Aims: The aims and objectives of this study are to evaluate the Von Mises stress and principle stress distribution and displacement of anterior teeth in a lingual orthodontics system along the periodontal ligament and alveolar bone by various combinations of mini-implants and lever arm during en-masse retraction.
Study Design: Four three-dimensional finite element models of the bilateral maxillary first premolar extraction cases were constructed.
Methods and Material: Lingual brackets were (0.018” slot) positioned over the center of the clinical crown. In all four models, 150 gm of retraction force was applied with the help of a NiTi closed coil spring with different combinations of mini-implants and lever-arm on each side. Finite element analysis was then performed to evaluate stress distribution, the principal stress, von Mises stress, and displacement of the anterior teeth using ANSYS 12.1 software..
Statistical analysis used: Finite element study was enough to validate the analysis results obtained by software tools with finite element simulation instead of experimental readings. Thus, statistical analysis was not required.
Results: In this study, maximum tensile stresses were observed in the periodontal ligament at the mesial cervical region of the canine with values of 1.84MPa, 2.02 MPa, 1.88MPa and 2.08MPaformodels 1 to 4, respectively. Maximum von mises stress in alveolar bone was 8.05 MPa, 8.23 MPa, 8.19 MPa and 8.37 MPa for models 1, 2, 3, and 4, respectively which was within the optimum limit (135 MPa).Variable amounts of displacements like lingual crown tipping, lingual root tipping, and extrusion were observed in all the models. The 15 mm long lever arm models (Model 2, 4) showed more controlled crown (0.015 mm) and root movement (0.004 mm) in comparison to 12 mm long lever arm models (Model 1, 3).
Conclusion: In Lingual Orthodontics (LiO), controlled root movement increased as we increased the length of the lever-arm. It was also concluded that the amount of increased controlled tipping found with the placement of the mini-implant towards the palatal slope.
Key-words: En-masse retraction, Finite element analysis, lingual orthodontics, Mini-implants, Principle &Von Mises stress