Second Molar Uprighting with Temporary Anchorage Devices: A Finite Element Study

BACKGROUND AND OBJECTIVE: Premature loss of mandibular first molar is a common problem in adults. Mesial tipping of second molar may occur in this situation. Various orthodontic mechanics have been proposed for molar uprighting. The aim of this study was to compare four methods of molar uprighting using Finite Element Analysis(FEM). METHODS: In first model of this finite element study, a 0.019×0.025 inch beta-titanium segmental arch wire with a T-loop was used. In second model a miniscrew was inserted in retromolar space and force was applied using elastomeric chain. The third model was a piece of 0.016×0.022inch beta-titanium wire with a bend which was placed more occlusal than the screw. The fourth model contained a mesially inserted miniscrew with an angle of 70 degrees to bone surface and a 0.018×0.025inch beta-titanium wire with helix. Extrusion, center of rotation and stress distribution in PDL during movement was compared between methods. FINDINGS: Buccal cusp extruded 1.36E-03, 1.13E-03, -9.74E-04 and 1.49E-03 mm in first, second, third and fourth model, respectively. Similarly, in lingual cusp, the amount of vertical displacement was at least in third model (-6.83E-04 mm). This amount in second and first method was 1.12E-03 and 4.05E-04 mm, respectively. The maximum amount of extrusion of lingual cusp occurred in fourth model (9.01E-03 mm). Mesial and distal cusps extruded 2.12E-04 and 1.58E-03 mm in first model, -1.14E-03 and 3.80E-03 mm in second method, -2.37E-03 and 7.04E-04 mm in third design and, 1.88E-03 and 8.57E-03 mm in the fourth model. The center of rotation was located at molar bifurcation in third model. CONCLUSION: The maximum amount of extrusion in both mesiodistal and buccolingual path was seen in fourth model. The best type of movement was found in third model, in which minimum extrusion occurred and center of rotation located at molar bifurcation

Numerical study of effect of elastomeric stress absorbers on stress reduction in bone-dental implant interface

Objective This paper focused on optimal stress distribution in the mandibular bone surrounding a dental implant and is devoted to the development of a modified Osteoplant® implant type in order to minimize stress concentration in the bone-implant interface. Material and Methods This study investigated 0.4 mm thick layers of two elastomeric stress barriers incorporated into the dental implant using 3-D finite element analysis. Results Overall, this proposed implant provoked lower load transfer in bone-implant interface due to the effect of the elastomers as stress absorbers. The stress level in the bone was reduced between 28% and 42% for three load cases: 75 N, 60 N and 27 N in corono-apical, linguo-buccal and disto-mesial direction, respectively. Conclusion The proposed model provided an acceptable solution for load transfer reduction to the mandible. This investigation also permitted to choose how to incorporate two elastomers into the Osteoplant® implant system

Finite element analysis of rapid canine retraction through reducing resistance and distraction

OBJECTIVE: The aims of this study were to compare different surgical approaches to rapid canine retraction by designing and selecting the most effective method of reducing resistance by a three-dimensional finite element analysis. MATERIAL AND METHODS: Three-dimensional finite element models of different approaches to rapid canine retraction by reducing resistance and distraction were established, including maxillary teeth, periodontal ligament, and alveolar. The models were designed to dissect the periodontal ligament, root, and alveolar separately. A 1.5 N force vector was loaded bilaterally to the center of the crown between first molar and canine, to retract the canine distally. The value of total deformation was used to assess the initial displacement of the canine and molar at the beginning of force loading. Stress intensity and force distribution were analyzed and evaluated by Ansys 13.0 through comparison of equivalent (von Mises) stress and maximum shear stress. RESULTS: The maximum value of total deformation with the three kinds of models occurred in the distal part of the canine crown and gradually reduced from the crown to the apex of the canine; compared with the canines in model 3 and model 1, the canine in model 2 had the maximum value of displacement, up to 1.9812 mm. The lowest equivalent (von Mises) stress and the lowest maximum shear stress were concentrated mainly on the distal side of the canine root in model 2. The distribution of equivalent (von Mises) stress and maximum shear stress on the PDL of the canine in the three models was highly concentrated on the distal edge of the canine cervix. CONCLUSIONS: Removal of the bone in the pathway of canine retraction results in low stress intensity for canine movement. Periodontal distraction aided by surgical undermining of the interseptal bone would reduce resistance and effectively accelerate the speed of canine retraction

Apical Third Morphology and Intrusive Force Application: 3D Finite Element Analysis

Objective: Intrusion as a type of tooth movement is managed by different mechanothera-pies during various treatment stages. The morphology of the apical third of the teeth to be intruded plays an important role in the risk of root resorption due to the raise of stresses.The main goal of this study was to compare various types of apical third of the teeth while loaded by an intrusive force.Materials and Methods: Four 3D Finite element models were designed with all support-ing structures. Normal, needle form, short and sharp apices were considered. Intrusiveforces of 0.5 N were applied and the VonMises stress along the mesial side of the root was assessed.Results: A tendency to show increased stresses at the cervical area of the teeth was no-ticed. The lowest stress was noticed in the blunt apex and the highest findings were shown to be in the needle form apex model.Conclusion: Normal variation in apical third of the teeth in intrusion can cause an in-creased stress level and also increased chance of root resorption which should be consid-ered carefully in force applications