Optimal force levels in different root morphologies on translation - a 3d finite element study

Background and Objective- The objective of this study was to access the stress patterns in the periodontal ligament of a central incisor with different root morphologies on different orthodontic loads, using the linear, non-linear and viscoelastic finite element analysis and to quantify the optimal force levels for roots with different root morphologies.
Materials and Method- A finite element model of a maxillary central incisor
with different root morphologies was taken and 120g of translative forces
were applied. The stress patterns and magnitude in the periodontal ligament was observed for linear, non-linear and viscoelastic properties of the PDL and were compared with the optimal stress range (0.012-0.020 MPa). Results- It was observed that, the stress patterns produced in the PDLon translative orthodontic forces were similar for linear, nonlinear and viscoelastic properties of the PDL. The magnitude of stress, varied for all three analyses. For 120 grams of translative force it was seen that, the stress produced were least in linear and highest in viscoelastic analyses. The force applied was decreased in increments of 0.1 gms by iteration, to obtain an minimal stress in the periodontal ligament (0.012 Mpa). It was observed that the force levels had to drop down by two fold in viscoelastic analysis in tooth with different root morphologies. Conclusion- From the results obtained, it was observed that the force levels required to produce the same amount of stresses in the PDL of a upper incisor, were the least in viscoelastic analysis, followed by non linear and the maximum in linear analysis. The optimal force levels recommended for translation movements in central incisor with normal root morphology is in accordance with the normal values given by Profitt, but optimal force levels varies in tooth with different root morphologies. Considering that the viscoelastic properties depicts a more realistic behaviour of the PDL, the force levels have to be closely monitored when teeth with different root morphologies is encountered.