Stress distribution changes after root canal therapy in canine model: a finite element study

The fracture strength of endodontically treated teeth compared to vital ones has long been a source of controversy. It is not clear how root canal therapy affects the stress distribution in teeth. The purpose of this study was to evaluate the changes in stress distribution after root canal therapy in a human maxillary canine by finite element analysis [FEM]. Two 3D FEM models of a maxillary canine were created; one represented a virgin tooth and the other represented the same tooth after root canal therapy. A single force of 14.1 N was applied 45 degrees to horizontal plane to the center of the palatal surface; stress distribution was then analyzed in both models. SEQV [VonMises stress] analysis demonstrated an obvious decrease after root canal therapy and the regions near cementoenamel junction [CEJ] showed the highest displacement. The endodontically treated tooth demonstrated higher deflection than the vital one. Maximum stress and displacement was repeatedly found in the cervical area, hence more emphasis should be placed on the reinforcement of this region

V-bend force system: 3D analysis using Finite Element Method

Several bracket characteristics are now in market. Preformed archwires are used without frequent need to add bends. V-bends are used in many situations. This bend as a basic maneuver is assessed thoroughly in this study. Finite Element Method [FEM] was selected to analyze the situation. A 3D model of two maxillary central incisors with their supporting structures and an archwire were modeled. A V-bend in different positions relative to the teeth was defined. Forces produced were monitored. Center V-bend [a/L=1/2] produced two moments in opposite direction. Moving towards one tooth added vertical forces in opposite direction. At a/L [almost equal to] 1/5, intrusive movement was noticed; while signs of intrusion and change in angulation was detected at 1/10< a/L<1/5. When a/L reached 0.42/6.408 same direction of moments were shown. V-bend force system is quite sensitive to its position

Free vector and different bracket base designs: 3D analysis using Finite element method

Introduction of new bracket designs in market and use with a range of inciso-apical dimension and base thickness arises a question in mind as. [Is it necessary to standardize various bracket bases from torque delivery efficiency?]. Two bracket bases of different incio-apical dimension [3 and 6 mm.] and also two different base thicknesses [1.6 and 3.5 mm.] were modeled and moments were applied. All displacements along a defined incio-apical path were monitored to be evaluated. No difference was found between the displacements along the defined path in each phase of study. In this way, it was concluded that torque delivery of different brackets is not related to their base size [inciso-apical] and dimension which is in complete agreement and confirmation of the principle of free vectors

Center of resistance revisited: 3D analysis using finite element method

Center of Resistance [CRes] remains constant while the environment is the same. CRes can experience a new situation while the periodontium remains the same. This study tried to show the effect and importance of canine torque on the applied force system to produce bodily movement. A 3D model of a canine with average size was modeled in a proper torque. FEM was selected as the manner to conduct the research. Different M/F ratios were applied to reach bodily movement and then the torque was increased and the same process was repeated to produce a bodily movement at new torque situation. The results for Anti-tip and Anti-rotation were then compared and the differences were shown. M/F ratio for bodily movement ranged between 8.19 and 8.80 for 45 degrees of torque and upright position respectively and between 1.54 and 0.5 for the anti-rotation for the same situation. So, the torque of canine should be considered as an important factor affecting the needed force system to produce bodily movement form tipping and rotation point of view