V. Bobak et al., STRESS-RELATED MOLAR RESPONSES TO THE TRANSPALATAL ARCH - A FINITE-ELEMENT ANALYSIS, American journal of orthodontics and dentofacial orthopedics, 112(5), 1997, pp. 512-518
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.