Stress Distribution Of Maxillary Embedded Canine Periodontium And Moving Tendency In Conditions Of Drawing Forces Regimens

The application of an orthodontic force results primarily in stress and strain distributions in the tooth and the supporting structures,finally resulting in bone resorption on the compression side and bone apposition on the tension side.This theory was used as a basis to make an orthodontic tooth movement. For every orthodontist it is important to know the biomechanics of the movement.Due to the complex composition of the tooth and tooth supporting stmctures,especially the positioning of the tooth in the alveolar bone by means of the periodontal ligament,and due to the numerous physical,biochemical and cellular processes involved,it seems unlikely that an accurate analytical model describing embedded tooth movement and stress distribution can be developed.But now it is possible to do this because of the development of the computer technology.Purpose: For simulation of the stress distribution of periodontaltissues the three dimensional finite element model of a maxillary embedded canine was established according to the anatomical configuration of a human embedded maxillary canine.The models in this study were implemented numerically by means of the finite element method (FEM) and CT and they were used to simulate the distribution of embedded tooth.Methods: A patient with a completely bone embedded maxillary canine was chosen.The CAD model of the canine and it's surroundingtissues was established using CT equipment,Mimics and Unigraphic.Thecanine axis was changed to make the angle of the canine axis and drawing direction different.Finally we got three models whose angles wererespectively 0°,45°and 90°. The three CAD models were changed to FEM models by MSC.Mentat that could cut nets in CAD models.Forces of 50g,100g and 150g were exerted to the models which could showequivalent stress clouds on it.Results:1 .Using this theoretical models present study demonstrates that the stress distribution of the periodontium can be simulated and that these simulations can be taken into account in the course of the treatment planning prior to starting therapy.2. At 0°drawings, the wink movement of the embedded tooth was to follow the drawing direction, and the movement was like an integer movement. At 45°and 90°drawings, the wink movement of the embedded tooth was to follow the drawing direction, but the movement was like an incline movement whose rotation center was at dental cervix.3. At 0°drawings, there was a very high mechanical stress value area located at toot tip and cuspis of the embedded tooth, and the biggeststress emerge at the cuspis; At 45°and 90°drawings, there was a stressconcentration area at the side facing drawing forces, and the biggest stress also emerge at the cuspis.4. At the same drawing angle, stress of periodontal tissues increased following with the growth of the drawing stress.Conclusions: The FEM models of maxillary embedded canine established by CT,Mimics,UG and MSC have good degrees of accuracy and geometrysimilarity that can meet the needs of simulation loading. Stress force distribution of embedded tooth is very advantageous in conditions of little drawing forces and little angles of drawing direction and tooth axis.