STRESS-RELATED MOLAR RESPONSES TO THE TRANSPALATAL ARCH - A FINITE-ELEMENT ANALYSIS

The finite element method of analysis (FEM) was used to analyze theore tically the effects of a transpalatal arch (TPA) on periodontal stress es of molars that were subjected to typical retraction forces. The pur poses of this investigation were (1) to construct an appropriate finit e element model, (2) to subject the model to orthodontic forces and de termine resultant stress patterns and displacements with and without t he presence of a TPA, and (3) to note any differences in stress patter ns and displacements between models with and without a TPA. Because an chorage is stress-dependent, a TPA must be able to modify periodontal stresses as a prerequisite for increasing orthodontic anchorage. A fin ite element model, consisting of two maxillary first molars, their ass ociated periodontal ligaments and alveolar bone segments, and a TPA, w as constructed. The model was subjected to simulated orthodontic force s (2 N per molar) with and without the presence of the TPA. Resultant stress patterns at the root surface, periodontal ligament, and alveola r bone, as well as displacements with and without a TPA, were calculat ed, Analysis of the results revealed minute differences of less than 1 % of the stress range in stress values with respect to the presence of a TPA. Modification of bone properties to allow for increased displac ement levels confirmed the ability of the TPA to control molar rotatio ns; however, no effect on tipping was noted. Results suggested that th e presence of a TPA has no effect on molar tipping, decreases molar ro tations, and affects periodontal stress magnitudes by less than 1%. Th e final results suggest an inability of the TPA to modify orthodontic anchorage through modification of periodontal stresses.