Factors contributing to stability of protraction facemask treatment of Class III malocclusion

Abstract

To identify the craniofacial characteristics that contribute to long-term stability of protraction facemask treatment of Class III malocclusion.

Fifty subjects who met the following criteria were recruited: subjects with an anterior crossbite and ‘Wits’ appraisal < -3.5 mm; subjects who had been successfully treated with a protraction facemask (at the end of active orthopaedic treatment the overjet was overcorrected by more than 4 mm); the facemask treatment was started at either CS1 or CS2 and the subjects were followed until CS4; no subject had a congenital craniofacial deformity. Based on the occlusal status at CS4, three groups were identified: Stable group (SG), Unstable group (USG) and a Failed group (FG). One-way analysis of variance and Scheffe’s post-hoc multiple comparisons were used to analyse the differences between the groups. Stepwise discriminant analysis was used to identify the craniofacial characteristics able to predict the stability of protraction facemask treatment.

There were no statistically significant differences between USG and FG. The N-S-Ar was significantly larger and Co-Gn, Wits and LAFH significantly smaller in the SG group as compared with the USG and FG groups. The critical score between SG and USG was 0.368 and between USG and FG it was -0.981. Individuals with scores higher than 0.368 showed relatively stable occlusions at CS4, whereas anterior crossbites returned in individuals with scores less than -0.981 at CS4. The overall percentage of correctly classified cases was 74 per cent, with 90.0 per cent in SG and 73.3 per cent in FG.

A severe maxillo-mandibular discrepancy, an increased vertical dimension and a prognathic mandible were unfavourable factors for long-term stability following early treatment of severe Class III subjects with protraction facemasks.