Factors affecting occlusal stability of Class II correction with Twin block followed by fixed appliances

2. A PROSPECTIVE EVALUATION OF FACTORS AFFECTING
OCCLUSAL STABILITY OF CLASS II CORRECTION WITH
TWIN BLOCK FOLLOWED BY FIXED APPLIANCES
Graham R. Oliver, Nikolaos Pandis, and Padhraig S. Fleming
London, United Kingdom, and Bern, Switzerland
Am J Orthod Dentofacial Orthop: 2020;157(1):35-41
PRESENTED BY -
Dr DEVENDER KUMAR
POST GRADUATE STUDENT
DEPARTMENT OF ORTHODONTICS

3. CONTENTS
 INTRODUCTION
 MATERIALS & METHODS
 STATISTICAL ANALYSIS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES

4. INTRODUCTION
■ Class II functional appliances are indicated in the correction of mandibular deficiencies as
they allow mandibular postural changes by holding the mandible forward and/or downward.
■ The muscles and soft tissues are stretched with the generated pressure transmitted to the
skeletal and dental structures potentially resulting in skeletal growth modification and tooth
movement.
■ Both fixed and removable Class II functional appliances are used to improve Class II
malocclusions. Since the success with removable appliances largely depends on patient’s
compliance, using a more tolerable appliance can increase the chances of a favourable
outcome.

5. ■ Twin-blocks are upper and lower acrylic bite
blocks with occlusal inclined planes that
interlock at a 70 degree angle and guide the
mandible forward and downward.
■ It has been suggested that compared to other
functional appliances, success rate with
Twin-block is favourable because it is
generally better tolerated by patients as it is
smaller than other functional appliances, has
no visible acrylic portion anteriorly, and its
interference with speech is minimal.

6. OCCLUSAL INCLINED PLANES
During the evolution of the technique the angulations used were 90 degree and then
changed to 45 degree.
Drawbacks of 45 angulations posterior open bite.
An angle of 45 also results in equal downward and forward force on the mandibular
dentition.
Finally changed to 70 to apply a more horizontal component of force.

7. PHASES OF TREATMENT
Stage 1 : Active Phase (6-9 months)
■ The aim in this stage is to achieve a class I occlusion with corrected overbite and overjet and a three point
Occlusal contact with incisors and molars.
Stage 2 : Support Phase (3-6 months)
■ The aim is to maintain the corrected incisor relation till the buccal segment is fully interdigitated. The upper
removable appliance is fitted with a anterior inclined plane to engage the lower incisor and canines and the
lower twin block is left out in this stage.
Stage 3 : Retention (9 months)
■ Treatment is followed by retention with the upper anterior inclined plane only, with wear reduced to night time
only.
TEXTBOOKOFTWIN BLOCK FUNCTIONALTHERAPY BY WILLIAM J CLARK

8. AIM
■ To assess the stability of Class II correction with Twin-block therapy
followed by fixed appliances (TBFA) and to evaluate factors that may
affect stability.

9. MATERIALS 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).
■ A convenience sample of participants was recruited before or at debonding as well as
at routine posttreatment review clinics.
■ 64 participants attended for posttreatment review at a 12-month follow-up. There were
34 male participants (n=34; 53%) and 30 female participants (n=30; 47%).

10. INCLUSION CRITERIA
■ The inclusion criteria were treated Class II Division 1 malocclusion as
defined by the British Standards Institute; treated with TB appliances
followed by preadjusted edgewise appliances; and willingness to
participate in the study.

11. EXCLUSION CRITERIA
■ Patients who failed to complete functional appliance therapy with the
subsequent loss to follow-up;
■ Single-arch preadjusted edgewise appliance treatment only;
■ Craniofacial syndromes (eg, cleft lip and palate).

12. ■ All participants were treated under consultant supervision with a combination of a
TB appliance, followed by preadjusted edgewise appliances.
■ The standard departmental protocol is to undertake functional appliance therapy
for 12 months.
■ Following the collection of post functional 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.

13. ■ All measurements were performed by the investigator who was calibrated
in the use of Peer Assessment Rating (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 with respect to the participant
identification as well as the time point of assessment.

14. ■ 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 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.
■ 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.

15. ■ 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.
■ Intraexaminer reliability for other model-based measures was assessed on 10 randomly selected sets of
models and cephalometric radiographs 2 weeks apart.

16. STATISTICAL ANALYSIS
■ Data were analyzed using a statistical package (version 15; StataCorp,
College Station, Tex).
■ Statistical analysis included descriptive analysis.
■ Participants were categorized as either stable (overjet relapse <1 mm) or
unstable (overjet relapse ≥1 mm).

17. RESULTS
■ 64 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.
■ Participants were treated with a 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 = 2;
3%) because of significantly proclined incisors or high-pull headgear (n = 5; 8%) were used
occasionally.
■ In addition, 63% of the participants (n = 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).

18. TABLE II

19. TABLE III

20. TABLE IV

21. ■ All participants received some form of retainer with vacuum-formed retainers (VFRs)
used most commonly in the maxillary arch (n = 51; 80%) and the remaining received
Hawley type retainers (n = 13; 20%).
■ To supplement this, 30% (n = 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 = 53; 83%),
with relatively few patients receiving Hawley type retainers (n = 5, 8%). In total, 29
participants (45%) had mandibular fixed retainers.

23. 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.
■ 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.
■ Very little relapse was observed with buccal segment relationships, with <0.2 mm relapse on average.
■ For every unit increase in overjet reduction, the odds of stability was found to be 33% lower after
adjusting for other variables.

24. ■ Pretreatment skeletal discrepancy was not found to be correlated with overjet relapse in
keeping with previous research with the Herbst 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.
■ 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 incisors and would, therefore,
appear somewhat independent of buccal segment interdigitation.

25. ■ 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.
■ 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, 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.

26. ■ 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 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.

27. REVIEW OF ARTICLES

28. ■ The aim of this study was to evaluate the effectiveness of Herbst and Twin-block appliances for
established Class II Division I malocclusion.
■ A total of 215 patients (aged 11-14 years) were randomized to receive treatment with either the Herbst or
the Twin-block appliance.
■ Treatment with the Herbst appliance resulted in a lower failure-to-complete rate for the functional
appliance phase of treatment (12.9%) than did treatment with Twin-block (33.6%).
■ There were no differences in treatment time between appliances, but significantly more appointments
were needed for repair of the Herbst appliance than for the Twin-block.
O’Brien, K.,Wright, J., Conboy, F., et al. Effectiveness of treatment for class II malocclusion with the herbst or twin-
block appliances: a randomized, controlled trial. Am J Orthod Dentofacial Orthop 2003, 124(2), 128–137.

29. ■ There were no differences in skeletal and dental changes between the appliances; however, the final
occlusal result and skeletal discrepancy were better for girls than for boys.
■ Because of the high cooperation rates of patients using it, the Herbst appliance could be the appliance
of choice for treating adolescents with Class II Division 1 malocclusion. The trade-off for use of the
Herbst is more appointments for appliance repair.
O’Brien, K.,Wright, J., Conboy, F., et al. Effectiveness of treatment for class II malocclusion with the herbst or twin-
block appliances: a randomized, controlled trial. Am J Orthod Dentofacial Orthop 2003, 124(2), 128–137.

30. ■ The objective of this study was to analyze the short-term occlusal stability of Herbst therapy in adults
with Class II Division 1 malocclusions.
■ Methods: The subjects comprised 26 adults with Class II Division 1 malocclusions exhibiting a Class II
molar relationship >0.5 cusp bilaterally or >1.0 cusp unilaterally and an overjet of >4.0 mm.
■ The average treatment time was 8.8 months (Herbst phase) plus 14.7 months (subsequent multi-bracket
phase). Study casts from before and after treatment and after an average retention period of 32 months
were analyzed.
■ Results: After retention, molar relationships were stable in 77.6% and canine relationships in 71.2% of
the teeth. True relapses were found in 8.2% (molar relationships) and 1.9% (canine relationships) of the
teeth. Overjet was stable in 92.3% and overbite in 96.0% of the patients; true relapse did not occur.
■ Conclusions: Herbst treatment showed good occlusal stability 2.5 years after treatment in adults with
Class II Division 1 malocclusions
Bock, N. C., 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(2), 146–151.

31. ■ The aim of this 2-arm parallel study was to compare the dentoalveolar and skeletal changes achieved
with Twin-block appliance therapy prescribed on either a part- or full-time basis for 12 months.
■ Sixty-two 10-14 year-old patients were randomly allocated to either full-time (FT, 22 hours daily) or
part-time (PT, 12 hours daily) wear of a modified Twin-block appliance and recalled at 6- to 8-week
intervals.
■ Study models and cephalograms were taken at baseline and after 12 months of treatment.
■ Data from 55 of the 62 participants were analyzed. Overjets were reduced by 7 mm (SD, 2.92) in the
PT group and 6.5 mm (SD, 2.62) in the FT group, with no statistical difference between the groups.
Parekh, J., Counihan, K., Fleming, P. S., Pandis, N., & Sharma, P. K. Effectiveness of part-time vs full-time wear protocols
ofTwin-block appliance on dental and skeletal changes: A randomized controlled trial. Am J Orthod Dentofacial
Orthop:2019:155(2), 165–172.

32. ■ Similarly, no clinical or statistical differences were noted for skeletal changes: ANB angle (PT= -
1.51; FT=-1.25), pogonion-sella vertical (PT= 3.25 mm; FT= 3.35 mm) or A-sella vertical (PT= 1.28
mm; FT=1.06 mm). Mean wear durations were 8.78 hours a day in the PT group and 12.38 hours in
the FT group.
■ Conclusions: There was no difference in either dental or skeletal changes achieved with PT or FT
wear of a Twin-block appliance over 12 months. PT wear regimens may therefore be a viable
alternative to FT wear of removable functional appliances.
Parekh, J., Counihan, K., Fleming, P. S., Pandis, N., & Sharma, P. K. Effectiveness of part-time vs full-time wear protocols
ofTwin-block appliance on dental and skeletal changes: A randomized controlled trial. Am J Orthod Dentofacial
Orthop:2019:155(2), 165–172.

33. CONCLUSION
Acceptable levels of stability with twin block 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 the 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.

34. LIMITATIONS
■ Limited sample size.
■ No control group.
■ Effect of growth and gender differences were not included.
■ As 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.

35. REFERENCES
■ 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.
■ O’Brien, K., Wright, J., Conboy, F., et al. Effectiveness of treatment for
class II malocclusion with the herbst or twin-block appliances: a
randomized, controlled trial. Am J Orthod Dentofacial Orthop 2003,
124(2), 128–137.
■ Parekh, J., Counihan, K., Fleming, P. S., Pandis, N., & Sharma, P. K.
Effectiveness of part-time vs full-time wear protocols of Twin-block
appliance on dental and skeletal changes: A randomized controlled trial.
Am J Orthod Dentofacial Orthop:2019:155(2), 165–172.

36. ■ Cheewapornpimol, J., Tangjit, N., Dechkunakorn, S., &
Anuwongnukroh, N. Treatment effects of twin block appliance in
hyperdivergent and normovergent patients. Mahidol Dental
Journal:2019;39(3), 277-291.
■ Graham R. Oliver, Nikolaos Pandis, and Padhraig S. Fleming. A
prospective evaluation of factors affecting occlusal stability of Class II
correction with Twin block followed by fixed appliances. Am J Orthod
Dentofacial Orthop: 2020;157(1):35-41
■ TEXTBOOK OF TWIN BLOCK FUNCTIONAL THERAPY BY WILLIAM J
CLARK