Evaluation of the miniplate-anchored Forsus Fatigue Resistant Device in skeletal Class II growing subjects: A randomized controlled trial
To evaluate the use of direct miniplate anchorage in conjunction with the Forsus Fatigue Resistant Device (FFRD) in treatment of skeletal Class II malocclusion. Forty-eight females with skeletal Class II were randomly allocated to the Forsus plus miniplates (FMP) group (16 patients, age 12.5 ± 0.9 years), Forsus alone (FFRD; 16 patients, age 12.1 ± 0.9 years), or the untreated control group (16 subjects, age 12.1 ± 0.9 years). After leveling and alignment, miniplates were inserted in the mandibular symphysis in the FMP group. The FFRD was inserted directly on the miniplates in the FMP group and onto the mandibular archwires in the FFRD group. The appliances were removed after reaching an edge-to-edge incisor relationship. Data from 46 subjects were analyzed. The effective mandibular length significantly increased in the FMP group only (4.05 ± 0.78). The mandibular incisors showed a significant proclination in the FFRD group (9.17 ± 2.42) and a nonsignificant retroclination in the FMP group (−1.49 ± 4.70). The failure rate of the miniplates was reported to be 13.3%. The use of miniplates with the FFRD was successful in increasing the effective mandibular length in Class II malocclusion subjects in the short term. The miniplate-anchored FFRD eliminated the unfavorable mandibular incisor proclination in contrast to the conventional FFRD.ABSTRACT
Objectives:
Materials and Methods:
Results:
Conclusions:
INTRODUCTION
Dimensional mandibular retrusion was shown to be the most common characteristic of skeletal Class II malocclusion.1 The Forsus Fatigue Resistant Device (FFRD; 3M Unitek, Monrovia, Calif)2 is an example of hybrid fixed functional appliances (FFAs), which are used for treatment of mandibular retrusion in growing subjects in which the factor of patient cooperation is controlled.
Recently, evidence3,4 concluded that the skeletal effects of FFAs were minimal and of negligible clinical importance. Reduced skeletal correction was associated with the anchorage loss caused by these appliances that could also jeopardize the stability of the results. Several attempts were proposed to counteract the unwanted dentoalveolar side effects of FFAs, including the use of skeletal anchorage. Studies5–7 showed that mini-screw anchorage reduced mandibular incisor proclination but was not able to enhance the skeletal changes.
Titanium miniplates were introduced for use in orthodontics in 1999.8 They were shown to be well accepted by patients and became popular for use in various applications.9–11 Recently, they were used for direct loading of FFRD for correction of skeletal Class II malocclusion. However, the available studies were either retrospective,12 noncontrolled,13 or nonrandomized.14
Cone-beam computed tomography (CBCT) has an advantage of improved visualization over conventional two-dimensional (2D) imaging techniques.15 Shortcomings of 2D radiographic techniques have been thoroughly described in the literature.16 Errors in landmark identification, visualization, and the superimposition of bilateral structures in 2D cephalograms have compromised the accuracy of their use in clinical research.
This study aimed to compare the skeletal and dental effects of FFRD alone or in conjunction with miniplates in the treatment of skeletal Class II malocclusion as compared with untreated Class II controls.
MATERIALS AND METHODS
Trial Design
This was a parallel-group, randomized, controlled trial with a 1:1:1 allocation ratio. The trial was registered at ClinicalTrials.gov with an identifier number of NCT02475785.
Participants
The participants were recruited at the Faculty of Dentistry, Cairo University outpatient orthodontic clinic. All participants and parents were informed about the procedures and radiation exposures and signed informed consents. The methods of the study were approved by the Ethical Committee of the Faculty of Dentistry, Cairo University. The study was self-funded by the authors. The participants' eligibility criteria are mentioned in Table 1.
Interventions and Data Analysis
A passive, soldered transpalatal arch was cemented to the maxillary first permanent molars. MBT prescription brackets with 0.022-inch slots (3M Unitek) were bonded to both arches in the FFRD group and to the maxillary arch only in the miniplates (FMP) group. Leveling and alignment progressed until reaching 0.019 × 0.025-inch cinched-back stainless-steel wires. The patients were then referred for the T1 CBCT scan. CBCT scanning was performed in maximum intercuspation with the next-generation i-CAT CBCT unit (Imaging Sciences International, Hatfield, Penn). The selected parameters were voxel dimension 0.3 mm, field of view 17 cm at 120 kV, and 18.54 mAs.
In the FMP group, surgical procedures were performed under local anesthesia. A single horizontal incision was made in the alveolar mucosa and the underlying muscle immediately below the mucogingival line from the mandibular canine on one side to that of the other using blade No. 15. Two long Y-shaped miniplates (Stryker, Leibinger, GmbH & Co, Freiburg, Germany) were adapted to the underlying bone (Figure 1). They were fixed by three titanium mini-screws (diameter 2 mm, lengths 8 and 10 mm). The flap was closed using resorbable (4/0) sutures, leaving the miniplate heads perforating the attached gingiva at the mandibular canine region. Postoperative anti-inflammatories and analgesics were prescribed; ice packs and soft diet were advised.
Citation: The Angle Orthodontist 89, 3; 10.2319/062018-468.1
In both treatment groups, the proper FFRD size was selected according to the manufacturer's instructions. The pushrods were inserted onto the mandibular archwires distal to the mandibular canines in the FFRD group and into the miniplate heads in the FMP group (Figure 2a,b). Follow-up visits were every 4 weeks, during which the miniplates were checked for stability and the appliance for activation. The FFRD was planned to be removed either after 10 months or after reaching an edge-to-edge incisor relationship, whichever occurred first. T2 CBCT scan was obtained afterward.
Citation: The Angle Orthodontist 89, 3; 10.2319/062018-468.1
The control group subjects were sent for the T1 CBCT after their random allocation. The observation period was 7.26 ± 1.74 months. Afterward, they were sent for the T2 CBCT that was considered their pretreatment record. Orthodontic treatment was then performed for all control patients.
CBCT analysis was done using Invivo Anatomage version 5.2 (San Jose, Calif). The landmarks and included measurements are described (Figure 3a–c; Table 2).
Citation: The Angle Orthodontist 89, 3; 10.2319/062018-468.1
Sample Size Calculation
Power and sample size calculation (PS) software (Vanderbilt University, Nashville, Tenn) was used. It was based on the work of Manni et al.,17 who reported a 3.7 ± 2.26 mm difference in the mandibular length. When the power was set at 90%, the required sample size was found to be 11 subjects per group. To account for patient dropouts, a sample size of 16 patients was recruited in each group.
Randomization and Blinding
A random sequence table was generated at random.org. To ensure a 1:1:1 allocation ratio, randomization was made in blocks. Allocation concealment was achieved through opaque well-sealed envelopes. Because of the nature of the study, the operator and patients could not be blinded. However, the outcome assessors and the statistician were blinded.
Statistical Analysis
Statistical analysis was performed with IBM SPSS (SPSS Inc, IBM Corporation, Armonk, NY) version 20 for Windows. All bilateral variables were measured for the right and left sides, and for the sake of simplification, averages were statistically analyzed. The measurements were done by the same observer twice and by a second observer. Concordance correlation coefficients (CCCs) were calculated to detect the intra- and interexaminer reliability of the measurements.
Data were explored for normality using Kolmogorov-Smirnov and Shapiro-Wilk tests. Paired t-test was performed to compare between the pre- and posttreatment and/or observation measurements within the groups. One-way analysis of variance (ANOVA) was used for comparison of the baseline data and the mean changes between groups. This was followed by multiple-comparison Bonferroni test for the significant ANOVA variables.
RESULTS
Patient Flow and Dropouts
Sixteen patients were randomly allocated in each group (Figure 4; FFRD: 12.5 ± 0.9 years, FMP: 12.1 ± 0.9 years; and control: 12.1 ± 0.9 years). Two patients were lost to follow-up; one each from the FMP and the FFRD groups. Thus, a total of 46 subjects were analyzed. Clinical examples of one patient of the FFRD and FMP groups are presented in Figures 5 and 6, respectively.
Citation: The Angle Orthodontist 89, 3; 10.2319/062018-468.1
Citation: The Angle Orthodontist 89, 3; 10.2319/062018-468.1
Citation: The Angle Orthodontist 89, 3; 10.2319/062018-468.1
Baseline Data and Measurement Error
At baseline, age; cervical maturational stages (Tables 3 and 4); anteroposterior, vertical, and transverse jaw measurements; and overjet, maxillary, and mandibular incisor measurements; and first molar measurements were reported and compared (Table 5). Normality tests revealed the data were normally distributed. Regarding the measurement error, the CCC values ranged from 0.725–0.995, indicating good to excellent agreement (Table 6).
Follow-up
The mean follow-up period of the FMP, FFRD, and control groups were (in months) 9.42 ± 0.98, 6.23 ± 1.61, and 7.26 ± 1.74, respectively, with a significant difference between them (Table 3). Annualization of the data was performed to account for the difference in treatment/observation durations by calculating the change per year for every measurement.
Skeletal Changes
A significant increase was found in the effective mandibular length (4.05 ± 0.78), SNB, and B-FP in the FMP as compared with the FFRD and control groups, even after data annualization (Tables 7 and 8). The gonial angle was significantly decreased in the controls (−0.88 ± 0.76) and increased in the FMP group (1.15 ± 0.85). The effective maxillary length and A-FP showed no significant difference between groups. The ANB angle showed a significant decrease in the FMP group only (−1.62 ± 1.37), indicating the skeletal Class II improvement.
No significant differences were reported regarding the maxillary and mandibular widths. In the vertical plane, there was a significant increase in the MP/SN (2.06 ± 1.44), indicating a clockwise mandibular rotation in the FMP group, which was confirmed after data annualization.
Dental Changes
The maxillary incisors were significantly retroclined in the FFRD (−8.98 ± 2.55) and FMP (−10.03 ± 4.39) groups (Tables 7 and 8). In the FFRD group, the mandibular incisors showed significant proclination (9.17 ± 2.42) and advancement relative to the A-pogonion line (2.96 ± 0.95). The FMP and control groups showed no significant difference in the mandibular incisor position; retroclination (−1.49 ± 4.70) occurred in the FMP group. The FFRD also showed significant mandibular incisor intrusion (−1.76 ± 0.64), while the FMP showed significant extrusion (1.14 ± 1.52).
Maxillary molars were significantly distalized and intruded in the FFRD and FMP groups. Mandibular molars were mesialized and extruded in all groups. The highest mesialization was found in the FFRD group (2.83 ± 1.31), while the maximum extrusion was found in the FMP group (2.75 ± 0.78).
Harms
Excessive miniplate mobility was considered a sign of failure and occurred in 4 of 30 miniplates (13.3%). Loading was discontinued, and new miniplates were inserted.
DISCUSSION
Undesirable tooth movements and anchorage loss complicate the treatment outcomes of FFAs. Skeletal anchorage was suggested to overcome the dentoalveolar side effects.6,7,12–14 Results of the current randomized trial showed that miniplate-anchored FFRD yielded favorable skeletal effects over the conventional FFRD and untreated controls and eliminated the unwanted mandibular anchorage loss in the short term.
The current study sample included only subjects with Class II division 1 incisor relationship with exclusion of Class II division 2. This was because they have been shown to be different in almost all of their skeletal and dental features.18 Molar relation was not considered during patient inclusion because it was reported that Angle classification does not match the jaw base relationships in one of every three individuals.19 Gender restriction to females was adopted because of the documented variations in growth timing, pattern, and rate between males and females,20 rendering the validity of combination of their skeletal outcomes questionable.
Skeletal age is superior to chronological age in determination of the growth status21; thus, the cervical vertebral maturational stage method according to Baccetti et al.22 was elected for use in subject selection. Subjects were selected to be in stages 3 or 4, and there were no significant differences between groups, indicating similar growth potentials. Inclusion of untreated skeletal Class II controls was based on previous recommendations to separate the treatment effects from the growth changes.23 Lack of growth studies in the population involved in this study resulted in the absence of historical control data; thus, prospective controls were recruited.
Miniplates were used for directly anchoring the FFRD without bonding the mandibular arch, in accordance with previous studies,12–14 because they provide more reliable anchorage over mini-screws upon application of orthopedic forces.10
Normal growth yielded a modest increase in the mandibular length in the controls that was almost the same as in the FFRD group. This confirmed the evidence that FFAs could not induce additional skeletal changes.3,4 On the contrary, miniplate-anchored FFRD (FMP) showed an increase of 4.05 mm in the Co-Gn measurement, which could have been due to the direct application of orthopedic forces to the bone that transmitted a downward and forward force vector to the condyles. Annualizing the data did not change this fact, so the difference was not due to the duration discrepancy between groups. The B point was significantly more retruded at baseline in the FMP group, which could be attributed to a random allocation error that might occur in randomized trials.24
Clockwise mandibular rotation was noted to be significantly higher in the FMP group, in accordance with previous studies.12–14 It could be explained by the application of the force more anterior to the mandibular center of resistance. This posterior rotation masked the increase in the SNB, which was shown previously to be an indicator of mandibular positional change rather than a change of its size.25 In addition, the increased gonial angle in the FMP group could indicate a change in the mandibular morphology because of bone bending following the directly applied downward and forward forces.
The maxillary skeletal changes showed no difference among all groups, in agreement with previous studies.12–14 The ANB angle showed limited improvement in the skeletal Class II in the FMP group only (1.6° ± 1.37°). This reduced magnitude could be attributed to the previously mentioned backward mandibular rotation. Previous studies showed no significant difference in the ANB change between the FFRD and the FFRD with miniplates.12,14
The current FFRD group results confirmed previous reports that FFRD resulted in a large amount of mandibular incisor proclination, reaching 9°–10°.6,26 However, the association between this and the inability of the mandible to surpass its normal growth amount is not fully understood. In the current study, mandibular incisor retroclination occurred in the FMP group, similar to previous studies evaluating the same technique,12–14 and it is considered favorable in Class II subjects. Vertically, the FFRD group showed significant mandibular incisor intrusion due to the downward and forward forces applied to the mandibular teeth by the conventional FFRD. In contrast, the FMP showed mandibular incisor extrusion. The maxillary incisors were similarly retroclined in the FFRD and FMP groups, consistent with the study by Turkkahraman et al.14
Regarding the mandibular molars, mesialization and extrusion were evident in all groups. Noteworthy of mention is that the FMP group showed almost double the molar extrusion of the FFRD group. This could be compensatory to the clockwise mandibular rotation and emphasizes the importance of vertical control during miniplate-anchored FFRD therapy.
The increase achieved in the mandibular length must be interpreted with caution, because it was evaluated only in the short term. Long-term follow-up could diminish the difference in mandibular growth between groups and reveal it was a temporary acceleration of growth. Celikoglu et al.12 achieved almost the same amount of mandibular lengthening that occurred in the current FMP group with both the skeletally anchored FFRD and the Herbst appliance. Concomitant with the invasiveness of the miniplate procedure, the Herbst appliance could be a more efficient tool to choose. The main difference between both appliances was the incisor proclination that was associated only with the Herbst appliance. This could limit the indications for the miniplate-anchored FFRD to those severe Class II subjects whose lower incisors were already proclined.
Limitations and Generalizability
The technique investigated in this study suffered from several limitations. A minimum of two surgeries were needed for miniplate insertion and removal. The additional cost is also an important disadvantage, rendering a cost-benefit analysis mandatory. Engagement of this modality as an integral part of treatment for Class II growing patients still needs further investigation in future studies to show the stability of its long-term outcomes. Another limitation in this study was the different experimental periods between the FFRD and FMP groups, which was managed by annualizing the data. Despite being performed in a university setting that received patients with rural and urban backgrounds, the generalizability of the results might be reduced due to gender restriction. Bigger trials including males and females with subgroup analysis are thus recommended.
CONCLUSIONS
-
The addition of miniplates to the FFRD (FMP group) enhanced the skeletal outcome of Class II malocclusion treatment in the short term.
-
Miniplate-anchored FFRD (FMP) resulted in a significant lengthening of the mandible that was coupled with clockwise mandibular rotation, reducing the apparent sagittal correction.
-
In contrast to the conventional FFRD, miniplate-anchored FFRD (FMP) showed retroclination of the mandibular incisors and no anchorage loss.
The miniplates inserted in the mandibular symphysis.
(A) FFRD insertion in the FMP group. (B) FFRD insertion in the FFRD group.
(A) The skeletal landmarks used in the CBCT analysis. (B, C) The dental landmarks used in the study.
CONSORT 2010 flow diagram.
Extra- and intraoral photographs for a patient in the FFRD group: (A) before treatment, (B) after FFRD removal.
Extra- and intraoral photographs for a patient in the FMP group: (A) before treatment, (B) after FFRD removal.
Contributor Notes