
A C T A U N I V E R S I T A T I S O U L U E N S I S
University Lecturer Tuomo Glumoff
University Lecturer Santeri Palviainen
Postdoctoral research fellow Sanna Taskila
Professor Olli Vuolteenaho
University Lecturer Veli-Matti Ulvinen
Planning Director Pertti Tikkanen
Professor Jari Juga
University Lecturer Anu Soikkeli
Professor Olli Vuolteenaho
Publications Editor Kirsti Nurkkala
ISBN 978-952-62-2009-3 (Paperback)ISBN 978-952-62-2010-9 (PDF)ISSN 0355-3221 (Print)ISSN 1796-2234 (Online)
U N I V E R S I TAT I S O U L U E N S I S
MEDICA
ACTAD
D 1478
AC
TALaura K
rooks
OULU 2018
D 1478
Laura Krooks
MALOCCLUSIONS IN RELATION TO FACIAL SOFT TISSUE CHARACTERISTICS,FACIAL AESTHETICS AND TEMPOROMANDIBULAR DISORDERS IN THE NORTHERN FINLAND BIRTH COHORT 1966
UNIVERSITY OF OULU GRADUATE SCHOOL;UNIVERSITY OF OULU, FACULTY OF MEDICINE;MEDICAL RESEARCH CENTER OULU;OULU UNIVERSITY HOSPITAL
ACTA UNIVERS ITAT I S OULUENS I SD M e d i c a 1 4 7 8
LAURA KROOKS
MALOCCLUSIONS IN RELATIONTO FACIAL SOFT TISSUE CHARACTERISTICS, FACIAL AESTHETICS AND TEMPOROMANDIBULAR DISORDERS IN THE NORTHERN FINLAND BIRTH COHORT 1966
Academic dissertation to be presented with the assent ofthe Doctoral Training Committee of Health andBiosciences of the University of Oulu for public defencein Auditorium F101 of the Faculty of Biochemistry andMolecular Medicine (Aapistie 7), on 2 November 2018, at12 noon
UNIVERSITY OF OULU, OULU 2018
Copyright © 2018Acta Univ. Oul. D 1478, 2018
Supervised byProfessor Pertti PirttiniemiDocent Raija LähdesmäkiProfessor Aune Raustia
Reviewed byDocent Janna Waltimo-SirénDocent Anna-Liisa Svedström-Oristo
ISBN 978-952-62-2009-3 (Paperback)ISBN 978-952-62-2010-9 (PDF)
ISSN 0355-3221 (Printed)ISSN 1796-2234 (Online)
Cover DesignRaimo Ahonen
JUVENES PRINTTAMPERE 2018
OpponentProfessor Timo Peltomäki
Krooks, Laura, Malocclusions in relation to facial soft tissue characteristics, facialaesthetics and temporomandibular disorders in the Northern Finland BirthCohort 1966. University of Oulu Graduate School; University of Oulu, Faculty of Medicine; MedicalResearch Center Oulu; Oulu University HospitalActa Univ. Oul. D 1478, 2018University of Oulu, P.O. Box 8000, FI-90014 University of Oulu, Finland
Abstract
Epidemiological studies on malocclusions in Finland have so far concentrated on children andadolescents. Regarding the Finnish adult population, there is scarce epidemiological knowledgeavailable on malocclusions even though the number of adults seeking orthodontic treatment hasincreased during the last decades. Occlusion is an important factor in the function of themasticatory system, and its role in the aetiology of temporomandibular disorders (TMD) is one ofthe most disputed topics in dentistry. Malocclusions can affect the characteristics of the facial softtissue profile.
The aim of the study was to investigate the prevalence of malocclusions and the role ofocclusion in TMD as well as the association of facial characteristics with malocclusions and facialaesthetics. The study population consisted of subjects from the Northern Finland Birth Cohort1966 (NFBC1966). Data were collected using questionnaires, standardized clinical examinationand facial photos. The profile photographs were analysed using linear and angular soft tissuecephalometric measurements.
The most common malocclusion in the NFBC1966 subjects was lateral crossbite. This studyshowed a significant association between asymmetric malocclusions and TMD. TMD signsassociated significantly with lateral crossbite, scissors bite, negative overjet, and the length andlateral deviation in slide between retruded contact position and intercuspal position (RCP-ICP).Soft tissue profile characteristics were highly correlated with negative overjet. The ANB-anglewas significantly associated with the perception of facial attractiveness.
In conclusion, malocclusions were associated with signs and symptoms of TMD in the Finnishadult population. Overjet appeared to affect the facial profile more than overbite. Facial convexityseemed to be a more important determinant of facial aesthetics for orthodontists than for dentistsand laypersons.
Keywords: aesthetics, cephalometry, cohort study, epidemiology, malocclusion,occlusion, orthodontics, soft tissue profile, temporomandibular disorders, TMDs
Krooks, Laura, Purennan poikkeamien yhteys kasvojen pehmytkudoksiin jaestetiikkaan sekä purentaelimistön toimintahäiriöihin Pohjois-Suomen syntymä-kohortissa 1966. Oulun yliopiston tutkijakoulu; Oulun yliopisto, Lääketieteellinen tiedekunta; Medical ResearchCenter Oulu; Oulun yliopistollinen sairaalaActa Univ. Oul. D 1478, 2018Oulun yliopisto, PL 8000, 90014 Oulun yliopisto
Tiivistelmä
Suomalaiset epidemiologiset tutkimukset purennan poikkeamista ovat tähän asti keskittyneet tar-kastelemaan lapsia ja nuoria. Tarkkaa epidemiologista tietoa suomalaisen aikuisväestön puren-nan poikkeamista on tällä hetkellä saatavilla vain niukasti, vaikka oikomishoitoon hakeutuvienaikuispotilaiden määrä on Suomessa viime vuosina lisääntynyt. Purennalla on tärkeä merkityspurentaelimistön toiminnassa ja sen rooli purentaelimistön toimintahäiriöiden (TMD) etiologias-sa on yksi kiistanalaisimpia aiheita hammaslääketieteessä. Purennan poikkeamat voivat vaikut-taa myös kasvojen pehmytkudosprofiilin piirteisiin.
Tutkimuksen tarkoituksena oli selvittää purennan poikkeamien esiintyvyyttä ja tutkia kasvo-jen piirteiden yhteyttä purennan poikkeamiin sekä kasvojen estetiikkaan. Lisäksi tutkittiin puren-nan poikkeamien yhteyttä TMD:hen. Tutkimusjoukko koostui Pohjois-Suomen syntymäkohortti1966 -tutkimukseen osallistuneista. Tutkimuksen aineisto kerättiin kyselomakkeiden, standar-doidun kliinisen tutkimuksen ja kasvovalokuvien avulla. Profiilivalokuvien analysointi perustuipehmytkudoksen kefalometrisiin lineaari- ja kulmamittauksiin.
Tässä tutkimuksessa yleisin purennan poikkeama oli sivualueen ristipurenta. Asymmetrisetpurennan poikkeamat olivat merkittävästi yhteydessä TMD:hen; erityisesti sivualueen ristipu-renta, saksipurenta, negatiivinen horisontaalinen ylipurenta sekä nivelaseman ja keskipurennan(RCP-ICP) välisen liu’un pituus ja sivuttainen deviaatio. Negatiivisen horisontaalisen ylipuren-nan todettiin vaikuttavan voimakkaasti kasvojen profiiliin. ANB-kulma oli merkitsevästi yhtey-dessä kasvojen arvioituun viehättävyyteen.
Purennan poikkeamilla näyttää olevan yhteys TMD:n oireisiin ja kliinisiin löydöksiin suoma-laisessa aikuisväestössä. Horisontaalinen ylipurenta näyttää vaikuttavan kasvojen profiiliinenemmän kuin vertikaalinen ylipurenta. Kasvojen kuperuus painottuu enemmän oikomishoidonerikoishammaslääkärien näkemyksessä kasvojen estetiikasta hammaslääkäreihin ja maallikoihinverrattuna.
Asiasanat: epidemiologia, estetiikka, kefalometria, kohorttitutkimus, oikomishoito,pehmytkudosprofiili, purennan poikkeama, purenta, purentaelimistön toimintahäiriöt,TMD
To my family
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Acknowledgments
This study was carried out at the Department of Oral Development and
Orthodontics, Research Unit of Oral Health Sciences, Institute of Dentistry, Faculty
of Medicine, University of Oulu. This study was financially supported by the
Finnish Dental Society Apollonia, Oulu University Hospital and the Finnish
Women Dentists’ Association.
I wish to address my greatest thanks to my corresponding supervisor, professor
Pertti Pirttiniemi, D.D.S, Ph.D. I am grateful that you gave me an opportunity to
familiarize myself with orthodontics and research even though I was a first-year
dental student when we first met. Your supportive attitude and inspiration for
science and orthodontics have helped me to work on the verge of my knowledge. I
express my warmest thanks to my other supervisors, docent Raija Lähdesmäki,
D.D.S., Ph.D., and professor Aune Raustia, D.D.S., Ph.D., for their support and
scientific guidance. Raija, I am grateful for the encouragement you gave me when
I had problems. Aune – thank you for the opportunity to do research also in
stomatognathic physiology.
I am grateful to my co-authors Georgios Kanavakis, D.D.S., and Päivi Jussila,
D.D.S., for their help and cooperation during this project. You have both done an
enormous amount of work for this study. Thank you Päivi for everything. I would
also like to thank my co-workers, Anna-Sofia Silvola, D.D.S., Ph.D., Ritva
Näpänkangas, D.D.S., Ph.D., Paula Pesonen, M.Sc., Mimmi Tolvanen, M.Sc.,
Ph.D., and Jari Päkkilä, M.Sc. Especially, I would like to thank you, Anna-Sofia,
for your kindness and helpfulness during this project. You have been a model of a
young orthodontist for me. I am grateful to the research director of the NFBC study,
associate professor Minna Männikkö, Ph.D., and to the other NFBC personnel for
all the support regarding the cohort material.
I also want to thank my follow-up group members, docent Virpi Harila, D.D.S.,
PhD., and docent Tuomo Heikkinen, D.D.S., Ph.D., for their beneficial advice and
the supportive atmosphere. I would like to thank the reviewers of this dissertation,
docent Anna-Liisa Svedström-Oristo, D.D.S., Ph.D., and docent Janna Waltimo-
Sirén, D.D.S., Ph.D., for their careful revision. Anna Vuolteenaho, M.Sc., is
acknowledged for the revision of the English language. I warmly thank my clinical pair and student friend Aija Kaukonen for her
supportive attitude toward my research. You have understood and helped me when
I have had a nearly impossible time schedule in my dental studies and clinical work
because of the research. I also want to thank my dear friend Sonja Sulkava, M.D.,
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Ph.D. student, for the great scientific discussions during this project. I deeply thank
my dear friend Piia Hissa for bringing happiness and warmth to my life.
I want to thank the Health Club Hukka for a relaxing and kind environment
where I could recharge my mental batteries during this project. Thanks to you it has
been easier for me to live in Oulu, far away from family and friends.
My warm gratitude goes to my parents Päivi and Jari as well as to my brother
Anssi who have loved and supported me. Thank you, mother, that you have
encouraged me and pushed me forward also when I have had problems. I am
sincerely grateful to my parents-in-law, Tuula and Raimo, for a loving and
supportive attitude. I have always been warmly welcome to your beautiful home.
Finally, my deepest gratitude belongs to my beloved husband Kalle Kantola,
M.D., Ph.D. I am grateful for your endless support and love. We have had numerous
scientific discussions where you have taught me a scientific way of thinking of life.
Without you this thesis would never had been possible. Along with medical
research, we have shared student life in medical school. It is now time to focus on
the most important things in life and open a new page in our story.
9th September, 2018 Laura Krooks
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Abbreviations
2D Two-dimensional
3D Three-dimensional
ANB-angle The magnitude of discrepancy between the jaws, comprised
of soft tissue A-point, nasion and B-point
A-point Deepest point of the curvature between subnasale and the
most prominent point of the upper lip (also known as soft
tissue A-point)
B-point Deepest point of the curvature between pogonion and the
most prominent point of the lower lip (also known as soft
tissue B-point)
CI Confidence interval
DC/TMD Diagnostic Criteria for Temporomandibular Disorders
E-line Rickett’s aesthetic line
E-plane Rickett’s aesthetic plane
f Aperture
FA Facial Axis
FA-point of
the lower lip The most prominent point of the lower lip
FA-point of
the upper lip The most prominent point of the upper lip
H-angle Holdaway’s H-angle
H-line Harmony line
ICC Intra-class correlation
ICP Intercuspal position
ISO International Organization of Standardization
LAFH Lower anterior facial height
LTR Laterotrusion
μ Mean of a population
N Population size
NFBC Northern Finland Birth Cohort
OR Odds ratio
P Probability value
Pog Soft tissue pogonion
PTR Protrusion
R2 Coefficient of determination
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RCP Retruded contact position
RDC/TMD Research Diagnostic Criteria for Temporomandibular
Disorders
SD Standard deviation
Sl Sublabiale
Sn Subnasale
Sn-N-Sl Subnasale-nasion-sublabiale; cutaneous analogue of ANB-
angle
TMDs Temporomandibular disorders
TMJ Temporomandibular joint
Tr-Na The line between tragus and nasion
Tragus line A vertical reference line at 70 degrees to the line connecting
tragus and nasion
VAS Visual Analogue Scale
X2 Chi-Square
Z-angle Merrifield’s Z-angle
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List of original publications
This thesis is based on the following publications, which are referred to throughout
the text by their Roman numerals:
I Krooks L, Pirttiniemi P, Kanavakis G & Lähdesmäki R (2016) Prevalence of malocclusion traits and orthodontic treatment in a Finnish adult population. Acta Odontol Scand 74(5): 362-367.
II Jussila P, Krooks L, Näpänkangas R, Päkkilä J, Lähdesmäki R, Pirttiniemi P & Raustia A (2018) The role of occlusion in temporomandibular disorders (TMD) in the Northern Finland Birth Cohort (NFBC) 1966. Cranio 8:1-7.
III Kanavakis G*, Krooks L*, Lähdesmäki R & Pirttiniemi P (2018) The influence of overjet and overbite on soft tissue profile in mature adults. A cross-sectional population study. Am J Orthod Dentofacial Orthop. In press.
IV Krooks L, Pirttiniemi P, Tolvanen M, Kanavakis G, Lähdesmäki R & Silvola AS (2018) Association of facial sagittal and vertical characteristics with facial aesthetics in the Northern Finland Birth Cohort 1966. Eur J Orthod. In press.
*The authors contributed equally to the study.
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Contents
Abstract Tiivistelmä Acknowledgments 9 Abbreviations 11 List of original publications 13 Contents 15 1 Introduction 17 2 Review of the literature 19
2.1 Malocclusion ........................................................................................... 19 2.1.1 Definition and classifications of malocclusion ............................. 19 2.1.2 Prevalence of malocclusion .......................................................... 21 2.1.3 Orthodontic treatment ................................................................... 25
2.2 Temporomandibular disorders and occlusion.......................................... 25 2.2.1 Definition of temporomandibular disorders ................................. 25 2.2.2 Aetiology of TMD ........................................................................ 26 2.2.3 Association of malocclusions with signs and symptoms of
TMD ............................................................................................. 28 2.2.4 The role of orthodontic treatment in TMD ................................... 29
2.3 Facial soft tissue characteristics .............................................................. 31 2.3.1 Cephalometric analysis ................................................................. 31 2.3.2 Linear and angular facial measurements ...................................... 32 2.3.3 Facial aesthetics ............................................................................ 33 2.3.4 Facial soft tissue profile and malocclusion ................................... 34
3 Aims of the study 37 4 Subjects and methods 39
4.1 Subjects ................................................................................................... 39 4.1.1 Study design ................................................................................. 39
4.2 Methods ................................................................................................... 40 4.2.1 Questionnaires (I, II) .................................................................... 40 4.2.2 Clinical examination (I-IV) .......................................................... 41 4.2.3 Facial soft tissue measurements (III, IV) ...................................... 45 4.2.4 Evaluation of facial aesthetics (IV) .............................................. 47
4.3 Statistics .................................................................................................. 48 4.4 Error of the method ................................................................................. 49
4.4.1 Error of the method in the clinical examination (I, II, III) ............ 49 4.4.2 Error of the method in facial soft tissue measurements (III,
IV) ................................................................................................ 50
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4.4.3 Error of the method in aesthetic evaluation (IV) .......................... 52 4.5 Ethical considerations ............................................................................. 52
5 Results 53 5.1 Prevalence of malocclusion traits (I) ....................................................... 53 5.2 Prevalence of previous orthodontic treatment (I) .................................... 56 5.3 Association between signs and diagnoses of TMD and occlusal
variables (II) ............................................................................................ 57 5.4 Distribution of TMD signs and diagnoses in subjects having had
orthodontic treatment (II) ........................................................................ 59 5.5 Distribution of occlusal interferences according to orthodontic
treatment in subjects with TMD (II) ........................................................ 62 5.6 Gender differences in facial soft tissue profile (III) ................................ 62 5.7 Correlation between facial soft tissue profile, and overbite and
overjet (III) .............................................................................................. 64 5.7.1 Entire sample population .............................................................. 64 5.7.2 Subgroup analysis ......................................................................... 66
5.8 Aesthetic evaluation (IV) ........................................................................ 67 5.8.1 Differences in perceived attractiveness between the panel
groups ........................................................................................... 67 5.8.2 Comparisons between the study groups and the control
group ............................................................................................. 68 5.8.3 Association between facial attractiveness and facial
characteristics ............................................................................... 68 6 Discussion 73
6.1 The prevalence of malocclusion traits and orthodontic treatment ........... 73 6.2 Association of occlusion with TMD ....................................................... 76 6.3 TMD and orthodontic treatment .............................................................. 77 6.4 Occlusal interferences in TMD subjects with orthodontic
treatment experience ............................................................................... 79 6.5 Association between facial soft tissue profile and malocclusions ........... 79 6.6 Perception of facial aesthetics between the panel groups........................ 81 6.7 Association between facial sagittal and vertical characteristics
and facial attractiveness .......................................................................... 81 6.8 Strengths and weaknesses of the study.................................................... 83 6.9 Clinical implications and future perspectives ......................................... 85
7 Conclusions 87 References 89 Appendix 105 Orginal articles 107
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1 Introduction
Malocclusion is a complex term that covers all deviations of occlusion and jaws
from normal alignment (Lombardi & Bailit 1972). The difference between
malocclusion and normal occlusion is not unambiguous (Harris & Corruccini 2008).
Epidemiologic data regarding malocclusion are an important part in treatment
planning and oral health-care management. Despite this, there is scarce
epidemiological malocclusion data available related to Finnish adult population. In
addition, the number of adults seeking orthodontic treatment has increased in the
last few years (Michelotti & Iodice 2010).
Temporomandibular disorders (TMD) is a collective term for pain and
dysfunction conditions related to the temporomandibular joints (TMJs), the
masticatory muscles and associated structures (Okeson 2013). The aetiology of
TMD is multifactorial and the occlusion as an aetiological factor of TMD is one of
the most disputed topics in dentistry (Chisnoiu et al. 2015, Okeson 2013).
Traditionally, diagnostics and treatment planning in orthodontics are based on
anamnesis, clinical examination and analysis of study models and lateral skull
radiographs (Mitchell 2013). Increasing concern about radiation exposure from
lateral skull radiographs has raised the role of photographs in imaging
malocclusions and facial profile (Dimaggio et al. 2007, Kale-Varlk 2008). Profile
photographs are a low-cost and non-invasive tool to detect facial soft tissue
characteristics (Kale-Varlk 2008, Staudt & Kiliaridis 2009, Wasserstein et al. 2015).
The present study was designed to investigate the prevalence of malocclusion
traits and orthodontic treatment, the role of occlusion in TMD, and the association
of facial soft tissue characteristics with anterior malocclusions and facial aesthetics
among mid-adulthood subjects in the Northern Finland Birth Cohort 1966
(NFBC1966).
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2 Review of the literature
2.1 Malocclusion
2.1.1 Definition and classifications of malocclusion
In the late 1900se, modern orthodontics was developed by Edward H. Angle
(Proffit et al. 2013). He has been regarded as the founder of orthodontics and he
also was interested in occlusion in natural dentition. In the 1890s, Angle developed
the first definition of normal occlusion and classified malocclusions into three
classes based on the sagittal occlusal relationships of the first permanent molars
(Angle 1899). Class I malocclusion exhibits a normal relationship of the first
molars. In class II malocclusion, the lower first molar is positioned distally
compared to the maxillary first molar. In class III malocclusion, the lower first
molar is positioned abnormally mesially compared to the upper first molar.
Andrews (1972) introduced six occlusal characteristics to describe normal
occlusion. The six keys to normal occlusion are correct molar relationship, correct
crown angulation and inclination, no rotations, no spaces, and a plane of occlusion
ranging from flat to a slight curve of Spee (Andrews 1972). Today, the concept of
occlusion includes not only morphological characteristics but also functional and
aesthetic aspects (Svedström-Oristo et al. 2001). Good function has been
considered to be the most important characteristic of an acceptable occlusion
(Svedström-Oristo et al. 2001).
Malocclusion is a complex concept because there is no specific threshold to
separate good occlusion and malocclusion (Harris & Corruccini 2008). According
to Lombardi and Bailit (1972), the concept of malocclusion includes all deviations
of the dentition and jaws from normal alignment. Malocclusion thus comprises
malpositioning of individual teeth, discrepancies between tooth and jaw, and
malrelations of the dental arches (Lombardi & Bailit 1972). It has also been
proposed that “malocclusion is any disharmonious variation from the accepted or
theoretical normal arrangements of the teeth. But, in nature some degree of
variation among individuals of a species is always present” (Grainger 1967).
Malocclusions can be observed in three planes of space: sagittal, vertical and
transversal (Figure 1.). Angle’s classification describes malocclusion in the sagittal
plane based on molar relationship. One can also examine incisor relationship in the
sagittal plane, and this malocclusion can be detected by increased or decreased
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overjet (Figure 1A.). Overjet is a horizontal distance between the labial surfaces of
the central upper and lower incisors (Harris & Corruccini 2008). The incisor
relationship also describes vertical malocclusions which can be detected by
increased overbite and anterior open bite (Figure 1A.). Overbite is the vertical
distance between the incisal edges of the central upper and lower incisors (Harris
& Corruccini 2008). In anterior open bite malocclusion, the incisors do not meet
each other in occlusion and there is a vertical gap between the upper and lower
incisor edges (Harris & Corruccini 2008). When looking at dental arches in
transversal plane, lateral crossbite and scissors bite malocclusions can be detected
(Figure 1B; and 1C.). In lateral crossbite, maxillary buccal cusps occlude too
lingually (Björk et al. 1964). In scissors bite, maxillary lingual cusps occlude too
buccally and the cusps have passed each other (Björk et al. 1964).
Fig. 1. Malocclusions in three planes of space (vertical, sagittal and transversal). A)
Overbite and overjet, B) lateral crossbite and C) scissors bite. Image modified from the
publication of Harris & Corruccini 2008.
An important clinical issue is whether malocclusion is of dental or skeletal origin.
Skeletal malocclusions are a result of defective jaw relationships in any
combination of the three planes of space and can be detected by radiography
(Proffit et al. 2013). By contrast, dental malocclusions are generated by malposition
of the teeth, as well as rotation, abnormal angulations and tipping of the teeth
(Harris & Corruccini 2008).
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2.1.2 Prevalence of malocclusion
Prevalence of malocclusion in children
Most of the epidemiological studies concerning malocclusion have concentrated on
children and adolescents. There are several epidemiological studies which have
shown the prevalence of malocclusion in Finnish child population (Hannuksela
1977, Heikinheimo 1978, Kerosuo et al. 1991, Keski-Nisula et al. 2003,
Myllärniemi 1970). Myllärniemi (1970) investigated the prevalence of
malocclusion in groups of different development stages of the dentition among
Finnish rural children. In that study, crowding was significantly more prevalent
among girls, while boys presented more often with a distal occlusion in the
deciduous and permanent dentitions (Myllärniemi 1970). The prevalence of
malocclusion was approximately three times higher in the permanent dentition
compared to deciduous dentition, and the most common malocclusion in permanent
dentition was deep bite (Myllärniemi 1970).
Hannuksela (1977) examined the prevalence of malocclusion in 9-year-old
Finnish schoolchildren. In that study, the total prevalence of malocclusion was 60.2
per cent (Hannuksela 1977), which is higher compared to the 38.9 per cent detected
by Myllärniemi in mixed dentition (Myllärniemi 1970). The most common
malocclusions were crowding (25.9%) and Class II occlusion (15.0%) (Hannuksela
1977). Differences between genders were not registered.
Heikinheimo (1978) studied 7-year-old Finnish children to determine the need
of orthodontic treatment. The prevalence of malocclusion in that study
(Heikinheimo 1978) was in the line with the study of Hannuksela (Hannuksela
1977) except for higher prevalence of deep bite.
Kerosuo et al. (1991) studied the prevalence of occlusal anomalies in 12- to
18-year-old Finnish urban schoolchildren. In their study, increased overjet and deep
bite were more common among boys than girls. The proportion of children without
any occlusal or space anomalies was 12 per cent. Crowding (40%) was found to be
the most prevalent type of malocclusion, while anterior open bite (1%), scissors
bite (3%), and lateral crossbite (6%) were rare in this adolescent population.
(Kerosuo et al. 1991)
Keski-Nisula et al. (2003) investigated malocclusion in early mixed dentition.
The prevalence of malocclusion varied between 67.7 per cent and 92.7 per cent
depending on threshold level. The study showed that overbite of 4 mm or more was
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more common than overjet of 4 mm or more among children aged 4.0–7.8 years.
(Keski-Nisula et al. 2003)
Thilander and Myrberg (1973) studied the prevalence of malocclusion among
Swedish schoolchildren. In their study, increased overbite was more common than
overjet, and crossbite was detected as the most prevalent occlusal anomaly
(Thilander & Myrberg 1973). A Swedish study on 3-year-old children showed
malocclusion traits (70%) to be common in early childhood as well (Dimberg et al. 2010). In that study, the most frequent malocclusions were anterior open bite, Class
II malocclusion, increased overjet, and posterior crossbite (Dimberg et al. 2010).
Tausche et al. (2004) investigated the prevalence of malocclusion in early mixed
dentition among German children. According to their study, increased overjet and
overbite were the most common types of malocclusion (Tausche et al. 2004). A
high prevalence of malocclusion traits (93%) in Italian school children has been
detected (Ciuffolo et al. 2005). In addition, boys showed an increased overbite
more often than girls (Ciuffolo et al. 2005).
Prevalence of malocclusion in adults
In Finland, most of the epidemiological malocclusion studies have so far
concentrated on children and adolescents. There are only few epidemiological
malocclusion studies based on adults (Laine & Hausen 1983, Pietilä & Nordblad
2008). In the study of Laine and Hausen (1983), the study population consisted of
451 Finnish university students. Laine and Hausen (1983) reported that 42 per cent
of the subjects had at least one occlusal anomaly, and the most frequent
malocclusions were crossbite (19%) and distal molar occlusion (15%). Subjects
who had received orthodontic treatment demonstrated significantly higher
frequency of overjet, anterior open bite and crossbite compared to untreated
subjects (Laine & Hausen 1983). Because the size of the study population was
relatively small and all subjects were selected university students, it is questionable
to generalize these study results to describe Finnish adult population.
A more recent Finnish malocclusion study on adults is part of the Health 2000
Survey (Pietilä & Nordblad 2008). The age of the study population varied from 30
to 75 years or older. In this population-based investigation, the study population
comprised 4,711 subjects and 31 per cent of the subjects displayed at least one
occlusal deviation. The study showed that the most common malocclusions were
anterior or lateral crossbite (18%), large overjet (7%) and scissors bite (6%).
According to the inclusion criteria of the study, only malocclusion types including
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an apparent risk of poor occlusion prognosis were examined. (Pietilä & Nordblad
2008)
When considering the prevalence of malocclusion in different adult
populations, one must keep in mind that malocclusion traits also vary between
countries due to different genetic background (Harris & Johnson 1991, Mossey
1999, Nikopensius et al. 2013, Xue et al. 2010). Another problem when comparing
epidemiologic malocclusion studies is that individual studies have used different
threshold level to separate continuous variables of malocclusion (overjet and
overbite) from normal occlusion (Jago 1974). As noted, there is no clear border to
separate most of the malocclusion traits from normal occlusion (McLain & Proffit
1985).
Although epidemiological malocclusion studies have mostly focused on
children and adolescents, studies from several countries have examined the
prevalence of malocclusion in adulthood (Bock et al. 2011, Brunelle et al. 1996,
Buttke & Proffit 1999, Haralur et al. 2014, Hensel et al. 2003, McLain & Proffit
1985, Stenvik et al. 1996, Tod & Taverne 1997).
In Swedish adult population, the prevalence of malocclusion has been reported
to vary between 17 and 53 per cent (Salonen et al. 1992). Crowding, Angle class
II-1 and crossbite have been detected to be the most prevalent malocclusions among
Swedish population (Salonen et al. 1992). Salonen et al. (1992) also found
significant gender differences concerning malocclusions. Angle Class III
malocclusion, spacing and unilateral crossbite were more common in men while
women showed more often crowding (Salonen et al. 1992). Mohlin (1982) and
Ingervall et al. (1978) have investigated malocclusions separately in women and
men in Sweden. Based on these studies, women have more often distal molar
occlusion compared to men (Ingervall et al. 1978, Mohlin 1982), and conversely,
Swedish men show more often class III malocclusion (Salonen et al. 1992).
In the Netherlands, the most frequent malocclusions were class II malocclusion,
overjet and deep bite (Burgersdijk et al. 1991). In Icelandic adult population, 33.9
per cent of the subjects had at least one malocclusion trait, and the most common
findings were distal molar occlusion (27.7%), mandibular anterior crowding
(13.4%), molar crossbite (11.9%) and increased overbite (11.8%) (Jonsson et al. 2007). In addition, significant sexual dimorphism was detected in the study, with
male dominance for anterior crossbite, mesial occlusion and scissors bite (Jonsson
et al. 2007).
In Germany, the most common malocclusions are reportedly anterior crowding
(62.9%), increased overjet (36.8%), and distal occlusion (34.9%) (Hensel et al.
24
2003). The German study also showed sexual dimorphism concerning
malocclusions so that anterior crowding, increased overjet and distal occlusion
were more frequent among women, while spacing, edge-to-edge bite, excessive
overbite and mesial occlusion were more prevalent in men (Hensel et al. 2003).
Partly different findings have been detected in epidemiological malocclusion
studies conducted outside Europe (Brunelle et al. 1996, Haralur et al. 2014, McLain
& Proffit 1985, Proffit et al. 1998, Tod & Taverne 1997). In the United States adult
population, overbite was more common compared to overjet (Brunelle et al. 1996).
In addition, a more recent study showed that increased overbite was more prevalent
in the United States adult population in contrast to increased overjet (Proffit et al. 1998). Conversely, increased overjet was more common than increased overbite in
an Australian adult study population (Tod & Taverne 1997). Tod and Taverne (1997)
found no significant gender differences for malocclusions in Australia. Among the
Saudi population, 42.8 per cent of the subjects were found to have malocclusion
(Haralur et al. 2014).
Based on earlier published literature, the prevalence of malocclusion among
adults seems to be high and quite at the same level compared to children and
adolescents (McLain & Proffit 1985). There are several factors which might
influence the prevalence of malocclusion in adulthood. Firstly, relapse and poor
stability of the treatment results in the long term are common problems in
orthodontics (Birkeland et al. 1997, Kerosuo et al. 2013). However, a recent study
on treatment of Class II-2 malocclusion has shown very good long-term stability
(Bock et al. 2017). The prevalence of malocclusion in adulthood is also affected by
tooth loss (Liegeois & Limme 1992, Pedersen et al. 1978). Another factor is
insufficient treatment during childhood due to limited access to orthodontic
treatment or refusal from treatment. When considering the prevalence of
malocclusion in adulthood, one must also pay attention to occlusal changes over
time (Bishara et al. 1989, Bondevik 1998, Henrikson et al. 2001). Mandibular
growth has been reported to continue in adulthood (Behrents 1985, Björk 1963).
Behrents (1985) published a work in which he presented that men expressed
mandibular growth at later age compared to women. In addition, several studies
have shown that dental arches do not remain stable during adulthood (Bishara et al. 1989, Bondevik 1998, Bondevik 2015, Henrikson et al. 2001). Mesial drift and
decrease of dental arch length has been reported in a longitudinal study (Harris
1997).
25
2.1.3 Orthodontic treatment
In Finland, orthodontic treatment for children and adolescents is mostly free of
charge and takes place in municipal health centres (Pietilä et al. 2008). By contrast,
orthodontic treatment for Finnish adults is chargeable, and only patients with severe
malocclusion have access to subsidized oral special care. Today, the number of
adult patients seeking orthodontic treatment has increased due to aesthetic
awareness (Michelotti & Iodice 2010).
In Finland, the prevalence of orthodontic treatment experience among adults
has been reported to vary from 11 per cent to 19 per cent (Laine & Hausen 1982,
Pietilä & Nordblad 2008). Among young Finnish adults, 38.5 per cent of the
subjects had received orthodontic treatment (Tuominen et al. 1994). Earlier studies
both globally and in Finland have shown a higher frequency of women having
received orthodontic treatment (Burgersdijk et al. 1991, Jonsson et al. 2007, Laine
& Hausen 1982, Tod & Taverne 1997, Tuominen et al. 1994). The more frequent
history of orthodontic treatment among women might be explained by differences
in treatment seeking and treatment attitude between the genders; Finnish boys have
been reported to be more satisfied with their occlusion without having had
orthodontic treatment (Pietilä & Pietilä 1996).
An earlier Finnish study on adults has reported a higher frequency of
malocclusion among adults with a history of orthodontic treatment than among
adults naive to orthodontics (Laine & Hausen 1983). Similar results have been
reported from elsewhere in Europe (Burgersdijk et al. 1991, Jonsson et al. 2007).
The study results of an earlier Finnish study on adults indicates that orthodontic
treatment in Finland has generally not been successful in eliminating malocclusion
to normal or ideal level (Laine & Hausen 1983).
2.2 Temporomandibular disorders and occlusion
2.2.1 Definition of temporomandibular disorders
Temporomandibular disorders (TMD) is a collective term for pain and dysfunction
conditions related to the temporomandibular joints (TMJs), the masticatory
muscles and associated structures (Okeson 2013). TMD can also be defined as
functional disturbances of the masticatory system (Okeson 2013). Over the years,
the terminology associated with functional disturbances of the masticatory system
has varied and several terms have been introduced (Bell 1982, Laskin 1969,
26
McNeill et al. 1980). Because of the great variety in terminology over the past years,
the American Dental Association introduced the concept temporomandibular disorders in 1983 (Griffiths 1983).
The most common signs and symptoms of TMD are pain and tenderness in the
TMJs and/or masticatory muscles, clicking and/or crepitus in the TMJs, and
limitation and deviations of mandibular movements (Carlsson 1984, Dworkin &
LeResche 1992, Okeson 2013). The most frequent symptom of TMD is pain either
in masticatory muscles or in TMJs (Dworkin & LeResche 1992). The most typical
age when symptoms of TMD occur is between 20 and 40 years (Marklund &
Wänman 2010).
Epidemiological studies have reported that signs and symptoms of TMD are
relatively common in populations (De Kanter et al. 1993, Kuttila et al. 1998,
Rutkiewicz et al. 2006). The prevalence of TMD symptoms has been reported to
vary from 25 to 50 per cent, while clinical findings of TMD have been shown to be
even more frequent (38–90%) in adult populations (Carlsson 1999, Rutkiewicz et al. 2006). In addition, several studies have found a higher prevalence of TMD signs
and symptoms in women than in men (Johansson et al. 2003, Jussila et al. 2017,
Rutkiewicz et al. 2006).
TMD can be classified primarily into three diagnostic subgroups: arthrogenous,
myogenous and combined (McCreary et al. 1991, Schiffman et al. 1990). The
subclassification of TMD is not, however, always unambiguous due to fluctuation
of the diagnostic subgrouping (Kuttila et al. 1997). Dworkin and LeResche (1992)
developed dual-axis research diagnostic criteria of TMD (RDC/TMD), which
included both physical conditions (Axis I) and psychological issues (Axis II). Later,
Schiffman et al. (2014) developed new dual-axis diagnostic criteria for
temporomandibular disorders (DC/TMD) for clinical and research applications
(Schiffman et al. 2014). Based on DC/TMD, TMD diagnoses include myalgia,
arthralgia, headache attributed to TMD, disc displacement with reduction, disc
displacement without reduction, degenerative joint disease and subluxation
(Schiffman et al. 2014).
2.2.2 Aetiology of TMD
Despite the abundance of published literature, the complex aetiology of TMD is
not clearly understood. There is general support that TMD is determined by a
dynamic interaction between biological, psychological and social factors (Carlson
et al. 1993, Dworkin & Burgess 1987, Dworkin et al. 1990, Epker et al. 1999,
27
Fillingim et al. 2011, Kotiranta et al. 2014, Okeson 1995, Sipilä et al. 2013,
Suvinen et al. 2005, Suvinen & Reade 1995). Earlier studies have shown that
disturbed function of TMJ (Costen 1934, Farrar 1978, Reade 1984, Stegenga et al. 1989), masticatory muscles (Schwartz 1959, Yemm 1976) and occlusal factors
(Agerberg & Carlsson 1973, Helkimo 1976) play a role as aetiologic factors of
TMD. In addition, trauma (Brown 1997, De Boever & Keersmaekers 1996,
Pullinger & Seligman 1991, Silvennoinen et al. 1998, Yun & Kim 2005) and
parafunction (Berger et al. 2017, Blanco Aguilera et al. 2014, Jiménez-Silva et al. 2017) can also occur in the background of TMD. Signs and symptoms of TMD
have been found to correlate with impaired general health (Johansson et al. 2004,
Yekkalam & Wänman 2014). Somatic diseases such as headache and pain in the
face, ear and neck are overrepresented among TMD patients (de Leeuw et al. 1994,
Kuttila et al. 1999, Kuttila et al. 2004, Rauhala et al. 2000). Psychological
problems such as depression have been shown to associate with pain-related
symptoms of TMD (Sipilä et al. 2001) and depressiveness has been reported to
increase the risk for chronic facial pain (Sipilä et al. 2013).
The role of occlusion in the aetiology of TMD
Occlusion as an aetiologic factor in the background of TMD has been widely
disputed for many years (Okeson 2013). Today, the role of occlusion as an
aetiologic factor of TMD is still controversial. The conclusion is that occlusion
belongs to the factors related to TMD. Occlusion might affect TMD in two ways:
acute changes in the occlusion can create a protective muscle co-contraction
response or induce orthopaedic instability of the mandible. When considering the
association between occlusal condition and TMD, one must take into account
occlusion both statically and dynamically. (Okeson 2013)
Earlier studies have reported conflicting results regarding the potential
association between occlusal factors and TMD. Several studies have shown
scientific evidence for a relationship between occlusion and TMD (Egermark et al. 2003, Egermark-Eriksson et al. 1983, Egermark-Eriksson et al. 1990, Mohlin et al. 2004, Pullinger & Seligman 2000, Raustia et al. 1995a, Sari et al. 1999, Sipilä et al. 2002, Sipilä et al. 2006, Wang et al. 2009). Disturbances of occlusal
relationships have been shown to be associated with morphological changes in TMJ
internal structure (Raustia et al. 1995b). It has also been suggested that TMD
patients might be more sensitive to even minor changes in occlusion (Le Bell et al. 2002). However, some of these earlier studies showed only a weak correlation
28
between occlusion and TMD (Egermark et al. 2003, Egermark-Eriksson et al. 1983,
Egermark-Eriksson et al. 1990, Pullinger & Seligman 2000), and moreover, a
number of studies have not detected any association at all between occlusal factors
and TMD (Carlsson et al. 2002, LeResche 1997, Mohlin et al. 2007, Reynders
1990, Seligman & Pullinger 1991). Notably, most of the earlier studies have only
focused on the association between occlusion and TMD without considering any
causal factors.
2.2.3 Association of malocclusions with signs and symptoms of
TMD
Even if the causal role of occlusion in TMD is still controversial, several studies
have reported a correlation between TMD signs and symptoms and malocclusions
(Alamoudi 2000, Celić et al. 2002, Raustia et al. 1995a). Based on the earlier
studies, TMD has been reported to be associated with crossbite, anterior open bite,
deep bite, Angle Class II malocclusion, Angle Class III malocclusion and increased
overjet (Alamoudi 2000, Celić et al. 2002, Egermark et al. 2003, Egermark-
Eriksson et al. 1990, Haralur et al. 2014, Jämsä et al. 1988, Marklund & Wänman
2010, Mohlin & Kopp 1978, Mohlin & Thilander 1984, Pullinger & Seligman 2000,
Sari et al. 1999, Schmitter et al. 2007, Thilander et al. 2002). In addition, crowding
has been found to be more common among TMD subjects compared to non-TMD
subjects (Mohlin et al. 2004). Furthermore, subjects with a higher number of
missing posterior teeth have been reported to have a higher prevalence of TMD
(Wang et al. 2009). By contrast, some earlier studies have found no association
between malocclusion and self-reported TMD symptoms (Gesch et al. 2005, John
et al. 2002).
Anterior open bite has been shown to increase the risk for myofascial pain
(Schmitter et al. 2007). In addition, anterior open bite has been demonstrated to be
associated with internal derangement (Byun et al. 2005) and osteoarthrosis of the
TMJ (Seligman & Pullinger 1989). Anterior crossbite has been found to be
associated with a reduced eminence height of TMJ (Wohlberg et al. 2012).
Posterior crossbite has been shown to be associated with disk displacement, and
increased overjet has been detected among osteoarthrosis patients (Pullinger et al. 1993, Pullinger & Seligman 2000).
Earlier studies have also investigated a correlation between TMD and occlusal
interferences between the upper and lower jaw. Occlusal interferences have been
reported to be more important than morphologic malocclusion in explaining the
29
existence of TMD (Egermark-Eriksson et al. 1983). Significant correlation has
been shown between TMD and mediotrusive interferences as well as RCP-ICP
slide (Haralur et al. 2014). In addition, TMD signs have been demonstrated to
correlate weakly with mediotrusive interferences in a young adult population (Celić
et al. 2002). The length of the sagittal RCP-ICP slide and its lateral deviation have
been shown to correlate with the signs and symptoms of TMD (Raustia et al. 1995a).
In addition, mediotrusive interferences have been detected among patients with
mandibular pain and dysfunction (Mohlin & Kopp 1978).
2.2.4 The role of orthodontic treatment in TMD
During the last decades, the role of orthodontic treatment as a contributing or risk
factor for development of TMD has been disputed. At least two different factors
have been introduced to explain how orthodontic treatment might affect TMD
(Michelotti & Iodice 2010, Olsson & Lindqvist 2002). It has been speculated
whether internal derangement may be the consequence of the changes in condylar
position during orthodontic treatment (Michelotti & Iodice 2010). Orthodontically
treated subjects have shown more often flattening of the articular surface and
subcortical sclerosis in panoramatomograms than untreated individuals (Peltola
1993). Lateral malocclusions have been detected to show a more asymmetric
position of the condyles (Pirttiniemi et al. 1991). In addition, condyle position
asymmetry has been found more often in TMD patients, and significant correlation
has been detected between signs and symptoms of TMD and occlusal variables
describing asymmetry (Raustia et al. 1995a). Therefore, the authors discussed the
indications for orthodontic treatment to prevent the predisposing influence of
occlusal discrepancy on TMD (Raustia et al. 1995a). Along with changes in
condylar position, another possible explanatory factor for the effect of orthodontic
treatment on TMD might be occlusal interferences (Olsson & Lindqvist 2002).
Earlier studies have found differences between orthodontically treated and
untreated subjects regarding the prevalence of TMD (Egermark & Thilander 1992,
Henrikson et al. 2000). In the study of Henrikson et al. (2000), the prevalence of
muscular signs of TMD decreased among orthodontically treated Class II subjects
two years after treatment. In addition, functional occlusal interferences were
reduced in orthodontically treated subjects compared to untreated Class II group
and normal occlusion group (Henrikson et al. 2000). An earlier study has found
less frequent symptoms of TMD after orthodontic treatment (Olsson & Lindqvist
1995). No propensity for increased prevalence of TMD signs has been found among
30
orthodontically treated subjects (Egermark-Eriksson et al. 1990, Henrikson et al. 2000).
Some studies found no differences regarding the symptoms of TMD when
comparing orthodontically treated and untreated subjects (Dahl et al. 1988,
Egermark et al. 2003, Sadowsky & Polson 1984). A lower percentage of TMD
symptoms has been detected among orthodontically treated subjects compared to
untreated group, even if the differences were not statistically significant (Sadowsky
& Polson 1984). On the other hand, in a Japanese study no differences were found
between orthodontically treated and untreated subjects concerning the incidence of
TMD signs (Hirata et al. 1992). A more recent study has shown that orthodontic
treatment is not related to signs and symptoms of TMD (Macfarlane et al. 2009).
Based on a meta-analysis, traditional orthodontic treatment has not been shown to
increase the prevalence of TMD (Kim et al. 2002). According to a review article,
orthodontic treatment carried out during adolescence does not in general affect the
risk for development of TMD in adulthood (McNamara et al. 1995).
Along with conventional orthodontic treatment, several studies have
investigated the effect of orthognathic surgery on TMD (Abrahamsson et al. 2013,
Panula et al. 2000, Rusanen et al. 2008, Wolford et al. 2003). Changes of the facial
skeleton after orthognathic surgery in patients with dentofacial deformities might
affect TMJs, masticatory muscles, surrounding soft tissues and changes of TMJ
symptoms (Jung et al. 2015). Improved occlusal relationships between the upper
and lower jaw, meaning improved masticatory function, have been noted as greatly
increased electromyographic activity in masticatory muscles during chewing after
mandibular sagittal split osteotomy (Raustia & Oikarinen 1994). The signs and
symptoms of TMD have been reported to decrease significantly after
surgical/orthodontic or orthodontic treatment (Rusanen et al. 2008, Silvola et al. 2015). In addition, longitudinal studies have reported a lower prevalence of signs
and symptoms of TMD after orthognathic surgery (Abrahamsson et al. 2013,
Panula et al. 2000). Panula et al. (2000) found a significant decrease in headache,
joint pain on palpation and muscle palpation tenderness after orthognathic surgery.
It has also been found that the association between self-reported symptoms of TMD
and severity of malocclusion in orthognathic-surgical patients is not unambiguous
(Svedström-Oristo et al. 2016). On the other hand, significant worsening of the
TMJ dysfunction has been reported after orthognathic surgery (Wolford et al. 2003).
In addition, orthognathic patients have developed condylar resorption after surgery
(Wolford et al. 2003). It has been concluded that orthognathic surgery seems to
31
have a mainly positive outcome regarding TMD pain in patients with dentofacial
deformities (Abrahamsson et al. 2013, Panula et al. 2000, Silvola et al. 2015).
2.3 Facial soft tissue characteristics
2.3.1 Cephalometric analysis
The craniofacial complex can be divided into five structural categories: the cranium
and cranial base, the skeletal maxilla, the skeletal mandible, maxillary
dentoalveolar structures, and mandibular dentoalveolar structures (Proffit et al. 2013). Cephalometry is a study of the facial bones based on the analysis and
interpretation of the patients’ radiographs (Mitchell 2013). Cephalometric analysis
is usually performed by examining lateral skull radiographs (Mitchell 2013).
Cephalometrics is an essential diagnostic tool for orthodontist to examine
malocclusion and skeletal pattern of the craniofacial complex (Proffit et al. 2013).
The purpose of cephalometric analysis is to find out how the cranial base, teeth and
jaws are related to each other (Proffit et al. 2013). Cephalometric analysis typically
includes localization of the cephalometric landmarks, determination of
cephalometric planes, linear and angular measurements, and interpretation of the
study results, preferably based on normal values of the same population.
Although cephalometrics have traditionally focused on skeletal and dental
measurements, towards the end of the past millennium more attention has been paid
on measurement of facial soft tissue characteristics (Bergman 1999). There is a
large body of published literature regarding associations between facial soft tissue
features and skeletal pattern (Halazonetis 2007, Kasai 1998, Rose et al. 2003,
Saxby & Freer 1985, Staudt & Kiliaridis 2009). Hard tissue variables, such as
sagittal relationship between the jaws (ANB-angle), lower facial height, point A
convexity and position of the lower incisors have been reported to be associated
with facial soft tissue profile (Kasai 1998, Saxby & Freer 1985, Staudt & Kiliaridis
2009).
Cephalometric facial soft tissue analysis
Cephalometric facial soft tissue analyses are important in diagnostics, treatment
planning and for understanding possible changes occurring in facial appearance as
a result of orthodontic treatment (Bergman 1999, Holdaway 1983). However, the
32
interpretation of facial soft tissue analysis is not simple because cephalometric
values might be influenced by several factors, such as skeletal relationships,
position of the teeth, soft tissue thickness, ethnic origin, gender and age (Bergman
1999, Saxby & Freer 1985). Moreover, they can be altered by momental factors
related to muscular activity, lip position and facial expression at the time of
exposure, particularly in children. Cephalometric analysis of facial soft tissue is
also an important part of the treatment plan in orthognathic surgery (Oh et al. 2017).
A good occlusion based on the conventional cephalometrics does not always
produce a balanced facial structure (Bergman 1999).
Most of the earlier studies have investigated facial soft tissue features using
lateral skull radiographs (AlBarakati 2011, Halazonetis 2007, Saxby & Freer 1985).
Radiation exposure by cephalometric radiographs and radiation protection
concerns have recently raised the role of profile photographs in soft tissue facial
analysis (Dimaggio et al. 2007, Kale-Varlk 2008). Correlation between hard and
soft tissue variables has been reported to be higher when measurements have been
performed from lateral cephalograms compared to profile photographs (Staudt &
Kiliaridis 2009). A more recent study has shown, however, that the analysis of
profile photographs is a noteworthy method to study sagittal soft tissue
relationships (Wasserstein et al. 2015).
2.3.2 Linear and angular facial measurements
Quantitative facial soft tissue profile analysis based on photographs can be divided
into two categories: linear and angular facial analyses (Fernández-Riveiro et al. 2002, Fernández-Riveiro et al. 2003). Several authors have studied the soft tissue
facial profile by using linear measurements (Arnett & Bergman 1993a, Arnett &
Bergman 1993b, Burstone 1958, Holdaway 1983, Ricketts 1968, Subtelny 1959).
Subtelny (1959) observed that facial soft tissue changes occurring during growth
are not analogous to changes in the skeletal profile. Various authors have introduced
new linear measurement variables to be used. Ricketts (1968) described the
aesthetic E-plane and E-line while Holdaway (1983) introduced the H-line. The
importance of natural head position in the soft tissue facial analysis has earlier been
demonstrated (Arnett & Bergman 1993a). A study based on facial photographs
described linear measurements of the soft tissue facial profile in an attempt to
identify an average profile of young white adults (Fernández-Riveiro et al. 2002).
Numerous soft tissue angular variables have also been described by various
authors (Anić-Milosević et al. 2008, Arnett & Bergman 1993a, Arnett & Bergman
33
1993b, Fernández-Riveiro et al. 2003, Holdaway 1983, Merrifield 1966). For
example, the H-angle (formed by the soft tissue facial plane and harmony line)
(Holdaway 1983), the Z-angle (formed by the profile line and the Frankfurt plane)
(Merrifield 1966) and angle of convexity (Legan & Burstone 1980) have been
created to evaluate facial soft tissue profile. The Z-angle describes the lower facial
relationship in the facial profile (Merrifield 1966). H-angle has been designed to
measure prominence of the upper lip or retrognathism of the soft tissue chin
(Holdaway 1983). Several studies have also investigated facial profile among
different malocclusions in relation to the angle of facial convexity (Arnett &
Bergman 1993a, Arnett & Bergman 1993b, Godt et al. 2013).
2.3.3 Facial aesthetics
Along with favourable occlusion, a harmonious and balanced facial appearance is
one of the main goals in orthodontic treatment (Bergman 1999, Spyropoulos &
Halazonetis 2001). Therefore, facial soft tissue studies have traditionally
concentrated on facial aesthetics (Merrifield 1966, Peck & Peck 1970).
Examination of facial appearance is an essential part in comprehensive treatment
planning because orthodontic treatment may alter facial soft tissue characteristics.
Profile outline has traditionally been used to evaluate facial attractiveness
(Spyropoulos & Halazonetis 2001).
Facial aesthetics is also commonly a major reason why patients seek
orthodontic treatment (McKiernan et al. 1992, Nurminen et al. 1999, Silvola et al. 2014). Improved facial appearance can affect individuals’ self-esteem and social
interaction (Knight & Keith 2005). In addition, aesthetic change in the craniofacial
complex is related to patient’s emotional wellness (Ackerman 2006). Treatment of
severe malocclusions has been demonstrated to improve the aesthetic satisfaction
and oral health-related quality of life (Silvola et al. 2014).
Due to the subjective nature of the evaluation of facial aesthetics, several
previous studies have used different panel groups to assess facial attractiveness
(Maple et al. 2005, Naini et al. 2012, Romani et al. 1993). A panel study, based on
professionals and laypersons, is an essential research method for the orthodontist,
since professional opinion regarding facial appearance may not be in line with the
patient’s perception. Earlier panel studies have shown contradictory results
regarding agreement of facial attractiveness between professionals and laypersons.
Some studies have found agreement in perception of facial attractiveness between
orthodontist or orthodontic residents and laypersons (Maple et al. 2005, Shelly et
34
al. 2000, Soni et al. 2016). Conversely, other studies found no agreement with
respect to facial attractiveness between orthodontist and laypersons (Bell et al. 1985, Cochrane et al. 1997, Cochrane et al. 1999). Orthognathic patients have been
demonstrated to be more critical than laypersons in their aesthetic opinion
regarding sagittal position of the mandible (Naini et al. 2012).
Previous studies have shown that both sagittal and vertical proportions of facial
soft tissue have an influence on facial attractiveness (Johnston et al. 2005a,
Johnston et al. 2005b, Varlik et al. 2010). Normal sagittal position of the mandible
and normal lower anterior facial height have been demonstrated as the most
important characteristics for aesthetic facial appearance (Johnston et al. 2005a,
Johnston et al. 2005b, Naini et al. 2012, Varlik et al. 2010). On the other hand, the
more extreme the deviations in vertical and sagittal dimensions the less attractive
has been the perception of facial appearance by raters (Maple et al. 2005).
2.3.4 Facial soft tissue profile and malocclusion
Earlier studies have demonstrated that facial soft tissue characteristics are related
to malocclusions (Bittner & Pancherz 1990, Dimaggio et al. 2007, Godt et al. 2013,
Maurya et al. 2014).
Children and adolescents
Godt et al. (2013) investigated the correlation between facial morphology and
sagittal and vertical malocclusions in 4- to 6-year-old children by 3D photographs.
According to the study, Class II malocclusion with increased overjet and Class III
malocclusion with decreased overjet influenced soft tissue morphology. Class III
children demonstrated increased total face angle (glabella-subnasale-pogonion)
and more concave profiles compared to the control group. Class II malocclusion
was shown to associate with a more anterior upper lip position. (Godt et al. 2013)
Dimaggio et al. (2007) studied the relationship between posterior occlusion
and soft tissue profile in 6-year-old children by 2D profile photographs. The study
showed that all angular variables and facial heights were significantly influenced
by variation in molar relationship (Dimaggio et al. 2007). For example, the facial
convexity angle was largest in children with Class III malocclusion while the Sn-
N-SI–angle (subnasale–nasion–sublabiale, cutaneous analogue of ANB-angle) was
greatest in children with Class II malocclusion (Dimaggio et al. 2007). Based on
35
3D soft tissue facial analysis on children, more convex faces in the sagittal plane
have been detected among Class II subjects (Ferrario et al. 1994).
Bittner and Pancherz (1990) have studied sagittal and vertical malocclusion
and their relationship to facial morphology in 12- to 14-year-old children by facial
photographs and lateral headfilms. According to the study, large overjet was most
related to facial appearance. In contrast, overbite and negative overjet could not be
detected on facial photographs. Thus, skeletal Class I and Class III malocclusions
were found to be problematic to detect from facial photographs. (Bittner &
Pancherz 1990)
Wasserstein et al. (2015) compared lateral photographic and radiographic
sagittal analyses in relation to Angle’s classification among adolescents. According
to the study, Class III malocclusion has the most characteristic soft tissue pattern.
The soft tissue angles A-N-B and A-N-Pog were reported to be significantly
different in Angle Class III malocclusion compared to Class I and Class II
malocclusions. (Wasserstein et al. 2015)
Adults
Staudt and Kiliaridis (2009) examined 2D profile photographs and lateral
cephalograms among young men in an attempt to detect Class III skeletal
discrepancies. According to the study, facial soft tissue features correlated highly
with skeletal structures of skeletal Class III subjects. Therefore, the authors of the
study concluded that profile photographs are reliable to detect a skeletal Class III
discrepancy. (Staudt & Kiliaridis 2009)
Maurya et al. (2014) investigated soft tissue features of Class II-1 malocclusion
in young adult population using lateral cephalograms. A more convex soft tissue
profile has been reported among Class II malocclusion (Hameed et al. 2008,
Maurya et al. 2014).
Saxby and Freer (1985) studied dentoskeletal variables in relation to the soft
tissue profile in females. In their study, overbite was negatively correlated with
horizontal position of the soft tissue B-point and its relation to soft tissue A-point
(Saxby & Freer 1985). On the other hand, overjet has only been shown to correlate
with upper lip convexity (Saxby & Freer 1985).
Even though previous studies have found associations between malocclusions
and facial soft tissue characteristics, none of the past studies included a large cross-
sectional cohort of middle-aged patients. In addition, most of the earlier
investigations have been based on lateral skull radiographs. An earlier profile
36
photograph study concluded that profile photographs could be useful for initial
consultations and screening of populations (Staudt & Kiliaridis 2009). Therefore,
deeper understanding is needed in order to conclude the underlying occlusal
relationships by evaluating facial soft tissue features using 2D profile photographs.
37
3 Aims of the study
This study was designed and carried out to increase understanding and knowledge
about the relationships between occlusal features and function and facial aesthetics
in adults. It was based on the Northern Finland Birth Cohort 1966 (NFBC1966).
The specific research objectives were:
1. To investigate the prevalence of malocclusion traits and orthodontic treatment
in middle-aged Finns (I).
2. To investigate the role of occlusion in TMD including orthodontically treated
individuals (II).
3. To study how deviations from normal overbite and overjet are reflected in
adults’ soft tissue facial profile (III).
4. To study whether there is agreement between orthodontists’, dentists’ and
laypersons’ perceptions of facial aesthetics (IV).
The working hypothesis was that there are differences in the prevalence of
malocclusions between genders and between orthodontically treated and untreated
groups (I). In study II, the hypothesis was that occlusal factors are associated with
TMD. It was also hypothesized that sagittal and vertical occlusal relationships
affect facial soft tissue profile (III). Facial aesthetics was hypothesized to be
associated with both facial sagittal and vertical soft tissue characteristics (IV).
38
39
4 Subjects and methods
4.1 Subjects
The study population for this investigation belongs to the Northern Finland Birth
Cohort 1966 (NFBC1966). The NFBC1966 is an epidemiological and longitudinal
research programme and its main goal is to improve the health and well-being of
the population in Northern Finland. The research programme is supervised by the
Department of Health Sciences, Faculty of Medicine, University of Oulu. The
NFBC1966 consists of 12,058 live-born individuals who were born in the two
northernmost provinces of Finland, Oulu and Lapland, in 1966. These children
correspond to 96.3 per cent of all births in Oulu and Lapland in 1966 (Rantakallio
1988).
All subjects of the NFBC1966 participated in follow-up examinations during
their lives at the ages of 6–12 years, 14–16 years, 31 years and 46 years. The first
two follow-up examinations included registration of variables related to general
health. The 31-year follow-up study also included a questionnaire concerning facial
pain. Of the 12,058 individuals of the whole cohort, 10,321 were alive in 2012;
3,150 of them lived in the city of Oulu (or within a radius of 100 km) and were
invited to take part in the clinical oral and dental examination. In 2012, a 46-year
follow-up study included a clinical oral and dental health examination with occlusal
assessment and cariological, periodontological and stomatognathic examination.
Of the invited individuals, 1,964 (912 men, 1,052 women) volunteered to
participate in the clinical examination.
4.1.1 Study design
In study I, the material consisted of 1,964 individuals (1,052 women, 912 men)
who all participated in the clinical oral and dental health examination. In study II,
the total number of subjects was 1,962 (1,050 women, 912 men) since two subjects
were excluded due to their refusal to give their data for the investigation after study
I. The subjects were included in study III if they had full records from the clinical
examination and the diagnostic quality of the photographs was good. In addition,
subjects with craniofacial syndromes or severe facial deformities were excluded.
Based on these criteria, the study population in study III comprised 1,630
individuals (711 men and 919 women). In study IV, two study groups and one
40
control group were selected based on linear and angular facial soft tissue
measurements. Based on the lower anterior facial height (LAFH) and soft tissue
ANB-angle, the following subgroups were created: LAFH min (30 subjects),
LAFH max (30 subjects), ANB min (30 subjects) and ANB max (30 subjects)
(Table 1.). A more detailed description of the study groups in study IV is shown in
Table 1. For the control group, subjects were first sorted with LAFH%. A median
value was located and 100 subjects nearest to the centre point of the study
population were chosen. The same sorting was performed for soft tissue ANB.
After sorting, both lists were compared with each other, and 30 subjects, who were
presented in most median values, were chosen as control group members.
Regarding the LAFH groups, LAFH min group included the first 30 subjects with
the smallest LAFH values while LAFH max group consisted of the first 30 subjects
with the greatest LAFH values. ANB min and max groups were selected
analogously to the LAFH groups. The total number of subjects in study IV was 147,
since three subjects were included both in extreme cases of lower anterior facial
height (LAFH) and soft tissue ANB (ANB min and LAFH min; ANB max and
LAFH max; ANB min and LAFH max).
Table 1. The study groups in study IV.
Study groups N Gender Range
Low LAFH 30 8 men, 22 women 48.1-54.3%
High LAFH 30 17 men, 13 women 64.5-70.8%
Low ANB-angle 30 5 men, 25 women 0.1-2°
High ANB-angle 30 24 men, 6 women 12.3-14.7°
Control group 30 15 men, 15 women 59.1-59.7%; 6.7-7.4°
4.2 Methods
4.2.1 Questionnaires (I, II)
Subjects with a known postal address answered two questionnaires before attending
the clinical examination. Questionnaire 1 included the subjects’ background
information, lifestyle and health questions. Questionnaire 1 contained two
questions (yes/no) related to TMD symptoms which have been demonstrated to be
adequate for screening TMD pain (Nilsson et al. 2006):
1. Do you have pain in your temples, temporomandibular joints, face, or jaw?
41
2. Do you have pain when you open your mouth wide or chew?
In questionnaire 2, the questions were related to economy, work and mental
resources. During the clinical examination, all subjects answered dental health-
related questionnaire 3. Questionnaire 3 included further questions (yes/no) related
to TMD, and questions 2-6 were based on the modified Diagnostic Criteria for
Temporomandibular Disorders (DC/TMD) (Schiffman 2010):
1. Have you had pain in areas of your face, jaws, temples, ears, or behind your
ears during the prior 30 days?
2. During the prior 30 days, have you felt pain that was modified by jaw
movement, function, parafunction, or being at rest?
3. Have you had jaw locking in the closed position that restricted maximum
mouth opening?
4. Did this restricted opening cause difficulty in mastication?
5. Have you had clicking noises in the TMJ during opening or closing jaw
movements or during mastication?
6. Have you had crepitation in the TMJ during opening or closing jaw movements
or during mastication?
Questionnaire 3 also contained two questions (yes/no) about eventual previous
orthodontic treatment:
1. Have you undergone orthodontic treatment before the age of 20?
2. Have you undergone orthodontic treatment after the age of 20?
4.2.2 Clinical examination (I-IV)
Occlusal assessment and measurements (I, II, III)
The clinical oral and dental health examination was performed at the Institute of
Dentistry, University of Oulu. The standardized clinical examination that included
intraoral occlusal measurements was carried out by six calibrated dentists and a
golden standard. The occlusion registration was based on the criteria described
earlier (Björk et al. 1964, Harris & Corruccini 2008). The occlusion was
investigated in all three planes: overjet in sagittal plane, overbite and anterior open
bite in vertical plane, as well as lateral crossbite and scissors bite in transversal
plane (Figure 1. on page 19). Crowding was not registered.
42
Overjet and overbite were measured in the maximal inter-cuspal position to the
nearest full millimetre with a manual scaler. Overjet was measured from the labial
surface of the right central maxillary incisor to the labial surface of the right central
mandibular incisor (Harris & Corruccini 2008). Negative overjet was recorded if
the mandibular incisor located more labially compared to the maxillary incisor.
Overbite was measured from the incisal edge of the maxillary right central incisor
to the incisal edge of the right central mandibular incisor (Harris & Corruccini
2008). In cases when a negative value was registered, the negative overbite was
marked as anterior open bite and the value was measured to the nearest full
millimetre. Lateral crossbite was recorded if one or more buccal cusps of the
maxillary teeth occluded lingually to the buccal cusps of the corresponding
mandibular teeth (Björk et al. 1964). Analogously, scissors bite was registered if
one or more lingual cusps of the maxillary teeth occluded buccally to the
corresponding mandibular teeth (Björk et al. 1964).
In study I, the subjects were divided into three subgroups based on overjet and
overbite. In overbite cases, the subgroups were overbite 6–7 mm, overbite > 7 mm
and anterior open bite. Concerning overjet, the subgroups were overjet 6–9 mm,
overjet > 9 mm and negative overjet (anterior crossbite). These subgroups were
compared to control groups, overjet 0–5 mm and overbite 0–5 mm. In study II, the
subgroups of overbite were overbite < 0 mm (anterior open bite) and overbite > 5
mm. Concerning overjet, the subgroups were overjet < 0 mm (negative overjet) and
overjet > 5 mm. In subgroup analysis of study III, only severe anterior
malocclusions were analysed, and thus the subgroups for overbite and overjet were
≥ 5 mm and ≤ 0 mm.
Stomatognathic examination (II)
In study II, a clinical stomatognathic examination was based on the modified
protocol of DC/TMD (Schiffman 2010). TMD signs recorded in this investigation
were clicking in TMJs, crepitus in TMJs, limited mouth opening (< 40 mm), pain
in masticatory muscles and pain in TMJs. The subject was considered positive for
TMD if one or more signs of TMD occurred in the clinical examination. TMJ noises
(clicking and crepitus) were registered during opening and closing movements and
during protrusive and lateral excursive movements. The registration of crepitus was
performed at a distance of 15 cm. Maximum mouth opening as well as lateral and
protrusive movement (< 7 mm restricted) were also measured. During the
examination, the subjects answered if they felt familiar pain in the TMJ area or
43
masticatory muscles in any movements. If the subjects had earlier had pain in the
same location during the past 30 days, the condition was defined as familiar pain.
The temporalis and masseter muscles were palpated bilaterally screening for
familiar pain on palpation with a pressure of 1.0 kg in the masticatory muscles and
around the TMJ pole. The lateral pole of the TMJ was palpated with a pressure of
0.5 kg. The calibration of the palpation force was based on a digital postage scale.
The TMD diagnostics was based on the modified DC/TMD protocol
(Schiffman 2010). The TMD diagnoses were myalgia, arthralgia, disc displacement
with reduction, disc displacement without reduction and degenerative joint disease.
More detailed criteria for diagnoses are presented in Table 2.
Occlusal interferences were registered at different contact positions of the
mandible (Dawson 1989). Tooth contacts were recorded in laterotrusive and
protrusive mandibular movements. In laterotrusive mandibular movement, the
tooth contacts were registered at the position of lateral gliding up to 3 mm from
ICP as canine guidance and interferences (Okeson 2013). Canine guidance was
registered if maxillary and mandibular canines came into contact during lateral
movements of the mandible. Correspondingly, interferences were registered if there
was guidance in the premolar and/or molar area, guidance in the incisor area or
mediotrusive contact. In protrusive mandibular movement, tooth contacts were
registered if the tooth contacts appeared on the anterior teeth and interferences were
registered if the tooth contacts appeared on the posterior teeth. In addition, the
clinical examination included the registration of RCP and ICP contact positions.
The protocol included the registration of the length of sagittal RCP-ICP slide and
lateral deviation between RCP-ICP.
After the clinical examination, TMD signs and diagnoses were compared with
the occlusal variables which included overjet (< 0 mm and > 5 mm), overbite (< 0
mm and > 5mm), anterior crossbite, lateral crossbite, lateral scissor bite, length of
RCP-ICP slide (3–5 mm), lateral deviation of RCP-ICP slide (over 0 mm), and
interferences in laterotrusive and protrusive mandibular movements.
44
Table 2. Subdiagnoses of TMD.
Diagnosis Criteria
Myalgia Reported pain in areas of the face, jaws, temples, ears, or behind the
ears; pain modified by movement during the prior 30 days; and familiar
pain in the masticatory muscles during jaw movements and/or pain on
palpation in any of the muscle sites
Arthralgia Reported pain in areas of the face, jaw, temples, ears, or behind the
ears; pain modified by movement during the prior 30 days; and familiar
pain in the TMJ during jaw movement and/or pain on palpation in the
right or left TMJ
Disc displacement with
reduction
Reported history of clicking noises in the TMJ and TMJ clicking
recorded by the examiner during opening and closing movements, or
during opening or closing movements and in either protrusive or lateral
movement
Disc displacement without
reduction
Self-reported jaw locking in closed position and restricted maximum
assisted opening
Degenerative joint disease Self-reported history of noises in the TMJ and TMJ crepitus recorded by
the examiner
Clinical photographs (III, IV)
Standardized clinical photographs were taken at the time of the clinical examination.
The protocol included two frontal (basic and smile) and one profile 2D photograph
from each subject under general illumination. In study III, only profile photographs
were used, while both frontal (basic facial expression) and profile photographs
were used in study IV. The facial photographs were taken without eyeglasses. The
type of camera used was Canon 600D with a Canon EF-S 60 mm F/2.8 MACRO
USM objective. During the photography, the position of the subject was determined
by a mark on the floor. The camera was mounted on a tripod and the distance
between the camera and the subject was 190 cm. Camera settings were f/5.6 and
ISO/200. In cases of extreme height deviations between the subject and the camera,
the subject either sat on a saddle chair (tall subject) or stood (short subject), and the
height of the camera was adjusted.
45
4.2.3 Facial soft tissue measurements (III, IV)
Profile photographs were transferred to ViewBox software (dHAL Software,
Kifissia, Athens, Greece) and facial soft tissue profile was analysed. In soft tissue
cephalometrics, 11 soft tissue landmarks were digitized by a single examiner (LK)
(Table 3.) (Figure 2.). As an objective to carry out soft tissue measurements, a
vertical reference line was designed at 70 degrees to the line connecting Tragus and
Nasion (Figure 3.). Selection of this vertical reference line was based on an earlier
profile image study (Wasserstein et al. 2015). In order to evaluate its reliability and
reproducibility, a pilot study on 30 randomly selected subjects was performed.
When the head was placed in natural head position, the line between Tragus and
Nasion (Tr-Na) formed a 70-degree angle with a true vertical line (μ = 69.83; SD
= 1.95). This line was named as Tragus line in the present study. The soft tissue
cephalometric analyses were based on linear and angular measurements and
calculations of ratios (Table 4.). After digitization of soft tissue points, all
measurements were calculated automatically in the Viewbox software. Intra-
examiner reliability was tested with redigitization of 200 randomly selected
photographs 4 weeks after the beginning of the analyses by the same examiner. All
facial soft tissue measurements were performed within 8 weeks.
Table 3. Soft tissue landmarks.
Soft tissue point Description
Glabella The most prominent point of the forehead as it appears on a profile picture
Nasion The deepest point of the curvature between glabella and the bridge of the
nose
Pronasale The most prominent point of the nose on the horizontal axis
Subnasale The deepest point of the curvature connecting the nose to the upper lip
FA-point of the upper lip The most prominent point of the upper lip
A-point The deepest point of the curvature between subnasale and FA point of the
upper lip
FA-point of the lower lip The most prominent point of the lower lip
Pogonion The most anterior point of the chin
B-point The deepest point of the curvature between pogonion and FA point of the
lower lip
Gnathion The most anterior-inferior point of the chin
Menton The most inferior point of the chin
46
Fig. 2. Soft tissue points. Image copyright was licensed from 123RF Ltd (Hong Kong,
China).
Fig. 3. Tragus line. A vertical reference line was designed at 70 degrees to the line
connecting Tragus and Nasion.
47
Table 4. Linear and angular measurements for evaluation of facial profile.
Measurements Description
A-point – B-point to Tragus The distance from A-point to Tragus line minus the distance from B-point to
Tragus line
Upper lip to Tragus line The distance between the FA-point of the upper lip and Tragus line
Lower lip to Tragus line The distance between the FA-point of the lower lip and Tragus line
Pogonion to Tragus line The distance between Pogonion and Tragus line
Convexity subnasale The angle between the lines connecting Glabella – Subnasale – Pogonion
Tragus Pogonion to
Tragus – Subnasale (%)
The ratio of the linear distances between Tragus – Pogonion and Tragus –
Subnasale
Tragus- Nasion to
Tragus – Subnasale (%)
The ratio of the linear distances between Tragus – Nasion and Tragus –
Subnasale
Tragus –A-point to
Tragus – Subnasale (%)
The ratio of the linear distances between Tragus – A-point and Tragus –
Subnasale
Tragus – B-point to
Tragus – Subnasale (%)
The ratio of the linear distances between Tragus – B-point and Tragus –
Subnasale
Lower facial height (%) The ratio of the distances between Subnasale – Menton and Nasion –
Menton
Upper facial height (%) The ratio of the distances between Nasion – Subnasale and Nasion –
Menton
Soft tissue ANB-angle The angle between the lines connecting A-point – Nasion – B-point
4.2.4 Evaluation of facial aesthetics (IV)
The study of facial aesthetics was based on vertical and sagittal facial soft tissue
measurements. Lower anterior facial height (LAFH, %) was selected to describe
facial vertical proportion and soft tissue ANB as the sagittal jaw relationships
(Table 4.). One profile and one frontal (basic facial expression) photograph from
each subject was placed in random order and numbered into the software Microsoft
PowerPoint. Each slide consisted of profile and frontal photographs of the same
subject. The size of the photographs was fixed at 16.8 x 11.2 cm. The photograph
presentation was shown to three panel groups: 5 orthodontists (2 men, 3 women;
mean age = 53.8 years; range = 35–62 years), 5 dentists (4 were specialist in
prosthodontics and stomatognathic physiology) (5 women; mean age = 56.2 years;
range 47–68 years) and 5 laypersons (3 men, 2 women; mean age = 41.4 years;
48
range 30–53 years). The orthodontists and dentists were personnel at the Research
Unit of Oral Health Sciences, University of Oulu. The laypersons were statisticians
at the Faculty of Medicine, University of Oulu. The raters sat undisturbed in the
same room and the photograph presentation was viewed with a data projector. Each
slide was shown to raters for 10 seconds. After every 10th slide, there was a 10-
second break. Before the beginning of the judging, the raters were instructed to pay
attention only to facial appearance and to assess facial aesthetics independently.
During the evaluation of the photographs each rater filled a paper form of 100-mm
Visual Analogue Scale (VAS) to assess facial appearance. In the Visual Analogue
Scale, a response of 0 mm meant “very unattractive” and a response of 100 mm
meant “very attractive”. After the photograph presentation, the results were
measured with an accuracy of one millimetre using a ruler.
4.3 Statistics
The data were analysed using IBM SPSS Statistics versions 22.0, 23.0, and 25.0
and R software version 3.3.2. The results of the statistical analyses were interpreted
as statistically significant if P-value was less than 0.05. Correlation coefficient was
interpreted weak if strength of association was 0.1–0.2, moderate if strength of
association was 0.3–0.5 and strong if values ranged from 0.6 to 1.0.
In study I, the statistical analyses were performed using Pearson’s Chi-square
test and Fisher’s exact test because of the categorical variables. The differences
between the genders and between treated and untreated groups were tested with the
tests mentioned above. The relation between scissors bite and increased overbite,
between negative overjet and crossbite on premolars, as well as between deep bite
and missing teeth was analysed with Pearson’s Chi-square test of independence.
In study II, Pearson’s Chi-square test was used to calculate gender differences
of occlusal disturbances. The association between TMD signs and occlusal factors
was tested with binary logistic regression models by R software. In this
investigation, the odds ratios (OR) and 95% confidence intervals (95% CI) were
accommodated for gender. The analyses concerning orthodontically treated groups
were performed with Pearson’s Chi-square test and Fisher’s exact test. These tests
were used to calculate differences in TMD signs and diagnoses as well as in
occlusal interferences between orthodontically treated and untreated subjects.
In study III, the gender dimorphism was tested with independent sample t-tests
for all facial profile measurements. Because of the significant gender differences in
facial profile, the data of the measurements were divided based on gender. Multiple
49
linear regression models were performed to test the association between profile
measurements, and overjet and overbite. Assumptions of normality and linearity
were analysed with Histograms and P-P plots of the regression standardized
residual values for overjet and overbite (Appendix, Supplementary Figures 1–2.).
In regression models, overjet and overbite represented dependent variables and the
profile measurements were independent variables. In order to test subjects with
severe anterior malocclusions, a separate multiple regression model was performed.
The separate analysis was based on subgroups with extreme overjet and overbite
values.
In study IV, parametric methods were chosen to analyse the data since the VAS
scores were normally distributed. Paired samples t-test was selected to study the
differences in aesthetic evaluation between the panel groups. Differences between
LAFH min, LAFH max and control group as well as between ANB min, ANB max
and control group were analysed with ANOVA with Tukey’s post hoc test. In order
to study the association in aesthetic VAS scores between different panel groups,
Pearson correlation coefficient was calculated. Associations between anterior lower
facial height (LAFH) and soft tissue ANB-angle in relation to aesthetic assessment
(VAS) of the three panel groups were investigated with quadratic regression models.
4.4 Error of the method
4.4.1 Error of the method in the clinical examination (I, II, III)
The repeatability of the clinical examination was confirmed by having the
investigators train under experienced a specialized dentist before the beginning of
the study. Inter-examiner agreement was determined regularly in follow-ups during
the clinical examination by a gold standard senior dentist (Table 5.).
50
Table 5. Intra- and inter-examiner agreements (Nintra-examiner=96, Ninter-examiner=100).
Examiner Intra-examiner agreement Inter-examiner agreement
ICC overjet ICC overbite ICC overjet ICC overbite
1 0.908 0.762 0.882 0.922
2 0.989 0.929 0.802 0.891
3 0.966 0.923 0.763 0.838
4 0.966 0.922 0.899 0.957
5 0.964 0.803 0.892 0.940
6 0.943 0.865 0.938 0.767
Total 0.969 0.912 0.865 0.913
ICC= Intra Class Correlation.
4.4.2 Error of the method in facial soft tissue measurements (III, IV)
During the soft tissue profile measurements, 200 randomly selected photographs
were re-digitized four weeks after the first digitization by the same examiner (LK).
In order to test the error of the method, Bland-Altman plots (Bland & Altman 1986)
were constructed, and the two measurements demonstrated very high agreement
(Figure 4.). Based on the Bland-Altman plots, the random error of the digitization
method was considered to be non-significant.
A)
51
B)
C)
Fig. 4. The Bland-Altman plots for A) A-point – B-point to tragus line, B) upper lip to
Tragus line, C) pogonion to tragus line. The horizontal axis represents the mean of two
measurements and the vertical axis the difference between two measurements.
52
4.4.3 Error of the method in aesthetic evaluation (IV)
In order to test error of the method, 12 randomly selected photographs were re-
evaluated at the end of the judging by each panel member. Paired samples t-test
was selected to test intra-rater reliability of the aesthetic evaluation. No statistically
significant differences were found in intra-class ratings (Table 6.). These values
justified the subsequent analyses of the data.
Table 6. Error of the method in aesthetic panel evaluation.
Panel groups Nrater Nevaluation VAS 1 VAS 2 Difference P value
Orthodontists 5 60 5.58 5.52 0.06 0.557
Dentists 5 60 5.63 5.65 -0.02 0.894
Laypersons 5 60 5.41 5.44 -0.03 0.821
Total 15 180 5.54 5.53 0.01 0.930
4.5 Ethical considerations
The Ethical Committee of the Northern Ostrobothnia Hospital District had
approved the study on 22 September 2011 (74/2011) and 17 September 2012
(227/2012). Participation in the study was voluntary for the subjects and they
received health information in the clinical examination. The subjects had the right
to refuse from participation at any time point during the study. In case of treatment
need, the subjects were referred to treatment.
53
5 Results
The study results are displayed in the order of the original articles. Roman numerals
refer to the original articles.
5.1 Prevalence of malocclusion traits (I)
The prevalence of malocclusion traits is presented in Tables 7–9. According to the
results, 39.5 per cent of the subjects had at least one malocclusion trait.
Malocclusion traits were significantly more prevalent among men (44.1%) than
among women (35.5%) (p<0.001).
Regarding the vertical incisor relationship, the frequency of overbite ≥ 6 mm
was 11.7 per cent (Table 7.). Anterior open bite was shown to be rare (1.3%) in this
adult population (Table 7.). Overbite 6–7 mm (p=0.016), overbite > 7 mm (p=0.030)
and overbite ≥ 6mm (p=0.001) were significantly more prevalent among men than
among women (Table 7.). More women (89.5%) than men (84.2%) had normal
occlusion regarding vertical incisor relationships (p<0.001) (Table 7.).
Table 7. Vertical incisor relationship.
Variable Women Men Total P value
(n) (%) (n) (%) (n) (%)
Normal 0-5 mm 933 89.5 760 84.2 1693 87.0 0.000
Overbite 6-7 mm 83 8.0 101 11.2 184 9.5 0.016
Overbite > 7 mm 16 1.5 27 3.0 43 2.2 0.030
Overbite ≥ 6 mm 99 9.5 128 14.2 227 11.7 0.001
Anterior open bite 10 1.0 15 1.7 25 1.3 0.171
Pearson’s Chi-square test. Incisor relationship vertical could not be registered in 19 subjects.
Sagittal incisor relationships are displayed in Table 8. According to the results, the
prevalence of overjet ≥ 6 mm (9.7%) was less common compared to the frequency
of overbite ≥ 6 mm (11.7%) (Tables 7–8). Negative overjet was uncommon in this
adult population (1.2%) and showed significant gender dimorphism with male
dominance (p<0.001) (Table 8.).
54
Table 8. Sagittal incisor relationship.
Variable Women Men Total P value
(n) (%) (n) (%) (n) (%)
Normal 0-5 mm 928 89.1 803 89.0 1731 89.0 0.980
Overjet 6-9 mm 94 9.0 70 7.8 164 8.4 0.319
Overjet > 9 mm 16 1.5 9 1.0 25 1.3 0.294
Overjet ≥ 6 mm 110 10.6 79 8.8 189 9.7 0.182
Negative overjet 4 0.4 20 2.2 24 1.2 0.000
Pearson’s Chi-square test. Incisor relationship sagittal could not be registered in 20 subjects.
The prevalence of crossbite and scissors bite is presented in Table 9. According to
the results, lateral crossbite (17.9%) was the most common malocclusion in this
study. Men presented a higher prevalence of crossbite on left premolars (8.1%) than
women (5.5%) (p=0.021). In addition, men presented a tendency for higher
prevalence of total crossbite (p=0.051) and scissors bite (p=0.078). More
transversal variation on the left than on the right side was seen, particularly in men
(Table 9.). The prevalence of scissors bite was 7.6 per cent in this adult population
(Table 9.). No significant gender differences were found concerning scissors bite
(Table 9.).
When the relationship between scissors bite and overbite was studied, the
association between these two malocclusions was significant (p<0.001). Regarding
the subjects with scissors bite, 23.6 per cent of the subjects were also diagnosed
with overbite (≥ 6 mm). Conversely, subjects without scissors bite were diagnosed
with increased overbite in 10.7 per cent of the cases. The association between
negative overjet and crossbite on left premolars was statistically significant
(p<0.001). In 41.7 per cent of the cases, subjects with negative overjet were also
diagnosed with crossbite on the left premolars, reflecting progenic occlusion. By
contrast, subjects without negative overjet had crossbite on the left premolars in 6.3
per cent of the cases.
55
Table 9. Transversal malocclusion.
Variable Women Men Total P value
(n) (%) (n) (%) (n) (%)
Crossbite on
right premolars
72 6.9 67 7.4 139 7.1 0.664
Crossbite on
left premolars
57 5.5 73 8.1
130 6.7 0.021
Crossbite on
right molars
71 6.8 76 8.4 147 7.6 0.183
Crossbite on left molars 50 4.8 49 5.4 99 5.1 0.530
Crossbite total (lateral) 170 16.3 178 19.7 348 17.9 0.051
Scissors bite on
right premolars
31 3 35 3.9 66 3.4 0.274
Scissors bite on
left premolars
38 3.6 48 5.3 86 4.4 0.074
Scissors bite on
right molars
7 0.7 4 0.4 11 0.6 0.502
Scissors bite on
left molars
5 0.5 6 0.7 11 0.6 0.588
Scissors bite total 69 6.6 79 8.7 148 7.6 0.078
Pearson’s Chi-square test. Transversal malocclusion could not be registered in 17 subjects because of
missing teeth.
The prevalence of malocclusion traits with respect to orthodontic treatment is
shown in Table 10. According to the results, no statistically significant differences
in the prevalence of malocclusions were found between orthodontically treated and
untreated subjects (Table 10.).
56
Table 10. Prevalence of malocclusion traits in orthodontically treated and untreated
subjects.
Variable Treated (n) Treated (%) Untreated (n) Untreated (%) P value
Overjet 6 mm or over 36 10.3 147 9.6 0.690
Negative overjet 3 0.9 21 1.4 0.601
Overbite 6 mm or over 45 12.8 179 11.6 0.549
Anterior open bite 4 1.1 18 1.2 1.000
Crossbite on premolars 49 13.9 174 11.3 0.176
Crossbite on molars 41 11.6 162 10.5 0.551
Scissors bite
on premolars
17 4.8 113 7.3 0.091
Scissors bite on molars 7 2.0 14 0.9 0.092
Variables were tested with Pearson’s Chi-square test and Fisher’s exact test. Overjet and negative
overjet could not be registered in 75 subjects. Overbite, open bite and scissors bite on molars could not
be registered in 74 subjects. Crossbite and scissors bite on premolars could not be registered in 72
subjects.
5.2 Prevalence of previous orthodontic treatment (I)
The prevalence of previous orthodontic treatment experience is presented in Table
11. Altogether 18.6 per cent of the subjects reported having had orthodontic
treatment (Table 11.). Women showed significantly higher previous orthodontic
treatment experience (20.3%) than men (16.6%) in this adult population (p=0.041).
Orthodontic treatment experience before the age of 20 was more common (13.8%)
compared to the treatment experience in adulthood (6.2%).
Table 11. Previous orthodontic treatment experience.
Treatment experience Women Men Total P value
(n) (%) (n) (%) (n) (%)
< 20 years 151 14.8 113 12.7 264 13.8 0.186
> 20 years 70 6.9 48 5.4 118 6.2 0.185
Total 207 20.3 148 16.6 355 18.6 0.041
Pearson’s Chi-square test. Treatment experience could not be registered in 55 subjects.
57
5.3 Association between signs and diagnoses of TMD and occlusal
variables (II)
When association between TMD diagnoses and occlusal variables (malocclusions
and occlusal interferences) was studied, two statistically significant relationships
were found. A statistically significant association was found between myalgia and
lateral scissors bite (p=0.034) as well as between arthralgia and lateral deviation in
RCP-ICP slide (p=0.005).
The association between TMD signs and occlusal variables is shown in Table
12. Limited mouth opening showed significant association with lateral crossbite
(OR=2.35; 95% CI=1.33–4.17), scissors bite (OR=2.13; 95% CI=1.00–4.53) and
lateral deviation in RCP-ICP slide (OR=2.27; 95% CI=1.11–4.65) (Table 12.). Pain
in masticatory muscles was significantly associated with overjet < 0 mm (OR=4.37;
95% CI=1.33–14.41) and RCP-ICP slide (3-5 mm) (OR=2.43; 95% CI=1.06–5.60)
(Table 12.). When analysing laterality, pain in the right masticatory muscles
(OR=1.88, 95% CI=1.08–3.28) was associated with lateral deviation in RCP-ICP
slide to the left. Scissors bite on the left site was associated with crepitus in both
TMJs (left OR=2.52, 95% CI=1.27–4.99; right OR=2.05, 95% CI=1.01–4.19).
58
Ta
ble
12
. L
og
isti
c r
eg
res
sio
n a
na
lysis
of
as
so
cia
tio
ns b
etw
een
TM
D s
ign
s a
nd
oc
clu
sa
l v
ari
ab
les.
Variable
Lim
ited m
outh
openin
g
C
licki
ng in
TM
Js
C
repitu
s in
TM
Js
P
ain
in m
ast
icato
ry
musc
les
P
ain
in T
MJs
O
R
95%
CI
O
R
95%
CI
O
R
95%
CI
O
R
95%
CI
O
R
95%
CI
Fe
ma
le g
en
de
r
2.8
0
(1.6
1-4
.88
)
1.4
1
(1.1
5-1
.74
)
1.6
0
(1.1
6-2
.20
)
2.7
9
(2.0
2-3
.86
)
2.4
4
(1.7
6-3
.37
)
Ove
rbite
< 0
mm
0
.95
(0
.11
-8.3
1)
1
.10
(0
.42
-2.9
2)
1
.80
(0
.56
-5.8
5)
1
.73
(0
.54
-5.5
7)
1
.06
(0
.29
-3.8
6)
Ove
rbite
> 5
mm
1
.93
(0
.98
-3.8
3)
1
.16
(0
.84
-1.6
0)
1
.17
(0
.71
-1.9
1)
1
.18
(0
.74
-1.8
6)
1
.10
(0
.68
-1.7
9)
Ove
rjet
< 0
mm
0.0
0
(0.0
0-
inf)
1.4
8
(0.5
3-4
.13)
0
.84
(0
.17
-4.0
5)
4
.37
(1
.33
-14
.41
)
1.7
3
(0.4
4-6
.81
)
Ove
rjet
> 5
mm
0.6
3
(0.2
6-1
.56)
1.1
5
(0.8
1-1
.63)
0.8
2
(0.4
7-1
.44
)
0.9
3
(0.5
7-1
.53
)
1.0
1
(0.6
1-1
.67
)
An
terio
r cr
oss
bite
0
.71
(0
.23
-2.1
5)
0
.89
(0
.58
-1.3
9)
1
.25
(0
.69
-2.2
7)
0
.82
(0
.43
-1.5
6)
0
.96
(0
.51
-1.8
0)
La
tera
l cro
ssb
ite
2.3
5
(1.3
3-4
.17
)
0.9
2
(0.6
9-1
.23
)
0.9
9
(0.6
5-1
.51
)
0.8
5
(0.5
6-1
.28
)
1.1
3
(0.7
6-1
.69
)
Sci
sso
rs b
ite
2.1
3
(1.0
0-4
.53
)
0.8
1
(0.5
4-1
.21
)
1.3
0
(0.7
5-2
.23
)
0.9
6
(0.5
5-1
.68
)
1.0
4
(0.5
9-1
.84
)
RC
P-I
CP
slid
e (
3-5
mm
) 1
.55
(0
.34
-7.0
9
0
.76
(0
.34
-1.6
9)
0
.22
(0
.03
-1.6
3)
2
.43
(1
.06
-5.6
0)
1
.39
(0
.52
-3.7
1)
De
via
tion
in R
CP
-IC
P
2.2
7
(1.1
1-4
.65
)
1.0
5
(0.7
1-1
.56
)
1.5
1
(0.9
0-2
.54
)
1.2
9
(0.7
7-2
.15
)
1.4
5
(0.8
7-2
.41
)
LT
R in
terf
ere
nce
s 0
.91
(0
.51
-1.6
1)
1
.04
(0
.82
-1.3
3)
1
.07
(0
.75
-1.5
3)
1
.15
(0
.83
-1.6
1)
0
.90
(0
.63
-1.2
8)
PT
R in
terf
ere
nce
s 0
.87
(0
.40
-1.9
2)
0
.89
(0
.64
-1.2
2)
1
.07
(0
.68
-1.6
9)
0
.80
(0
.51
-1.2
7)
1
.11
(0
.71
-1.7
2)
OR
= o
dds
ratio
, C
I =
confid
ence
inte
rval.
59
5.4 Distribution of TMD signs and diagnoses in subjects having
had orthodontic treatment (II)
According to the results, TMD was significantly slightly more prevalent in
orthodontically treated (47.8%) than in untreated subjects (41.3%) (p=0.027).
Distribution of TMD signs in subjects having received orthodontic treatment is
presented in Table 13. Clicking in TMJs (29.2%) was the most common TMD sign
in subjects having received orthodontic treatment (Table 13.). Crepitus in TMJs
was more common among orthodontically treated (14.2%) than among untreated
subjects (7.8%) and this difference was statistically significant (p=0.001).
Table 13. Distribution of TMD signs in subjects with orthodontic treatment experience
(N=353).
TMD signs Treated Untreated χ2 value P value
(n) (%) (n) (%)
Clicking in TMJs 90 29.2 353 25.0 2.356 0.125
Crepitus in TMJs 36 14.2 90 7.8 10.230 0.001
Limited mouth opening
(< 40 mm)
15 4.3 56 3.6 0.324 0.569
Pain in masticatory muscles 44 12.5 169 10.9 0.732 0.392
Pain in TMJs 41 11.6 154 9.9 0.911 0.340
When analysing treatment experience separately before and after 20 years, crepitus
in TMJs was significantly more common among subjects having had orthodontic
treatment before the age of 20 (14.1%) compared to untreated subjects (8.2%)
(p=0.010) (Table 14.). Subjects having received orthodontic treatment after the age
of 20 showed no statistically significant difference in TMD signs compared to
untreated subjects (Table 15.). Clicking in TMJs was significantly more common
among subjects having had orthodontic treatment in childhood (30.9%) compared
to subjects having received treatment after the age of 20 (21.6%) (p=0.038).
60
Table 14. Distribution of TMD signs in subjects with orthodontic treatment experience < 20 yrs (N = 263).
TMD signs < 20 yrs Treated Untreated P value
(n) (%) (n) (%)
Clicking in TMJs 71 30.9 372 25.0 0.057
Crepitus in TMJs 26 14.1 100 8.2 0.010
Limited mouth opening (< 40 mm) 12 4.6 59 3.6 0.439
Pain in masticatory muscles 32 12.2 181 11.0 0.580
Pain in TMJs 31 11.8 164 10.0 0.368
Table 15. Distribution of TMD signs in subjects with orthodontic treatment experience > 20 yrs (N = 116).
TMD signs Treated Untreated P value
(n) (%) (n) (%)
Clicking in TMJs 22 21.6 421 26.0 0.319
Crepitus in TMJs 13 14.0 113 8.6 0.081
Limited mouth opening (< 40 mm) 5 4.3 66 3.7 0.6191
Pain in masticatory muscles 18 15.5 195 10.9 0.125
Pain in TMJs 18 15.5 177 9.9 0.052
1 Fisher’s exact test.
Distribution of TMD diagnoses in subjects is shown in Table 16. Degenerative joint
disease (8.0%) and arthralgia (6.8%) were the most common TMD diagnoses in
orthodontically treated subjects (Table 16.). Based on the results, degenerative joint
disease was significantly more prevalent among orthodontically treated (8.0%) than
among untreated subjects (4.7%) (p=0.012).
61
Table 16. Distribution of TMD diagnoses in subjects with orthodontic treatment
experience (N = 353).
TMD diagnoses Treated Untreated χ2 value P value
(n) (%) (n) (%)
Myalgia 23 6.5 74 4.8 1.825 0.177
Arthralgia 24 6.8 79 5.1 1.648 0.199
Disk displacement with reduction 23 6.5 114 7.4 0.313 0.576
Disk displacement without
reduction
0 0 4 0.3 1.0001
Degenerative joint disease 28 8.0 72 4.7 6.261 0.012
1 Fisher’s exact test.
When analysing treatment experience separately before and after 20 years,
degenerative joint disease was significantly more common among subjects having
had treatment before the age of 20 (8.4%) compared to untreated subjects (4.8%)
(p=0.015) (Table 17.). Conversely, arthralgia presented with a significantly higher
frequency among subjects having received treatment after the age of 20 (11.3%)
than among untreated subjects (5.1%) (p=0.004) (Table 18.). Arthralgia was
significantly more common among subjects having had orthodontic treatment in
adulthood (11.3%) compared to subjects having received treatment before the age
of 20 (5.0%) (p=0.021).
Table 17. Distribution of TMD diagnoses in subjects with orthodontic treatment experience < 20 yrs (N=263).
TMD signs Treated Untreated P value
(n) (%) (n) (%)
Myalgia 15 5.7 82 5.0 0.625
Arthralgia 13 5.0 90 5.5 0.716
Disk displacement with reduction 19 7.2 118 7.2 0.993
Disk displacement without reduction 0 0 4 0.2 1.0001
Degenerative joint disease 22 8.4 78 4.8 0.015
1 Fisher’s exact test.
62
Table 18. Distribution of TMD diagnoses in subjects with orthodontic treatment
experience > 20 yrs (N=116).
TMD signs Treated Untreated P value
(n) (%) (n) (%)
Myalgia 10 8.6 87 4.9 0.074
Arthralgia 13 11.3 90 5.1 0.004
Disk displacement with reduction 5 4.3 132 7.4 0.213
Disk displacement without reduction 0 0 4 0.2 1.0001
Degenerative joint disease 9 7.8 91 5.1 0.215
1 Fisher’s exact test.
5.5 Distribution of occlusal interferences according to orthodontic
treatment in subjects with TMD (II)
Frequencies of occlusal interferences in subjects with TMD are presented in Table
19. No significant differences in distribution of occlusal interferences were found
between orthodontically treated and untreated subjects with TMD (Table 19.).
According to the results, laterotrusion interferences (75.2%) were the most
common interferences in orthodontically treated subjects (Table 19.). Conversely,
RCP-ICP slide (3–5 mm) was shown to be quite rare (2.4%) among subjects with
orthodontic treatment experience (Table 19.).
Table 19. Distribution of occlusal interferences according to orthodontic treatment in
subjects with TMD.
Interferences Treated Untreated χ2 value P value
(n) (%) (n) (%)
Protrusion interferences 41 24.8 205 32.7 3.802 0.051
Laterotrusion interferences 124 75.2 471 75.1 0.000 0.993
RCP-ICP slide (3-5 mm) 4 2.4 14 2.2 0.7771
Deviation in RCP-ICP > 0 mm 10 6.1 43 7.0 0.160 0.689
1 Fisher’s exact test.
5.6 Gender differences in facial soft tissue profile (III)
Soft tissue differences in facial profile between genders are presented in Table 20.
According to the results, most of the profile measurements showed significant
gender dimorphism (Table 20.). No gender differences were found in
63
measurements of convexity subnasale (p=0.206) and Tragus – B-point to Tragus –
Subnasale (p=0.469) (Table 20.). Due to significant gender differences in most of
the facial profile variables, the data were stratified based on gender in later analyses.
Table 20. Gender dimorphism of facial profile measurements (Nmale=711, Nfemale=919).
Profile measurements Gender Mean SD P value
A-point – B-point to Tragus line (mm) M 3.10 1.63 < 0.001
F 2.50 1.43
Upper lip to Tragus line (mm) M 3.36 1.95 < 0.001
F 3.00 1.78
Lower lip to Tragus line (mm) M 2.74 2.21 < 0.001
F 2.19 2.05
Pogonion to Tragus line (mm) M 1.5 3.01 < 0.001
F 0.94 2.83
Convexity Subnasale (degree) M 170.3 6.3 0.206
F 170.7 6.28
Tragus – Pogonion to Tragus – Subnasale (%) M 114.40 4.77 0.007
F 113.78 4.56
Tragus – Nasion to Tragus – Subnasale (%) M 97.40 3.28 < 0.001
F 98.45 3.26
Tragus – A-point to Tragus – Subnasale (%) M 100.76 1.25 < 0.001
F 100.38 1.11
Tragus – B-point to Tragus – Subnasale (%) M 105.01 3.73 0.469
F 105.15 3.40
Lower facial height (%) M 59.70 2.31 < 0.001
F 58.97 2.24
Upper facial height (%) M 42.16 2.35 < 0.001
F 42.83 2.30
M=male, F=female.
64
5.7 Correlation between facial soft tissue profile, and overbite and
overjet (III)
5.7.1 Entire sample population
The correlation between facial profile and overjet as well as overbite is presented
in Table 21. According to the results, a significant moderate correlation between
facial profile and overjet (R2males= 0.296; R2
females= 0.279) was detected (Table 21.).
Table 21. Multiple regression models for overjet and overbite within genders.
Malocclusion Gender R2 P value
Overjet Males 0.296 < 0.001
Females 0.279 < 0.001
Overbite Males 0.200 < 0.001
Females 0.167 < 0.001
Predictors: (Constant), A-point – B-point to Tragus line, Tragus – A-point to Tragus –Subnasale, Tragus –
Nasion to Tragus – Subnasale, Lower facial height, Tragus – Pogonion to Tragus – Subnasale, Upper lip
to Tragus line, Tragus – B-point to Tragus – Subnasale, Convexity subnasale, Lower lip to Tragus line,
Pogonion to Tragus line, A-point to Tragus line, Upper facial height, B-point to Tragus line.
The effect of separate profile measurements on overjet is displayed in Table 22.
Based on the multiple linear regression models, the upper lip to Tragus line (the
anterior-posterior position of the upper lip) showed a strong association with
overjet both in men (p<0.001) and women (p<0.001) (Table 22.). In addition, the
positions of soft tissue A-point to the face (Tragus – A-point to Tragus – Subnasale)
and soft tissue B-point to the face (Tragus – B-point to Tragus – Subnasale) were
moderately to strongly associated with overjet in both genders (Table 22.). The
Tragus – Nasion to Tragus – Subnasale also showed a significant association with
overjet (pmale< 0.001; pfemale< 0.001) (Table 22.).
65
Table 22. Multiple linear regression models for overjet.
Profile measurements Gender Standardized
Coefficients-Beta
P value
A-point – B-point to Tragus line (mm) M 1.050 0.339
F 1.390 0.080
Upper lip to Tragus line (mm) M 0.730 < 0.001
F 0.897 < 0.001
Lower lip to Tragus line (mm) M -0.429 0.002
F 0.053 0.708
Pogonion to Tragus line (mm) M 0.176 0.436
F 0.208 0.378
Convexity subnasale (degree) M -0.084 0.423
F -0.224 0.035
Tragus – Pogonion to Tragus – Subnasale (%) M -0.012 0.916
F 0.020 0.844
Tragus – Nasion to Tragus – Subnasale (%) M -0.469 < 0.001
F -0.413 < 0.001
Tragus – A-point to Tragus – Subnasale (%) M 0.349 < 0.001
F 0.417 < 0.001
Tragus – B-point to Tragus – Subnasale (%) M -0.567 < 0.001
F -0.556 < 0.001
Lower facial height (%) M -0.493 0.029
F -0.185 0.327
Upper facial height (%) M -0.644 0.008
F -0.250 0.219
M=male, F=female.
Multiple linear regression models for overbite are presented in Table 23. According
to the results, the position of soft tissue A-point to the face (Tragus – A-point to
Tragus – Subnasale) was associated weakly to moderately with overbite
(pmale<0.001; pfemale<0.001) (Table 23.). In addition, the position of soft tissue B-
point to the face (Tragus – B-point to Tragus – Subnasale) showed strong
association with overbite (pmale<0.001; pfemale<0.001) (Table 23.)
66
Table 23. Multiple linear regression models for overbite.
Profile measurements Gender Standardized
Coefficients-Beta
P value
A-point – B-point to Tragus line (mm) M 0.935 0.424
F -1.496 0.079
Upper lip to Tragus line (mm) M 0.286 0.035
F 0.362 0.026
Lower lip to Tragus line (mm) M -0.239 0.098
F -0.439 0.004
Pogonion to Tragus line (mm) M 0.331 0.169
F 0.176 0.436
Convexity subnasale (degree) M 0.109 0.328
F -0.118 0.301
Tragus – Pogonion to Tragus – Subnasale (%) M 0.081 0.505
F 0.209 0.059
Tragus – Nasion to Tragus – Subnasale (%) M -0.448 < 0.001
F -0.084 0.423
Tragus – A-point to Tragus – Subnasale (%) M 0.240 < 0.001
F 0.349 < 0.001
Tragus – B-point to Tragus – Subnasale (%) M -0.569 < 0.001
F -0.567 < 0.001
Lower facial height (%) M -0.108 0.653
F -0.493 0.029
Upper facial height (%) M -0.098 0.706
F -0.644 0.008
M=male, F=female.
5.7.2 Subgroup analysis
In the entire sample population (n=1,630), most of the detected overjet and overbite
values were within normal limits. In other words, 1,313 subjects were diagnosed
with overjet of 1–4 mm, and 1,158 subjects presented with overbite of 1–4 mm. In
order to analyse subjects with deviant anterior occlusal relationships, a multiple
linear regression analysis was performed based on the subgroups with extreme
overjet and overbite values (Table 24.).
According to the results, a strong association between facial soft tissue
characteristics and negative overjet (R=0.665, p=0.011) was observed (Table 24.).
In addition, significant moderate correlations between facial soft tissue
characteristics and increased positive overjet (R=0.400, p<0.001) and deep bite
(R=0.342, p<0.001) were detected (Table 24.).
67
Table 24. Multiple regression models for extreme overjet and overbite values.
Malocclusion N Mean R2 P value
Overjet ≥ 5 mm 261 6.30 0.163 < 0.001
Negative overjet ≤ 0 mm 56 -0.70 0.442 0.011
Deep bite ≥ 5 mm 389 5.81 0.117 < 0.001
Open bite ≤ 0 mm 84 -0.48 0.150 0.509
Predictors: (Constant), A-point – B-point to Tragus line, Tragus – A-point to Tragus – Subnasale, Tragus
– Nasion to Tragus – Subnasale, Lower facial height, Tragus – Pogonion to Tragus –Subnasale, Upper
lip to Tragus line, Tragus – B-point to Tragus – Subnasale, Convexity subnasale, Lower lip to Tragus line,
Pogonion to Tragus line, A-point to Tragus line, Upper facial height, B-point to Tragus line.
5.8 Aesthetic evaluation (IV)
5.8.1 Differences in perceived attractiveness between the panel
groups
Aesthetic evaluation VAS mean scores are presented in Table 25. Range (SD)
values in VAS scores were 4.0–7.9 (0.7) among orthodontists, 3.3–7.7 (0.9) among
dentists, and 3.0–7.4 (0.9) among laypersons. Laypersons gave significantly lower
aesthetic VAS scores compared to orthodontists and dentists, especially in the
LAFH (lower anterior facial height) and control groups (Table 25.). Orthodontists
gave significantly higher VAS scores than laypersons (p=0.038) in the ANB min
group (Table 25.). In addition, orthodontists showed a tendency for higher VAS
scores compared to dentists (p=0.057) in the ANB min group (Table 25.). All panel
groups evaluated LAFH min faces to be more attractive than LAFH max faces
(Table 25.). Pearson correlation coefficients for associations in aesthetic VAS
scores between different panel groups varied between 0.733 and 0.839 (p<0.001
for all).
68
Table 25. Aesthetic evaluation VAS mean scores for different facial groups (n = 30 at
each group) by evaluators’ occupation.
Variable LAFH min LAFH max ANB min ANB max Controls
Orthodontists 5.86 5.45 5.49 5.10 5.99
Dentists 5.83 5.49 5.27 5.15 6.11
Laypersons 5.24 5.03 5.26 5.21 5.70
p1 0.612 0.616 0.057 0.614 0.177
p2 0.010 0.001 0.038 0.210 0.007
p3 0.009 <0.001 0.967 0.667 <0.001
p1, orthodontists vs. dentists; p2, orthodontists vs. laypersons; p3, dentists vs. laypersons.
5.8.2 Comparisons between the study groups and the control group
Regarding LAFH groups, the LAFH max group differed from the control group
statistically significantly in all panel groups’ evaluations (porthodontists=0.011, pdentists
=0.008, playpersons=0.015) while the LAFH min group did not (porthodontists=0.767,
pdentists=0.360, playpersons=0.786). Regarding the ANB groups, the ANB max group
differed from the control group significantly in all panel groups’ assessments (p
<0.001 among orthodontists and dentists, playpersons=0.036) while the ANB min
group differed from the control group among orthodontists (p=0.003) and dentists
(p<0.001), but not among laypersons (p=0.070).
5.8.3 Association between facial attractiveness and facial
characteristics
Entire sample population
For ANB, mean (SD) values were 1.36° (0.54°) among the ANB min group, 12.92°
(0.62°) among the ANB max group, and 7.06° (0.21°) among the control group.
Curve estimation showed a quadratic association between aesthetic VAS evaluation
and ANB-angle for all panel groups: R2=0.268 (p<0.001) among orthodontists
(Figure 5a), R2=0.195 (p<0.001) among dentists (Figure 5b), and R2=0.067
(p=0.048) among laypersons (Figure 5c).
69
Fig. 5. Quadratic regression models for association between VAS scores and ANB-
angle at different panel groups: (a) Orthodontists, (b) Dentists, (c) Laypersons.
Mean (SD) value for LAFH was 53.25% (1.27%) among the LAFH min group,
65.33% (1.23%) among the LAFH max group, and 59.41% (0.20%) among the
control group. The best fitting model for the association between aesthetic VAS and
LAFH was the quadratic model for all panel groups: R2=0.063 (p=0.059) among
orthodontists (Figure 6a), R2=0.064 (p=0.057) among dentists (Figure 6b), and
R2=0.050 (p=0.108) among laypersons (Figure 6c).
70
Fig. 6. Quadratic regression models for association between VAS scores and LAFH% at
different panel groups: (a) Orthodontists, (b) Dentists, (c) Laypersons.
Differences between male and female faces
The association between ANB-angle and perceived facial attractiveness appeared
to be highest among orthodontists (R2=0.276, p=0.001 for males; R2=0.285,
p=0.001 for females) (Figure 7a). For dentists, the association was R2=0.188
(p=0.014) among males and R2=0.231 (p=0.004) among females (Figure 7b). For
71
laypersons, the association between VAS evaluation and ANB-angle was R2=0.075
(p=0.201) among males and R2=0.269 (p=0.001) among females (Figure 7c).
Fig. 7. Quadratic regression models for association between VAS scores and ANB-
angle at different panel groups: (a) Orthodontists, (b) Dentists, (c) Laypersons.
Associations between LAFH and perceived attractiveness among orthodontists
(R2=0.146, p=0.054 for males; R2=0.058, p=0.244 for females) and laypersons
(R2=0.044, p=0.436 for males; R2=0.064, p=0.211 for females) were non-
significant (Figures 8a and 8c). For dentists, a weak association was found among
males (R2=0.172, p=0.031) while among females the association between LAFH
72
and perceived facial attractiveness was non-significant (R2=0.032, p=0.471)
(Figure 8b).
Fig. 8. Quadratic regression models for association between VAS scores and LAFH% at
different panel groups: (a) Orthodontists, (b) Dentists, (c) Laypersons.
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6 Discussion
6.1 The prevalence of malocclusion traits and orthodontic
treatment
The present study was designed to investigate the prevalence of malocclusion traits
among 1,964 mid-adulthood subjects in the Northern Finland Birth Cohort 1966.
The overall prevalence of malocclusion traits in this study was 39.5 per cent when
crowding was excluded. This finding is in line with the 42 per cent detected in a
previous Finnish study on adults (Laine & Hausen 1983). In the Health 2000 Survey,
31 per cent of the subjects had one or more occlusal deviation (Pietilä & Nordblad
2008). A lower prevalence of malocclusion in this earlier Finnish study on adults
can be explained by the different study design. In the Health 2000 Survey, only
malocclusions including an apparent risk of poor occlusion prognosis were
examined (Pietilä & Nordblad 2008). When interpreting the study results, one must
also take into account that crowding was not recorded in the present study.
The most common malocclusion trait in the present study was lateral crossbite
(17.9%). This study result is in concordance with the 19 per cent prevalence
observed among Finnish university students (Laine & Hausen 1983). Anterior or
lateral crossbite was also detected as the most common malocclusion in the Health
2000 Survey (Pietilä & Nordblad 2008). When crowding is excluded, the present
study and the earlier Finnish studies demonstrate that crossbite is the most common
malocclusion in the Finnish adult population. In comparison with the present study
results, a lower prevalence of lateral crossbite has been reported among adult
populations in Sweden (Salonen et al. 1992), Germany (Hensel et al. 2003) and
Iceland (Jonsson et al. 2007).
Along with lateral crossbite, the most common malocclusions in the present
study were increased overbite ≥ 6 mm (11.7%) and overjet ≥ 6mm (9.7%). In the
study of Laine and Hausen (1983), the prevalence of deep bite was only 3 per cent.
However, the methodological section of this study does not reveal how deep bite
was specified (Laine & Hausen 1983). The prevalence of overjet ≥ 6 mm in the
present study was higher compared to the Health 2000 Survey (Pietilä & Nordblad
2008) and the earlier Finnish study on adults (Laine & Hausen 1983). A possible
explanation for the higher prevalence of overjet detected in the present study
compared to earlier studies might be a different cut-off point of overjet (Pietilä &
74
Nordblad 2008) and age differences of the study populations (Laine & Hausen
1983).
Anterior open bite (1.3%) and negative overjet (1.2%) were both quite rare in
this adult population. Regarding anterior open bite, a higher frequency was
registered in the Health 2000 Survey (Pietilä & Nordblad 2008) and in Dutch
(Burgersdijk et al. 1991) and German (Hensel et al. 2003) adult populations.
Nevertheless, the prevalence of anterior open bite in the present study is in line with
that reported for Icelandic adult population (Jonsson et al. 2007). Regarding
negative overjet, the present study demonstrated that it was very rare in Northern
Finland adult population. This is in line with the earlier studies that have shown
that negative overjet is uncommon in Finland (Laine & Hausen 1983) and generally
in other European adult populations (Burgersdijk et al. 1991, Hensel et al. 2003,
Jonsson et al. 2007).
The present study showed a significant gender dimorphism regarding the
overall prevalence of malocclusion. Men showed a higher prevalence of crossbite
on the left, increased overbite and negative overjet. Male dominance in the
prevalence of malocclusion has not earlier been reported in Finland. In the study of
Laine and Hausen (1983), some gender variation in the prevalence of malocclusion
occurred even though the differences were not statistically significant. Deep bite
has been found to be more common in Finnish boys than in girls (Myllärniemi
1970). Deep bite has also been found to be more prevalent among men in the
German adult population (Hensel et al. 2003). Male dominance in the prevalence
of negative overjet has also been detected in Swedish (Salonen et al. 1992) and
British (Lavelle 1976) populations. Male dominance in left lateral crossbite and
negative overjet and the significant relationship between these malocclusions can
be explained by prognathic malocclusion. The results of the present study are in
accordance with the earlier study demonstrating sexual dimorphism in late
mandibular growth (Behrents 1985). An earlier Finnish study on adults also
detected a positive association between negative overjet and crossbite (Laine 1985).
In this study, no statistically significant difference in the prevalence of
malocclusions was found with respect to experience of orthodontic treatment. This
study result is opposite to an earlier Finnish study on adults (Laine & Hausen 1983).
Higher frequencies of malocclusions have been detected among subjects having
received orthodontic treatment in earlier studies (Burgersdijk et al. 1991, Jonsson
et al. 2007, Laine & Hausen 1983). A higher prevalence of malocclusion among
orthodontically treated subjects in some studies might reflect unstable or
unsuccessful treatment results (Jonsson et al. 2007, Laine & Hausen 1983). The
75
prevalence of malocclusion in adulthood might be influenced by relapse of the
treatment results, insufficient treatment in childhood due to small extent of the
treatment and normal occlusal changes over time (Heikinheimo et al. 2012, Jonsson
et al. 2007). The present study indicates that orthodontic treatment provided in
childhood in Northern Finland has been sufficient in reducing malocclusion traits
to the level observed in the general population. The present study results also reflect
the lack of systematic screening of malocclusions in Northern Finland in the 1970s
and the beginning of 1980s, which might have caused variation in the degree of
treatment. Common recommendations for selecting children for orthodontic
treatment were first introduced by the Medical Board of Finland in 1988 (Medical
Board of Finland 1988). These criteria were modified from those in Graingers’
Treatment Priority Index (Grainger 1967).
In the present study, the extent of previous orthodontic treatment experience
was 18.6 per cent, which is in line with the earlier Finnish study on adults (age
group 30–44 years, 19%) (Pietilä & Nordblad 2008). In contrast, the prevalence of
orthodontic treatment experience among Finnish university student was only 11 per
cent (Laine & Hausen 1982). Possible explanations for the difference in the
prevalence of orthodontic treatment between the present study and the earlier study
could be the geographic location and different period of time. In the present study,
the subjects lived in close proximity to a large health centre while the previous
study included more rural areas and possibly more basic-level healthcare (Laine &
Hausen 1982). In addition, orthodontic treatment became more common in Finland
in the 1980s, which might explain the lower frequency of orthodontic treatment
experience in the earlier Finnish study on adults (Laine & Hausen 1982). A more
recent study of young Finnish adults showed a higher prevalence of previous
orthodontic treatment experience compared to the present study (Tuominen et al. 1994). However, most of the subjects in the earlier study came from cities and
especially from the Helsinki region (Tuominen et al. 1994). The authors of the
earlier investigation suggest that a possible explanation for the relatively high
prevalence of earlier orthodontic treatment experience might be the good access to
care in the Helsinki region (Tuominen et al. 1994).
In this study, women had a history of orthodontic treatment more frequently
than men. The study result is in line with earlier studies (Burgersdijk et al. 1991,
Jonsson et al. 2007, Laine & Hausen 1982). Among young Finnish adults, more
women than men had received orthodontic treatment but the difference was not
statistically significant in the study of Tuominen et al. 1994. A male dominance in
the prevalence of malocclusion and a lower experience of orthodontic treatment
76
among males can be explained by gender differences in treatment seeking and in
attitude towards treatment. Men have been reported to be more often satisfied with
their dentition compared to women among young Finnish adults (Tuominen et al. 1994). Among Finnish adolescents, boys have been shown to be more satisfied than
girls with the alignment of their teeth without having had orthodontic treatment,
even though the gender difference was not statistically significant (Pietilä & Pietilä
1996).
6.2 Association of occlusion with TMD
This study showed a statistically significant association between occlusion and
TMD. Based on a recent systematic review, occlusion is considered as a cofactor
in the aetiology of TMD (Michelotti & Iodice 2010). The present study showed that
occlusion seems to have a role in TMD and that occlusal disturbances should be
considered as risk factors. However, understanding the causal-effect relationship
between malocclusions and TMD is not possible based on association alone. In the
case of causal-effect relationship, the association must be strong, but in addition, a
more severe malocclusion must lead to more severe symptoms of TMD (Michelotti
& Iodice 2010). Therefore, more studies are needed to evaluate the role of occlusion
in the background of TMD.
Two significant relationships regarding the association between occlusal
variables and diagnoses of TMD were found in the present study. Firstly, the
association between myalgia and lateral scissors bite, and secondly, between
arthralgia and lateral deviation in RCP-ICP slide showed to be statistically
significant. Regarding the association between scissors bite and TMD, two earlier
studies found no significant relationship (Kritsineli & Shim 1992, Sari et al. 1999).
By contrast, scissors bite was shown to be significantly associated with clicking in
TMJs (Riolo et al. 1987). The association between myalgia and lateral scissors bite
might be explained by asymmetric position of the condyles (Pirttiniemi et al. 1991).
According to earlier studies, lateral malocclusions showed a more asymmetric
position of the condyles (Kecik et al. 2007, Pirttiniemi et al. 1991). In addition, the
signs and symptoms of TMD have been shown to correlate with the length and
lateral deviation of slide between RCP-ICP, deviation in protrusion and asymmetry
in lateral cuspid occlusion (Raustia et al. 1995a).
In this study, limited mouth opening showed a significant association with
lateral crossbite. Several earlier studies have also reported a significant association
between crossbite and the signs and symptoms of TMD (Alamoudi 2000, Egermark
77
et al. 2003, Egermark-Eriksson et al. 1990, Marklund & Wänman 2010). Compared
to other malocclusions, posterior crossbite has been thought to have the largest
effect on the function of the masticatory system (Michelotti & Iodice 2010). The
present study indicates that lateral crossbite is related to internal derangements of
TMJ. The present finding is in line with the earlier studies (Marklund & Wänman
2010, Pullinger et al. 1993, Pullinger & Seligman 2000). According to the general
assumption, posterior crossbite may lead to alterations of the disc-condyle
relationship, which in turn can lead to disc displacement and clicking of the joint
(Buranastidporn et al. 2006, Egermark et al. 2003, Pullinger et al. 1993, Pullinger
& Seligman 2000). An association between unilateral posterior crossbite and TMJ
disc displacement with reduction has been found in an earlier study (Pullinger et al. 1993). Marklund and Wänman (2010) found that crossbite is related to the
incidence and persistence of TMJ dysfunction, i.e. to alterations of the disc-condyle
relationship.
In this study, pain in masticatory muscles was significantly associated with
negative overjet and RCP-ICP slide (3–5 mm). An earlier study has demonstrated
that a longer RCP-ICP slide associates with muscle tenderness (Ingervall et al. 1980). Previous studies have reported conflicting results regarding the relationship
between negative overjet and TMD (John et al. 2002, Riolo et al. 1987, Sari et al. 1999, Thilander et al. 2002). No relationship has been found between negative
overjet and self-reported symptoms of TMD (John et al. 2002). By contrast,
negative overjet has been found to be significantly associated with joint noise and
TMJ pain (Riolo et al. 1987). In addition, significant association has been detected
between Angle Class III malocclusion and TMD (Sari et al. 1999, Thilander et al. 2002).
6.3 TMD and orthodontic treatment
The results of this study showed that some signs of TMD were significantly more
common among orthodontically treated than among untreated subjects. This
finding is in contrast with most of the results reported earlier. Based on review
articles, most of the previous studies have not shown a significant relationship
between orthodontic treatment and TMD (McNamara et al. 1995, Michelotti &
Iodice 2010). In addition, traditional orthodontic treatment has not been shown to
increase the prevalence of TMD (Kim et al. 2002). In a systematic review, none of
the included studies suggested that orthodontic treatment caused TMD (Mohlin et al. 2007). On the contrary, a lower prevalence of TMD after orthodontic treatment
78
has been found in longitudinal studies (Henrikson et al. 2000, Olsson & Lindqvist
1995). Orthodontically treated subjects have demonstrated a lower prevalence of
subjective symptoms of TMD compared to untreated subjects (Egermark &
Thilander 1992). On the other hand, a longitudinal study has concluded that
orthodontic treatment neither results in nor prevents TMD (Macfarlane et al. 2009).
The present study showed that clicking in TMJs was significantly more
common in subjects having received orthodontic treatment in childhood compared
to subjects having had treatment after the age of 20. It has earlier been concluded
that orthodontic treatment does not have influence on TMJ clicking (Henrikson et al. 2000). On the other hand, a slight increase in joint clicking has been reported
after orthognathic surgery (Panula et al. 2000).
In this study, crepitus in TMJs and degenerative joint disease were significantly
more common among orthodontically treated than among untreated subjects. It is
known that crepitus in TMJs is a clinical sign of degenerative joint disease
(Schiffman et al. 2014). The results of the present study are in accordance with
some earlier investigations (Pahkala & Heino 2004, Rodrigues-Garcia et al. 1998).
The prevalence of crepitation has been shown to increase after orthognathic surgery
(Pahkala & Heino 2004). The authors of the earlier study reported that a possible
explanation for the higher prevalence of crepitus after orthognathic treatment could
be changes in condylar position which in turn may lead to degenerative changes in
the articular joint surfaces (Rodrigues-Garcia et al. 1998). However, it must be
taken into account that both of the earlier investigations were based on orthognathic
surgery patients instead of traditional orthodontic treatment (Pahkala & Heino 2004,
Rodrigues-Garcia et al. 1998). There have been contradictory results as to whether
traditional orthodontic treatment might cause changes in condylar position
(McNamara et al. 1995, Michelotti & Iodice 2010).
Higher frequency of arthralgia was found in subjects having been treated
orthodontically in adulthood compared to subjects who had received orthodontic
treatment in childhood. A possible explanation for this might be that the subjects
who had received orthodontic treatment in adulthood had had malocclusions longer
before getting treatment. Therefore, TMJs in those subjects have also been affected
for a longer time by malocclusions. On the other hand, TMD symptoms may have
been one of the reasons to seek orthodontic treatment in the first place.
Even though the orthodontically treated subjects in this study demonstrated
higher prevalence of TMD signs and diagnoses, especially crepitus in TMJs and
degenerative joint disease, one must take into account methodological limitations.
In the present study, the orthodontic treatment experience was based on a
79
questionnaire which can affect the study results, by recall bias, for instance. In
addition, the patients were only asked whether they had undergone orthodontic
treatment without specifying different treatment types. In addition, no information
was available regarding the condition of TMJs before orthodontic treatment.
6.4 Occlusal interferences in TMD subjects with orthodontic
treatment experience
This study found no significant differences in distribution of occlusal interferences
between orthodontically treated and untreated subjects with TMD. This finding is
in line with a long-term study (Sadowsky & Polson 1984). In a prospective long-
term study, the prevalence of occlusal interferences was on the same level in the
orthodontic group as in the untreated group in the final follow-up, but no statistical
analysis was performed (Egermark et al. 2005). A previous investigation has
shown a lower prevalence of RCP/ICP interferences among orthodontically treated
subjects compared to untreated subjects, which is an opposite result to the findings
of the present study (Olsson & Lindqvist 2002).
6.5 Association between facial soft tissue profile and
malocclusions
The study was carried out to evaluate the sagittal incisor relationship (overjet) and
vertical incisor relationship (overbite) and their association with facial soft tissue
profile. The present study demonstrated a significant association between
malocclusions and facial soft tissue profile, which is in line with earlier
investigations (Bittner & Pancherz 1990, Dimaggio et al. 2007, Godt et al. 2013,
Maurya et al. 2014). The results of the present study showed a positive moderate
correlation between facial profile and overjet in both genders. In addition, the
correlation between overbite and facial profile was weak while this correlation was
also detected to be significant in both genders. An earlier study also showed
stronger correlation between overjet and facial soft tissue than between overbite
and facial soft tissue (Saxby & Freer 1985). In addition, a large overjet has most
often been shown to be reflected in facial morphology while negative overjet and
overbite could not be detected from facial photographs (Bittner & Pancherz 1990).
On the other hand, Class II malocclusion with increased overjet and Class III
malocclusion with decreased overjet have been demonstrated to influence soft
tissue morphology (Godt et al. 2013).
80
The results of the present study showed a weak to moderate correlation
between facial soft tissue profile and incisor relationships. Variability in soft tissue
thickness, ethnic origin, gender and age might influence cephalometric soft tissue
values (Bergman 1999, Saxby & Freer 1985). A possible explanation for the quite
low correlations in this adult population might be the growth process which occurs
during lifetime (Pecora et al. 2008). A longitudinal cephalometric study has shown
that facial soft tissues undergo significant changes during adulthood as part of the
craniofacial complex growth (Pecora et al. 2008).
In the present study, the anterior-posterior position of the upper lip (upper lip
to Tragus line) showed a strong association with overjet in both genders. This
finding is similar to the results seen in earlier studies (Dimaggio et al. 2007, Godt
et al. 2013, Hameed et al. 2008, Saxby & Freer 1985). Children with Class II
malocclusion with increased positive overjet exhibited more anterior upper lip
position (Godt et al. 2013). Overjet has been shown to correlate with upper lip
convexity (Saxby & Freer 1985). The authors of the latter study supposed that the
horizontal position of the upper incisor determines the horizontal position of the
upper lip (Saxby & Freer 1985). In addition, more prominent lip profile has been
detected among Class II subjects (Dimaggio et al. 2007, Hameed et al. 2008). The
result of the present study indicates that overjet affects the anterior-posterior
position of the upper lip.
The results of the present study showed that the positions of soft tissue A-point
and soft tissue B-point were moderately to strongly associated with both overjet
and overbite. The important role of soft tissue A- and B-points in the facial profile
has also been detected in earlier studies (Saxby & Freer 1985, Wasserstein et al. 2015). It has been shown that soft tissue A-point and B-point belong to the most
reliable soft tissue reference points (Wasserstein et al. 2015). In addition, the
authors of an earlier study concluded that point-A convexity is a very important
factor in determining the soft tissue outline (Saxby & Freer 1985).
It is interesting that the positions of soft tissue A- and B-points correlated with
overbite. This finding is, however, in accordance with an earlier study (Saxby &
Freer 1985). Overbite has been shown to correlate with the horizontal position of
the soft tissue B-point and its relation to soft tissue A-point (Saxby & Freer 1985).
One must, however, consider that the correlations detected were not very high
(Saxby & Freer 1985). Moderate to strong association between the positions of soft
tissue A- and B-points and overjet is in line with earlier literature (Wasserstein et al. 2015). An earlier study has shown that sagittal malocclusion and jaw
relationships are associated with soft tissue A- and B-points (Wasserstein et al.
81
2015). In other words, the soft tissue angle A’N’B’ has been shown to differ
according to Angle’s classifications and a high correlation between skeletal ANB
and A’N’B’ is evident (Wasserstein et al. 2015). The present study demonstrated
that soft tissue A- and B-points are good predictors of anterior malocclusions.
Regarding severe sagittal malocclusions, a strong association was found
between facial soft tissue profile and extreme negative overjet. This finding is in
accordance with an earlier study that documented a significant association between
Class III malocclusion and soft tissue profile characteristics (Staudt & Kiliaridis
2009). In the study by Staudt and Kiliaridis (2009), the authors concluded a high
diagnostic value of profile photographs in detecting Class III malocclusion.
Altogether, the present study indicates that it is not reliable to fully form an opinion
about the underlying occlusal relationships of a patient by examining a 2D profile
photograph except in cases with negative overjet.
6.6 Perception of facial aesthetics between the panel groups
This study showed significant differences in aesthetic evaluation between the panel
groups based on raters’ education. The present results are in accordance with an
earlier soft tissue profile study which found differences between dentists and
laypersons in the assessment of profile attractiveness (Abu Arqoub & Al-Khateeb
2011). According to the results of the present study, orthodontists evaluated
individuals with a prognathic mandible as more attractive compared to dentists and
laypersons. However, four of the dentists were specialists in prosthodontics and
stomatognathic physiology, which might have affected the evaluation of facial
attractiveness. Differences in the assessed level of facial attractiveness regarding
prognathic mandible have earlier been found between orthodontists and laypersons
(Sena et al. 2017). The previous investigation was, however, based on digitally
manipulated facial profiles with different facial convexity angles of persons with
different soft tissue ANB-angles whereas the present study was based on non-edited
facial photos (Sena et al. 2017).
6.7 Association between facial sagittal and vertical characteristics
and facial attractiveness
The present investigation demonstrated significant association between soft tissue
ANB-angle and facial aesthetics, measured using VAS scores, in all panel groups.
This result indicates that antero-posterior discrepancy or facial convexity, as
82
measured by soft tissue ANB-angle, is associated with facial attractiveness. This
finding is in line with several previous studies (Johnston et al. 2005a, Kuroda et al. 2009, Naini et al. 2012, Sena et al. 2017). An earlier facial photograph study found
strong association with sagittal position of the mandible and the level of facial
attractiveness (Sena et al. 2017). In addition, both facial photo (Kuroda et al. 2009)
and facial silhouette (Johnston et al. 2005a, Naini et al. 2012) studies have found
sagittal prominence of the mandible to be an essential factor to determine the profile
aesthetics. By contrast, an earlier facial photo study found only slight association
between facial attractiveness and soft tissue ANB-angle (Knight & Keith 2005).
When interpreting the results, one must keep in mind that the study of Knight &
Keith (2005) was based on young adults while the present study material consisted
of middle-aged adults. A longitudinal study has demonstrated that the craniofacial
complex undergoes changes in soft and skeletal tissues from late adolescence to
late adulthood (Pecora et al. 2008). In addition, a previous investigation (Bishara
et al. 1998) found soft tissue profile changes during adulthood regarding facial
convexity. The angle of soft tissue convexity has been observed to decrease
between 25 and 45 years of age in both genders (Bishara et al. 1998).
Soft tissue ANB-angle explained 27 per cent of the variability in aesthetic VAS
scores among orthodontists in the present study. The proportions among dentists
and laypersons were 20 per cent and 7 per cent, respectively. This finding
highlights the importance of the ANB-angle in the perception of facial aesthetics
among orthodontists in contrast to dentists and especially in contrast to laypersons.
A possible explanation for this might be differences in the perception of facial
proportions and facial profile between orthodontists and laypersons. Due to
education and training, orthodontists are probably more analytical when observing
facial sagittal and vertical characteristics. In addition, orthodontists might be more
sensitive to special aspects of the facial profile in comparison to laypersons (Ng et al. 2013). It has earlier been suggested that laypersons might highlight more the
overall features of the face (Cochrane et al. 1997). Laypersons might also focus
more on jaw shape, nose and hair colour (Cochrane et al. 1999).
According to quadratic regression model, perceived facial attractiveness was
not significantly associated with lower anterior facial height. Only a weak
association was found in male faces assessed by dentists. This result is parallel with
findings of a cephalometric study, where it was reported that lower facial height
did not significantly influence profile attractiveness among clinicians and
laypersons (Chew et al. 2007). However, it has been shown that lower facial height
affects perceived frontal facial attractiveness among laypersons when illustrated
83
with facial silhouettes (Varlik et al. 2010). It has also been demonstrated that both
lower facial height and sagittal position of the mandible affect perceived facial
attractiveness (Johnston et al. 2005a, Johnston et al. 2005b, Maple et al. 2005). A
potential confounding factor in the present study might be overweight of the
subjects. As an age-independent variable, overweight might hide and modify facial
characteristics. It can also be speculated that in the presence of overweight the
facial soft tissue features do not necessarily correspond equally well to the
underlying skeletal characteristics.
According to earlier literature, gender is an important factor in aesthetic
evaluation of facial features, and significant differences have been shown between
genders related to facial attractiveness (Knight & Keith 2005, Orsini et al. 2006,
Varlik 2010). This was confirmed by the present study. A slightly convex profile in
female subjects was evaluated as most attractive by orthodontists and dentists. An
earlier study showed a similar finding as professionals were found to prefer a
slightly convex profile for females (Czarnecki 1993). However, no significant
differences have been found among orthodontists in the perception of facial
aesthetics between retrognathic and prognathic profiles (Orsini et al. 2006).
6.8 Strengths and weaknesses of the study
The study population of the present study was part of a large unselected population-
based birth cohort, NFBC1966. The large population size increases the statistical
significance, which is undoubtedly a major strength of this study. The two earlier
epidemiologic malocclusion studies on Finnish adults have been based on selected
populations (Laine & Hausen 1983, Pietilä & Nordblad 2008). In the study of Laine
& Hausen (1983), the study population consisted of 451 Finnish university students.
Because all subjects were selected university students, it is questionable to
generalize the results of that study to describe Finnish adult population. In a more
recent study, the population size was large, but only malocclusions including an
apparent risk of poor prognosis for the occlusion were examined (Pietilä &
Nordblad 2008).
Another methodological advantage of this study is the standardized clinical
examination. The stomatognathic examination and the registration of occlusion was
performed by six calibrated dentists. All investigators trained with experienced
specialized dentists before the beginning of the study, which confirmed the
repeatability of the examination. In addition, inter-examiner agreement was tested
constantly during the clinical examination against a gold standard senior dentist.
84
Angle’s classes and crowding were not registered in the clinical examination,
which can be seen as a limitation of this study, particularly as earlier studies have
shown that crowding is among the most frequent forms of malocclusion in Europe
(Hensel et al. 2003, Jonsson et al. 2007, Salonen et al. 1992). The evaluation of
occlusal variables and malocclusion in sagittal, vertical, and transversal dimensions
was, however, likely to reflect both inter-arch anteroposterior relationships as well
as clinically significant crowding to a marked extent. Notably, collection of data on
molar Angle’s classification particularly in an ageing population and without
history of earlier dental treatment could be misleading, because the molar
relationship is not neutral to eventual tooth extractions and hypodontia.
Nevertheless, in study I, the comparison of the study results to earlier
epidemiological investigations would have been easier if molar relationships had
been examined. Study III showed that the positions of soft tissue A-point and soft
tissue B-point to the face were strongly associated with both overjet and overbite.
In addition, an earlier study has demonstrated that the soft tissue angle A’N’B’
differs according to Angle’s classifications (Wasserstein et al. 2015). Consequently,
it would have been interesting to know if the positions of soft tissue A- and B-
points would also have associated with Angle’s classes in this study.
A weakness in studies I and II is the lack of specificity of the questionnaire
regarding earlier orthodontic treatment experience. In addition, no data were
available regarding the subjects’ original diagnoses or earlier treatment and its
objective. The subjects were only asked whether they had received orthodontic
treatment before the age of 20 or after the age of 20 without specifying different
orthodontic treatment types. Because the earlier orthodontic treatment experience
was based on a questionnaire, distortion of the study results is possible due to recall
bias.
In study III, measurements were based on two-dimensional photographs.
Three-dimensional facial photographs would be more accurate to describe soft
tissue morphology. In addition, another weakness of the study is that data on lip
thickness was not available.
A major limitation in study IV is the subjective nature of perception of facial
attractiveness. This can produce distraction between the raters. According to an
earlier study, same positioning of the lines in VAS does not necessarily express the
same feeling for different raters (Aitken 1969). Since all subjects were members of
the NFBC1966, age variation did not exist. According to earlier literature, rater’s
age (Kiekens et al. 2007, Kiekens et al. 2008, Türkkahraman & Gökalp 2004),
gender (Cochrane et al. 1999, Kiekens et al. 2007, Türkkahraman & Gökalp 2004)
85
and education (Türkkahraman & Gökalp 2004) have an influence on perceived
facial attractiveness. It has earlier been shown that females and younger individuals
tend to be stricter raters of facial attractiveness than males and older adults (Foos
et al. 2011, Soler et al. 2012). Due to the unequal distribution of raters’ gender in
the present study, the influence of raters’ gender and education on perceived facial
aesthetics could not be separated and examined. The mean age of the raters varied
between 41 and 56 years of age and it was thus similar to the study population. It
would have been better if there had been no age and gender variation among the
raters and if all dentists had been general dentists. For study ethical reasons, the
raters had to have permission to see the facial photos which limited the number and
composition of the raters. Therefore, all laypersons were statisticians working at
the Faculty of Medicine, University of Oulu. In addition, the effect of overweight
on facial characteristics could have been analysed in more detail.
6.9 Clinical implications and future perspectives
This study showed a statistically significant association between morphological
malocclusions, occlusal disturbances and TMD. The present study demonstrated
that occlusal disturbances should be considered as potential risk factors of TMD.
Positive moderate correlation was found between facial soft tissue profile
measurements and the severity of overjet. The facial profile was less affected by
overbite. An increased concern about radiation exposure of lateral skull
radiographs has recently raised the role of photographs in imaging of malocclusion
and facial soft tissue profile (Dimaggio et al. 2007, Kale-Varlk 2008). In addition,
profile photographs are a low-cost and non-invasive tool to document facial soft
tissue characteristics (Kale-Varlk 2008, Staudt & Kiliaridis 2009, Wasserstein et al. 2015). This study presented mean values of the soft tissue profile measurements in
a large homogeneous population of adults. The present results can be used as gold
standard values in future studies in an attempt to examine whether it is possible to
detect malocclusion from facial soft tissue profile photos. In other words, this study
showed that anterior-posterior position of the upper lip and positions of soft tissue
A- and B-points were moderately to strongly associated with sagittal incisor
relationships.
The soft tissue profile was significantly affected among subjects with cases of
negative overjet. Therefore, in patients with negative overjet, 2D profile
photographs provide significantly relevant information regarding the underlying
anterior occlusal relationships. It has already been demonstrated that profile
86
photographs can detect a skeletal Class III discrepancy with high probability
(Staudt & Kiliaridis 2009). The authors of the earlier study concluded that even
though lateral cephalograms might be indicated for differential diagnosis, profile
photographs might be useful during the initial consultation (Staudt & Kiliaridis
2009). Related to screening of malocclusion, it is especially important to find
children with skeletal Class III sufficiently early. Therefore, it would be interesting
to study in the future if facial profile is sensitive for Class III discrepancy in all age
groups.
Significant differences were found in the perception of facial attractiveness
between orthodontists and laypersons regarding the soft tissue ANB-angle.
Clinically, this highlights the importance of considering patient’s opinion on facial
aesthetics regarding facial convexity in the orthodontic treatment plan. Interestingly,
this investigation showed that soft tissue A- and B-points are good predictors for
overjet, overbite and facial aesthetics.
Facial soft tissue profile was significantly associated with anterior
malocclusions. The role of genetics in the development of malocclusion has been
studied extensively (Cruz et al. 2011, Mossey 1999, Nikopensius et al. 2013, Xue
et al. 2010). Earlier studies have also managed to quantify craniofacial variability
among patients with identical malocclusion (Bui et al. 2006, Moreno Uribe et al. 2014). In the future, it would therefore be interesting to study if there are specific
genetic loci related to facial characteristics and malocclusions.
87
7 Conclusions
I The most common malocclusion in the Finnish adult population in Northern
Finland was lateral crossbite. A significant male dominance was demonstrated
in the prevalence of malocclusion traits. Females showed a higher history of
orthodontic treatment. This study indicates that orthodontic treatment carried
out in childhood was, on average, adequate in reducing the prevalence of
malocclusion traits to the level observed in the general population.
II A significant association was found between occlusion and TMD. TMD signs
were associated with lateral crossbite, scissors bite, negative overjet and the
length and lateral deviation in RCP-ICP slide. Orthodontically treated subjects
presented more often with TMD than untreated subjects. Especially crepitus in
TMJs and degenerative joint disease were significantly more common among
orthodontically treated compared to untreated subjects.
III Moderate significant correlation was found between overjet and facial soft
tissue profile while facial profile was less affected by overbite. Soft tissue A-
point and soft tissue B-point are good predictors of overjet and overbite. A
profile photograph provides significantly relevant information regarding the
anterior occlusal relationships in negative overjet cases.
IV Facial sagittal dimensions appeared to influence facial aesthetics more than
vertical characteristics in middle-aged Finnish adults. Soft tissue ANB-angle
was more significant in explaining facial attractiveness among orthodontists
than among dentists and laypersons. The overall perception of facial
attractiveness related to facial characteristics differed between orthodontists,
dentists and laypersons.
88
89
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Appendix
Fig. 9. Supplementary Figure 1. Histograms for overjet and overbite.
106
Fig. 10. Supplementary Figure 2. P-P plots of the regression standardized residual
values for overjet and overbite.
107
Orginal articles
I Krooks L, Pirttiniemi P, Kanavakis G & Lähdesmäki R (2016) Prevalence of malocclusion traits and orthodontic treatment in a Finnish adult population. Acta Odontol Scand 74(5): 362-367.
II Jussila P, Krooks L, Näpänkangas R, Päkkilä J, Lähdesmäki R, Pirttiniemi P & Raustia A (2018) The role of occlusion in temporomandibular disorders (TMD) in the Northern Finland Birth Cohort (NFBC) 1966. Cranio 8:1-7.
III Kanavakis G *, Krooks L *, Lähdesmäki R & Pirttiniemi P (2018) The influence of overjet and overbite on soft tissue profile in mature adults. A cross-sectional population study. Am J Orthod Dentofacial Orthop. In press.
IV Krooks L, Pirttiniemi P, Tolvanen M, Kanavakis G, Lähdesmäki R & Silvola AS (2018) Association of facial sagittal and vertical characteristics with facial aesthetics in the Northern Finland Birth Cohort 1966. Eur J Orthod. In press.
Reprinted with permission from Taylor & Francis (I-II), Elsevier (III) and Oxford
University Press (IV).
Original publications are not included in the electronic version of the dissertation.
108
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MALOCCLUSIONS IN RELATION TO FACIAL SOFT TISSUE CHARACTERISTICS,FACIAL AESTHETICS AND TEMPOROMANDIBULAR DISORDERS IN THE NORTHERN FINLAND BIRTH COHORT 1966
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