CEPHALOMETRIC AND OCCLUSAL CHANGES FOLLOWING MAXILLARY EXPANSION AND PROTRACTION

A prospective clinical trial was conducted to determine the cephalomet ric and occlusal changes following maxillary expansion and protraction . Twenty Southern Chinese patients (eight males and 12 females with a mean age of 8.4 +/- 1.8 years) with skeletal Class III malocclusions w ere treated consecutively with maxillary expansion and a protraction f acemask. Growth adaptation of these patients was followed for 2 years after removal of the appliances and compared with a control group of s ubjects with no treatment. Lateral cephalometric radiographs were used to quantify the skeletal and dental changes before treatment (T-1), i mmediately after treatment (T-2) and 2 years after removal of applianc es (T-3). With 8 months of treatment (T-2 - T-1), overjet was.overcorr ected from a -2.0 to 3.5 mm. The maxilla moved forwards by an average of 2.1 mm and the molar relationship was improved to, a:Class I dental arch relationship. The palatal and occlusal planes were tilted upward 1.0 and 2.0 degrees, respectively. Two years following removal of the appliances (T-3 - T-2), a positive overjet was maintained in 18 out o f 20 patients. The maxilla continued to move forwards in the treated s ubjects similar to the controls. The mandible outgrew the maxilla. In most instances, dental compensation with proclination of the maxillary incisors was observed. The palatal plane returned to pre-treatment va lue. The occlusal plane continued to tilt upward due to eruption of th e molars and proclination of the incisors. Analysis of dental casts sh owed a significant increase in maxillary intercanine (2.2 mm) and inte rmolar widths (2.3 mm) with 7 days of rapid palatal expansion followed by maxillary protraction. The percentage relapse in maxillary intermo lar widths was 30-45 per cent after 1 year, in most cases with minimal retention. In the mandibular arch, the concurrent increase in intermo lar width (2.3 mm) was primarily due to buccal uprighting of the poste rior molars when the maxilla was protracted into a Class I skeletal re lationship and was stable after 1 year. The results of this study indi cate stability of orthopaedic treatment of Class III malocclusions dir ected at the maxilla. Despite some relapse, a net improvement in maxil lomandibular relationship and a positive overjet was maintained in 18 out of 20 patients at the end of the follow-up period.