A Biomechanical Study Of Changing Bracket Position Gingivallyon Tooth Movement With Alveolar Bone Loss

Objective: To investigate the effect of decreasing tooth movement velocity by using atypical bracket position gingivally and losing alveolar bone with Typodont model and FEM. Method: Alignment stage of low alveolar bone height was simulated by Typodont model. First three groups of models were taken from 2 mm of simulated periodontal tissue with different bracket position, and the model of normal alveolar height and routine bracket position as control group. Tooth movement velocities of the 4 groups were compared. Three-dimensional finite element model of mandibular central incisors with different height of alveolar bone loss were constructed. The stress of periodontal ligament in models were analyzed;each model was exerted three kinds of forces, which have the same magnitude, the same orientation and different positions. Result: In the 3 low-alveolar-height groups, tooth movement velocity decreases slowly, which trends to the situation of the normal control group. With the decrease of the alveolar height, both the maximum stress of labial side( σ1) and the minimum stress of lingual side( σ 3) of alveolar crest remarkably increased on the same action point,σ1 and σ3 decreased when the action point moved towards the cervical margin on the one model. Conclusion: It is also shown that bracket moving to the cervical margin could compensate for the injury of alveolar bone loss.