Comparison of 2 treatment protocols using fixed functional appliances in Class II malocclusion: Treatment results and stability

Introduction

The objective of this research was to compare the 2 treatment protocols including a functional mandibular advancer (FMA; Forestadent, Pforzheim, Germany) followed by multibracket appliances (MBAs) vs a Forsus device (3M Unitek, Monrovia, Calif) in combination with MBA concerning treatment outcomes and posttreatment stability.

Methods

This study was conducted using lateral cephalograms of patients who were treated with MBA, which was used either after an FMA or concurrently with a Forsus device, and of patients who had untreated Class II malocclusion (control group). Each group consisted of 19 subjects in cervical stage 2 or cervical stage 3 stages according to the cervical vertebral maturation index. Cephalograms were taken for the treated groups at T1 (pretreatment), T2 (completion of the MBA treatment), and T3 (at least 2 years after T2).

Results

Significant intergroup differences at the T1-T2 period were observed in favor of the FMA concerning mandibular advancement, intermaxillary relationship, and mandibular elongation. With Forsus treatment, restrained maxillary growth and a slightly improved intermaxillary relationship rebounded after treatment ( P <0.05). At the end of treatment, mandibular incisor protrusion and occlusal plane rotation were greater in the Forsus group than in the FMA group ( P <0.05), and maxillary incisor retroclination was significant in the Forsus group. During the posttreatment period, although no significant changes were present in the incisors’ inclination, relapses of the T1-T2 improvements in overjet and overbite and the recidive of the occlusal plane rotation were significantly higher in the Forsus group.

Conclusions

Treatment protocol including an FMA was found to be more effective with mandibular skeletal effects and was more stable with a lesser degree of relapse in overjet and overbite than the Forsus protocol.

Highlights

  • Rigidity of the fixed functional appliance (FFA) has an impact on treatment outcomes and stability.

  • Treatment protocols with rigid FFA are more effective in mandibular growth promotion.

  • Forsus treatment is less stable than the functional mandibular advancer.

Fixed functional appliance (FFA) use is a treatment approach engaged widely in subjects with Class II mandibular retrognathism owing to a lack of patient compliance with removable functional appliances and Class II elastics. The functional mandibular advancer (FMA; Forestadent, Pforzheim, Germany), introduced in 2002, is a tooth-borne variant belonging to the FFA group that has rigid guide pins fixed to molar teeth. It is possible to use an FMA alone as a phase 1 appliance or in combination with a multibracket appliance (MBA) in the mixed or permanent dentition. By contrast, the Forsus fatigue resistant device (3M Unitek, Monrovia, Calif) is a semirigid FFA that is designed for use in combination with an MBA and is one of the most popular FFAs of the last 2 decades.

It has been claimed that Class II correction with an FFA is mainly at the dentoalveolar level with small mandibular and/or maxillary sagittal skeletal changes. Although similar effects have been expected from the Forsus device and an FMA during Class II correction, the amount of dental and skeletal therapeutic components and potential relaps may not be the same for those 2 kinds of FFAs. A recent systematic review pointed out that though the rigidity of an FFA used was believed to have an impact on treatment outcomes, owing to the scarcity of the appropriate articles, this assumption could not be proven. When comparisons of variants of FFAs are taken into account, there is limited evidence concerning relative amounts of skeletal and dental changes in the rigidity of the FFA. ,

The studies regarding treatments using FFAs have assessed the changes taking place during the active treatment period. The scientific evidence concerning the stability of treatment results is nonexistent for most FFAs. Stability data for Forsus appear to be rare, , and a corresponding FMA study is lacking.

The aim of this study was to compare the 2 treatment protocols including an FMA followed by an MBA vs a Forsus device in combination with an MBA for the treatment of Class II malocclusion in treatment outcomes and stability over time.

Material and methods

The study protocol was approved by the Ethics Committee of the School of Medicine (18-10/8), and written consent was obtained from all patients. According to the power analysis with a 0.05 level and 80% power (based on a 1.9-mm standard deviation and a 2-mm detectable difference for mandibular length), the needed minimum sample size was 16 for each group. Three groups were established, each consisting of 19 subjects accounting for the possible dropouts, and classified as Forsus, FMA, and control groups.

The inclusion criteria were patients with Class II Division 1 malocclusion who underwent a treatment protocol including an MBA and either a Forsus device or an FMA, had a nonextraction treatment approach, followed for a posttreatment period of at least 2 years, and presented with cervical stage 2 (CS2) or cervical stage 3 (CS3) stages, which correspond to prepeak or peak of pubertal growth period according to the cervical vertebral maturation index at the start of the treatment.

This study was conducted using lateral cephalograms obtained at 3 observation times: at the start of treatment (T1), after the removal of the MBA (T2), and at a nonactive posttreatment period of at least 2 years (T3). T1 and T2 records were selected from the files belonging to patients whose treatment was provided during the same periods by 3 orthodontists working in the same faculty. These patients were recalled for T3 records. Thirteen patients included in the FMA group were identical with those included in a previous study.

A sample of 19 subjects with untreated Class II malocclusion was selected from the American Association of Orthodontists Foundation Craniofacial Growth Legacy Collection, similar to other Forsus, , , MARA, , and FMA studies. The required lateral cephalograms were requested electronically from the American Association of Orthodontists Foundation Craniofacial Growth Legacy Collection ( www.aaoflegacycollection.org ). A substantial effort was directed toward matching the groups as closely as possible to dentoskeletal features and skeletal maturity stages at T1 and the duration of observation intervals. At T1, of the 19 patients in the Forsus group, 11 (5 boys and 6 girls) were at CS2, and 8 were at CS3 (5 boys and 3 girls). Of the 19 patients in the FMA group, 9 (5 boys and 4 girls) were at CS2, and 10 were at CS3 (6 boys and 4 girls). The number of patients at CS2 and CS3 were 10 (6 boys and 4 girls) and 9 (5 boys and 4 girls) in the control group, respectively.

The treatment of the patients in the FMA group was carried out in 2 phases. Treatments were started with stainless-steel splint FMA appliances, which extended from the first premolars posteriorly to include all the erupted teeth with transpalatal and lingual arches. The FMA appliance was activated as stepwise. The orthopedic phase was followed by a 0.022-inch slot preadjusted MBA.

The other treatment protocol consisted of a Forsus device used in combination with preadjusted fixed appliances. The Forsus was installed when passive rectangular stainless-steel archwires of 0.019 × 0.025 inch were applied on the maxillary and mandibular arches. The activations were done by inserting a crimp on the pushrod at 2-3-month intervals. After removal of the MBAs in both groups, the retention protocol consisted of a bonded canine-to-canine retainer in the maxillary and mandibular arches.

Lateral cephalograms were digitized and analyzed with Dolphin Imaging software (version 11.0; Dolphin Imaging & Management Solutions, Chatsworth, Calif). The Frankfort horizontal plane (constructed by drawing a second line having a −7° difference with the SN plane) and FHP (a line drawn at sella and perpendicular to the Frankfort horizontal) were used for the measurements pertaining to the horizontal positions of the first molars. The examiner who analyzed the cephalograms was blind to which group each individual patient was part of.

Lateral cephalograms at T1, T2, and T3 of 10 randomly selected patients were redigitized at 2-week intervals after the first evaluation. The Dalberg formula was used to assess measurement repeatability. The error ranged between 0.4 and 1.2 mm for the linear measurements and between 0.6° and 1.3° for the angular measurements.

Statistical analysis

Cephalometric data revealed a normal distribution according to the Shapiro-Wilk test. Comparisons of differences among the 3 groups on the T1-T2 and T2-T3 changes and the homogeneity of the groups at T1 were evaluated by 1-way analysis of variance (ANOVA) followed by Tukey test. ANOVA was used also to assess if the groups were comparable for the mean duration of observation intervals. Furthermore, the comparison of means of chronological ages was tested with ANOVA. Comparison of treatment groups regarding treatment durations with functional appliances was performed by means of the independent t tests. All tests were carried out with SPSS software (version 25.0; SPSS Inc, Chicago, III). Statistical significance was set at P <0.05.

Results

For the T1-T2 period, the FMA group showed a tendency toward shorter duration than the control group. However, the intergroup differences were not statistically significant regarding observation times. When the durations of active FFA treatment are compared, mean treatment time of function phase with the Forsus device was significantly shorter. A significant difference was not observed among the groups concerning the mean of chronological ages ( Table I ).

Table I
Comparison of mean ages and treatment and/or observation durations of patients
Variable Forsus FMA Control ANOVA Forsus vs FMA Forsus vs control FMA vs control
Mean ± SD Mean ± SD Mean ± SD P P P P
Chronological age at T1, y 13.4 ± 1.0 13.6 ± 1.3 14.0 ± 1.1 0.314 0.905 0.302 0.539
Observation times T1-T2, y 2.3 ± 0.5 2.0 ± 0.2 2.5 ± 0.9 0.073 0.431 0.520 0.058
Observation times T2-T3, y 2.4 ± 0.4 2.3 ± 0.3 2.8 ± 0.9 0.060 0.885 0.169 0.064
Functional treatment time, mo 8.0 ± 1.3 9.3 ± 1.1 0.003

SD , standard deviation.

P <0.05.

The statistical comparison on initial values among the 3 groups did not reveal any significant differences for any of the cephalometric variables, except the angle between mandibular plane and mandibular incisor axis and the distance between the upper first molar to horizontal reference plane. The mandibular incisor inclination was significantly greater in the Forsus group than in the control group, and the maxillary molars in the Forsus group had significantly higher amounts of dentoalveolar height compared with the FMA group ( Table II ).

Table II
Initial cephalometric values for treatment and control groups
Measurement Forsus FMA Control ANOVA Forsus vs FMA Forsus vs control FMA vs control
Mean SD Mean SD Mean SD P P P P
SNA 82.15 1.66 81.17 1.38 81.36 1.87 0.157 0.165 0.305 0.932
SNB 75.91 1.47 75.24 1.35 76.02 1.91 0.273 0.404 0.975 0.295
ANB 6.24 0.58 5.93 0.65 5.34 1.84 0.065 0.696 0.056 0.277
SNGoGn 32.44 3.68 31.24 3.73 31.05 3.39 0.441 0.563 0.465 0.985
Occl P-SN 20.02 2.76 21.15 2.39 19.84 2.84 0.270 0.399 0.976 0.293
Wits 4.36 2.05 4.52 2.18 3.98 1.64 0.688 0.966 0.824 0.677
Co-Gn 103.67 4.81 102.56 4.95 106.01 6.96 0.169 0.818 0.416 0.155
Co-Go 55.83 4.02 56.11 4.17 58.69 4.76 0.090 0.978 0.113 0.167
Overjet 7.51 1.77 8.08 1.51 7.14 1.34 0.180 0.498 0.743 0.157
Overbite 4.66 1.68 5.82 0.96 4.88 1.47 0.032 0.036 0.879 0.107
1-SN 108.41 4.01 110.06 3.84 111.27 4.82 0.124 0.459 0.104 0.656
IMPA 103.86 4.14 101.77 4.38 99.55 5.01 0.018 0.336 0.013 0.293
U6-V 30.56 3.49 33.29 3.03 31.56 2.96 0.034 0.028 0.597 0.221
U6-H 26.22 2.61 27.55 2.89 26.08 3.01 0.222 0.327 0.987 0.257
L6-V 36.77 3.08 35.23 2.91 37.10 2.12 0.089 0.202 0.927 0.098
L6-H 28.55 1.97 27.31 2.76 27.92 3.04 0.355 0.321 0.742 0.756
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May 12, 2020 | Posted by in Orthodontics | Comments Off on Comparison of 2 treatment protocols using fixed functional appliances in Class II malocclusion: Treatment results and stability
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