Effects of rapid maxillary expansion on treatment of classIII malocclusion with maxillary protraction in mixed dentition.

Objective:To determine the effects of rapid maxillary expansion on treatment of ClassⅢ malocclusion with maxillary protraction in mixed dentition. Method:14 boys and 10 girls with maxillary deficiency,aging from 8 to 10,were randomly divided into two groups:the expansion group was treated with maxillary protraction after rapid maxillary expansion for a week and the nonexpansion group was only treated with maxillary protraction .Cephalograms were taken before and after treatment. Hard tissue changes were analyzed by both traditional and Pancherz analysis to evaluate the effects of rapid maxillary expansion. Result:(1)There was significant difference between the expansion group and nonexpansion group in treatment duration: 19.2±3.2 weeks compared to 22.4±3.6 weeks;(2)Significant difference was found in lower anterior facial height increase:4.10±1.92 mm compared to 3.75±2.01 mm;(3)Significant difference was also found in labial inclination increase of upper incisors:2.55°±2.68°compared to 4.70°±2.74°. Conclusion:Treatment of skeletal anterior crossbite with maxillary expansion and protraction was more effective and rapid than that with protraction merely;It also restrained the labial inclination of upper incisors but would result in more posteroinferior rotation of the mandible.