INTRODUCTION

One of the most problematic clinical aspects of dentofacial orthopedics in Class III malocclusions is the possibility of relapse after the active treatment period.1–3 Although there is much literature about the dentofacial changes induced by different treatment protocols in the short term,4–13 only a few authors have studied the posttreatment changes in Class III patients.14 Even fewer are those studies that have analyzed the stability of treatment results at a postpubertal stage of development.15–17 The most recent of these investigations17 evaluated the therapeutic effects of a treatment protocol for Class III malocclusion consisting of mandibular cervical headgear (MCH) followed by fixed appliances. The favorable skeletal effects of the treatment protocol consisted mainly of smaller increases in mandibular length and advancement, with the final outcome of significant improvement in sagittal skeletal and dental relationships. A concurrent study18 demonstrated that the prevalence of TMJ problems in subjects treated with MCH and fixed appliances was not greater than in untreated subjects or subjects with Class I malocclusions treated with standard fixed appliances.

MATERIALS AND METHODS

In the current follow-up study, the treated group consisted of 20 patients with dentoskeletal Class III malocclusion treated consecutively with MCH followed by fixed appliances by one operator. Success of the therapy was not a determinant for selection of patients. One patient dropped out from the original treatment sample during the follow-up interval because he could not be located at recall. Lateral cephalograms were taken 2 years after the end of two-phase treatment (PT) and about 5 years after the end of treatment as a long-term observation (LT).

A control group of 18 untreated subjects with dentoskeletal Class III malocclusion was obtained from the Department of Orthodontics at the University of Florence, Italy, and the University of Michigan. Long-term observations could not be obtained for two subjects of the original control sample used in our previous study.17 All subjects in the treatment group were of white ancestry. Lateral cephalograms were available at two time periods that matched PT and LT. Magnification was corrected to 8% enlargement for all radiographs of both the treated and the control samples. Demographics for the two examined groups are shown in Table 1. No forward functional displacement of the mandible was present in any of the subjects in either group.

Table 1.  Ages of the Class III Study Groups and Duration of Treatment or Observation

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RESULTS

The statistical comparison of the craniofacial forms at PT between the two groups showed several significant effects of two-phase therapy of Class III malocclusion followed by retention (Table 2). These results were already described by the previous report,17 which also showed the absence of significant pretreatment differences between the two groups, with the exception of more proclined upper incisors in the starting form of the treatment group.17 At PT, the treatment group showed significantly smaller values for Co-Gn, SNB angle, maxillomandibular differential, and molar relation. When compared with the controls, at PT the treated patients exhibited also greater values for ANB angle, Wits appraisal, and overjet.

Table 2.  Statistical Comparison of the Treated and Control Class III Groups at the Short-term Posttreatment Observation (PT)^a

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All of these differences remained statistically significant at LT (Table 3), with the addition of significantly smaller values for the distance from pogonion to the nasion perpendicular and of significantly greater values for the MPA in the treated group in the LT.

Table 3.  Statistical Comparison of the Treated and Control Class III Groups at the Long-term Posttreatment Observation (LT)

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No significant differences between the two groups were assessed for the changes in the dentofacial variables from PT to LT time points (Table 4). This outcome revealed absence of a relapse tendency in the transition from the posttreatment to the long-term observations.

Table 4.  Statistical Comparison of the Changes in the Treated and Control Class III Groups During the Interval From Short-term to Long-term Posttreatment Observation (PT to LT)

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DISCUSSION

In the present controlled clinical trial on consecutively treated patients, we evaluated the long-term posttreatment effects of MCH and fixed appliances in growing subjects with Class III malocclusions following a preliminary report that described the treatment and short-term posttreatment outcomes for this protocol.17 Several methodological and clinical features of the research need to be clarified:

• The long-term follow-up observation was recorded approximately 5 years after the end of treatment, when all subjects had reached CS6 in skeletal maturity.

• The posttreatment changes in the treated group were compared with the growth changes in the untreated controls with Class III malocclusions.

• The treated and control groups had no statistically significant differences as to race, gender distribution, mean age, mean observation intervals, or craniofacial characteristics at initial observation (as assessed in the preliminary report17).

To our knowledge, this study represents the first attempt to evaluate the stability of Class III treatment results by taking into account records collected by the end of active craniofacial growth (CS6) and by including longitudinal long-term observations of untreated Class III controls. All treated subjects exhibited a stage CS6 at LT when they were recalled for the long-term reevaluation. Most of them (all the 16 females, and 1 male) had reached CS6 at least 2 years before the final recall (LT). The age of patients at LT ranged from 16 years 9 months (female patient) to 20 years 6 months (male patient). As indicated previously, the group of untreated Class III subjects who served as controls was followed longitudinally until young adulthood as well, similarly to the treated group. All Class III control subjects showed CS6 at LT: once again, this mature developmental stage had been attained at least 2 years before LT in the vast majority of control subjects (all 12 females and 2 males). The age of Class III controls at LT ranged from 16 years 3 months (female subject) to 20 years 4 months (male subject).

The short-term posttreatment effects recorded at PT remained substantially stable at LT. The differences between the two study groups at the long-term observation revealed significantly smaller values in the treatment group for mandibular length (Co-Gn, −5.7 mm) and protrusion (NPog, −1.9 mm: SNB, −2.2°), thus leading to significant improvements in the Wits (6.6 mm), maxillomandibular differential (−6.5 mm), ANB (3.8°), overjet (3.9 mm), and molar relation (−4.5 mm). In addition to these dentoskeletal effects, a greater value for the mandibular plane angle (2.5° difference) was recorded in the treated group versus the controls in the long term. The treated sample did not exhibit the tendency to a counterclockwise rotation of the mandibular plane to the cranial base that was apparent in the Class III controls. This finding confirms previous indications that recommended MCH and fixed appliance therapy in Class III patients with a low-angle tendency.17 The amount of dental compensation through proclination of upper incisors and lingual inclination of lower incisors was very limited in the current study, both after treatment and in the long term. This was probably due to a specific use of the fixed appliances, and it may explain differences in dental outcomes with regard to previous studies.13

When the changes between the short-term posttreatment observation and the long-term posttreatment observation were compared between the treated group and the controls, no significant differences were found. Generally, the differences between the two groups for the modifications in the dentofacial variables were modest, never exceeding 1.5 mm or 1.5°. It should be noted that sagittal and occlusal relationships did not show any tendency to relapse, with the exception of a smaller amount of sagittal growth of the maxilla (Co-A, −0.8 mm in the treatment group compared with controls, not statistically significant).

From the analysis of the results of the present long-term controlled clinical trial, it can be derived that, when left untreated, Class III malocclusion does not show any improvement during the postpubertal ages until the completion of active growth. These data are in agreement with previous observations from both large cross-sectional studies24 and smaller longitudinal investigations of growth in untreated Class III malocclusion.11

In the long term, the effects of an orthopedic/orthodontic treatment protocol such as MCH and fixed appliances appear to be stable since the dentoskeletal improvements achieved during active treatment are successfully able to withstand unfavorable posttreatment growth trends in Class III patients. It should be emphasized that active treatment and retention were not discontinued in any of the treated patients until a postpubertal stage of skeletal development had been attained (CS4 to CS6). The persistence of therapy during the pubertal growth spurt was probably one of the factors accounting for the substantial stability of the outcomes in the postretention period. In fact, long-term observations on chin cup treatment25 have shown that therapeutic effects achieved before puberty may be challenged significantly by the recurrence of the Class III growth pattern at puberty. Similar findings have been described for the RME and facial mask protocol in Class III malocclusion.11

The MCH and fixed appliances protocol did not produce any therapeutic effect in the maxilla either after active therapy or in the long term, in accordance with previously reported data.17 Therefore, it appears that this treatment regimen can be particularly indicated for the treatment of moderate Class III malocclusions associated with mandibular prognathism and normal- to low-angle vertical relationships. Finally, the cephalometric analysis used in the present study did not include any soft-tissue profile measurements for the facial profile (eg, soft-tissue pogonion) or facial proportions. These aspects deserve to be examined by further research.

CONCLUSIONS

• Significant dentoskeletal outcomes in terms of improvement of mandibular prognathism, Wits appraisal, overjet, and molar relationship induced by MCH and fixed appliances remained stable in the long term.

• In the long term, the treatment protocol produced less anterior rotation of the mandibular plane than untreated Class III controls.