Abstract:
Aim: aiming to find mathematical criteria for determination of tension forces on both sides' brackets to ensure vertical intrusion of upper first molar.
Methods: A 3D finite element model was built for upper first molar by laser scanning of natural extracted tooth. The modeled tooth was placed in a simplified bone model. Palatal and Buccal brackets were modeled on engineering CAD software then placed on the scanned tooth to apply the tensile forces on them. Stepped loading cases were analyzed, for total 200gm (2N) intrusive force started by equal tension force of (1N) on each side. A gradual reduction of force magnitude from palatal side tension was applied to obtain a more homogenous stress distribution to determine the suitable ration between both sides.
Results: The stepped analyses showed that; applying load of 1N (100gm) buccally and gradual reduction of the applied force magnitude from palatal side resulted in using of 0.80N palatal will be the most suitable value to ensure pure vertical intrusion. This ratio was correlated to tooth geometry by FEA to conduct the aimed criterion.
Conclusion: Applying palatal side tension force of order 80% of the buccal side tension force may insure pure vertical intrusion of upper first molar. This empirical ration may slightly differ among patient's age, sex, and ethnic groups due to changing in tissue characteristics and tooth geometry.