INTRODUCTION

Early treatment of a Class III dentoskeletal disharmony through growth modification can be accomplished by means of several therapeutic strategies aimed both to restrict mandibular growth and to enhance maxillary growth along with dentoalveolar modifications. Among these treatment options, two orthopedic approaches have demonstrated effectiveness in the treatment of growing Class III patients: the combination of the rapid maxillary expander with the orthopedic facemask (RME/FM) and the mandibular cervical headgear (MCH). Whereas the former appliance has been investigated extensively, the outcome of the latter treatment approach has been studied more sporadically.

During the past 10 years, a number of studies1–12 have described the treatment effects of RME/FM during a single phase of treatment, with a combination of skeletal and dentoalveolar modifications in both the maxilla and mandible noted. Several studies127–12 have evaluated also the craniofacial modifications that occur in the period after the orthopedic correction. They have indicated that in the years after active treatment the pattern of Class III disharmony is reestablished. A recent investigation12 of the postpubertal outcome of RME/FM therapy with the use of untreated Class III controls showed that the favorable skeletal change observed over the long-term was attributed almost entirely to the amount of orthopedic correction achieved during the first intervention with the RME/FM protocol. Aggressive “overcorrection” of the Class III skeletal malocclusion, even toward a Class II occlusal relationship, appears to be advisable, with the establishment of positive overbite and overjet relationships essential to the long-term stability of the treatment outcome.

On the other hand, the outcomes of MCH therapy for Class III malocclusion have been investigated less often. After classical studies on experimental animals,1314 the clinical use of the MCH in human patients15–18 has shown that treatment of Class III patients with MCH for a period of 1 year produced a significant inhibition of mandibular growth, an increase of lower face height, and distalization of the lower molars. Recently, MCH therapy followed by fixed appliances proved to be an effective treatment for the correction of skeletal Class III malocclusion at postpubertal observation.18 The favorable skeletal effects consisted mainly of smaller increases in mandibular length and advancement with respect to controls, with the final outcome a significant improvement in the sagittal skeletal and dental parameters. The MCH treatment protocol also induced a significant downward rotation of the mandible.

The purpose of the present cephalometric study was to compare the effectiveness of the RME/FM and MCH protocols when followed by fixed appliances and evaluated at a postpubertal observation in patients with dentoskeletal Class III malocclusion.

MATERIALS AND METHODS

The sample treated with the RME/FM followed by fixed appliances included 32 patients (12 boys and 20 girls). The sample treated with the MCH followed by fixed appliances included 26 patients (eight boys and 18 girls). The two treatment groups were composed of consecutive patients who satisfied the following inclusion criteria:

• Caucasian ancestry;

• Class III malocclusion at the time of the first observation (T₁) characterized by an anterior cross-bite or edge-to-edge incisal relationship and a Wits appraisal of −1.5 mm or less;

• No permanent teeth congenitally missing or extracted before or during treatment;

• Cephalograms of adequate quality available before the start of therapy (T₁) and at the time of long-term observation after the two-phase treatment (T₂);

• Patients had to present with prepubertal skeletal maturation (stage 1, 2, or 3 in cervical vertebral maturation [CVM]) at the beginning of the first phase of treatment (T₁) and postpubertal skeletal maturation at the final observation (T₂) based on the CVM method of developmental staging (stage 4, 5, or 6 in CVM).19

Lateral cephalograms for each patient were analyzed at the two observation periods. All linear measurements were standardized at an 8% enlargement factor. The mean ages of the treated group at T₁ and T₂ along with mean duration of observation interval are reported in Table 1.

Table 1.  Demographics of the Study Groupsa

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RESULTS

No significant differences were found between the RME/FM group and the MCH group at the time of the first observation (T₁) with the exception of the gonial angle, which was significantly larger in the MCH group (Table 2).

Table 2.  Statistical Comparison on Cephalometric Measures Be tween the Two Treated Class III Samples at the Time of First Ob servation (T1)a

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The statistical analysis of the T₂-T₁ changes in the two treatment groups revealed several significant differences (Table 3). Midfacial length (Co-PtA), mandibular length (Co-Gn), and the sagittal position of the chin (Pg to nasion perpendicular) all showed significantly smaller increases in the MCH group than in the RME/FM group. The amount of increase in overjet was also significantly smaller in the MCH group, whereas the amount of molar correction was greater. The upper incisors were significantly less proclined and the lower incisors were significantly less retroclined in the MCH group when compared with the RME/FM group.

Table 3.  Statistical Comparison of the T2-T1 Changes in the Cephalometric Measures Between the Two Treated Class III Samplesa

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DISCUSSION

The present study was aimed at comparing two orthopedic treatment approaches to Class III malocclusion in the growing patient that have been demonstrated effective in previous research in the literature: the RME/FM protocol and the MCH protocol. Features of the current investigation were the inclusion of a second phase of treatment with fixed appliances in the observation period for both treatment protocols and the appraisal of skeletal maturation at the beginning of therapy and at the long-term observation (postpubertal for all patients in both groups).

The results of the present study showed that the RME/FM protocol was able to induce a more effective enhancement of maxillary growth. A significant 2.3-mm difference in the change in midfacial length was found between the two treatment groups. This favorable outcome in the RME/FM patients, however, was not associated with a significant improvement of the sagittal position of the maxilla when measured by the SNA or PtA to nasion perpendicular.

On the other hand, the MCH protocol appeared to be significantly more effective in controlling the amount of mandibular growth. A significant net difference of almost 3 mm was assessed between the two treatment approaches in favor of the MCH protocol. These findings are in agreement with previous data127–1015–18 and they directly reflect the mode of action of the two different orthopedic appliances. The RME/FM exerted primarily posteroanterior forces on the maxilla, and the MCH delivered anteroposterior forces to the mandibular region through the mandibular dentition. Some definite indications for treatment of Class III malocclusion can be derived from these two different outcomes. The use of the RME/FM has to be preferred in patients with a Class III malocclusion associated with maxillary retrusion, whereas the MCH is a viable treatment option in patients with Class III malocclusion attributed to mandibular prognathism.

The evaluation of maxillary and mandibular measures revealed the lack of a substantial difference between the two treatment approaches regarding the effectiveness on the overall sagittal skeletal relationships of treated patients at a postpubertal observation. The two treatment protocols were also similar as to the response of the craniofacial structures in the vertical dimension. A slight increase in the mandibular plane angle was assessed in the MCH group with respect to the RME/FM group (1.2°). This difference, however, was not statistically significant. When compared with untreated Class III samples in previous studies,1018 a significant opening of the mandibular plane angle was apparent after MCH therapy, whereas the RME/FM did not modify the vertical skeletal relationships significantly.

At the dentoalveolar level, the changes in both the overjet and the molar relation showed statistically significant differences between the two treatment groups, though the absolute value of these differences was limited (1.4 mm for the overjet, 0.8 mm for the molar relation). The improvement in the overjet was greater in the RME/FM sample, whereas the improvement in the molar relation was greater in the MCH sample. This latter difference can be explained by the fact that bands on the lower molars constitute the attachment of the MCH to the dentition. Therefore, a direct effect of distal movement of the lower molars during the MCH therapy was expected.

As for the changes in the overjet, the different modifications produced by the two treatment protocols in the inclination of the incisors need to be taken into consideration. RME/FM treatment followed by fixed appliances induced significantly greater amounts of both proclination of the upper incisors and retroclination of the lower incisors when compared with the MCH protocol. The MCH followed by fixed appliances left the upper and lower incisor positions relatively unchanged from T₁ to T₂, thus achieving the final clinical improvement of the malocclusion without the need for significant dentoalveolar compensation in the anterior portion of the occlusion.

A previous investigation by Battagel and Orton16 compared a group of Class III patients treated with a MCH and a group of Class III patients treated with a customized FM (without the use of RME). The authors did not include a phase II treatment in their investigation, and their final observation was at a mean age of 14.5 years for the MCH group and 12.9 years for the FM group. No postpubertal observation was included in the study. In their short-term study, Battagel and Orton16 reported results similar to the findings of the current investigation, with a forward development of the maxilla and labial movement of the upper incisors seen only in the FM group. Increases in mandibular length (measured as Ar-Pg) were smaller in the MCH group, though not at a significant level. The counterclockwise rotation of the mandible that the authors described in both treatment groups was found only in the RME/FM group of the present investigation.

From a clinical point of view it should be noted that the duration of wear is different for the two appliances examined here. Whereas the RME/FM appliances are worn for approximately 1 year, the MCH requires at least 2 years to produce the orthopedic correction of the disharmony. However, this difference in efficiency of the appliances is compensated by the fact that the RME/FM therapy usually has to be followed by an interim period with removable plates as retention appliances before fixed appliances, whereas patients treated with the MCH are able to start fixed appliance therapy during the use of the MCH.23

CONCLUSIONS

• The RME/FM protocol produces a greater enhancement of maxillary growth, whereas increases in mandibular length are smaller in patients treated with the MCH protocol.

• The RME/FM protocol leads to a greater improvement in the overjet. However, this is achieved by means of a greater degree of proclination of the upper incisors and retroclination of the lower incisors.