Treatment effects of a fixed intermaxillary device to correct class II malocclusions in growing patients

BACKGROUND The objective of this study was to evaluate the treatment effects of Forsus™ Fatigue Resistant Device (FRD; 3M Unitek, Monrovia, CA, USA) in growing patients with Class II non-extraction malocclusions. METHODS A retrospective sample of 24 class II patients treated consecutively with the FRD followed by comprehensive orthodontic treatment was compared to a sample of untreated control subjects from the Bolton Brush Study who was matched in age, sex, and craniofacial morphology. Lateral cephalometric radiographs were taken before treatment (T1) and after removal of fixed appliances (T2). Growth changes were subtracted from the treatment changes to obtain the treatment effects of the appliance. Data were analyzed using ANOVA and a match paired t test. RESULTS Significant differences were found between the treated and control groups for 12 of the 29 measured variables (Co-Gn minus Co-Apt, Wits, Is-OLp, Ii-OLp, overjet, Mi-OLp, molar relationship, overbite, Mic-ML, SNA, ANB, and Ii-ML). With 27.8 months of treatment, all patients were corrected to a class I dental arch relationship. Overjet and molar relationships were improved by an average of 4.7 and 3.1 mm, respectively. This was contributed by a 1.2 mm of restraint in forward maxillary growth, 0.7 mm of forward movement of the mandible, 1.5 mm of backward movement of the maxillary incisors, 1.3 mm forward movement of the mandibular incisors, 0.5 mm backward movement of the maxillary molars, and 1.3 mm of forward movement of the mandibular molars. The overbite was decreased by 2 mm with no significant change in the occlusal, palatal, or mandibular plane. Individual variations in response to the FRD treatment were large for most of the parameters tested. Significant differences in treatment changes between male and female subjects were found only in a few parameters measured. CONCLUSIONS These results demonstrate that significant overjet and overbite corrections can be obtained with the Forsus FRD in conjunction with comprehensive orthodontic treatment.