University of Groningen

Implant-supported removable partial dentures in the mandibleLouwerse, Charlotte

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Citation for published version (APA):Louwerse, C. (2017). Implant-supported removable partial dentures in the mandible. RijksuniversiteitGroningen.

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23

CHAPTER 2

IMPLANT-SUPPORTED REMOVABLE PARTIAL DENTURES IN THE MANDIBLE:

A 3-16 YEAR RETROSPECTIVE STUDY

24

This chapter is an edited version of the manuscript.Jensen C, Meijer HJ, Raghoebar GM, Kerdijk W, Cune MS. Implant-supported removable partial dentures in the mandible: A 3-16 year retrospective study. J Prosthodont Res. 2016. Epub ahead of print.

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Abstract

Purpose. The purpose of this retrospective study was to assess performance, together with biological and technical complications, of implant-supported removable partial dentures (ISRPD) in mandibular Kennedy class I situations with implants placed in the premolar (PM) or molar (M) region.

Methods. 23 subjects with two endosseous implants to support a bilateral-free-ending mandibular removable denture were examined. Eight subjects had implants in the PM region (PM group) and 15 subjects implants in the M region (M group). Biological and technical complications were recorded from the patients’ medical record. Patients filled out a validated questionnaire regarding their appreciation of oral health related quality of life (OHIP-NL49) and a VAS score on overall satisfaction.

Results. Over a mean follow-up period of 8 years (median 8 years, range 3-16 years) the cumulative implant survival rate was 91.7% (SE 0.05). Mean peri-implant bone loss was 0.9mm (SD 1.0mm). Scores for bleeding on probing, plaque and mucosal health were generally low, but significantly worse for implants placed in the M region. Significantly more biological complications occurred in the M group (X2(1)=3.9; p=0.048). In 65% of the cases no technical complications were registered. Mean overall OHIP score was 16.1 (SD 18.4) and patients were highly satisfied (VAS: 8.4; SD 2.1).

Conclusions. Within the limitations of this retrospective study, in case of a Kennedy class I situation in the mandible, an ISRPD is a viable treatment option with a high implant survival rate and satisfied patients after a maximum of 16 years. Technical and biolog-ical complications should be anticipated. Implants placed in the PM region performed slightly better.

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Introduction

Fixed implant-borne restorations have a good prognosis and seem the ideal solution in case of extended posterior uni- or bilateral partial edentulism in the mandible.1 Un-fortunately, such treatment is expensive and local anatomical conditions often render treatment comprising of multiple implant crowns infeasible. Removable dentures are the economic alternative in case of partial edentulism 2 that may improve quality of life 3, although conventional distal extension partial dentures generally yield poor patients’ acceptance. Adding occlusal units has aesthetic and functional benefits 4 but the effect on patients’ oral health-related quality of life (OHRQoL) and oral comfort seems unwar-ranted.5 Approximately 10, 25 and 50% of such removable partial dentures (RPD) are no longer in service after respectively 1, 5 and 10 years.6

Not surprisingly, ‘pain when wearing a removable partial denture’ is significantly related to patients’ appreciation of treatment7. Because of the discrepancy between the compressibility of the alveolar mucosa on the one hand and the limited freedom of movement of a natural tooth in its alveolus on the other hand, discomfort in free-end-ing RPD’s can be expected. Under such conditions occlusal forces are also detrimental for the abutment teeth. To reduce or more evenly distribute the load on abutment teeth and on the residual alveolar ridge several ‘solutions’ have been proposed, among which are a reduction in the number of artificial teeth and their occlusal surface, lengthening of the saddle, meticulous attention to occlusion and articulation and several variations in retainer design.8 In selected patients with free-ending RPD’s extra retention and re-lieve of the mucosal tissues can also be created by placing implants distally from the most posterior natural teeth. It reduces tissue-ward rotation around the fulcrum line through the most distally positioned natural abutment teeth.9-14

The first report suggesting the potential benefits of implants to support an RPD dates from 1991.15 Since then several retrospective studies and case-studies have point-ed out the benefits, but also addressed some pitfalls: mainly frequent need for repairs of the implant-supported removable partial denture (ISRPD).14,16 In a recent systematic review on removable implant-tooth supported mandibular partial dentures, 9 studies have been included. It is tentatively concluded that an improvement in function, aes-thetics and denture stability has been demonstrated, whereas prosthetic maintenance and implant complications are minor. The authors of this systematic review stress the need for prospective studies to demonstrate the efficacy of this treatment module.17 In another recent systematic review the same conclusions have been drawn.18

The patient-reported benefits of implant support in removable partial denture treatment have been established in a recent prospective clinical trial.19 Although the follow-up period after supporting the RPD by implants is only two months, the reported improvement of patient satisfaction and mastication is reported promising.

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From a clinical perspective the choice for the position of the implant bears relevance. The influence of implant position on peri-implant tissue health, implant survival, pros-thetic maintenance and patient satisfaction has never been subject of investigation in clinical practice although finite element analyses report a better stress-distribution and increasing displacement of an ISRPD with an implant placed in the premolar region in combination with a distal plate.20

The purpose of this retrospective study was to assess performance, together with biological and technical complications, of implant-supported removable partial dentures (ISRPD) in mandibular Kennedy class I situations with implants placed in the premolar (PM) or molar (M) region.

Materials and Methods

Study designA retrospective analyses was performed of all patients treated between 1-1-1999 and 1-1-2014 with a Kennedy class I situation with two implants (either tissue level (TL) im-plants or bone level (BL) implants) bilateral in the mandible supporting a removable par-tial denture in a private referral practice (De Mondhoek, Apeldoorn, the Netherlands) and a general hospital (Nij Smellinghe Hospital, department of Oral and Maxillofacial Surgery, Drachten, the Netherlands). Inclusion criteria for treatment were:- a shortened dental arch in the mandible (premolar or cuspid as most posterior abut-ment tooth) and the need for improvement of oral function;- sufficient bone volume to place two implants in PM or M region of the mandible on the left and right side.- adequate oral hygiene.

Patients with medical and general contraindications for the surgical procedures, were excluded from treatment as well as patients with active periodontal disease. Twenty-six patients were eligible and invited to participate. After consulting the Medi-cal Ethical Committee of the University Medical Center Groningen, it appeared that this retrospective study was not subject to the Medical Research Involving Human Subjects Act (Number M15.180693).

Patients were categorized in two subgroups depending on the position of the implants: patients with implants in the premolar region (the PM group) and patients who had im-plants placed in the molar region (the M group). Because of the retrospective character of this study it was not always clear on what criteria the implant position was deter-mined. An example of a typical case for the PM group is shown in Figure 1.

Two moments of observation were used to obtain the data. A panoramic radio

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Figure 1a. A typical case of a Kennedy class I Implant-supported Remova-

ble Partial Denture in the mandible. Ball attachment in situ

Figure 1b. Bottom side of an Implant Supported Removable Partial Den-

ture showing the retentive matrix.

Figure 1c. Panoramic radiograph showing two implants with ball attach-

ment in the premolar region (group anterior) after 8 years of function.

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graph, taken two weeks after implant placement, was collected from the medial file (Tbaseline). Data were obtained during a regular control visit (Tfollow-up).

Clinical assessmentsClinical assesments were calibrated with investigators from previous studies using the same criteria. Thereafter clinical data were collected by one observer (CJ). The following clinical variables were assessed at Tfollow-up.- Plaque: assessed per implant using the index according to Mombelli et al. 21 (score range 0-3). - Bleeding on probing: assessed per implant using the bleeding index according to Mombelli et al. 21 (score range 0-3).- Soft tissue health: assessed per implant using the gingiva index according to Loë & Silness 22 (score range 0-3).- Probing pocket depth: assessed at three sites per implant using a manual standardized pressure periodontal probe (Click-Probe®, Kerr, Bioggio, Switzerland) measuring to the nearest 1 mm. The highest value per implant was recorded.

The prevalence of peri-implant mucositis and peri-implantitis was calculated. The translation from bleeding index into Bleeding on Probing (BoP) was score 0 = BoP - and score 1,2 and 3 = BoP + 23. As definition for peri-implant mucositis and peri-implantitis, the consensus reached at the Seventh European Workshop on Periodontology has been used 24, being: peri-implant mucositis (radiographic bone loss <2 mm): BoP+ and/or suppuration and peri-implantitis: BoP+ and/or suppuration in combination with radio-graphic bone loss ≥2 mm.

Radiographic assessmentsTwo weeks after implant (Tbaseline) placement panoramic radiographs were taken of all patients and at Tfollow-up a new panoramic radiograph was ordered if no recent ra-diograph was available. The marginal bone levels (MBL) were analysed using the known implant length as a reference. The interface of the implant and the abutment was used as a reference line, from which all distances were measured using designated software (DicomWorks, Biomedical Engineering, University Medical Center Groningen, the Netherlands).25 The error of the method used was reported 0.13 ± 0.01 mm for the assessment of the radiographic marginal bone height.26 All radiographic assessments were performed by a single observer (CJ). Marginal bone loss was calculated both me-sially and distally per implant. The highest scores per implant were used to calculate the overall mean marginal bone loss.

Implant survival rateImplant survival was defined as the presence of an immobile implant at Tfollow-up.

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Implant mobility was tested by tapping on the implant and testing mobility between 2 back ends of a dental hand instrument.

Clinical record assessmentsThe following issues were scored from medical record and Tfollow-up to calculate bio-logical and technical complications:- Post-operative complications: sensibility disturbances, excessive pain;- Implant complications: early- and late failure, peri-implant mucositis and peri-implan-titis;- Maintenance of the ISRPD: repair or replacement.

Patient-based assessmentsPatients filled out a validated questionnaire regarding their appreciation of oral health related quality of life (OHIP-NL49)27,28 and a Visual Analogue Scale (VAS) on overall sat-isfaction. OHIP-NL49 relates to a questionnaire on which the subjects answers 49 items on a 0-4 scale,that are subsequently arranged into 7 domains. The sum-score ranges from 0-196 points. The lower the score, the higher the oral health related quality of life of the patient. All data were retrieved by one examiner (CJ), who was not involved with the original treatment.

Statistical analysesDemographic characteristics were summarized for included patients. Differences in clin-ical and radiographical measurements and patients’ OHIP-NL49 and VAS scores be-tween the PM and M group were analyzed using Mann-Whitney U tests. As a measure of effect size of the Mann-whitney U tests r was calculated and reported. An r of 0.1, 0.3 and 0.5 correspond with a small, medium and large effect size, respectively. The in-cidence of biological and technical complications was compared across conditions with chi-squared tests. Implant survival rate was established by means of the Kaplan-Meier estimate.29 P-values <0.05 were considered statistically significant. All computations were performed using a standard statistical program (SPSS, version 23.0 for Windows, SPSS inc., Chicago, USA).

Results

From the 26 included patients, three patients were unable to attend because of travel distance or health problems. Their data were not obtained. Two patients did fulfill the inclusion criteria upon Tbaseline, but lost their remaining mandibular dentition after re-spectively 4.5 and 14.4 years of functioning with the ISRPD. A mandibular overdenture

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was provided, for which additional implants were placed in the interforaminal region. Therefore, their data were only used for clinical outcomes and not for patient-based assessments. Consequently data from 23 and 21 patients was obtained for clinical out-comes and patient-based assessments respectively.

Patient- and treatment characteristics of the study group are depicted in Table 1. Attachment types were ball attachments, Locator attachments or healing abutments. The healing abutments were not used as retentive attachments but were used as studs. Usually three teeth were replaced at both sides. Eight patients had PM implants, while fifteen patients had M implants. Participants had an average follow up period of 8.1 years (SD 3.7) with a minimum of 3 and a maximum of 16 years. For the PM and M group the average follow-up period was 7.4 years (SD 4.1) and 8.5 years (SD 3.6) re-spectively.

Clinical outcomesClinical outcome measures are presented in Table 2. Overall plaque-, bleeding- and soft tissue health scores were low. However, M implants scored significantly higher on the plaque (U= 138.0; p=0.035; r=0.32) and gingiva index (U=91.5; p<0.001; r=0.54). The overall mean probing depth was 3.3 mm (SD 1.4mm) and did not differ significantly between groups.

Change in marginal bone levelMean change in MBL is presented in Table 2. A mean change in MBL of -0.9 mm (SD 1.0mm) was observed between Tbaseline and Tfollow-up after a mean period of 8 years (range 3-16 years). There was no significant difference between the PM and M group.

Implant survival rateNo implants were lost in the PM group. In total, three implants were lost in the M group. One implant failed to osseointegrate and was lost within six months following implant placement. Another two implants in two patients were lost due to peri-implan-titis after 3 and 6 years of function, respectively. The lost implants were not replaced in these two patients. The ISRPD was supported by the one remaining implant on the contralateral side. This resulted in an overall cumulative implant survival rate of 91.7% (SE 0.05%) after 16 years (Figure 2).

Biological complicationsBiological complications occurred in 29 out of 46 implants (63%; Table 3). Implants in the M region demonstrated significantly more complications than in the PM region (X2(1)=3.9; p=0.048). These complications mainly concerned peri-implant mucositis. The 3 out of 46 implants that were lost, were also all in the M group.

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Technical complicationsOverall, in 65% (n=15) of 23 cases no complications occurred during the mean obser-vation period of 8 years. Two prostheses required minor repairs whilst three had been replaced (n=3) after 5.5, 5.5 and 7 years of function. In three patients the implant borne removable partial denture was not in function anymore. Two cases were reverted to a full overdenture. One patients’ appreciation of oral function was disappointing and the patient decided to function without ISRPD. There were no significant differences between the RPD’s on M and PM implants. (X 2(1)=1.25; p=0.26, Table 3).

Patient-based assessments Table 4 gives an overview of the patients’ oral health related quality of life and the pa-tients’ satisfaction at Tfollow-up. The overall sum score of the OHIP-NL 49 questionnaire was 16.1 points (SD 18.4) on a 0-196 scale, which corresponds to favourable perceived oral health related quality of life. The patients scored 8.4 (SD 2.1) on general satisfac-tion on a 0-10 numeric scale. There were no significant differences between the PM and M group.

Figure 2. Cumulative survival of implants supporting mandibular

removable partial dentures according to Kaplan-Meier.

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Tab

le 1

. Pat

ien

t ch

arac

teri

stic

s

All

pat

ien

tsPa

tien

ts a

t fo

llow

up

Nu

mb

er o

f p

arti

cip

ants

2623

Cen

ter

(Ap

eld

oo

rn/D

rach

ten

)14

/12

12/1

1

Ag

e (m

ean

/ran

ge)

59/5

1-75

59/5

1-75

Gen

der

(m

ale/

fem

ale)

7/19

6/17

Rem

ain

ing

den

titi

on

(P1

-P1/

C-C

) *

8/18

8/15

Imp

lan

t ty

pe

(Tis

sue

Leve

l /B

on

e Le

vel)

11/1

510

/13

Imp

lan

t lo

cati

on

(p

rem

ola

r/m

ola

r)9/

178/

15

Att

ach

men

t ty

pe

(bal

l/Lo

cato

r/h

ealin

g a

bu

tmen

t)21

/3/2

18/3

/2

* fir

st-p

rem

olar

to

first

pre

mol

ar a

nd c

uspi

d to

cus

pid

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Tab

le 2

. Clin

ical

ass

essm

ents

at

follo

w u

p

(n=

23 p

atie

nts

an

d 4

3 im

pla

nts

, 3 im

pla

nts

wer

e lo

st, m

ean

an

d s

tan

dar

d d

evia

tio

n (

SD)

Tota

l A

nte

rio

rPo

ster

ior

p-v

alu

eEf

fect

siz

e (r

)

(n=

43)

(n=

16)

(n=

24)

Plaq

ue

Ind

ex0.

9 (0

.7)

0.6

(0.7

)1.

1 (0

.7)

0.03

5 0.

32

Ble

edin

g In

dex

0.7

(0.6

)0.

5 (0

.6)

0.8

(0.6

)0.

074

0.27

Gin

giv

a In

dex

0.5

(0.7

)0.

1 (0

.3)

0.8

(0.8

)<

0.00

10.

54

Pro

bin

g D

epth

(m

m)

3.3

(1.4

)3.

3 (1

.2)

3.3

(1.5

) 0

.634

0.07

Ch

ang

e in

mar

gin

al b

on

e b

evel

(m

m)*

-0.9

(1.0

)-1

.0 (1

.1)

-0.8

(1.0

)0.

821

0.03

* fir

st-p

rem

olar

to

first

pre

mol

ar a

nd c

uspi

d to

cus

pid

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Table 3. Number of biological and technical complications related to implants and removable partial dentures (RPD) respectively.

Total Anterior Posterior

Biological complications implants* (n=46) (n=16) (n=30)

No complications 17 9 8

Complications 29 7 22

Peri-implant mucositis 24 6 18

Peri-implantitis 2 1 1

Implant loss 3 0 3

* Statistically significant more complications associated with posterior implants (p=0.048).

Total Anterior Posterior

Technical complications RPD’s (n=23) (n=8) (n=15)

No complications 15 4 11

Complications 8 4 4

Minor repair 2 1 1

Replaced 3 2 1

Not in function 1 1 0

Reverted into a full arch denture 2 0 2

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Tab

le 4

. Mea

n s

um

sco

res

of

OH

IP-N

L49

(SD

bet

wee

n b

rack

ets)

an

d m

ean

VA

S sc

ore

(ra

ng

e 0-

10).

Tota

l A

nte

rio

rPo

ster

ior

(n=

21)

(n=

8)

(n=

13)

p-va

lue

effe

ct s

ize

(r)

Fun

ctio

nal

lim

itat

ion

(m

ax. s

core

36)

5.1

(3.1

)5.

9 (4

.7)

4.6

(1.6

)0.

941

0.02

Phys

ical

pai

n (

max

. sco

re 3

6)4.

6 (4

.6)

5.5

(6.1

)4.

0 (3

.4)

0.74

20.

07

Psyc

ho

log

ical

dis

com

fort

(m

ax. s

core

20)

2.0

(3.8

)2.

9 (5

.6)

1.4

(2.3

)0.

863

0.04

Phys

ical

dis

abili

ty (

max

. sco

re 3

6))

2.0

(3.1

)2.

9 (4

.2)

1.5

(2.0

)0.

513

0.14

Psyc

ho

log

ical

dis

abili

ty (

max

. sco

re 2

4)1.

3 (2

.8)

1.6

(3.9

)1.

1 (2

.0)

0.69

6 0.

09

Soci

al d

isab

ility

(m

ax. s

core

20)

0.4

(1.7

)1.

0 (2

.8)

0.1

(0.3

)0.

670

0.09

Han

dic

ap (

max

. sco

re 2

4)0.

8 (2

.0)

1.1

(3.2

)0.

5 (1

.0)

0.46

7 0.

16

OH

IP-N

L49

(to

tal)

(m

ax. s

core

196

)16

.1 (1

8.4)

20.9

(27.

8)13

.2 (9

.4)

0.97

10.

01

Ove

rall

sati

sfac

tio

n s

core

(m

ax. s

core

10)

8.4

(2.1

)7.

6 (3

.2)

8.9

(1.0

)0.

423

0.18

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tive

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Discussion

The results from the present study, with a mean observation period of over 8 years (range 3-16 years) suggests a good prognosis with respect to implant survival (91.7%). Results in other studies are even better with survival rates varying from 93.8 to 100% after follow-up periods of up to 15 years.16,18,30,31 In the present study, the three patients who experienced implant loss still could function successfully with the one remaining implant. The lower cumulative survival rate compared to other studies might be due to the group of patients that was examined, with all Kennedy class I situations in the mandible. In a recent study the authors conclude that implants placed in the mandible are at higher risk of complications compared to the maxilla.32

The complication rate of the ISRPD’s is considered relatively low as well, as can be concluded both from the data in the present study as from the observations of oth-ers. Kaufmann et al. concluded that 30% of the ISRPD’s needed maintenance within 3 years, but this consisted mainly of minor repairs like tightening, loosening or replacing the matrices. Another study shows hardly any prosthetic complications in a group of 20 patients with mandibular and maxillary ISRPD’s during 15 years of follow up.31

Most studies report stable implant conditions over time 31,33, nevertheless Bortolini et al. reported that almost every patient with an ISRPD exhibited a slightly inflamed peri-im-plant mucosa.30 It is striking that in our study, the implants placed in the PM zone per-form significantly better regarding plaque and (absence of) signs of inflammation. The reason might be a compromised cleaning possibility for distally placed implants: This emphasizes the importance of permanently monitoring and adjusting oral hygiene and this is confirmed by others.16

Two patients had lost their remaining natural dentition after respectively five and fourteen years of functioning with an ISRPD. They both received extra implants in the interforaminal region to support a full arch implant-retained overdenture. Strategic implant positioning implies that the implants can support both the present ISPRD and future prosthetic provisions. From a biomechanical perspective implants placed more to the posterior enhance a more favourable loading situation by moving the fulcrum-axis distally and reducing the load to the soft tissues and underlying bone. However, given the fact that healthier peri-implant conditions were generally observed around implants placed in the PM region compared to implants placed in the M region and the fact that, in case of further tooth loss, an implant-retained denture is better served with implants in the position of the premolars, the PM position may be preferred from a clinical per-spective.

Maintenance protocols differed between centers and for individuals, and the disadvantages of a retrospective study should be emphasised as well. A limitation is the multi-centre design with different clinicians and the lack of a uniform treatment proto-

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col. Also, there is a rather long inclusion period with a relatively low number of patients; this means that the treatment is not carried out on a regular basis, which hampers stan-dardization and familiarization with the method. In addition, different implant systems with different attachment systems have been used throughout the treatment period; this means that possible complications and also patient satisfaction could be influenced by the system, hindering a clear causality with the treatment method as such and with the position of the implants. No corrections were made for multiple observations within the same patient the impact of this dependency in the data is uncertain. However, giv-en the clinical difference that were found have medium to large effect sizes, they are likely to hold if dependency was not present. In general, peri-implant probing depths of implants placed in sites outside the aesthetic zone range between 2-4 mm under healthy conditions, depending on the implant type.24,34 Although change in probing depth over time can give an indication on the health of peri-impant tissue 35, it is im-portant to realize that these measurements are more sensitive to force variation than periodontal pocket probing.36 Therefore we used the criteria for peri-implant mucositis and peri-implantitis described in an earlier study by Lang et al. to determine whether peri-implant tissues were healthy or not.24 Although the overall plaque-, bleeding- and gingiva indexes are rather low in our study, the overall mean probing depth is within the above mentioned healthy range and the overall MBL change is acceptable, peri-implant mucositis was seen in 57% of the implants (n=24). This finding was confirmed by Derks et al.32 This too urges the need for a strict oral health regime consisting in regular visits and a constant monitoring of self-care, although the impact on marginal bone levels within the studied time frame seems limited.

Patients filled out questionnaires after having functioned with the ISRPD’s for dif-ferent periods of time, the effect of which was not studied in further detail. In addition, the position of the implant was determined by the subjective perception of the treat-ing surgeon/prosthodontist that an individual patient may benefit most from PM or M support. Hence, for instance, patients are included that have a cuspid as most posterior tooth, yet an implant positioned at the M position. To the knowledge of the authors, this choice cannot (yet) be substantiated by results from the literature. Patient outcome should be interpreted bearing this in mind.

Overall patient satisfaction seems to be very good with an overall score of 8.4 (SD 2.1) on a scale from 0 to 10. The standard deviation is somewhat high and is ex-plained by the one outlier in our study group who scored very low compared to the other patients. Analysing the data without this outlier results in an even higher overall patient satisfaction of 8.8 (SD 1.0). Several other studies report a high overall patient satisfaction as well.31,33,37

The OHIP-49 questionnaire is a commonly used tool to measure the oral health related quality of life. Despite the fact that questions are standardized, the differences

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in reporting the outcome of this questionnaire makes comparisons difficult.5,37 In a prospective study, Gates et al. observed a reduction of more than 41 units on the OHIP questionnaire when turning an RPD into an ISRPD, resulting in a mean overall score of approximately 20.38 The findings of Fueki et al. are comparable with a mean score of 23.8 (range 15.1-32.6) for patients with an ISRPD, in a prospective study with a fol-low-up of at least 1 year.39

The outcome can be considered indicative for the long-term prognosis of an ISRPD. Even though there was no randomization, the group under study is very homog-enous with all Kennedy class I situations in the mandible. Nevertheless, the disadvantag-es of this retrospective study should be emphasised, like the multi-centre design with a different clinicians and the lack of a uniform treatment protocol. Therefore a prospec-tive randomized clinical trial is mandatory to be able to make strong and universal rec-ommendations for the ISRPD in a Kennedy class I in the mandible with a randomization on the implant position.

Conclusions

Within the limitations of this retrospective study, in case of a Kennedy class I situation in the mandible, an implant-supported removable partial denture is a viable treatment option with a high implant survival rate after a maximum of 16 years. Technical and bi-ological complications should be anticipated. Implants placed in the PM region showed slightly better clinical results. Overall patient satisfaction is high.

Acknowledgement

The authors thank Dr. Felix Guljé (De Mondhoek, Apeldoorn, the Netherlands) and Dr. Jan-Peter Wymenga (Nij Smellinghe Hospital, department of Oral and Maxillofacial Sur-gery, Drachten, the Netherlands) for their time, support and hospitality to investigate patients at their clinics.

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