Lower Inter-canine Uprighting and Arch Width Change with RPE

OBJECTIVES: To determine any lower cuspid (3-3) uprighting and arch width changes due to: 1) 11-15mm Rapid Palatal Expansion (RPE) and 2 months stabilization and 2)completion of subsequent orthodontic treatment. METHODS: Three (PA) cephalograms for 30 posterior X-bite patients (17f; 13m) (ranging 9-31 yrs.) who had RPE Tx followed by fixed orthodontics were selected, traced and measured. Lower (3-3) arch width was measured between (3-3) cusp tip images on (PAs) taken at (T1)=PreTx,(T2)=2mos. post RPE stabilization and (T3)=end of fixed appliance therapy. Compensation formula was figured and applied to correct for growth and magnification factors. Lower (3-3) inclination changes were determined by measuring angles between long axes of lower canines and tabulated as (3-3) inclination for each T1, T2 and T3. Differences between all T1, T2 and T3 measures were calculated as the changes. Data was analyzed. RESULTS: Concordance reliability estimates show 84-100% repeatability. From T1 to T2 lower cuspids uprighted (mean =0.93 degrees +/- 8.9) with a (95% confidence interval (CI) between 4.25 and -2.4). The (3-3) arch width (AW) increased; mean=1.05mm (+/-3.4); (95%Cl=0.23 to -2.32). From T1 to T3 the cuspids uprighted a total (mean = 5.25 deg +/- 10.2) (95% CI = 9.06 to 1.44). Mean change from T2-T3 =4.2 deg. T1- T3 AW increased (3.64mm +/- 4.27) (95%CI= 5.23 to 2.04). Mean AW change from T2-T3 = 2.59mm. CONCLUSIONS: The (3-3) lower arch width increased and the canines uprighted slightly (but clinically insignificantly) independant of any mandibular appliances (T1-T2). From T2-T3 the edgewise appliances were associated with significantly greater uprighting and increase of(3-3) width. Nevertheless the lower arch was finished with an expanded dimension relative to the original arch form. Reportedly that will be unstable. Future research is recommended to determine post-retention stability of expanded lower anterior arch form and width.