[Effects of the directions of an extraoral retractive force on the displacement of and stress distribution in palate]

Abstract

Objective: The aim of this study was to assess the effects of varying retractive force directions on the displacement of and stress distributions in palate.

Methods: A three-dimensional finite element model of the nasomaxillary complex was created, consisting of 1638 isoparametric elements and 1827 nodes. An extraoral retractive force of 9.8N was applied to the upper canines in 3 different directions, i.e. parallel, 30 degrees upwards and downwards to the functional occlusal plane. Then we investigated the nature of stress distributions, the directions and amounts of displacement in palate by finite element analysis.

Results: In the midpalatal suture and transpalatal suture, all displacement directed to bone suture and increased gradually when the retractive force direction ranged from +30 degrees to -30 degrees. In the midmost part of palate, correlation between stress distributions and retractive force directions was not significant. Relatively compressive stresses were induced in the front and middle of the midpalatal suture, whereas nearly no stress was induced in the back. In the lateral part of palate, compressive stresses were nearly equal to tensile stresses in the front, while tensile stresses were induced in the middle and back. Meanwhile, there was no significant correlation between stress distributions and force directions.

Conclusion: This study showed that the directions of retractive force had obvious effects on displacement but but little effect on stress distributions.