ANALYSIS OF THE EFFECTS AND PREDICTORS OF ORTHODONTIC FACE MASK THERAPY IN GROWING CLASS III PATIENTS

Abstract

Introduction Treatment of growing patients with Class III malocclusion (CL III) remains one of the most challenging problems to treat orthopedically because of the difficulty to predict the mandibular growth potential, thus the possible relapse after treatment with uncontrolled additional growth. Early prediction of the long-term outcome of Face Mask Therapy (FMT) will help fine-tune the treatment plan to deliver optimal treatment strategy and results.

Aims Chapter 1 To investigate immediate and post-adolescent growth spurt changes induced by FMT and growth on the maxillo-mandibular inter-relationship. Chapter 2 Investigate the Cephalometric, Facial and Dental predictors of successful and unsuccessful FMT, and the differences between gender and age groupings. Chapter 3 Check the validity and accuracy of the different proposed predicting formulas in the literature. Chapter 4 Propose a new prediction model for long term FMT outcome.

Methods Records of 120 growing CL III patients who received a first phase of orthopedic treatment with facemask alone or with facemask and palatal expansion followed by comprehensive, preadjusted, edgewise therapy. The records were provided through the Dentofacial Clinic at the American University of Beirut-Medical Center and part-time faculty affiliated with the department. The radiographic images were collected at three different timepoints: Pre-treatment (T1), Post-facemask treatment (T2), post-pubertal follow-up (T3) indicated by skeletal maturation evaluation (CVSM 5 or 6). Patients who simultaneously met 2 of the following inclusion criteria, at the time of the first evaluation (Pre-treatment, T1), were included in the study: - Edge to edge relationship or negative overjet, reflecting a Class III dental malocclusion - ANB angle of 0o or less, reflecting a maxillo-mandibular discrepancy in relation to the cranial base - Wits appraisal (AoBo) of -2.5mm or less The final sample of CL III patients who met the criteria consisted of 85 patients having records at T1 and T2, of which 52 had an additional T3 post-pubertal follow up. The sample was divided into two groups, a favorable and unfavorable response group, based on the Overjet at T3 being OJ>0 or OJ<0 respectively. Linear and angular measurements gauging relations among cranial base and both jaws were taken on pre- and post-treatment lateral cephalograms. Various appropriate statistical analyses were applied, including discriminant analysis to determine pretreatment predictors of a favorable CL III orthopedic treatment outcome with face mask.

Results FMT induced skeletal improvements, notably a significant increase in the ANB angle (T2-T1=1.58o, p<0.05) and in the Wits appraisal (T2-T1=3mm, p<0.05), as well as differential growth between the maxilla and the mandible, the maxilla moving forward 4 times as much as the mandible. It resulted also in dental compensations, with proclination of the maxillary incisors by 5o on average and retroclination of the mandibular incisors by 2o. All these changes contributed to the improvement of the overjet and the facial profile. At the post-pubertal follow-up T3, 80.8% of the treated patients remained stable (successful) while 19.2% relapsed back into an anterior edge to edge occlusion or crossbite (unsuccessful). Relapse tendencies were observed in both groups, but mandibular growth was more noticeable in the unsuccessful group resulting in a more severe reversion. Male subjects are more prone for relapse than female subjects. The unsuccessful group exhibited a significantly more severe wits appraisal, a more obtuse gonial angle and a more hyperdivergent pattern at the initial timepoint when compared to the successful group. The application of predictive models was found to be deficient in forecasting either success and/or failure. The greatest correspondences were found in a discriminant model based on Wits and Gonial angle. (Success predicted correctly in 95%; failure predicted correctly in 30%)

Conclusion Facemask therapy in growing subjects with CL III malocclusion is effective in the short term. However, the clinician should be aware of the potential of relapse on the long term and take it into consideration during treatment planning. The wits appraisal, the gonial angle and the vertical pattern as well as the gender might be early predictors of the long-term outcome. Early forecasting of treatment outcome remains challenging, since mandibular growth leading to relapse occurs post-pubertally after the orthopedic treatment period.