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A prospective evaluation of factors affecting occlusal stability of Class II correction with Twin-block followed by fixed appliances
ORIGINAL ARTICLE
A prospective evaluation of factors affecting occlusal stability of Class II correction with Twin-block followed by fixed appliances Graham R. Oliver,a Nikolaos Pandis,b and Padhraig S. Fleminga London, United Kingdom, and Bern, Switzerland Introduction: Modified Twin-block therapy followed by fixed appliances (TBFA) is a standard treatment modality in Class II malocclusion; however, there is little information regarding the stability of this approach. We aimed to assess the stability of Class II correction with TBFA and to evaluate factors that may affect stability. Methods: A prospective evaluation involving convenience sampling of 64 participants treated with TBFA was undertaken over 12 months. Study models and lateral cephalometric radiographs were obtained to record overjet and molar relationship, Peer Assessment Rating score, and skeletal parameters, and a new objective buccal segment interdigitation scoring system was developed. Multivariate logistic regression analysis was used to assess the stability of anteroposterior occlusal correction and the degree of buccal interdigitation, pretreatment skeletal discrepancy, and change in overjet during treatment. Results: Mean overjet reduction of 6.22 mm arose during treatment, with the canine and molar relationships improving by 3.34 mm and 2.67 mm, respectively. In the 12 months posttreatment, a relapse of 0.67 mm and 0.06 mm in overjet and molar relationship, respectively, was observed, with 25% of subjects having overjet relapse of .1 mm. There is weak evidence that the treatment-induced change in overjet is linked with overjet relapse (P 5 0.05; odds ratio, 0.67; 95% confidence interval, 0.44, 1.01). No significant relationship was observed, however, between anteroposterior stability and buccal segment interdigitation (P 5 0.99), pretreatment skeletal discrepancy (P 5 0.10) or prescribed retention regime (P 5 0.63). Conclusions: Overall, acceptable levels of stability were observed, although appreciable relapse was noted in 25% of participants. Neither the degree of buccal segment interdigitation nor pretreatment skeletal discrepancy was predictive of anteroposterior occlusal stability. (Am J Orthod Dentofacial Orthop 2020;157:35-41)
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unctional appliances are known to effectively reduce increased overjet1 and decrease the anchorage requirements for subsequent preadjusted edgewise appliance therapy. Class II correction stems predominantly from dental change (60%-70%), with skeletal contribution accounting for the remainder.2,3 Skeletal change includes an acceleration in mandibular growth during the pubertal growth spurt,4 but mandibular length is ultimately believed to
a Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom. b Department of Orthodontics and Dentofacial Orthopedics, School of Dental Medicine, Medical Faculty, University of Bern, Bern, Switzerland. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Padhraig S. Fleming, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, Whitechapel, London E1 2AD; e-mail: padhraig.fl[email protected]. Submitted, November 2018; revised and accepted, January 2019. 0889-5406/$36.00 Ó 2019 by the American Association of Orthodontists. All rights reserved. https://doi.org/10.1016/j.ajodo.2019.01.024
be determined genetically.5 As such, the majority of prolonged benefit appears to reside at the occlusal level. Although the stability of Class II correction is generally perceived to be satisfactory,3 there is little evidence to support this assumption and a limited appreciation of the factors that might influence the stability of treatment following comprehensive functional and fixed appliance therapy. The most in-depth analysis of functional appliance stability centered on the Herbst appliance with up to 32 years of retrospective follow-up.6 Decreases in arch perimeter and lower incisor crowding consistent with maturational changes were noted. Molar and canine correction was stable in 64% and 14%, respectively, whereas 86% of overjet correction was maintained. The majority of relapse occurred in the first 6 years posttreatment, with only minor changes arising after that with poor interdigitation, continuing habits, or inadequate retention predisposing to instability.6 The Twin-block (TB) is universally popular because of its versatility and high levels of patient tolerance.7 35
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Notwithstanding this, a potential limitation is the development of lateral open bites during the functional phase associated with impeded posterior eruption and related to acrylic coverage. The judicious trimming of the blocks allied to phased or complete withdrawal of the appliance mitigates this issue. However, preadjusted edgewise appliances typically follow functional appliance therapy to align the dentition and improve interdigitation purportedly promoting more stable occlusal correction.3 There is no prospective research related to the stability of treatment with functional appliances, particularly the TB, followed by contemporary preadjusted edgewise appliances. The attainment of optimal occlusal interdigitation following active treatment is speculated to promote stability; however, the quality of interdigitation was assessed subjectively in previous research.6 We, therefore, aimed to determine the stability of Class II correction with modified TB followed by fixed appliances and to evaluate factors that may affect the stability of anteroposterior occlusal correction with this approach. MATERIAL AND METHODS
A prospective evaluation was undertaken at the Orthodontic Departments of Barts Health NHS Trust (The Royal London Hospital and Whipps Cross University Hospital) over 12 months following completion of orthodontic treatment with approval from Barts Health NHS Trust Clinical Effectiveness Unit (ID 6274). The inclusion criteria were treated Class II Division 1 malocclusion as defined by the British Standards Institute8; treated with TB appliances followed by preadjusted edgewise appliances; and willingness to participate in the study. Exclusion criteria included failure to complete functional appliance therapy with the subsequent loss to follow-up; single-arch preadjusted edgewise appliance treatment only; and craniofacial syndromes (eg, cleft lip and palate). A convenience sample of participants was recruited before or at debonding as well as at routine posttreatment review clinics. All participants were treated under consultant supervision with a combination of a TB appliance (Figure 1), followed by preadjusted edgewise appliances. The standard departmental protocol is to undertake functional appliance therapy for 12 months. Following the collation of postfunctional records, preadjusted edgewise appliances are placed after a brief period of either night-only wear or complete withdrawal. Removable retainers were prescribed only for night use. Lateral cephalometric radiographs were taken in centric occlusion and hand-traced on cephalometric acetate tracing film (G.R.O.) using a 2HB 0.5-mm
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Fig 1. Standard Twin-block design.
mechanical pencil and measurements made using a 3M Unitek Cephalometric Protractor. Sagittal Occlusal analysis was used to assess the discrepancy in the skeletal bases relative to the occlusal line. Study model analysis involved measurements using digital calipers (Tesa Technology, Renens, Switzerland; resolution 0.01 mm) and Peer Assessment Rating (PAR) ruler. All measurements were performed by the investigator (G.R.O.) who was calibrated in the use of PAR. Study models were blocked randomized in groups of 20. Identifiable information was removed from the models with a unique, random number. Following the measurement of the models, the investigator was unblinded to record participant identity as well as stage of treatment. The investigator was therefore kept blind to the participant identification as well as the time point of assessment. The primary outcome was the stability of overjet reduction (mm). Secondary outcomes included anteroposterior stability of molar and canine relationship and the PAR score. Independent variables to be assessed were occlusal interdigitation at debonding, pretreatment sagittal skeletal discrepancy, treatment-induced change in overjet, and prescribed retention regime. A novel
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Table I. Scoring system for occlusal interdigitation Vector Anteroposterior Assess the relation of the cusp tip of maxillary canines and premolars relative to the distal contact point of the opposing mandibular tooth. First molars assess the position of maxillary mesiobuccal cusp relative to mandibular buccal groove. Vertical Relation of occlusal surfaces of canines, premolars, and first molars.
Score 2 1 0
2 1 0
Description Class I or III relationship or \1 mm Class II .1 mm and \2 mm Class II .2 mm Class II
Contact of all teeth Clear and distinct (.1 mm) absence of occlusal contact on 1 tooth Clear and distinct (.1 mm) absence of occlusal contact on more than 1 tooth
Table II. Participant demographics Age-related to peak growth spurt Age at Prepubertal, Pubertal, Age functional Age at posttreatment Gender n (%) n (%) n (%) Postpubertal, n (%) fitted (SD), y debonding (SD), y review (SD), y Follow-up period, (SD), y Male 34 (53) 13 (20) 21 (33) 0 (0) 12.52 (1.38) 15.78 (1.77) 16.88 (1.71) 1.10 (0.31) Female 30 (47) 0 (0) 27 (42) 3 (5) 12.56 (1.38) 15.83 (1.98) 16.93 (2.06) 1.10 (0.23) Overall 64 (100) 13 (20) 48 (75) 3 (5) 12.55 (1.40) 15.80 (1.86) 16.85 (1.87) 1.10 (0.29)
objective method (Royal London Occlusal Interdigitation Scoring System) was developed to grade occlusal interdigitation accounting both for anteroposterior as well as vertical relationships of the buccal segments. Both left and right buccal segments are considered, and an overall score was given (Table I). A maximum score of 16 can be assigned to a set of study models based on the anteroposterior discrepancy; for extraction cases, the maximum score is 12. In the vertical plane, the occlusal contact of the maxillary first molar, premolars and canine were assessed with a maximum score of 4 for each set of study models. The anteroposterior and vertical score is then combined and converted to a percentage based on the maximum possible score. The reliability of this novel approach was assessed on 20 sets of study models measured 2 weeks apart by the investigator (G.R.O.). Statistical analysis included a Bland-Altman plot used to visually determine the random and systematic error and the Pitman-Morgan test to gauge homogeneity of variance. A mean difference of 2.75 (standard deviation [SD] 2.76) and 95% limits (Bland-Altman) of –26.29 and 20.79 indicate no significant difference between the variances for the 2 sets of scores and an acceptable level of random error. Intraexaminer reliability for other model-based measures was assessed on 10 randomly selected sets of models and cephalometric radiographs 2 weeks apart. Randomization models were generated in Microsoft Excel (Redmond, Wash). Intraclass correlation estimates and their 95% confidence intervals were at acceptable levels, all above 0.90.
Statistical analysis
Data were analyzed using a statistical package (version 15; StataCorp, College Station, Tex). Statistical analysis included descriptive analysis. Participants were categorized dichotomously as either stable (overjet relapse \ 1 mm) or unstable (overjet relapse $ 1 mm). Logistic regression analysis was undertaken to assess the potential predictive ability of buccal segment interdigitation at debonding, pretreatment skeletal discrepancy (sagittal occlusal analysis, A/OLp–Pg/OLp), change in overjet during active treatment, and retention regime (dual-arch fixed, single-arch fixed, dual-arch vacuum-formed retainers [VFRs], or other approach) on the stability of overjet reduction. RESULTS
Sixty-four participants attended for posttreatment review at a 12-month follow-up. Data were unavailable for some participants because of absence or poor-quality study models or cephalometric radiographs. Overall, there were more male (n 5 34; 53%; Table II) than females (n 5 30; 47%; Table II). The mean age of commencement of functional therapy was 12.55 years. The majority (n 5 48; 75%) started treatment during the peak pubertal growth. Pretreatment skeletal measurements from lateral cephalometric radiographs reflected a moderate skeletal II pattern (ANB, 5.58 ) secondary to mandibular retrognathia (SNB, 74.80 ) with reduced vertical proportions (FMPA, 24.45 ; LAFH, 53.67%; Table III). Pretreatment
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Table III. Pretreatment cephalometric variables Pretreatment cephalometric variables Sagittal skeletal SNA ( ) SNB ( ) ANB ( ) Vertical skeletal FMPA ( ) LAFH (%) Dental UI Mx ( ) LI Mn ( ) SO analysis Overjet (mm) (Is/OLp-Ii/OLp) Molar relationship (mm) (Ms/OLp-Mi/OLp)_ Maxillary base (mm) (A point to OLp) Mandibular base (mm) (Pg/OLp) Skeletal discrepancy (mm) (A/OLp-Pg/OLp)
Mean 80.38 74.80 5.58 24.45 53.67 117.82 95.58 10.50
SD 4.61 4.01 2.22 5.90 2.19 8.14 7.18 2.94
1.72
2.82
76.32
4.46
76.37 –0.05
5.27 3.57
SNA, Angle determined by points S, N, and A; SNB, angle determined by points S, N, and B; ANB, angle determined by points A, N, and B; FMPA, Frankfort mandibular plane angle; LAFH, lower anterior facial height; UI Mx, Incisor–palatal plane angle; LI Mn, Incisor–mandibular plane angle; Is, incision superius; Olp, occlusal plane perpendicular; Ii, incision inferior; Ms, molar superius; Mi, molar inferius; Pg, pogonion; SO, sagittal occlusal analysis.
dental measurements from study models showed overjet was 9.8 mm and buccal segment relationships were Class II, with maxillary canine and molar positions being 5.42 mm and 3.47 mm mesial of Class I relationships, respectively (Table IV). Participants were treated with a modified TB appliance for a mean duration of 1.15 years (SD, 0.45) followed by a transition period of 0.24 (SD, 0.25) years. Most functional appliance designs followed the department protocol; however, a labial bow (n 5 2; 3%) because of significantly proclined incisors or high-pull headgear (n 5 5; 8%) were used occasionally. In addition, 63% of the participants (n 5 41) were treated on a nonextraction basis. The fixed appliance phase lasted 1.88 years (SD, 1.15) on average, resulting in a total treatment time of 3.26 years (SD, 1.30). All participants received some form of retainer with VFRs used most commonly in the maxillary arch (n 5 51; 80%) and the remaining received Hawleytype retainers (n 5 13; 20%). To supplement this, 30% (n 5 19) also had a maxillary bonded retainer. In the mandibular arch, 6 participants received no removable retainer; however, these participants did have a fixed retainer. VFRs were used most commonly (n 5 53; 83%), with relatively few patients receiving Hawleytype retainers (n 5 5, 8%). In total, 29 participants (45%) had mandibular fixed retainers. Overall, overjet decreased by 6.22 mm (9.80 to 3.58 mm; Table IV). At debonding, the buccal segment interdigitation scores
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varied, ranging from excellent to poor interdigitation (60.13%; range, 15%-100%; SD, 20.98). The overjet relapsed by 0.67 mm (SD, 0.69) over the 12 months equating to an 11.33% relapse in overjet relative to the active phase. There was minimal change with molar (0.06 mm; SD, 0.94) and canine relationship (0.09 mm; SD, 0.87). These changes were reflected in the PAR score with a deterioration of 4.44 over the 12 months. Posterior interdigitation improved marginally (2.76%) because of improvement in vertical contact scores. Close assessment of the overjet relapse (Figure 2) showed that 25% of participants experienced overjet relapse . 1 mm; however, the majority (59%) showed minimal posttreatment overjet changes (\0.5 mm). Logistic regression analysis was used to evaluate the possible effect of occlusal interdigitation, change in overjet during treatment, and magnitude of pretreatment skeletal discrepancy on overjet stability (Table V). Stability was not affected by the level of posterior interdigitation at debonding or pretreatment skeletal discrepancy. There was weak evidence that a more significant change in overjet during treatment may be associated with a lower odds ratio for stability (odds ratio: 0.67; P 5 0.05; 95% confidence interval: 0.44, 1.01). Retention regime was not found to be a significant predictor of stability (Table V). The likelihood ratio chisquare test between models with and without retainers (0.92; P 5 0.631) suggests the overall retention regime is not significant. DISCUSSION
In the present study, an overall significant sustained Class II correction was observed with an overjet relapse of 0.67 mm in 12 months, which is consistent with previous studies focused on the stability of Class II correction.9-11 Most participants had clinically insignificant overjet changes (\1 mm); however, 16 (25%) subjects underwent overjet relapse of .1 mm. The main etiological factor in this relapse remains unclear. More prolonged periods of follow-up may be required to isolate these factors more clearly, although previous research has highlighted that the majority of relapse in Class II cases arises relatively soon after cessation of the active treatment phase.6 Very little relapse was observed with buccal segment relationships, with \0.2 mm relapse on average. Bock et al12 reported more significant degrees of relapse with the posterior relationships12; however, this study involved a longer follow-up period of 50 months with Herbst appliances. Our study showed \15% of participants with relapse of .1 mm in the buccal segments,
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Table IV. Treatment and posttreatment occlusal changes Variable Overjet (mm) Canine relationship (mm) Molar relationship (mm) Interdigitation score (%) Peer assessment rating
Pretreatment (T1) 9.80 (2.28) 5.42 (2.37) 3.47 (2.07) 27.23 (18.44) 39.91 (11.73)
Debond (T2) 3.58 (0.95) 2.08 (1.13) 0.80 (1.27) 60.13 (32.90) 7.50 (5.59)
Treatment-induced change (T2-T1) 6.22 (2.46) 3.34 (2.12) 2.67 (1.82) 35.76 (25.36) 32.41 (9.15)
12-month review (T3) 4.26 (0.99) 1.99 (1.33) 0.86 (1.43) 62.89 (20.16) 11.94 (6.59)
Posttreatment changes (T3-T2) 0.67 (0.69) 0.09 (0.87) 0.06 (0.94) 2.76 (16.85) 4.44 (5.44)
Note. All values are mean (6SD).
Fig 2. Overjet relapse.
which is consistent with the results of other functional appliance studies.13 Fidler et al14 similarly identified posttreatment relapse of 0.3 mm in Class II cases undergoing mean correction of 3.4 mm treated with fixed appliances and cervical-pull headgear. It does appear that posterior changes are dwarfed by relapse in the anterior region, most likely because of the influence of soft tissues on the anterior dentition following the withdrawal of active appliances. For every unit increase in overjet reduction, the odds of stability was found to be 33% lower after adjusting for other variables. Janson et al13,15,16 equated a treatment-induced change in overjet, canine and molar relationship during treatment with relapse; however, this finding was based on fixed appliances combined with headgear. Drage and Hunt9 found a weak correlation between the overjet reduction with activator appliances without fixed appliances and posttreatment changes.9 Other studies concerning functional appliances have not found an association between initial overjet and posttreatment changes.6,17 Pretreatment skeletal discrepancy was not found to be correlated with overjet relapse in keeping with previous research with the Herbst appliance.18,19 Faltin et al20 followed
Table V. Logistic regression analysis 95% CI Stability Odds ratio Logistic regression Interdigitation 1.00 Skeletal discrepancy 0.77 Change in overjet 0.67 Intercept 0.14 Logistic regression including retainers Interdigitation 1.00 Skeletal discrepancy 0.74 Change in overjet 0.62 Retainer Single-arch fixed retainer 1.51 Bimaxillary VFR 1.33 Other retention regime 1.00 Intercept 0.00
SEM
P
0.02 0.12 0.14 0.39
0.99 0.10 0.05 0.72
0.96 0.56 0.44 0.65
1.04 1.05 1.01 0.94
0.02 0.99 0.14 0.11 0.15 0.05
0.96 0.51 0.38
1.05 1.07 1.01
1.79 1.54 – 0.00
0.15 15.43 0.14 12.79 – – 0.00 10.2
0.73 0.81 – 0.11
Lower Upper
Note. Likelihood ratio chi-square test between analyses with and without retainers 0.92, P 5 0.63. CI, Confidence interval; SEM, standard error of the mean.
up subjects treated with Bionator, followed by not only finding superior Class II correction during pubertal growth but also observing better levels of stability with fixed appliances. Notwithstanding, variations may exist
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because of differences with age and subsequent use of fixed appliances. Occlusal interdigitation at debonding was not correlated with sagittal relapse, contradicting previous findings.6,21 Pancherz et al6 linked good interdigitation with anteroposterior stability despite a period of occlusal settling before monitoring anteroposterior stability.6 Conversely, Ferguson22 reported that ideal sagittal molar intercuspation did not guarantee stability with fixed appliance. Optimal interdigitation is associated with interlocking of buccal segment relationships in static intercuspal position; however, a physiological rest position with freeway space is habitual with estimates that teeth are in contact for \30 minutes daily based on chewing and swallowing activity.23 Therefore, it is unsurprising that interdigitation is not key to buccal segment stability. Posttreatment relapse in terms of overjet appears to be predominantly associated with dentoalveolar changes of the maxillary and mandibular incisors9,14,24 and would, therefore, appear somewhat independent of buccal segment interdigitation. Retention regime appeared to play no role in the stability of overjet reduction with all participants receiving some retainer for both arches in the present study. Pancherz et al6 suggested that retention in a 32-year followup varied between no retainer to the use of active retainers, including activators, which maintain a postured bite.6 It was suggested that an inconsistent retention regime seemed to contribute to anteroposterior relapse. Furthermore, retention was advocated until the cessation of growth, and as such, retention was ceased after a set time. No other studies have assessed the effect of retention regime on anteroposterior relapse in cases treated with functional appliances, with the majority focusing on the alignment of lower incisors rather than interarch relationships. It is accepted that there remains insufficient evidence in the literature regarding the ideal retention regime,25 and this statement appears to apply equally to the preservation of alignment and sagittal stability. Nonetheless, posterior occlusal coverage during retention following significant sagittal correction may be inadvisable because of the risk of impairment of occlusal interlock. The present study may have been insufficiently powered to demonstrate this effect. Despite efforts to recall all identified participants meeting the inclusion criteria, there was a relatively high dropout rate with a third lost to follow-up with some data missing at random. Attrition of the sample was limited with use of appointment reminders for participants in the form of telephone calls before the appointments. It is difficult to speculate as to whether those attending were more or less likely to have
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experienced relapse. Furthermore, loss to follow-up is expected to have little effect on the possible predictors of instability as this was not a comparative study. There was no control over the treatment provided, such as modifications to the TB design as well as approach to managing the transition to fixed appliances, preadjusted edgewise appliance prescription, extraction protocol, and treatment mechanics. Although this variation may introduce potential confounders, neither headgear nor fixed Class II correctors were required in any case during the fixed phase. Because of the constraints of limited sample size, assessment of the effect of growth and gender differences were not included in the statistical model. However, as these patients were in the postpubertal phase following the completion of treatment, gender and growth-related differences likely had minimal impact on the stability of occlusal change. CONCLUSIONS
Acceptable levels of stability with TB followed by fixed appliance therapy were observed in the short term, with relatively minor degrees of relapse in Class II correction, particularly in terms of overjet. A weak relationship between change in overjet during treatment and overjet relapse was found. Instability could not be associated with the degree of buccal segment interdigitation, pretreatment anteroposterior skeletal discrepancy, or retention regime. REFERENCES 1. Ehsani S, Nebbe B, Normando D, Lagravere MO, Flores-Mir C. Short-term treatment effects produced by the Twin-block appliance: a systematic review and meta-analysis. Eur J Orthod 2015; 37:170-6. 2. O’Brien K, Wright J, Conboy F, Sanjie Y, Mandall N, Chadwick S, et al. Effectiveness of early orthodontic treatment with the Twin-block appliance: a multicenter, randomized, controlled trial. Part 1: dental and skeletal effects. Am J Orthod Dentofacial Orthop 2003;124:234-43: quiz 339. 3. Pancherz H. A cephalometric analysis of skeletal and dental changes contributing to Class II correction in activator treatment. Am J Orthod 1984;85:125-34. 4. Marschner JF, Harris JE. Mandibular growth and Class II treatment. Angle Orthod 1966;36:89-93. 5. Pancherz H, Fackel U. The skeletofacial growth pattern pre- and post-dentofacial orthopaedics. A long-term study of Class II malocclusions treated with the Herbst appliance. Eur J Orthod 1990; 12:209-18. 6. Pancherz H, Bjerklin K, Lindskog-Stokland B, Hansen K. Thirtytwo-year follow-up study of Herbst therapy: a biometric dental cast analysis. Am J Orthod Dentofacial Orthop 2014;145:15-27. 7. Chadwick SM, Banks P, Wright JL. The use of myofunctional appliances in the UK: a survey of British orthodontists. Dent Update 1998;25:302-8.
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8. British Standards Institution. British Standard glossary of dental terms 5 glossaire des termes utilises en art dentaire. London: British Standards Institution; 1983. 9. Drage KJ, Hunt NP. Overjet relapse following functional appliance therapy. Br J Orthod 1990;17:205-13. 10. Bock NC, von Bremen J, Ruf S. Occlusal stability of adult Class II Division 1 treatment with the Herbst appliance. Am J Orthod Dentofacial Orthop 2010;138:146-51. 11. Francisconi MF, Henriques JF, Janson G, Freitas KM, Santos PB. Stability of Class II treatment with the Bionator followed by fixed appliances. J Appl Oral Sci 2013;21:547-53. 12. Bock NC, von Bremen J, Ruf S. Stability of Class II fixed functional appliance therapy—a systematic review and meta-analysis. Eur J Orthod 2016;38:129-39. 13. Janson G, Busato MC, Henriques JF, de Freitas MR, de Freitas LM. Alignment stability in Class II malocclusion treated with 2- and 4premolar extraction protocols. Am J Orthod Dentofacial Orthop 2006;130:189-95. 14. Fidler BC, Artun J, Joondeph DR, Little RM. Long-term stability of Angle Class II, Division 1 malocclusions with successful occlusal results at end of active treatment. Am J Orthod Dentofacial Orthop 1995;107:276-85. 15. Janson G, Camardella LT, Araki JD, de Freitas MR, Pinzan A. Treatment stability in patients with Class II malocclusion treated with 2 maxillary premolar extractions or without extractions. Am J Orthod Dentofacial Orthop 2010;138:16-22. 16. Janson G, Araki J, Camardella LT. Posttreatment stability in Class II nonextraction and maxillary premolar extraction protocols. Orthodontics (Chic.) 2012;13:12-21.
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17. Antonarakis GS, Kjellberg H, Kiliaridis S. Bite force and its association with stability following Class II/1 functional appliance treatment. Eur J Orthod 2013;35:434-41. 18. Pancherz H. The nature of Class II relapse after Herbst appliance treatment: a cephalometric long-term investigation. Am J Orthod Dentofacial Orthop 1991;100:220-33. 19. Pancherz H. Fr€ uh- oder Sp€atbehandlung mit der Herbst-Apparatur—Stabilit€at oder Rezidiv? Inf Orthod Kieferorthop 1994;26: 437-45. 20. Faltin KJ, Faltin RM, Baccetti T, Franchi L, Ghiozzi B, McNamara JA Jr. Long-term effectiveness and treatment timing for Bionator therapy. Angle Orthod 2003;73: 221-30. 21. Lloyd TG, Stephens CD. Spontaneous changes in molar occlusion after extraction of all first premolars: a study of Class II Division 1 cases treated with removable appliances. Br J Orthod 1979;6: 91-4. 22. Ferguson JW. Changes in sagittal molar relationship during and after fixed appliance extraction treatment. J Orthod 2010;37: 16-28. 23. Graf H. Bruxism. Dent Clin North Am 1969;13:659-65. 24. Lucchesi L. A Prospective Study Comparing the Post-Treatment Hard and soft Tissue Changes Following Fifteen Months Treatment with the Twin Block and Dynamax Appliances. Queen Mary University of London; 2009. 25. Littlewood SJ, Millett DT, Doubleday B, Bearn DR, Worthington HV. Retention procedures for stabilising tooth position after treatment with orthodontic braces. Cochrane Database Syst Rev 2016;1:CD002283.
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A prospective evaluation of factors affecting occlusal stability of Class II correction with Twin-block followed by fixed appliances Graham R. Oliver,a Nikolaos Pandis,b and Padhraig S. Fleminga London, United Kingdom, and Bern, Switzerland Introduction: Modified Twin-block therapy followed by fixed appliances (TBFA) is a standard treatment modality in Class II malocclusion; however, there is little information regarding the stability of this approach. We aimed to assess the stability of Class II correction with TBFA and to evaluate factors that may affect stability. Methods: A prospective evaluation involving convenience sampling of 64 participants treated with TBFA was undertaken over 12 months. Study models and lateral cephalometric radiographs were obtained to record overjet and molar relationship, Peer Assessment Rating score, and skeletal parameters, and a new objective buccal segment interdigitation scoring system was developed. Multivariate logistic regression analysis was used to assess the stability of anteroposterior occlusal correction and the degree of buccal interdigitation, pretreatment skeletal discrepancy, and change in overjet during treatment. Results: Mean overjet reduction of 6.22 mm arose during treatment, with the canine and molar relationships improving by 3.34 mm and 2.67 mm, respectively. In the 12 months posttreatment, a relapse of 0.67 mm and 0.06 mm in overjet and molar relationship, respectively, was observed, with 25% of subjects having overjet relapse of .1 mm. There is weak evidence that the treatment-induced change in overjet is linked with overjet relapse (P 5 0.05; odds ratio, 0.67; 95% confidence interval, 0.44, 1.01). No significant relationship was observed, however, between anteroposterior stability and buccal segment interdigitation (P 5 0.99), pretreatment skeletal discrepancy (P 5 0.10) or prescribed retention regime (P 5 0.63). Conclusions: Overall, acceptable levels of stability were observed, although appreciable relapse was noted in 25% of participants. Neither the degree of buccal segment interdigitation nor pretreatment skeletal discrepancy was predictive of anteroposterior occlusal stability. (Am J Orthod Dentofacial Orthop 2020;157:35-41)
F
unctional appliances are known to effectively reduce increased overjet1 and decrease the anchorage requirements for subsequent preadjusted edgewise appliance therapy. Class II correction stems predominantly from dental change (60%-70%), with skeletal contribution accounting for the remainder.2,3 Skeletal change includes an acceleration in mandibular growth during the pubertal growth spurt,4 but mandibular length is ultimately believed to
a Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom. b Department of Orthodontics and Dentofacial Orthopedics, School of Dental Medicine, Medical Faculty, University of Bern, Bern, Switzerland. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Padhraig S. Fleming, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, Whitechapel, London E1 2AD; e-mail: padhraig.fl[email protected]. Submitted, November 2018; revised and accepted, January 2019. 0889-5406/$36.00 Ó 2019 by the American Association of Orthodontists. All rights reserved. https://doi.org/10.1016/j.ajodo.2019.01.024
be determined genetically.5 As such, the majority of prolonged benefit appears to reside at the occlusal level. Although the stability of Class II correction is generally perceived to be satisfactory,3 there is little evidence to support this assumption and a limited appreciation of the factors that might influence the stability of treatment following comprehensive functional and fixed appliance therapy. The most in-depth analysis of functional appliance stability centered on the Herbst appliance with up to 32 years of retrospective follow-up.6 Decreases in arch perimeter and lower incisor crowding consistent with maturational changes were noted. Molar and canine correction was stable in 64% and 14%, respectively, whereas 86% of overjet correction was maintained. The majority of relapse occurred in the first 6 years posttreatment, with only minor changes arising after that with poor interdigitation, continuing habits, or inadequate retention predisposing to instability.6 The Twin-block (TB) is universally popular because of its versatility and high levels of patient tolerance.7 35
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Notwithstanding this, a potential limitation is the development of lateral open bites during the functional phase associated with impeded posterior eruption and related to acrylic coverage. The judicious trimming of the blocks allied to phased or complete withdrawal of the appliance mitigates this issue. However, preadjusted edgewise appliances typically follow functional appliance therapy to align the dentition and improve interdigitation purportedly promoting more stable occlusal correction.3 There is no prospective research related to the stability of treatment with functional appliances, particularly the TB, followed by contemporary preadjusted edgewise appliances. The attainment of optimal occlusal interdigitation following active treatment is speculated to promote stability; however, the quality of interdigitation was assessed subjectively in previous research.6 We, therefore, aimed to determine the stability of Class II correction with modified TB followed by fixed appliances and to evaluate factors that may affect the stability of anteroposterior occlusal correction with this approach. MATERIAL AND METHODS
A prospective evaluation was undertaken at the Orthodontic Departments of Barts Health NHS Trust (The Royal London Hospital and Whipps Cross University Hospital) over 12 months following completion of orthodontic treatment with approval from Barts Health NHS Trust Clinical Effectiveness Unit (ID 6274). The inclusion criteria were treated Class II Division 1 malocclusion as defined by the British Standards Institute8; treated with TB appliances followed by preadjusted edgewise appliances; and willingness to participate in the study. Exclusion criteria included failure to complete functional appliance therapy with the subsequent loss to follow-up; single-arch preadjusted edgewise appliance treatment only; and craniofacial syndromes (eg, cleft lip and palate). A convenience sample of participants was recruited before or at debonding as well as at routine posttreatment review clinics. All participants were treated under consultant supervision with a combination of a TB appliance (Figure 1), followed by preadjusted edgewise appliances. The standard departmental protocol is to undertake functional appliance therapy for 12 months. Following the collation of postfunctional records, preadjusted edgewise appliances are placed after a brief period of either night-only wear or complete withdrawal. Removable retainers were prescribed only for night use. Lateral cephalometric radiographs were taken in centric occlusion and hand-traced on cephalometric acetate tracing film (G.R.O.) using a 2HB 0.5-mm
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Fig 1. Standard Twin-block design.
mechanical pencil and measurements made using a 3M Unitek Cephalometric Protractor. Sagittal Occlusal analysis was used to assess the discrepancy in the skeletal bases relative to the occlusal line. Study model analysis involved measurements using digital calipers (Tesa Technology, Renens, Switzerland; resolution 0.01 mm) and Peer Assessment Rating (PAR) ruler. All measurements were performed by the investigator (G.R.O.) who was calibrated in the use of PAR. Study models were blocked randomized in groups of 20. Identifiable information was removed from the models with a unique, random number. Following the measurement of the models, the investigator was unblinded to record participant identity as well as stage of treatment. The investigator was therefore kept blind to the participant identification as well as the time point of assessment. The primary outcome was the stability of overjet reduction (mm). Secondary outcomes included anteroposterior stability of molar and canine relationship and the PAR score. Independent variables to be assessed were occlusal interdigitation at debonding, pretreatment sagittal skeletal discrepancy, treatment-induced change in overjet, and prescribed retention regime. A novel
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Table I. Scoring system for occlusal interdigitation Vector Anteroposterior Assess the relation of the cusp tip of maxillary canines and premolars relative to the distal contact point of the opposing mandibular tooth. First molars assess the position of maxillary mesiobuccal cusp relative to mandibular buccal groove. Vertical Relation of occlusal surfaces of canines, premolars, and first molars.
Score 2 1 0
2 1 0
Description Class I or III relationship or \1 mm Class II .1 mm and \2 mm Class II .2 mm Class II
Contact of all teeth Clear and distinct (.1 mm) absence of occlusal contact on 1 tooth Clear and distinct (.1 mm) absence of occlusal contact on more than 1 tooth
Table II. Participant demographics Age-related to peak growth spurt Age at Prepubertal, Pubertal, Age functional Age at posttreatment Gender n (%) n (%) n (%) Postpubertal, n (%) fitted (SD), y debonding (SD), y review (SD), y Follow-up period, (SD), y Male 34 (53) 13 (20) 21 (33) 0 (0) 12.52 (1.38) 15.78 (1.77) 16.88 (1.71) 1.10 (0.31) Female 30 (47) 0 (0) 27 (42) 3 (5) 12.56 (1.38) 15.83 (1.98) 16.93 (2.06) 1.10 (0.23) Overall 64 (100) 13 (20) 48 (75) 3 (5) 12.55 (1.40) 15.80 (1.86) 16.85 (1.87) 1.10 (0.29)
objective method (Royal London Occlusal Interdigitation Scoring System) was developed to grade occlusal interdigitation accounting both for anteroposterior as well as vertical relationships of the buccal segments. Both left and right buccal segments are considered, and an overall score was given (Table I). A maximum score of 16 can be assigned to a set of study models based on the anteroposterior discrepancy; for extraction cases, the maximum score is 12. In the vertical plane, the occlusal contact of the maxillary first molar, premolars and canine were assessed with a maximum score of 4 for each set of study models. The anteroposterior and vertical score is then combined and converted to a percentage based on the maximum possible score. The reliability of this novel approach was assessed on 20 sets of study models measured 2 weeks apart by the investigator (G.R.O.). Statistical analysis included a Bland-Altman plot used to visually determine the random and systematic error and the Pitman-Morgan test to gauge homogeneity of variance. A mean difference of 2.75 (standard deviation [SD] 2.76) and 95% limits (Bland-Altman) of –26.29 and 20.79 indicate no significant difference between the variances for the 2 sets of scores and an acceptable level of random error. Intraexaminer reliability for other model-based measures was assessed on 10 randomly selected sets of models and cephalometric radiographs 2 weeks apart. Randomization models were generated in Microsoft Excel (Redmond, Wash). Intraclass correlation estimates and their 95% confidence intervals were at acceptable levels, all above 0.90.
Statistical analysis
Data were analyzed using a statistical package (version 15; StataCorp, College Station, Tex). Statistical analysis included descriptive analysis. Participants were categorized dichotomously as either stable (overjet relapse \ 1 mm) or unstable (overjet relapse $ 1 mm). Logistic regression analysis was undertaken to assess the potential predictive ability of buccal segment interdigitation at debonding, pretreatment skeletal discrepancy (sagittal occlusal analysis, A/OLp–Pg/OLp), change in overjet during active treatment, and retention regime (dual-arch fixed, single-arch fixed, dual-arch vacuum-formed retainers [VFRs], or other approach) on the stability of overjet reduction. RESULTS
Sixty-four participants attended for posttreatment review at a 12-month follow-up. Data were unavailable for some participants because of absence or poor-quality study models or cephalometric radiographs. Overall, there were more male (n 5 34; 53%; Table II) than females (n 5 30; 47%; Table II). The mean age of commencement of functional therapy was 12.55 years. The majority (n 5 48; 75%) started treatment during the peak pubertal growth. Pretreatment skeletal measurements from lateral cephalometric radiographs reflected a moderate skeletal II pattern (ANB, 5.58 ) secondary to mandibular retrognathia (SNB, 74.80 ) with reduced vertical proportions (FMPA, 24.45 ; LAFH, 53.67%; Table III). Pretreatment
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Table III. Pretreatment cephalometric variables Pretreatment cephalometric variables Sagittal skeletal SNA ( ) SNB ( ) ANB ( ) Vertical skeletal FMPA ( ) LAFH (%) Dental UI Mx ( ) LI Mn ( ) SO analysis Overjet (mm) (Is/OLp-Ii/OLp) Molar relationship (mm) (Ms/OLp-Mi/OLp)_ Maxillary base (mm) (A point to OLp) Mandibular base (mm) (Pg/OLp) Skeletal discrepancy (mm) (A/OLp-Pg/OLp)
Mean 80.38 74.80 5.58 24.45 53.67 117.82 95.58 10.50
SD 4.61 4.01 2.22 5.90 2.19 8.14 7.18 2.94
1.72
2.82
76.32
4.46
76.37 –0.05
5.27 3.57
SNA, Angle determined by points S, N, and A; SNB, angle determined by points S, N, and B; ANB, angle determined by points A, N, and B; FMPA, Frankfort mandibular plane angle; LAFH, lower anterior facial height; UI Mx, Incisor–palatal plane angle; LI Mn, Incisor–mandibular plane angle; Is, incision superius; Olp, occlusal plane perpendicular; Ii, incision inferior; Ms, molar superius; Mi, molar inferius; Pg, pogonion; SO, sagittal occlusal analysis.
dental measurements from study models showed overjet was 9.8 mm and buccal segment relationships were Class II, with maxillary canine and molar positions being 5.42 mm and 3.47 mm mesial of Class I relationships, respectively (Table IV). Participants were treated with a modified TB appliance for a mean duration of 1.15 years (SD, 0.45) followed by a transition period of 0.24 (SD, 0.25) years. Most functional appliance designs followed the department protocol; however, a labial bow (n 5 2; 3%) because of significantly proclined incisors or high-pull headgear (n 5 5; 8%) were used occasionally. In addition, 63% of the participants (n 5 41) were treated on a nonextraction basis. The fixed appliance phase lasted 1.88 years (SD, 1.15) on average, resulting in a total treatment time of 3.26 years (SD, 1.30). All participants received some form of retainer with VFRs used most commonly in the maxillary arch (n 5 51; 80%) and the remaining received Hawleytype retainers (n 5 13; 20%). To supplement this, 30% (n 5 19) also had a maxillary bonded retainer. In the mandibular arch, 6 participants received no removable retainer; however, these participants did have a fixed retainer. VFRs were used most commonly (n 5 53; 83%), with relatively few patients receiving Hawleytype retainers (n 5 5, 8%). In total, 29 participants (45%) had mandibular fixed retainers. Overall, overjet decreased by 6.22 mm (9.80 to 3.58 mm; Table IV). At debonding, the buccal segment interdigitation scores
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varied, ranging from excellent to poor interdigitation (60.13%; range, 15%-100%; SD, 20.98). The overjet relapsed by 0.67 mm (SD, 0.69) over the 12 months equating to an 11.33% relapse in overjet relative to the active phase. There was minimal change with molar (0.06 mm; SD, 0.94) and canine relationship (0.09 mm; SD, 0.87). These changes were reflected in the PAR score with a deterioration of 4.44 over the 12 months. Posterior interdigitation improved marginally (2.76%) because of improvement in vertical contact scores. Close assessment of the overjet relapse (Figure 2) showed that 25% of participants experienced overjet relapse . 1 mm; however, the majority (59%) showed minimal posttreatment overjet changes (\0.5 mm). Logistic regression analysis was used to evaluate the possible effect of occlusal interdigitation, change in overjet during treatment, and magnitude of pretreatment skeletal discrepancy on overjet stability (Table V). Stability was not affected by the level of posterior interdigitation at debonding or pretreatment skeletal discrepancy. There was weak evidence that a more significant change in overjet during treatment may be associated with a lower odds ratio for stability (odds ratio: 0.67; P 5 0.05; 95% confidence interval: 0.44, 1.01). Retention regime was not found to be a significant predictor of stability (Table V). The likelihood ratio chisquare test between models with and without retainers (0.92; P 5 0.631) suggests the overall retention regime is not significant. DISCUSSION
In the present study, an overall significant sustained Class II correction was observed with an overjet relapse of 0.67 mm in 12 months, which is consistent with previous studies focused on the stability of Class II correction.9-11 Most participants had clinically insignificant overjet changes (\1 mm); however, 16 (25%) subjects underwent overjet relapse of .1 mm. The main etiological factor in this relapse remains unclear. More prolonged periods of follow-up may be required to isolate these factors more clearly, although previous research has highlighted that the majority of relapse in Class II cases arises relatively soon after cessation of the active treatment phase.6 Very little relapse was observed with buccal segment relationships, with \0.2 mm relapse on average. Bock et al12 reported more significant degrees of relapse with the posterior relationships12; however, this study involved a longer follow-up period of 50 months with Herbst appliances. Our study showed \15% of participants with relapse of .1 mm in the buccal segments,
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Table IV. Treatment and posttreatment occlusal changes Variable Overjet (mm) Canine relationship (mm) Molar relationship (mm) Interdigitation score (%) Peer assessment rating
Pretreatment (T1) 9.80 (2.28) 5.42 (2.37) 3.47 (2.07) 27.23 (18.44) 39.91 (11.73)
Debond (T2) 3.58 (0.95) 2.08 (1.13) 0.80 (1.27) 60.13 (32.90) 7.50 (5.59)
Treatment-induced change (T2-T1) 6.22 (2.46) 3.34 (2.12) 2.67 (1.82) 35.76 (25.36) 32.41 (9.15)
12-month review (T3) 4.26 (0.99) 1.99 (1.33) 0.86 (1.43) 62.89 (20.16) 11.94 (6.59)
Posttreatment changes (T3-T2) 0.67 (0.69) 0.09 (0.87) 0.06 (0.94) 2.76 (16.85) 4.44 (5.44)
Note. All values are mean (6SD).
Fig 2. Overjet relapse.
which is consistent with the results of other functional appliance studies.13 Fidler et al14 similarly identified posttreatment relapse of 0.3 mm in Class II cases undergoing mean correction of 3.4 mm treated with fixed appliances and cervical-pull headgear. It does appear that posterior changes are dwarfed by relapse in the anterior region, most likely because of the influence of soft tissues on the anterior dentition following the withdrawal of active appliances. For every unit increase in overjet reduction, the odds of stability was found to be 33% lower after adjusting for other variables. Janson et al13,15,16 equated a treatment-induced change in overjet, canine and molar relationship during treatment with relapse; however, this finding was based on fixed appliances combined with headgear. Drage and Hunt9 found a weak correlation between the overjet reduction with activator appliances without fixed appliances and posttreatment changes.9 Other studies concerning functional appliances have not found an association between initial overjet and posttreatment changes.6,17 Pretreatment skeletal discrepancy was not found to be correlated with overjet relapse in keeping with previous research with the Herbst appliance.18,19 Faltin et al20 followed
Table V. Logistic regression analysis 95% CI Stability Odds ratio Logistic regression Interdigitation 1.00 Skeletal discrepancy 0.77 Change in overjet 0.67 Intercept 0.14 Logistic regression including retainers Interdigitation 1.00 Skeletal discrepancy 0.74 Change in overjet 0.62 Retainer Single-arch fixed retainer 1.51 Bimaxillary VFR 1.33 Other retention regime 1.00 Intercept 0.00
SEM
P
0.02 0.12 0.14 0.39
0.99 0.10 0.05 0.72
0.96 0.56 0.44 0.65
1.04 1.05 1.01 0.94
0.02 0.99 0.14 0.11 0.15 0.05
0.96 0.51 0.38
1.05 1.07 1.01
1.79 1.54 – 0.00
0.15 15.43 0.14 12.79 – – 0.00 10.2
0.73 0.81 – 0.11
Lower Upper
Note. Likelihood ratio chi-square test between analyses with and without retainers 0.92, P 5 0.63. CI, Confidence interval; SEM, standard error of the mean.
up subjects treated with Bionator, followed by not only finding superior Class II correction during pubertal growth but also observing better levels of stability with fixed appliances. Notwithstanding, variations may exist
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because of differences with age and subsequent use of fixed appliances. Occlusal interdigitation at debonding was not correlated with sagittal relapse, contradicting previous findings.6,21 Pancherz et al6 linked good interdigitation with anteroposterior stability despite a period of occlusal settling before monitoring anteroposterior stability.6 Conversely, Ferguson22 reported that ideal sagittal molar intercuspation did not guarantee stability with fixed appliance. Optimal interdigitation is associated with interlocking of buccal segment relationships in static intercuspal position; however, a physiological rest position with freeway space is habitual with estimates that teeth are in contact for \30 minutes daily based on chewing and swallowing activity.23 Therefore, it is unsurprising that interdigitation is not key to buccal segment stability. Posttreatment relapse in terms of overjet appears to be predominantly associated with dentoalveolar changes of the maxillary and mandibular incisors9,14,24 and would, therefore, appear somewhat independent of buccal segment interdigitation. Retention regime appeared to play no role in the stability of overjet reduction with all participants receiving some retainer for both arches in the present study. Pancherz et al6 suggested that retention in a 32-year followup varied between no retainer to the use of active retainers, including activators, which maintain a postured bite.6 It was suggested that an inconsistent retention regime seemed to contribute to anteroposterior relapse. Furthermore, retention was advocated until the cessation of growth, and as such, retention was ceased after a set time. No other studies have assessed the effect of retention regime on anteroposterior relapse in cases treated with functional appliances, with the majority focusing on the alignment of lower incisors rather than interarch relationships. It is accepted that there remains insufficient evidence in the literature regarding the ideal retention regime,25 and this statement appears to apply equally to the preservation of alignment and sagittal stability. Nonetheless, posterior occlusal coverage during retention following significant sagittal correction may be inadvisable because of the risk of impairment of occlusal interlock. The present study may have been insufficiently powered to demonstrate this effect. Despite efforts to recall all identified participants meeting the inclusion criteria, there was a relatively high dropout rate with a third lost to follow-up with some data missing at random. Attrition of the sample was limited with use of appointment reminders for participants in the form of telephone calls before the appointments. It is difficult to speculate as to whether those attending were more or less likely to have
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experienced relapse. Furthermore, loss to follow-up is expected to have little effect on the possible predictors of instability as this was not a comparative study. There was no control over the treatment provided, such as modifications to the TB design as well as approach to managing the transition to fixed appliances, preadjusted edgewise appliance prescription, extraction protocol, and treatment mechanics. Although this variation may introduce potential confounders, neither headgear nor fixed Class II correctors were required in any case during the fixed phase. Because of the constraints of limited sample size, assessment of the effect of growth and gender differences were not included in the statistical model. However, as these patients were in the postpubertal phase following the completion of treatment, gender and growth-related differences likely had minimal impact on the stability of occlusal change. CONCLUSIONS
Acceptable levels of stability with TB followed by fixed appliance therapy were observed in the short term, with relatively minor degrees of relapse in Class II correction, particularly in terms of overjet. A weak relationship between change in overjet during treatment and overjet relapse was found. Instability could not be associated with the degree of buccal segment interdigitation, pretreatment anteroposterior skeletal discrepancy, or retention regime. REFERENCES 1. Ehsani S, Nebbe B, Normando D, Lagravere MO, Flores-Mir C. Short-term treatment effects produced by the Twin-block appliance: a systematic review and meta-analysis. Eur J Orthod 2015; 37:170-6. 2. O’Brien K, Wright J, Conboy F, Sanjie Y, Mandall N, Chadwick S, et al. Effectiveness of early orthodontic treatment with the Twin-block appliance: a multicenter, randomized, controlled trial. Part 1: dental and skeletal effects. Am J Orthod Dentofacial Orthop 2003;124:234-43: quiz 339. 3. Pancherz H. A cephalometric analysis of skeletal and dental changes contributing to Class II correction in activator treatment. Am J Orthod 1984;85:125-34. 4. Marschner JF, Harris JE. Mandibular growth and Class II treatment. Angle Orthod 1966;36:89-93. 5. Pancherz H, Fackel U. The skeletofacial growth pattern pre- and post-dentofacial orthopaedics. A long-term study of Class II malocclusions treated with the Herbst appliance. Eur J Orthod 1990; 12:209-18. 6. Pancherz H, Bjerklin K, Lindskog-Stokland B, Hansen K. Thirtytwo-year follow-up study of Herbst therapy: a biometric dental cast analysis. Am J Orthod Dentofacial Orthop 2014;145:15-27. 7. Chadwick SM, Banks P, Wright JL. The use of myofunctional appliances in the UK: a survey of British orthodontists. Dent Update 1998;25:302-8.
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8. British Standards Institution. British Standard glossary of dental terms 5 glossaire des termes utilises en art dentaire. London: British Standards Institution; 1983. 9. Drage KJ, Hunt NP. Overjet relapse following functional appliance therapy. Br J Orthod 1990;17:205-13. 10. Bock NC, von Bremen J, Ruf S. Occlusal stability of adult Class II Division 1 treatment with the Herbst appliance. Am J Orthod Dentofacial Orthop 2010;138:146-51. 11. Francisconi MF, Henriques JF, Janson G, Freitas KM, Santos PB. Stability of Class II treatment with the Bionator followed by fixed appliances. J Appl Oral Sci 2013;21:547-53. 12. Bock NC, von Bremen J, Ruf S. Stability of Class II fixed functional appliance therapy—a systematic review and meta-analysis. Eur J Orthod 2016;38:129-39. 13. Janson G, Busato MC, Henriques JF, de Freitas MR, de Freitas LM. Alignment stability in Class II malocclusion treated with 2- and 4premolar extraction protocols. Am J Orthod Dentofacial Orthop 2006;130:189-95. 14. Fidler BC, Artun J, Joondeph DR, Little RM. Long-term stability of Angle Class II, Division 1 malocclusions with successful occlusal results at end of active treatment. Am J Orthod Dentofacial Orthop 1995;107:276-85. 15. Janson G, Camardella LT, Araki JD, de Freitas MR, Pinzan A. Treatment stability in patients with Class II malocclusion treated with 2 maxillary premolar extractions or without extractions. Am J Orthod Dentofacial Orthop 2010;138:16-22. 16. Janson G, Araki J, Camardella LT. Posttreatment stability in Class II nonextraction and maxillary premolar extraction protocols. Orthodontics (Chic.) 2012;13:12-21.
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17. Antonarakis GS, Kjellberg H, Kiliaridis S. Bite force and its association with stability following Class II/1 functional appliance treatment. Eur J Orthod 2013;35:434-41. 18. Pancherz H. The nature of Class II relapse after Herbst appliance treatment: a cephalometric long-term investigation. Am J Orthod Dentofacial Orthop 1991;100:220-33. 19. Pancherz H. Fr€ uh- oder Sp€atbehandlung mit der Herbst-Apparatur—Stabilit€at oder Rezidiv? Inf Orthod Kieferorthop 1994;26: 437-45. 20. Faltin KJ, Faltin RM, Baccetti T, Franchi L, Ghiozzi B, McNamara JA Jr. Long-term effectiveness and treatment timing for Bionator therapy. Angle Orthod 2003;73: 221-30. 21. Lloyd TG, Stephens CD. Spontaneous changes in molar occlusion after extraction of all first premolars: a study of Class II Division 1 cases treated with removable appliances. Br J Orthod 1979;6: 91-4. 22. Ferguson JW. Changes in sagittal molar relationship during and after fixed appliance extraction treatment. J Orthod 2010;37: 16-28. 23. Graf H. Bruxism. Dent Clin North Am 1969;13:659-65. 24. Lucchesi L. A Prospective Study Comparing the Post-Treatment Hard and soft Tissue Changes Following Fifteen Months Treatment with the Twin Block and Dynamax Appliances. Queen Mary University of London; 2009. 25. Littlewood SJ, Millett DT, Doubleday B, Bearn DR, Worthington HV. Retention procedures for stabilising tooth position after treatment with orthodontic braces. Cochrane Database Syst Rev 2016;1:CD002283.
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