Stability of rapid maxillary expansion and facemask therapy: A long-term controlled study

Introduction

The aim of this prospective controlled study was to evaluate the long-term effects of rapid maxillary expansion and facemask therapy in Class III subjects.

Methods

Twenty-two subjects (9 boys, 13 girls; mean age, 9.2 years ± 1.6) with Class III disharmony were treated consecutively with rapid maxillary expansion and facemask therapy followed by fixed appliances. The patients were reevaluated at the end of the 2-phase treatment (mean age, 14.5 years ± 1.9) and then recalled about 8.5 years after the end of rapid maxillary expansion and facemask treatment (mean age, 18.7 years ± 2.1). Two groups of controls with untreated Class III malocclusion were used for statistical comparisons of the short-term and long-term intervals. Statistical comparisons were performed with the Mann-Whitney U test.

Results

In the long term, no significant differences in maxillary changes were recorded, whereas the treatment group showed significantly smaller increases in mandibular protrusion. The sagittal maxillomandibular skeletal variables maintained significant improvements in the treatment group vs the control groups.

Conclusions

In the long term, rapid maxillary expansion and facemask therapy led to successful outcomes in about 73% of the Class III patients. Favorable skeletal changes were mainly due to significant improvements in the sagittal position of the mandible.

Rapid maxillary expansion and facial mask (RME/FM) therapy is the most common orthopedic treatment protocol for Class III malocclusion. The literature includes many articles on the short-term results of RME/FM therapy in growing subjects with Class III disharmonies, as described in a recent systematic review. Several studies have also evaluated the outcomes of the orthopedic treatment protocol at postpubertal observations after fixed appliance therapy, either with or without untreated Class III controls. Both short-term and postpubertal observations indicated a fair-to-good effectiveness of RME/FM therapy, with about 70% to 80% of the patients showing favorable results after puberty. The dentoskeletal changes induced by therapy consist of a combined effect of the protocol on both maxillary and mandibular components. Optimal timing for the orthopedic approach to Class III malocclusion is related to early treatment, at either a prepubertal or a pubertal phase of development.

No data are available in the literature with regard to the outcomes of RME/FM therapy revaluated at the end of active craniofacial growth—ie, after the circumpubertal developmental period. This information is vital for the appraisal of orthopedic treatment results in patients with Class III malocclusion for at least 2 main reasons. First, a significant tendency for the reestablishment of the Class III growth pattern has been widely demonstrated after active protraction therapy, with special emphasis during the pubertal growth spurt. Second, pubertal growth tends to last longer in Class III subjects compared with Class I subjects. On the other end, long-term observations at the end of active craniofacial growth are available for different orthopedic and orthodontic approaches: chincup therapy, with favorable short-term changes often not maintained at the end of growth, and mandibular cervical headgear, with greater long-term stability of favorable mandibular modifications.

The aim of this study was to analyze the long-term outcomes of RME/FM therapy in Class III subjects. The study included Class III subjects treated consecutively with the orthopedic protocol in a prospective design and subjects with untreated Class III malocclusions as controls.

Material and methods

A sample of 30 subjects with Class III dentoskeletal disharmony were treated consecutively with RME/FM therapy followed by comprehensive preadjusted edgewise therapy at the Departments of Orthodontics of the University of Florence and the University of Rome Tor Vergata. All patients had the following dentoskeletal features before therapy (T1) when the pretreatment lateral cephalogram was taken: European ancestry (white), anterior crossbite or edge-to-edge incisor relationship, Class III molar relationship, Wits appraisal of −2.0 mm or less, no discrepancy between centric occlusion and centric relation (indicating pseudo-Class III malocclusion), and prepubertal skeletal maturation (CS 1-CS 3).

The patients were reevaluated with a lateral cephalogram at the end of the 2-phase treatment (T2) and then recalled at an average of 4 years after T2 (T3, about 8.5 years from the end of RME/FM treatment). Eight of the 30 initial subjects could not be located at T3 or did not agree to be reevaluated radiographically in the long term. Therefore, a lateral cephalogram at T3 was taken in the 22 subjects (9 male, 13 female) who represented the final sample of the study. The T3 cephalograms were taken at least 2 years after the attainment of stage 6 in cervical vertebral maturation (completion of circumpubertal active craniofacial growth) for all treated subjects.

Two samples of controls with untreated Class III malocclusions were used for statistical comparisons of the short-term (T1-T2) and long-term (T1-T3) observation intervals. All subjects in the control groups had been followed longitudinally at the Department of Orthodontics of the University of Florence, and they matched the treated group according to ancestry, dentoskeletal Class III characteristics, age, skeletal maturation at all observation periods, duration of observation intervals, and sex distribution.

The 3 components of the RME/FM therapy used in this study were a maxillary expansion appliance, a facemask, and heavy elastics. Treatment began with the placement of a bonded or banded maxillary expander to which were attached vestibular hooks extending in a superior and anterior direction. The patients were instructed to activate the expander once or twice a day until the desired transverse width was achieved.

The patients were given facemasks with pads fitted to the chin and forehead for support either during or immediately after expansion. Elastics were attached from the soldered hooks on the expander to the support bar of the facemask in a downward and forward vector, producing orthopedic force levels up to 400 to 500 g per side. The patients were instructed to wear the facemask for a minimum of 14 hours per day. All patients were treated at least to a positive dental overjet before discontinuing treatment; most patients were overcorrected toward a Class II occlusal relationship. The average duration of the RME/FM treatment was 1.1 years ± 5 months.

As occurs in studies involving any removable device, compliance with the instructions of the orthodontist and staff varied among patients. Therefore, compliance was appraised with a 3-point Likert scale (poor, moderate, good). Nineteen of the 22 subjects (86.3%) underwent a second phase of preadjusted edgewise therapy after an interim period, during which a removable mandibular retractor typically was worn or, in a few instances, immediately after the rapid maxillary expansion and protraction treatment. On average, fixed appliance therapy lasted 18 months. During the T2-T3 period, the patients wore a standard Hawley retainer at night for about 2 years, and thereafter they wore no retention appliance.

A customized digitization regimen and cephalometric analysis provided by Viewbox (version 3.0, dHAL Software, Kifissia, Greece) was used for all cephalograms examined in this study. The customized cephalometric analysis, containing measurements from the analyses of Jacobson, McNamara, and Steiner, generated 19 variables, 9 angular and 10 linear, for each tracing. Magnification was standardized to an 8% enlargement for all radiographs in both treated and control samples.

Statistical analysis

Descriptive statistics were calculated for age at T1, T2, and T3, and for the T1-T2 and T1-T3 age intervals in all groups. Statistical comparisons on these data were performed with the Mann-Whitney U test. Chi-square tests were used to assess differences in sex distributions between groups. The comparison between the treated group and the controls on the dentoskeletal features at T1 (starting forms) was performed with Kruskal-Wallis and Tukey post-hoc tests.

The following statistical comparisons were carried out with the Mann-Whitney U test: (1) treatment effects (T1-T2: T1-T2 changes in the treatment group vs T1-T2 changes in the T1-T2 control group; and (2) overall long-term effects (T1-T3: T1-T3 changes in the treatment group vs T1-T3 changes in the T1-T3 control group.

The prevalence rate of successful patients in the long term (at T3) was calculated in the treatment group. As reported earlier, an unsuccessful outcome of treatment was defined as a concurrent Class III permanent molar relationship and a negative overjet. The prevalence rate of compliance was calculated in treatment group, and the association with the long-term outcome of treatment was appraised with the chi-square test.

The power of the study was calculated on the basis of the difference between the treated and control groups for a relevant cephalometric variable (ANB angle) as reported in a previous longitudinal investigation of similar nature and on the basis of the standard deviation of this difference. The power exceeded 0.90 at an α level of 0.05.

The method error was determined with 15 lateral cephalograms, selected randomly, traced and measured twice within a week by the same operator (C.M.). The measurements at both times for each patient were analyzed with the intraclass correlation coefficient, which varied between 0.966 for the SNB angle and 0.995 for the inclination of the maxillary incisor to the SN line. These values indicated a high level of intraobserver agreement. Linear measurement errors averaged 0.3 mm (SD, 0.8 mm), and angular measurement errors averaged 0.4° (SD, 0.6°).

The stage of cervical vertebral maturation was assessed for each film in a patient’s series by using the method described by Baccetti et al. Staging of cervical vertebrae for each cephalogram was performed by the senior author (T.B.) and then verified by 2 independent investigators (C.M., L.F.) experienced in this method.

Results

The demographic data of the treated group and the control groups (T1-T2 and T1-T3) are reported in the Table I , along with the statistical comparisons showing no significant difference for age at observation periods, age intervals, or sex distribution. The comparisons of the starting forms of the treated group vs the control group T1-T2 and the control group T1-T3 ( Table II ) showed no significant differences with the exception of a smaller inclination of the maxillary incisors to SN in the control group T1-T2 with respect to the control group T1-T3.

Table I
Demographics for the treated and the control groups
Treated group (9 male, 13 female) Control group T1-T2 (9 male, 7 female) Control group T1-T3 (8 male, 5 female)
Period/interval n Mean (y) SD (y) Period/interval n Mean (y) SD (y) Period/interval n Mean (y) SD (y)
T1 22 9.2 1.6 T1 16 8.6 1.8 T1 13 8.4 0.9
T2 22 14.5 1.9 T2 16 14.8 2.1
T3 22 18.7 2.1 T3 13 17.5 1.1
T1-T2 22 5.3 1.9 T1-T2 16 6.2 2.0
T1-T3 22 9.4 2.5 T1-T3 13 9.5 1.8
There were no significant differences either between the treated group and the respective control group at any age period or observation interval (Mann-Whitney U test, P <0.05), or sex distribution (z test on proportions, P <0.05).

Table II
Analysis of starting forms
Cephalometric measures Treated group (TG) n = 22 Control group (CG T1-T2) n = 16 Control group (CG T1-T3) n = 13 TG vs CG T1-T2 TG vs CG T1-T3 CG T1-T2 vs CG T1-T3
Mean SD Mean SD Mean SD
Cranial base
Cranial flexure (°) 130.5 5.8 127.2 4.9 126.3 3.6 NS NS NS
Maxillary skeletal
Co-point A (mm) 81.6 4.9 80.2 5.4 79.5 4.8 NS NS NS
SNA (°) 79.8 4.3 79.7 3.5 80.1 2.8 NS NS NS
Point A to nasion perp (mm) 0.0 3.0 −1.4 2.1 −1.5 1.9 NS NS NS
Mandibular skeletal
Co-Gn (mm) 109.3 7.6 108.9 8.7 106.5 7.7 NS NS NS
SNB (°) 79.5 3.7 80.2 3.9 79.7 3.5 NS NS NS
Pg to nasion perp (mm) −1.0 5.2 −1.6 7.1 −2.9 7.2 NS NS NS
Gonial angle (°) 127.1 4.3 131.2 6.0 129.3 6.3 NS NS NS
Maxillary/mandibular
Wits appraisal (mm) −6.1 2.2 −7.0 3.1 −6.6 3.8 NS NS NS
Max/mand differential (mm) 27.8 4.7 28.6 6.0 27.0 6.2 NS NS NS
ANB (°) 0.4 1.8 −0.5 2.7 0.4 2.6 NS NS NS
Vertical skeletal
FH to palatal plane (°) −1.7 2.2 −2.0 3.4 −0.7 4.0 NS NS NS
MPA (°) 25.5 4.5 28.7 5.6 27.9 6.1 NS NS NS
ANS to Me (mm) 63.2 5.4 61.1 4.2 60.9 4.4 NS NS NS
Interdental
Overjet (mm) 0.1 1.6 −0.8 1.7 −0.6 1.8 NS NS NS
Overbite (mm) 0.3 1.6 0.5 1.8 −0.4 1.8 NS NS NS
Molar relationship (mm) 4.1 1.7 5.4 1.6 5.2 2.0 NS NS NS
Dentoalveolar
U1 to SN (°) 107.0 10.6 99.9 8.7 118.7 19.7 NS NS
L1 to MPA (°) 84.2 5.3 82.5 7.6 85.2 8.0 NS NS NS
Statistical comparisons were performed with Kruskal-Wallis and Tukey post-hoc tests ( P <0.05).
NS , Not significant.

P <0.05.

The success rate in the long term (at T3) in the treated group was 16 of 22 patients, or 72.7%.

Table III reports the treatment effects when comparing the T1-T2 changes in the treated group vs the control group T1-T2. These effects comprise the outcomes of active RME/FM therapy followed by fixed appliances in a 2-phase treatment protocol. The treated group showed a significantly greater amount of maxillary advancement (Point A to nasion perp, 1.4 mm), along with significant decrements in the size and sagittal position of the mandible (Co-Gn, −4.2 mm; SNB, −1.6°; Pg to nasion perp, −2.8 mm). The sagittal maxillomandibular skeletal variables all showed highly significant improvements in the treated group vs the control group (Wits appraisal, 3.9 mm; max/mand differential, −5.2 mm; ANB angle, 2.1°).

Table III
Analysis of treatment effects (T1-T2) and comparisons (Mann-Whitney U test, P <0.05) of T1-T2 changes in the treated group vs T1-T2 changes in the control group T1-T2
Cephalometric measurement Treated group (TG) n = 22 Control group (CG T1-T2) n = 16 TGvs CG T1-T2
Mean SD Mean SD Net difference P value
Cranial base
Cranial flexure (°) −0.2 2.8 −0.2 2.0 0.0 0.919 NS
Maxillary skeletal
Co-point A (mm) 8.3 4.1 7.3 2.6 1.0 0.438 NS
SNA (°) 1.9 2.9 1.5 1.8 0.4 0.965 NS
Point A to nasion perp (mm) 1.7 1.8 0.3 1.6 1.4 0.036
Mandibular skeletal
Co-Gn (mm) 14.1 4.8 18.3 5.3 −4.2 0.021
SNB (°) 2.0 3.1 3.6 2.3 −1.6 0.042
Pg to nasion perp (mm) 4.2 4.0 7.0 4.0 −2.8 0.048
Gonial angle (°) −3.0 3.3 −2.5 3.5 −0.5 0.827 NS
Maxillary/mandibular
Wits appraisal (mm) 1.1 2.6 −2.8 1.8 3.9 0.000
Max/mand differential (mm) 5.8 3.3 11.0 3.3 −5.2 0.000
ANB (°) 0.0 1.4 −2.1 1.6 2.1 0.000
Vertical skeletal
FH to palatal plane (°) 0.0 1.9 −0.5 1.9 0.5 0.137 NS
MPA (°) −2.2 3.0 −2.3 3.4 0.1 0.849 NS
ANS to Me (mm) 6.5 2.3 8.2 3.8 −1.7 0.060 NS
Interdental
Overjet (mm) 1.8 2.6 −0.7 3.1 2.5 0.037
Overbite (mm) 1.4 1.4 0.6 1.9 0.8 0.161 NS
Molar relationship (mm) −0.5 1.8 4.4 2.5 −4.9 0.000
Dentoalveolar
U1 to SN (°) 2.4 8.9 8.9 6.1 −6.5 0.024
L1 to MPA (°) −0.5 3.9 −1.0 5.7 0.5 0.589 NS
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Apr 11, 2017 | Posted by in Orthodontics | Comments Off on Stability of rapid maxillary expansion and facemask therapy: A long-term controlled study
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