Apical stress distribution on maxillary central incisor during various orthodontic tooth movements by varying cemental and two different periodontal ligament thicknesses: A FEM study.

Context: During fixed orthodontic therapy, when the stress levels in the periodontal ligament (PDL) exceedsan optimum level, it could lead to root resorption. Aims: To determine an apical stress incident on the maxillary central incisor during tooth movement with varying cemental and periodontal ligament thickness by Finite Element Method (FEM) modeling. Settings and Design: A three dimensional finite element model of a maxillary central incisor along with enamel, dentin, cementum, PDL and alveolar bone was recreated using EZIDCOM and AUTOCAD software. ALTAIR Hyper mesh 7.0 version was used to create the Finite Element meshwork of the tooth. This virtual model was transferred to Finite Element Analysis software, ANSYS where different tooth movements were performed. Materials and Methods: Cemental thickness at the root apex was varied from 200 μm to 1000 μm in increments of 200 μm. PDL thickness was varied as 0.24 mm and 0.15 mm. Intrusive, Extrusive, Rotation and Tipping forces were delivered to determine an apical stress for each set of parameters. Results: Results indicated that an apical stress induced in the cementum and PDL, increased with an increase in cementum and PDL thickness respectively. Apical stress induced in the cementum remained the same or decreased with an increase in the PDL thickness. Apical stress induced in the PDL decreased with an increase in the cementum thickness. Conclusion: The study concluded that the clinical delivery of an orthodontic forces will cause stress in the cementum and PDL. Hence, it is necessary to limit the orthodontic force to prevent root resorption.

A comparative evaluation of metallurgical properties of stainless steel and TMA archwires with timolium and titanium niobium archwires - An in vitro study.

Objectives: This study aims to evaluate and compare the mechanical and metallurgical properties of stainless steel and titanium molybdenum alloy (TMA) archwires, with recently introduced timolium and titanium niobium arch wires. Materials and Methods: Archwires were categorized into four groups (group I to IV) with 10 samples in each group. They were evaluated for tensile strength, yield strength, modulus of elasticity, load deflection, frictional properties and weld characteristics. Results: The results were statistically analyzed using ANOVA test and it indicated that stainless steel has high strength, high stiffness and low friction compared to other arch wires, thereby proving that it is the best choice for both sliding as well as frictionless retraction mechanics. TMA with its high formability, low stiffness and low load deflection property is suited to apply consistent force in malaligned teeth but, high friction limits its use in retraction only with loop mechanics. Conclusion: Timolium possesses comparatively low stiffness, better strength and behaves as an intermediate between stainless steel and TMA and hence can be tried for almost all clinical situations. Low springback and high formability of titanium-niobium archwire allows creation of finishing bends and thus it can be used as finishing archwire.