Effect of the alveolar bone level and inclination of the tooth on periodontal stress for a maxillary central incisor : finite element analysis

Abstract

With increasing number of adult orthodontic patients, it has become necessary to understand movement of the tooth with alveolar bone loss. Numerous finite element analysis(FEA) studies have been conducted to analyze type of movement and stress patterns in orthodontic tooth movement. The purpose of this study was to determine the effect of alveolar bone loss together with inclination of the tooth on the magnitude and distribution of stresses within the PDL for a maxillary central incisor when controlled tipping was simulated with FEA. Stress in the PDL and type of tooth movement were investigated using finite element analysis program. 20 three-dimensional models were created, representing a maxillary central incisor with facial inclination and alveolar bone loss. Each of the 20 models were subjected to three loads on the crown to simulate controlled tipping movement with varying M/f ratio from 0 to 10.M/F ratio for controlled tipping(M/Fcont) at each alveolar bone level and incisor inclination was investigated. As incisor is more inclined, M/Fcont becomes smaller, while alveolar bone loss resulted in increased M/Fcont .As more bone loss occurs the displacement of the apex(Δ) becomes larger under the same inclination and M/F ratio, The variation of Δ between each level of bone loss becomes smaller as M/F ratio get closer to the M/Fcont under the same inclination. M/F ratio for uncontrolled tipping or root movement caused larger principal stress than M/Fcont. Also the variation of the stress value between each level of bone loss becomes larger when M/F ratio gets closer to 0 or 10. With more alveolar bone loss, the stress changes more sharply as M/F ratio varies under the same inclination. When M/F ratio varies near the M/Fcont, compressive stresses dominate in the labial apical region(M/F below M/Fcont)move to palatal apical area(M/F over the M/Fcont).

Meanwhile, tensile stresses dominate in the labial area(M/F below M/Fcont) move from the cervical to midroot(M/F over the M/Fcont). These patterns were the similar for all the experimental conditions. The results of this study will be the basis of further research examining the stress distribution process of PDL after orthodontic loading. When bone loss increases the displacement of the apex and maximum compressive and tensile stresses also increased. Also Δ and stresses changed more sharply when M/F ratio varies. Which means inadequate force system causes larger displacement of apex and higher stress at the apical area in patients with alveolar bone loss and facial inclination of the incisor.