Date of Graduation

1999

Document Type

Thesis

Degree Type

MS

College

School of Dentistry

Department

Orthodontics

Committee Chair

Peter Ngan

Committee Member

Mark Durkee

Committee Member

Kavita Kohli

Abstract

Expansion of the maxilla is used to correct skeletal and dental transverse discrepancies between the maxilla and mandible. These discrepancies are corrected through a combination of skeletal expansion (separation of the maxillary midpalatal suture) and dental expansion ( lateral tipping of the maxillary posterior teeth). A recently introduced temperature-activated, nickel titanium (NITI) palatal expander is claimed to produce a light, continuous force which is capable of expanding the maxilla and correcting molar rotations. The skeletal and dental effects of the NITI expander on the maxilla have not been scientifically evaluated. The purpose of this study was to evaluate and compare the dental and skeletal changes produced by a NITI expander to the changes produced by a rapid palatal expansion (RPE) appliance. 25 patients (12 RPE, 13 NITI) had orthodontic study models taken before and after treatment. The models were evaluated via palatal contour tracings and photographs for changes in intermolar width, palatal width, palatal depth, alveolar tipping, molar tipping, and molar rotation. Data were analyzed using Paired t-tests, Pearson Correlation Coefficients, and a Stepwise Multiple Regression Analysis. Also occlusal radiographs, taken before and 2 weeks following insertion and activation of the appliances, were evaluated for evidence of separation of the midpalatal suture. The results were analyzed using a Chi-square test. Both the RPE and NITI expansion appliances were able to produce significant increases in intermolar width, palatal width, alveolar tipping and molar tipping. No significant changes were found in palatal depth in either group. However, the NITI

appliances were able to produce significant increases in molar rotation, whereas, the RPE appliances were not. In comparison, RPE appliances produced a greater percentage of skeletal expansion along with significantly greater radiographic evidence of midpalatal sutural separation. Also, in the RPE group, expansion of the maxilla was more predictable with alveolar tipping, palatal width change, and molar tipping explaining 82 % of the increase in intermolar width. In comparison, the NITI group showed much more unexplained variability with none of the variables being significantly related to intermolar width increase. Also age was found not to be significantly related to palatal expansion in either the NITI expansion group or RPE group. Results of this study suggest that both appliances are capable of expanding the maxilla. In comparison, RPE appliances produce more skeletal expansion and are more predictable in their affect on the maxilla, whereas, NITI expansion appliances are less predictable in their affect on the maxilla but are capable of correcting molar rotations. Neither method of expansion was found to be dependent on the patient’s age.

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