TREATMENT RESPONSE TO MAXILLARY EXPANSION AND PROTRACTION

A prospective clinical trial was conducted to determine the skeletal a nd dental contributions to the correction of overjet and overbite in C lass III patients. Thirty patients (12 males and 18 females with a mea n age of 8.4+/-1.7 years) were treated consecutively with protraction headgear and fixed maxillary expansion appliances. For each patient, a lateral cephalogram was taken 6 months before treatment (T-0); immedi ately before treatment (T-1); and 6 months after treatment (T-2). The time period (T-1-T-0) represented changes due to 6 months of growth wi thout treatment; (T-2-T-1) represented 6 months of growth and treatmen t. Each patient served as his/her own control. Cephalometric analysis described by Bjork (1947) and Pancherz (1982a,b) was used. Sagittal an d vertical measurements were made along the occlusal plane (OLs) and t he occlusal plane perpendicular (OLp), and superimposed on the mid-sag ittal cranial structure. The results revealed the following. with 6 mo nths of treatment, all subjects were treated to Class I or overcorrect ed to Class I or Class II dental arch relationships. Overjet and sagit tal molar relationships improved by an average of 6.2 and 4.5 mm, resp ectively. This was a result of 1.8 mm of forward maxillary growth, a 2 .5-mm of backward movement of the mandible, a 1.7-mm of labial movemen t of maxillary incisors, a 0.2-mm of lingual movement of mandibular in cisors, and a 0.2-mm of greater mesial movement of maxillary than mand ibular molars. The mean overbite reduction was 2.6 mm. Maxillary and m andibular molars were erupted occlusally by 0.9 and 1.4 mm, respective ly. The mandibular plane angle was increased by 1.5 degrees and the lo wer facial height by 2.9 mm, Individual variations in response to maxi llary protraction was large for most of the parameters tested. Signifi cant differences in treatment changes between male and female subjects were found only in the vertical eruption of mandibular incisors and m axillary and mandibular molars. These results demonstrate that signifi cant overjet and overbite corrections can be obtained with 6 months of maxillary protraction in combination with a fixed expansion appliance .