[Comparison of upper molars movements in use of cervical headgear and pendulum appliance by finite element method]

The movement of molars has been evaluated in many studies to correct C1 II malocclusion by non-compliance appliances but the results are controversial. The aim of this study was to compare the upper first and second molars' movement in cervical headgear [HG] and pendulum appliance [PEND] by finite element method. For modeling process, one of the best dry skulls was CT scanned [1mm slices]. Modeling was done according to the mechanical properties of cortical and trabecular bone of maxilla and PDM and teeth and transferred to computer by scanner. Elementing, meshing and loading was done. The magnitude of force for both appliances was 250 gr and line of force for HG was 20 degree above the occlusal plane ac ion and for PEND was along the midlingual surface of upper first molar crown. Tooth movement analysis was performed by the software named Ansys 5.71. The amount of dislocation of the 1st molar cusps tip [mesiobuccal, mesiopalatal, distibuccal, distopalatal] at presence of second molar in bucco-lingual dimension showed distal-in rotation in HG and mesial-in rotation for pendulum. In mesio-distal dimension, the four cusps of 1st molar moved distally in HG and palatal cusps moved more in PEND. In vertical dimension, 1st molar showed extrusion in HG and intrusion in PEND for distal cusps. The presence of second molar had impact on the quality of upper first molar in both appliances and it moved in a distal direction, extruded and buccal drifted in both of them. Therefore, with regard to the cooperation of the patients, pendulum appliance is recommended to correct C1 II malocclusion instead of cervical headgear

[ effect ofpost type on stress distribution in endodontically treated maxillary central incisors: a finiie element study]

Following endodontic therapy, teeth need to be protected from fracture. The likelihood of fracture depends on the type of restoration. This simulated study was designed to compare the effect of two different restorations on stress transmission to dental tissue. Four 3-dimentional models of maxillary central incisor were created as following by finite element analysis: [I] Restored with prefabricated stainless steel post, composite core and full ceramic crown [IPS lmpress2], [2] restored with prefabricated Fiber glass post, composite core and full ceramic crown [IFS lmpress2], [3] restored with Accessory Fiber glass post, composite core and full ceramic crown [[PS Impress 2] and [4] without restoration. Each of the models received 100 loads to incisal edge at an angle of 45 degrees to tooth long axis Von Mises Stress analysis was performed for each model, comparing maximum stress intensity observed. In all groups the greatest stress was observed in the cervical region. The stress increased steadily from apex to C.E.J and decreased from C.E.J to incisal edge. The Von Misses Stress in CEJ was highest in Accessory pin group to compared the other groups. Prefabricated stainless steel post, Fiber Glass post and vital tooth groups showed slight differences in CEJ stress. In all groups the greatest stress was observed in the cervical region. It seems the use of Fiber glass posts in weakened anterior teeth acts better than accessory fiber glass post

Apical third morphology and intrusive force application: 3D finite element analysis

Intrusion as a type of tooth movement is managed by different mechanotherapies 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. Four 3D Finite element models were designed with all supporting structures. Normal, needle form, short and sharp apices were considered. Intrusive forces of 0.5 N were applied and the VonMises stress along the mesial side of the root was assessed. A tendency to show increased stresses at the cervical area of the teeth was noticed. The lowest stress was noticed in the blunt apex and the highest findings were shown to be in the needle form apex model. Normal variation in apical third of the teeth in intrusion can cause an increased stress level and also increased chance of root resorption which should be considered carefully in force applications