European Journal of Orthodontics 35 (2013) 230–235doi:10.1093/ejo/cjr121Advance Access publication 19 October 2011

© The Author 2011. Published by Oxford University Press on behalf of the European Orthodontic Society.All rights reserved. For permissions, please email: journals.permissions@oup.com

European Journal of Orthodontics 1 of 6 © The Author 2011. Published by Oxford University Press on behalf of the European Orthodontic Society.doi:10.1093/ejo/cjr121 All rights reserved. For permissions, please email: journals.permissions@oup.com

Introduction

Occlusal and dentoalveolar changes in the primary and permanent dentitions during the rst two rst decades of life are well documented ( Persson and Thilander, 1995 ; Bishara and Ferguson, 2001 ; Prof t, 2007 ). Less is known about occlusal and dentoalveolar changes in adulthood, after the ages of 20 – 25 years. Because of the increasing demand for adult orthodontic treatment , an understanding of occlusal and dentoalveolar changes is of relevance to modern orthodontic practice.

Harris (1997) reported that in 60 subjects (43 men and 17 women), overbite and overjet remained constant during an observation period of 35 years, from 20 to 55 years of age. Akgul and Toygar (2002) investigated a group of 30 subjects (14 females and 16 males) over an observation period from 22 to 32 years and reported a signi cant mean increase in overbite in the females, while the overjet showed no signi cant changes in males or females. In a study of 27 subjects (14 females and 13 males) from age 21 to 28 years, Tibana et al. (2004) reported a signi cant increase in mean overbite, but no signi cant changes in mean overjet at the end of the observation period.

With respect to transverse relationships, Harris (1997) found that arch width increased with age. Maxillary intercanine and mandibular intermolar widths, as well as maxillary intermolar width increased. Mandibular intercanine width remained constant during the 35 year s observation period. In contrast, Tibana et al. (2004) reported

A 40 years follow-up of dental arch dimensions and incisor

irregularity in adults

Nikolaos Tsiopas * , Maria Nilner ** , Lars Bondemark * and Krister Bjerklin * Departments of * Orthodontics and ** Stomatognathic Physiology, Faculty of Dentistry, Malmö University, Sweden

Correspondence to: Nikolaos Tsiopas, Birger Jarlsgatan 9C, 55463 Jönköping, Sweden. E-mail: nicco85@hotmail.com

SUMMARY Dentoalveolar changes in adulthood have not been extensively documented. Such changes may have important implications for the long-term stability of orthodontic treatment. To analyse occlusal and dentoalveolar changes in adults from the age of 20 years to the age of 60 years. The material comprised 18 Swedish dentists, 16 men and 2 women, with no missing teeth and no prosthodontic or orthodontic treatment. Measurements were recorded on study casts made between 1949 and 1989 at the Department of Stomatognathic Physiology at the Faculty of Odontology in Malmö, thus documenting changes over an average period of 38.4 years. Malocclusion traits, overbite, overjet, dental arch length and width, and Little ’ s irregularity index were registered. There was a signifi cant increase in Little ’ s irregularity index in the mandible (1.0 mm, P < 0.01) and a decrease in arch length in both jaws (0.5 – 0.9 mm, P < 0.05). The maxillary and mandibular intercanine widths decreased by 0.8 and 1.0 mm, respectively ( P < 0.001). The malocclusion traits, overbite, and overjet remained unchanged during the observation period. The results confi rm that dentoalveolar changes occur as a continuous process throughout adult life. The fi ndings of potential clinical importance are decreases in arch length and depth, resulting in a decrease in intercanine width and an increase in anterior crowding. In clinical orthodontic practice, these fi ndings have important implications for treatment planning and long-term stability after orthodontic treatment.

no signi cant changes in maxillary intermolar and intercanine widths. Mandibular intercanine width showed a mean decrease of 0.4 mm (SD 0.55). Moreover, the studies by Harris (1997) and Akgul and Toygar (2002) reported that arch lengths decreased in the maxilla and the mandible.

There are few studies of dentoalveolar changes in older adults, primarily because of the dif culties inherent in gathering longitudinal data ( Bishara et al. , 1994 , 1996 , 1997 , 1998 ; Harris, 1997 ). These studies reported contradictory ndings, probably because of age differences in the study samples, different time intervals, missing teeth, and intervening orthodontic and/or prosthodontic treatment.

The aim of the present study was to record and analyse occlusal and dentoalveolar changes from the age of 20 years to the age of 60 years in a group of Swedish subjects.

Subjects and methods

Subjects

The initial sample group comprised 35 individuals, 22 males and 13 females, with two sets of dental stone study casts, made from alginate impressions, with an average interval of 10 years, from 1949 to 1960. Twenty-three of the subjects (20 males and 3 females) were originally dental students. The remaining 12 (2 males and 10 females) were patients who had undergone treatment at the Department of Occlusal Analysis and Rehabilitation at the Royal Dental

N. TSIOPAS ET AL.2 of 6

School, Malmo, Sweden. At baseline , few of the subjects had had occlusal adjustment by grinding, some had small llings placed involving occlusal and proximal tooth surfaces , and few others had had minor prosthodontic restaurations performed, i.e. single crowns ( Lammie and Posselt, 1965 ).

In 1989 , an attempt was made to recall these 35 subjects, in order to obtain a third set of study models.

The inclusion criteria for the present study were

1. No missing teeth or history of extractions, including second permanent molars.

2. No history of orthodontic or prosthodontic treatment. 3. Aged more than or equal to 20 years at the initial

registration. Eighteen subjects (16 males and 2 females) ful lled the

inclusion criteria ( Figure 1 and Table 1 ) and thus constituted the sample for the present study.

Methods

The occlusion and dentoalveolar changes were classi ed according to the criteria by Björk et al. (1964) . ‘ Overbite ’was registered as the surface of the mandibular incisors in the vertical plane that are covered by the maxillary incisors. ‘ Overjet ’ was measured at the most protruding maxillary incisor. ‘ Arch length ’ was measured from the mesial contact point of the rst permanent molar to the mesial surface of the canine and from the mesial aspect of the canine to the midline ( Figure 2a , A + B). ‘ Intercanine width ’ was measured as the transverse distance between the left and right canines at the gingival margin ( Figure 2a , C). ‘ Intermolar width ’ was measured as the distance between the left and right molars at the gingival margin ( Figure 2a , D). The ‘ arch depth ’ was measured from the buccal surfaces of the central incisors at the midline to the distal surfaces of the canines ( Figure 2b , E) and to the distal surfaces of the rst permanent molars ( Figure 2b , E + F). ‘ Little ’ s irregularity index ’ ( Little, 1975 ) was used to measure the irregularity in the anterior part of the maxilla and mandible, respectively ( Figure 3 ). The linear displacement of the anatomic contact points of each incisor and canine from the adjacent tooth was measured: the sum of these ve displacements represented the relative degree of anterior irregularity. All registrations were made with the use of a digital caliper (Mitutoyo Absolute coolant proof IP 67) to the nearest 0.1 mm.

Data analyses

The data were analysed with Student ’s t -test. A P value <0.05 was considered as statistically signi cant. The error of the method, determined according to Dahlbergs formula, Dahlberg (1940) , ranged from 0.12 to 0.26 mm. The precision of the registrations was tested by double measurements of 20 randomly selected study casts.

Table 1� Age distributions at the three registrations . SD, standard deviation.

T1 T2 T3

Mean age 22.7 32.3 61.3 SD 2.0 2.6 2.7

T1 = 1949 ; T2 = 1960 ; T3 = 1989 .

Figure 1 � Subjects that fullled the inclusion criteria.

Figure 2 � (a) Arch length A + B, intercanine C , and intermolar width D. (b) Arch depths, to the canine E and to the rst molars E + F.

Results

The mean values for the dental cast measurements and standard deviations at the three registrations are presented in Table 2 . Descriptive statistics of the mean value changes between the occlusal registrations are presented in Table 3 . The malocclusion traits, overbite , and overjet remained

OCCLUSAL AND DENTOALVEOLAR CHANGES IN ADULTHOOD 231European Journal of Orthodontics 1 of 6 © The Author 2011. Published by Oxford University Press on behalf of the European Orthodontic Society.doi:10.1093/ejo/cjr121 All rights reserved. For permissions, please email: journals.permissions@oup.com

Introduction

Occlusal and dentoalveolar changes in the primary and permanent dentitions during the rst two rst decades of life are well documented ( Persson and Thilander, 1995 ; Bishara and Ferguson, 2001 ; Proft, 2007 ). Less is known about occlusal and dentoalveolar changes in adulthood, after the ages of 20 – 25 years. Because of the increasing demand for adult orthodontic treatment , an understanding of occlusal and dentoalveolar changes is of relevance to modern orthodontic practice.

Harris (1997) reported that in 60 subjects (43 men and 17 women), overbite and overjet remained constant during an observation period of 35 years, from 20 to 55 years of age. Akgul and Toygar (2002) investigated a group of 30 subjects (14 females and 16 males) over an observation period from 22 to 32 years and reported a signi cant mean increase in overbite in the females, while the overjet showed no signicant changes in males or females. In a study of 27 subjects (14 females and 13 males) from age 21 to 28 years, Tibana et al. (2004) reported a signicant increase in mean overbite, but no signicant changes in mean overjet at the end of the observation period.

With respect to transverse relationships, Harris (1997) found that arch width increased with age. Maxillary intercanine and mandibular intermolar widths, as well as maxillary intermolar width increased. Mandibular intercanine width remained constant during the 35 year s observation period. In contrast, Tibana et al. (2004) reported

A 40 years follow-up of dental arch dimensions and incisor

irregularity in adults

Nikolaos Tsiopas * , Maria Nilner ** , Lars Bondemark * and Krister Bjerklin * Departments of * Orthodontics and ** Stomatognathic Physiology, Faculty of Dentistry, Malmö University, Sweden

Correspondence to: Nikolaos Tsiopas, Birger Jarlsgatan 9C, 55463 Jönköping, Sweden. E-mail: nicco85@hotmail.com

SUMMARY Dentoalveolar changes in adulthood have not been extensively documented. Such changes may have important implications for the long-term stability of orthodontic treatment. To analyse occlusal and dentoalveolar changes in adults from the age of 20 years to the age of 60 years. The material comprised 18 Swedish dentists, 16 men and 2 women, with no missing teeth and no prosthodontic or orthodontic treatment. Measurements were recorded on study casts made between 1949 and 1989 at the Department of Stomatognathic Physiology at the Faculty of Odontology in Malmö, thus documenting changes over an average period of 38.4 years. Malocclusion traits, overbite, overjet, dental arch length and width, and Little ’ s irregularity index were registered. There was a significant increase in Little ’ s irregularity index in the mandible (1.0 mm, P < 0.01) and a decrease in arch length in both jaws (0.5 – 0.9 mm, P < 0.05). The maxillary and mandibular intercanine widths decreased by 0.8 and 1.0 mm, respectively ( P < 0.001). The malocclusion traits, overbite, and overjet remained unchanged during the observation period. The results confirm that dentoalveolar changes occur as a continuous process throughout adult life. The findings of potential clinical importance are decreases in arch length and depth, resulting in a decrease in intercanine width and an increase in anterior crowding. In clinical orthodontic practice, these findings have important implications for treatment planning and long-term stability after orthodontic treatment.

no signicant changes in maxillary intermolar and intercanine widths. Mandibular intercanine width showed a mean decrease of 0.4 mm (SD 0.55). Moreover, the studies by Harris (1997) and Akgul and Toygar (2002) reported that arch lengths decreased in the maxilla and the mandible.

There are few studies of dentoalveolar changes in older adults, primarily because of the difculties inherent in gathering longitudinal data ( Bishara et al. , 1994 , 1996 , 1997 , 1998 ; Harris, 1997 ). These studies reported contradictory ndings, probably because of age differences in the study samples, different time intervals, missing teeth, and intervening orthodontic and/or prosthodontic treatment.

The aim of the present study was to record and analyseocclusal and dentoalveolar changes from the age of20 years to the age of 60 years in a group of Swedishsubjects.

Subjects and methods

Subjects

The initial sample group comprised 35 individuals, 22 males and 13 females, with two sets of dental stone study casts, made from alginate impressions, with an average interval of 10 years, from 1949 to 1960. Twenty-three of the subjects (20 males and 3 females) were originally dental students. The remaining 12 (2 males and 10 females) were patients who had undergone treatment at the Department of Occlusal Analysis and Rehabilitation at the Royal Dental

N. TSIOPAS ET AL.2 of 6

School, Malmo, Sweden. At baseline , few of the subjects had had occlusal adjustment by grinding, some had small llings placed involving occlusal and proximal tooth surfaces , and few others had had minor prosthodontic restaurations performed, i.e. single crowns ( Lammie and Posselt, 1965 ).

In 1989 , an attempt was made to recall these 35 subjects, in order to obtain a third set of study models.

The inclusion criteria for the present study were

1. No missing teeth or history of extractions, includingsecond permanent molars.

2. No history of orthodontic or prosthodontic treatment. 3. Aged more than or equal to 20 years at the initial

registration. Eighteen subjects (16 males and 2 females) ful lled the

inclusion criteria ( Figure 1 and Table 1 ) and thus constituted the sample for the present study.

Methods

The occlusion and dentoalveolar changes were classi ed according to the criteria by Björk et al. (1964) . ‘ Overbite ’ was registered as the surface of the mandibular incisors in the vertical plane that are covered by the maxillary incisors. ‘ Overjet ’ was measured at the most protruding maxillary incisor. ‘ Arch length ’ was measured from the mesial contact point of the rst permanent molar to the mesial surface of the canine and from the mesial aspect of the canine to the midline ( Figure 2a , A + B). ‘ Intercanine width ’ was measured as the transverse distance between the left and right canines at the gingival margin ( Figure 2a , C). ‘ Intermolar width ’ was measured as the distance between the left and right molars at the gingival margin ( Figure 2a , D). The ‘ arch depth ’ was measured from the buccal surfaces of the central incisors at the midline to the distal surfaces of the canines ( Figure 2b , E) and to the distal surfaces of the rst permanent molars ( Figure 2b , E + F). ‘ Little ’ s irregularity index ’ ( Little, 1975 ) was used to measure the irregularity in the anterior part of the maxilla and mandible, respectively ( Figure 3 ). The linear displacement of the anatomic contact points of each incisor and canine from the adjacent tooth was measured: the sum of these ve displacements represented the relative degree of anterior irregularity. All registrations were made with the use of a digital caliper (Mitutoyo Absolute coolant proof IP 67) to the nearest 0.1 mm.

Data analyses

The data were analysed with Student ’ s t -test. A P value <0.05 was considered as statistically signi cant. The error of the method, determined according to Dahlbergs formula, Dahlberg (1940) , ranged from 0.12 to 0.26 mm. The precision of the registrations was tested by double measurements of 20 randomly selected study casts.

Table 1 � Age distributions at the three registrations . SD, standard deviation.

T1 T2 T3

Mean age 22.7 32.3 61.3 SD 2.0 2.6 2.7

T1 = 1949 ; T2 = 1960 ; T3 = 1989 .

Figure 1 � Subjects that ful lled the inclusion criteria.

Figure 2 � (a) Arch length A + B, intercanine C , and intermolar width D. (b) Arch depths, to the canine E and to the rst molars E + F.

Results

The mean values for the dental cast measurements and standard deviations at the three registrations are presented in Table 2 . Descriptive statistics of the mean value changes between the occlusal registrations are presented in Table 3 . The malocclusion traits, overbite , and overjet remained

232 N. TSIOPAS ET AL.3 of 6 OCCLUSAL AND DENTOALVEOLAR CHANGES IN ADULTHOOD

unchanged during the observation period ( Table 4 ). All the other variables changed on avarage 1.1 mm or less ( Table 3 ).

Mandibular incisor crowding increased: the mean change in Little ’ s irregularity index from the initial to the nal registrations was 1.0 mm (SD 1.14). From the initial to the second registrations, there were no signi cant changes in maxillary incisor crowding.

The maxillary arch lengths decreased from the initial to the nal registrations, but no changes occurred from the initial to the second registrations. Similar changes were recorded in the mandible, i.e. from the initial to the nal registrations, the mean decrease in arch length was 0.7 mm (SD 0.74 ; Table 3 ).

The average maxillary and mandibular intercanine widths decreased by a mean of 0.8 mm (SD 0.62) and 1.1 mm (SD 0.78), respectively ( Table 3 ). Maxillary intermolar width

Figure 3 � Measuring Little ’ s irregularity index.

Table 2 � Mean values for the dental cast measurements and standard deviations (SDs) at T1 = 1949, T2 = 1960, and T3 = 1989.

Parameter Mean T1 SD Mean T2 SD Mean T3 SD

Overjet 3.7 1.33 3.7 1.33 3.8 1.54 Overbite 3.5 1.81 3.5 1.81 3.3 1.77 Maxilla � Irregularity index 2.9 3.09 3.2 3.09 2.9 2.89 Mandible � Irregularity index 3.2 3.66 3.6 3.57 4.2 4.1 Maxilla � Arch length right 36.6 3 36.5 3.15 36.1 3.37 � Arch length left 36.8 2.43 36.7 2.71 36.2 2.79 Mandible � Arch length left 31.4 2.04 31.0 2.21 30.9 2.25 � Arch length right 30.8 2.73 30.6 2.78 29.9 2.74 Maxilla � Transverse width 23.9 2.06 23.6 1.91 23.1 2.26 � Transverse width 35.2 3.03 35.3 3.05 35.5 3.14 Mandible � Transverse width 18.1 1.59 18.0 1.37 17.0 1.93 � Transverse width 34.6 3.79 34.0 3.81 35.3 3.95 Maxilla � Arch depth 13.4 1.63 13.2 1.66 12.8 2.9 � A`rch depth 37.0 2.99 36.5 3.41 36.1 3.19 Mandible � Arch depth 10.1 1.69 9.6 1.73 9.3 1.66 � Arch depth 32.4 2.19 31.9 2.34 31.6 2.67

remained unchanged but increased in the mandible from the initial to the nal registrations ( Table 3 ).

A decrease in arch depth was observed in both jaws, indicating a gradual mesial migration of the dentition. In the maxilla, the arch depth at the canines decreased by 0.6 mm (SD 0.98) from the initial to the nal registrations and by 0.5 mm (SD 0.54) in the mandible . The arch depth measurements for the molars also decreased in both jaws ( Table 3 ).

Discussion

The purpose of this longitudinal study was to investigate occlusal and dentoalveolar changes from early adulthood to middle age. Although the final sample was small, the material was unique. Stringent inclusion criteria were applied and the observation period was approximately 40 years. In order to evaluate only changes occurring in adulthood, the subjects were limited to those whose active growth was completed.

Long-term studies of the adult dentition present particular challenges. Physiologically, there is a wide variation in the age at which active growth is completed. Logistically, it is dif cult to locate subjects to make follow-up appointments. Clinically, the subject ’ s dental status may have changed over time because of treatment interventions: thus , the subject may present at follow-up with a history of extractions or orthodontic or prosthodontic treatment in the intervening years. The inclusion criteria in the present study were, however, no missing teeth or history of extractions and no

N. TSIOPAS ET AL.4 of 6

orthodontic or prosthodontic treatment carried out during the observation period.

The present study showed that the occlusion, overbite , and overjet was stable, but dentoalveolar changes occur in the adult dentition. In the anterior part of the dentition, decreases in arch length and width lead to anterior crowding. There was also an increase in dental arch width at the rst permanent molar.

Overjet

The values for overjet did not change signicantly during theobservation period. Similar ndings have been reported inprevious studies by Bishara et al. (1996) , Tibana et al. (2004) ,Harris (1997) , and Akgul and Toygar (2002) . However, in thestudy by Bishara et al. (1996) , some subjects had lost two orthree teeth. Only the study by Bondevik (1998) reported asignicant decrease in overjet among the male subjects, but30 – 35 per cent of these patients had undergone orthodontic

Table 3� Descriptive statistics of the mean value changes between T1 – T2, T1 – T3, and T2 – T3. SD standard deviation.

Parameter T1 – T2 SD P T1 – T3 SD P T2 – T3 SD P

Overjet 0 0.51 ns 0.1 0.77 ns 0.1 0.69 ns Overbite 0 0.71 ns − 0.2 1.28 ns − 0.2 0.94 ns Maxilla� Irregularity index 0.3 1 ns 0 1.33 ns − 0.3 0.59 ns Mandible� Irregularity index 0.4 0.94 ns 1 1.14 ** 0.6 1.21 * Maxilla� Arch length right − 0.1 0.55 ns − 0.5 0.85 * − 0.4 0.84 ns � Arch length left − 0.1 0.56 ns − 0.6 0.67 ** − 0.5 0.54 ** Mandible� Arch length left − 0.4 0.72 * − 0.5 0.74 ** − 0.1 0.76 ns � Arch length right − 0.2 0.72 ns − 0.9 1 ** − 0.7 0.83 ** Maxilla� Transverse width − 0.3 0.49 * − 0.8 0.62 ** − 0.5 0.47 ** � Transverse width 0.1 0.4 ns 0.3 0.71 ** 0.3 0.68 ** Mandible� Transverse width − 0.1 0.41 * − 1.1 0.78 *** − 1.0 0.54 ** � Transverse width 0.4 0.54 * 0.7 1.17 ** 0.3 0.95 * Maxilla� Arch depth − 0.2 0.54 ns − 0.6 0.98 * − 0.4 0.8 * � Arch depth − 0.5 0.56 ns − 0.9 0.95 ** − 0.4 0.8 * Mandible� Arch depth − 0.7 1.68 * − 0.5 0.54 * − 0.2 0.3 ns � Arch depth − 0.6 0.54 ns − 0.8 0.85 ns − 0.2 0.54 ns

ns, non-signicant. T1 = 1949 ; T2 = 1960 ; T3 = 1989. *0.01 < P < 0.05; **0.001 < P < 0.01; *** P < 0.001.

Table 4� Malocclusion traits from 1949 to 1989 according to Björk et al. (1964) for the 18 subjects .

1949 1989

Angle I 14 14 Angle II 4 4 Crossbite 1 1 Open bite 1 1 Deep bite 2 2

treatmen t . The minor decrease in overjet reported (mean 0.14mm) is, however, not clinically relevant.

Overbite

The present study failed to disclose any signicant change inoverbite from age 20 to 60 years. In contrast, several previousstudies have reported considerable increases in overbite. In asample observed from age 21 to 28 years, Tibana et al.(2004) reported an increase of 0.39 mm (SD 0.45). Signi cantincreases in overbite are also reported in earlier studies byAkgul and Toygar (2002) and Bishara et al. (1996) in a groupof females from age 25 to 45 years: mean 0.5 mm (SD 0.19)and 1 mm (SD 0.5) , respectively. The contradictory results inthe present study might be attributable to the predominantlymale sample and high mean ages. Nevertheless , our resultsare in accordance with those of Harris (1997) : in a samplecomprising both male and female subjects ; overbite andoverjet remained constant from 20 to 55 years of age.

Arch length

Signicant decreases in arch lengths occurred in both themaxilla and the mandible, the most pronounced changesoccurring between the second and the nal registrations.Similar ndings were observed by Harris (1997) , Akgul andToygar (2002) , and Bishara et al. (1998) . In contrast,Bondevik (1998) reported that arch length remainedunchanged from age 23 to 34 years. Several factors may have

OCCLUSAL AND DENTOALVEOLAR CHANGES IN ADULTHOOD 2333 of 6 OCCLUSAL AND DENTOALVEOLAR CHANGES IN ADULTHOOD

unchanged during the observation period ( Table 4 ). All the other variables changed on avarage 1.1 mm or less ( Table 3 ).

Mandibular incisor crowding increased: the mean change in Little ’s irregularity index from the initial to the nal registrations was 1.0 mm (SD 1.14). From the initial to the second registrations, there were no signicant changes in maxillary incisor crowding.

The maxillary arch lengths decreased from the initial to the nal registrations, but no changes occurred from the initial to the second registrations. Similar changes were recorded in the mandible, i.e. from the initial to the nal registrations, the mean decrease in arch length was 0.7 mm (SD 0.74 ; Table 3 ).

The average maxillary and mandibular intercanine widths decreased by a mean of 0.8 mm (SD 0.62) and 1.1 mm (SD 0.78), respectively ( Table 3 ). Maxillary intermolar width

Figure 3 � Measuring Little ’ s irregularity index.

Table 2� Mean values for the dental cast measurements and standard deviations (SDs) at T1 = 1949, T2 = 1960, and T3 = 1989.

Parameter Mean T1 SD Mean T2 SD Mean T3 SD

Overjet 3.7 1.33 3.7 1.33 3.8 1.54 Overbite 3.5 1.81 3.5 1.81 3.3 1.77 Maxilla� Irregularity index 2.9 3.09 3.2 3.09 2.9 2.89 Mandible� Irregularity index 3.2 3.66 3.6 3.57 4.2 4.1 Maxilla� Arch length right 36.6 3 36.5 3.15 36.1 3.37 � Arch length left 36.8 2.43 36.7 2.71 36.2 2.79 Mandible� Arch length left 31.4 2.04 31.0 2.21 30.9 2.25 � Arch length right 30.8 2.73 30.6 2.78 29.9 2.74 Maxilla� Transverse width 23.9 2.06 23.6 1.91 23.1 2.26 � Transverse width 35.2 3.03 35.3 3.05 35.5 3.14 Mandible� Transverse width 18.1 1.59 18.0 1.37 17.0 1.93 � Transverse width 34.6 3.79 34.0 3.81 35.3 3.95 Maxilla� Arch depth 13.4 1.63 13.2 1.66 12.8 2.9 � A`rch depth 37.0 2.99 36.5 3.41 36.1 3.19 Mandible� Arch depth 10.1 1.69 9.6 1.73 9.3 1.66 � Arch depth 32.4 2.19 31.9 2.34 31.6 2.67

remained unchanged but increased in the mandible from the initial to the nal registrations ( Table 3 ).

A decrease in arch depth was observed in both jaws, indicating a gradual mesial migration of the dentition. In the maxilla, the arch depth at the canines decreased by 0.6 mm (SD 0.98) from the initial to the nal registrations and by 0.5 mm (SD 0.54) in the mandible . The arch depth measurements for the molars also decreased in both jaws ( Table 3 ).

Discussion

The purpose of this longitudinal study was to investigate occlusal and dentoalveolar changes from early adulthood to middle age. Although the final sample was small, thematerial was unique. Stringent inclusion criteria wereapplied and the observation period was approximately40 years. In order to evaluate only changes occurring in adulthood, the subjects were limited to those whose active growth was completed.

Long-term studies of the adult dentition present particular challenges. Physiologically, there is a wide variation in the age at which active growth is completed. Logistically, it is difcult to locate subjects to make follow-up appointments. Clinically, the subject ’s dental status may have changed over time because of treatment interventions: thus , the subject may present at follow-up with a history of extractions or orthodontic or prosthodontic treatment in the intervening years. The inclusion criteria in the present study were, however, no missing teeth or history of extractions and no

N. TSIOPAS ET AL.4 of 6

orthodontic or prosthodontic treatment carried out during the observation period.

The present study showed that the occlusion, overbite , and overjet was stable, but dentoalveolar changes occur in the adult dentition. In the anterior part of the dentition, decreases in arch length and width lead to anterior crowding. There was also an increase in dental arch width at the rst permanent molar.

Overjet

The values for overjet did not change signi cantly during the observation period. Similar ndings have been reported in previous studies by Bishara et al . (1996) , Tibana et al. (2004) , Harris (1997) , and Akgul and Toygar (2002) . However, in the study by Bishara et al . (1996) , some subjects had lost two or three teeth. Only the study by Bondevik (1998) reported a signi cant decrease in overjet among the male subjects, but 30 – 35 per cent of these patients had undergone orthodontic

Table 3 � Descriptive statistics of the mean value changes between T1 – T2, T1 – T3, and T2 – T3. SD standard deviation.

Parameter T1 – T2 SD P T1 – T3 SD P T2 – T3 SD P

Overjet 0 0.51 ns 0.1 0.77 ns 0.1 0.69 ns Overbite 0 0.71 ns − 0.2 1.28 ns − 0.2 0.94 ns Maxilla � Irregularity index 0.3 1 ns 0 1.33 ns − 0.3 0.59 ns Mandible � Irregularity index 0.4 0.94 ns 1 1.14 ** 0.6 1.21 * Maxilla � Arch length right − 0.1 0.55 ns − 0.5 0.85 * − 0.4 0.84 ns � Arch length left − 0.1 0.56 ns − 0.6 0.67 ** − 0.5 0.54 ** Mandible � Arch length left − 0.4 0.72 * − 0.5 0.74 ** − 0.1 0.76 ns � Arch length right − 0.2 0.72 ns − 0.9 1 ** − 0.7 0.83 ** Maxilla � Transverse width − 0.3 0.49 * − 0.8 0.62 ** − 0.5 0.47 ** � Transverse width 0.1 0.4 ns 0.3 0.71 ** 0.3 0.68 ** Mandible � Transverse width − 0.1 0.41 * − 1.1 0.78 *** − 1.0 0.54 ** � Transverse width 0.4 0.54 * 0.7 1.17 ** 0.3 0.95 * Maxilla � Arch depth − 0.2 0.54 ns − 0.6 0.98 * − 0.4 0.8 * � Arch depth − 0.5 0.56 ns − 0.9 0.95 ** − 0.4 0.8 * Mandible � Arch depth − 0.7 1.68 * − 0.5 0.54 * − 0.2 0.3 ns � Arch depth − 0.6 0.54 ns − 0.8 0.85 ns − 0.2 0.54 ns

ns, non-signi cant. T1 = 1949 ; T2 = 1960 ; T3 = 1989. *0.01 < P < 0.05; **0.001 < P < 0.01; *** P < 0.001.

Table 4 � Malocclusion traits from 1949 to 1989 according to Björk et al. (1964) for the 18 subjects .

1949 1989

Angle I 14 14 Angle II 4 4 Crossbite 1 1 Open bite 1 1 Deep bite 2 2

treatmen t . The minor decrease in overjet reported (mean 0.14 mm) is, however , not clinically relevant.

Overbite

The present study failed to disclose any signi cant change in overbite from age 20 to 60 years. In contrast, several previous studies have reported considerable increases in overbite. In a sample observed from age 21 to 28 years, Tibana et al. (2004) reported an increase of 0.39 mm (SD 0.45). Signi cant increases in overbite are also reported in earlier studies by Akgul and Toygar (2002) and Bishara et al . (1996) in a group of females from age 25 to 45 years: mean 0.5 mm (SD 0.19) and 1 mm (SD 0.5) , respectively. The contradictory results in the present study might be attributable to the predominantly male sample and high mean ages. Nevertheless , our results are in accordance with those of Harris (1997) : in a sample comprising both male and female subjects ; overbite and overjet remained constant from 20 to 55 years of age.

Arch length

Signi cant decreases in arch lengths occurred in both the maxilla and the mandible, the most pronounced changes occurring between the second and the nal registrations. Similar ndings were observed by Harris (1997) , Akgul and Toygar (2002) , and Bishara et al . (1998) . In contrast, Bondevik (1998) reported that arch length remained unchanged from age 23 to 34 years. Several factors may have

234 N. TSIOPAS ET AL.5 of 6 OCCLUSAL AND DENTOALVEOLAR CHANGES IN ADULTHOOD

contributed to the contradictory results, in particular , the difference in the ages of the subjects and the confounding effect of orthodontic treatment: thus , Bondevik (1998) followed his subjects through early adulthood, from age 23 to 34 years, whereas the subjects in the other studies, including ours, underwent nal registration at the age of 50 – 60 years.

A slow decrease in arch length implies gradual anterior migration of the dentition. Mesial drift of the rst permanent molars will result in a decrease in arch length and depth in both arches. This also explains the anterior crowding , which increases with age, reported by Thilander (2009) and Henriksson et al. (2001) . A decrease in arch length may have an even more plausible explanation in other factors, such as changed intrinsic forces by tongue and lips ( Prof t, 2007 ). This physiological age-related dentoalveolar change needs to be taken into account in orthodontic treatment planning.

Intercanine width

Intercanine width decreased signi cantly in both arches and was more pronounced in the mandible. The greatest changes occurred between the second and the nal registrations and similar ndings are reported by Akgul and Toygar (2002) and Tibana et al. (2004) . Bondevik (1998) reported signi cant decreases only in the lower arch.

The changes in intercanine width may be attributable to mesial drift of the rst permanent molars. Our ndings suggest that the decrease in mandibular intercanine width leads to reduced space for the lower incisors. In general, the later decrease in intercanine widths with age were more pronounced in the mandible than in the maxilla arch. The clinical implications of this nding are of particular importance in orthodontic treatment planning because anterior crowding continues throughout middle age, i.e. beyond 60 years of age.

Intermolar width

Intermolar width increased signi cantly in both arches but was more pronounced in the maxilla. The greatest changes occurred between the second and the nal registrations. Similar ndings are reported by Harris (1997) and Bondevik (1998) . In contrast, other authors such as Tibana et al. (2004) and Bishara et al. (1997) found no signi cant changes in arch width.

Small or no change is more often reported in intermolar width. Contradictory ndings can be explained by differences in the ages of the study subjects: Akgul and Toygar (2002) reported on changes observed in early adulthood, whereas the study by Harris (1997) and the present study followed the subjects through to late middle age and reported a slight increase in width.

Arch depth

Arch depth decreased in both arches. One interesting nding was that in both arches, the greatest changes occurred between the initial and the second registrations. Similar ndings are reported by Akgul and Toygar (2002) and

Harris (1997) . Mesial drift of the rst permanent molars seems to re ect a physiological movement of the dentition, which increases crowding in the mandibular anterior region. This could also explain why the transverse width of the canines decreases, as well as the arch length. The long- term prognosis of anterior crowding seems to be unfavourable and continues beyond age 60 years.

Irregularity index

Little ’ s irregularity index increased signi cantly only in the mandible. The most pronounced changes were observed between the second and the nal registrations. Tibana et al. (2004) reported that from 21 to 28 years of age, incisor irregularity increased with a mean of 0.54 mm (SD 0.43) in the lower arch and a mean of 0.38 mm (SD 0.50) in the upper arch. In the present study , there was a correlation between an increase in lower incisor irregularity and decreases in mandibular arch length and intercanine width.

Conclusions

The dentoalveolar processes continue to undergo physiological changes throughout adult life. Of particular clinical relevance is the nding that decreases in arch length and depth result in a decrease in intercanine width and increased crowding of the anterior teeth. These ndings have important clinical implications in orthodontic practice, particularly in treatment planning and long- term post-treatment stability/retention .

Acknowledgement

Professor emeritus Per-Olof Glanz is acknowledged for giving us access to the study cast material.

References Akgul A A , Toygar T U 2002 Natural craniofacial changes in the third

decade of life: a longitudinal study . American Journal of Orthodontics and Dentofacial Orthopedics 122 : 512 – 522

Bishara S E , Ferguson D 2001 Introduction to the growth of the face . In: Bishara S E (ed.). Textbook of orthodontics . W B Saunders Company , Philadelphia , pp. 43 – 82

Bishara S E , Jakobsen J R , Treder J E , Damon P , Olsen M 1996 Changes in the dental arches and dentition between 25 and 45 years of age . Angle Orthodontist 66 : 417 – 422

Bishara S E , Jakobsen J R , Treder J , Nowak A 1994 Facial and dental changes in adulthood . American Journal of Orthodontics and Dentofacial Orthopedics 106 : 175 – 186

Bishara S E , Jakobsen J R , Treder J , Nowak A 1997 Arch width changes from 6 weeks to 45 years of age . American Journal of Orthodontics and Dentofacial Orthopedics 111 : 401 – 409

Bishara S E , Jakobsen J R , Treder J , Nowak A 1998 Arch length changes from 6 weeks to 45 years . Angle Orthodontist 68 : 69 – 74

Björk A , Krebs A , Solow B 1964 A method for epidemiological registration of malocclusion . Acta Odontologica Scandinavica 22 : 27 – 41

Bondevik O 1998 Changes in occlusion between 23 and 34 years . Angle Orthodontist 68 : 75 – 80

N. TSIOPAS ET AL.6 of 6

Dahlberg G 1940 Statistical methods for medical and biological students . Allen and Unwin , London

Harris E F 1997 A longitudinal study of arch size and form in untreated adults . American Journal of Orthodontics and Dentofacial Orthopedics 111 : 419 – 427

Henriksson J , Persson M , Thilander B 2001 Long-term stability of dental arch form in normal occlusion from 13 to 31 years of age . European Journal of Orthodontics 23 : 51 – 61

Lammie G A , Posselt U 1965 Progressive changes in the dentition of adults . Journal of Periodontology 36 : 443 – 454

Little R M 1975 The irregularity index: a quantitative score of mandibular anterior alignment . American Journal of Orthodontics 68 : 554 – 563

Persson M , Thilander B 1995 Craniofacial development and growth . In: Thilander B , Rönning O (eds). 1995 Introduction to orthodontics , 2nd edn . Gothia , Karlshamn , pp. 10 – 38

Proft W R 2007 Later stages of development . In: Proft W R (ed.). Contemporary orthodontics , 4th edn . Mosby , St Louis , pp. 107 – 129

Thilander B 2009 Dentoalveolar development in subjects with normal occlusion. A longitudinal study between the ages of 5 and 31 years . European Journal of Orthodontics 31 : 109 – 120

Tibana R H W , Palagi L M , Miguel J A M 2004 Changes in dental arch measurements of young adults with normal occlusion — a longitudinal study . Angle Orthodontist 74 : 618 – 623

OCCLUSAL AND DENTOALVEOLAR CHANGES IN ADULTHOOD 2355 of 6 OCCLUSAL AND DENTOALVEOLAR CHANGES IN ADULTHOOD

contributed to the contradictory results, in particular, thedifference in the ages of the subjects and the confoundingeffect of orthodontic treatment: thus , Bondevik (1998)followed his subjects through early adulthood, from age 23 to34 years, whereas the subjects in the other studies, includingours, underwent nal registration at the age of 50 – 60 years.

A slow decrease in arch length implies gradual anterior migration of the dentition. Mesial drift of the rst permanent molars will result in a decrease in arch length and depth in both arches. This also explains the anterior crowding , which increases with age, reported by Thilander (2009) and Henriksson et al. (2001) . A decrease in arch length may have an even more plausible explanation in other factors, such as changed intrinsic forces by tongue and lips ( Proft, 2007 ).This physiological age-related dentoalveolar change needs tobe taken into account in orthodontic treatment planning.

Intercanine width

Intercanine width decreased signicantly in both arches and was more pronounced in the mandible. The greatest changes occurred between the second and the nal registrations and similar ndings are reported by Akgul and Toygar (2002) and Tibana et al. (2004) . Bondevik (1998) reported signicant decreases only in the lower arch.

The changes in intercanine width may be attributable tomesial drift of the rst permanent molars. Our ndings suggestthat the decrease in mandibular intercanine width leads toreduced space for the lower incisors. In general, the laterdecrease in intercanine widths with age were more pronouncedin the mandible than in the maxilla arch. The clinicalimplications of this nding are of particular importance inorthodontic treatment planning because anterior crowdingcontinues throughout middle age, i.e. beyond 60 years of age.

Intermolar width

Intermolar width increased signicantly in both arches but wasmore pronounced in the maxilla. The greatest changes occurredbetween the second and the nal registrations. Similar ndingsare reported by Harris (1997) and Bondevik (1998) . In contrast,other authors such as Tibana et al. (2004) and Bishara et al.(1997) found no signicant changes in arch width.

Small or no change is more often reported in intermolar width. Contradictory ndings can be explained by differences in the ages of the study subjects: Akgul and Toygar (2002) reported on changes observed in early adulthood, whereas the study by Harris (1997) and the present study followed the subjects through to late middle age and reported a slight increase in width.

Arch depth

Arch depth decreased in both arches. One interesting nding was that in both arches, the greatest changes occurred between the initial and the second registrations. Similar ndings are reported by Akgul and Toygar (2002) and

Harris (1997) . Mesial drift of the rst permanent molars seems to reect a physiological movement of the dentition, which increases crowding in the mandibular anterior region. This could also explain why the transverse width of the canines decreases, as well as the arch length. The long- term prognosis of anterior crowding seems to be unfavourable and continues beyond age 60 years.

Irregularity index

Little ’ s irregularity index increased signicantly only in the mandible. The most pronounced changes were observed between the second and the nal registrations. Tibana et al.(2004) reported that from 21 to 28 years of age, incisor irregularity increased with a mean of 0.54 mm (SD 0.43) inthe lower arch and a mean of 0.38 mm (SD 0.50) in the upperarch. In the present study, there was a correlation between anincrease in lower incisor irregularity and decreases inmandibular arch length and intercanine width.

Conclusions

The dentoalveolar processes continue to undergo physiological changes throughout adult life. Of particular clinical relevance is the nding that decreases in arch length and depth result in a decrease in intercanine width and increased crowding of the anterior teeth. These ndings have important clinical implications in orthodontic practice, particularly in treatment planning and long- term post-treatment stability/retention .

Acknowledgement

Professor emeritus Per-Olof Glanz is acknowledged for giving us access to the study cast material.

References Akgul A A , Toygar T U 2002 Natural craniofacial changes in the third

decade of life: a longitudinal study. American Journal of Orthodontics and Dentofacial Orthopedics 122 : 512 – 522

Bishara S E , Ferguson D 2001 Introduction to the growth of the face . In: Bishara S E (ed.). Textbook of orthodontics . W B Saunders Company , Philadelphia , pp. 43 – 82

Bishara S E , Jakobsen J R , Treder J E , Damon P , Olsen M 1996 Changes in the dental arches and dentition between 25 and 45 years of age . Angle Orthodontist 66 : 417 – 422

Bishara S E , Jakobsen J R , Treder J , Nowak A 1994 Facial and dental changes in adulthood . American Journal of Orthodontics and Dentofacial Orthopedics 106 : 175 – 186

Bishara S E , Jakobsen J R , Treder J , Nowak A 1997 Arch width changes from 6 weeks to 45 years of age . American Journal of Orthodontics and Dentofacial Orthopedics 111 : 401 – 409

Bishara S E , Jakobsen J R , Treder J , Nowak A 1998 Arch length changes from 6 weeks to 45 years . Angle Orthodontist 68 : 69 – 74

Björk A , Krebs A , Solow B 1964 A method for epidemiological registration of malocclusion . Acta Odontologica Scandinavica 22 : 27 – 41

Bondevik O 1998 Changes in occlusion between 23 and 34 years . Angle Orthodontist 68 : 75 – 80

N. TSIOPAS ET AL.6 of 6

Dahlberg G 1940 Statistical methods for medical and biological students . Allen and Unwin , London

Harris E F 1997 A longitudinal study of arch size and form in untreated adults . American Journal of Orthodontics and Dentofacial Orthopedics 111 : 419 – 427

Henriksson J , Persson M , Thilander B 2001 Long-term stability of dental arch form in normal occlusion from 13 to 31 years of age . European Journal of Orthodontics 23 : 51 – 61

Lammie G A , Posselt U 1965 Progressive changes in the dentition of adults . Journal of Periodontology 36 : 443 – 454

Little R M 1975 The irregularity index: a quantitative score of mandibular anterior alignment . American Journal of Orthodontics 68 : 554 – 563

Persson M , Thilander B 1995 Craniofacial development and growth . In: Thilander B , Rönning O (eds). 1995 Introduction to orthodontics , 2nd edn . Gothia , Karlshamn , pp. 10 – 38

Prof t W R 2007 Later stages of development . In: Prof t W R (ed.). Contemporary orthodontics , 4th edn . Mosby , St Louis , pp. 107 – 129

Thilander B 2009 Dentoalveolar development in subjects with normal occlusion. A longitudinal study between the ages of 5 and 31 years . European Journal of Orthodontics 31 : 109 – 120

Tibana R H W , Palagi L M , Miguel J A M 2004 Changes in dental arch measurements of young adults with normal occlusion — a longitudinal study . Angle Orthodontist 74 : 618 – 623