COMPARISON OF DENTAL ARCH AND ARCH PERIMETER CHANGES BETWEEN BONDED RAPID AND SLOW MAXILLARY EXPANSION PROCEDURES

The purpose of this study was to evaluate and compare the dental effec ts of bonded rapid maxillary expansion (RME) and bonded slow maxillary expansion (SME) treatment methods. Subjects with a maxillary bilatera l crossbite were selected and two treatment groups each with 12 patien ts were constructed. At the beginning of treatment, the average chrono logical ages were 11.96 years for the RME group and 12.31 years for th e SME group. The Hyrax screw in the RME treatment group and the spring of the Minne-Expander in the SME treatment group were embedded in the posterior bite planes, which had a thickness of 1 mm. The treatment t ime for the RME group varied from 0.70 to 1.60 months and for the SME group 1.00-5.16 months. At the end of active treatment the appliances were worn for retentive purpose for an additional 3 months. Orthodonti c casts taken at the beginning and end of treatment, and at the end of the retention period formed the material for the study. Increases in the transversal width between the upper molars, upper first premolars, upper canines, lower canines, and in the upper arch perimeter were ob tained. The increase in the upper inter-canine width was found to be s ignificantly greater in the RME group compared with the SME group. Reg ression analysis indicated that arch perimeter gain through the treatm ent could be predicted as 0.65 times the amount of the posterior expan sion for the RME group and 0.60 times the amount of posterior expansio n for the SME group.