Evaluation of Stress Distribution in Overdenture-Retaining Bar with Different Levels of Vertical Misfit

Purpose: To evaluate the effects of different levels of vertical misfit between implant and bar framework on distribution of static stresses in an overdenture-retaining bar system using finite element analysis. Material and Methods: A 3D finite element model (11,718 elements and 21,625 nodes) was created and included two titanium implants and a bar framework placed in the medial region of the anterior part of a severely reabsorbed-jaw. All materials were presumed to be linear elastic, homogenous, and isotropic. Mechanical simulation software (NEiNastran 9.0) was used, where displacements were applied on the end of the bar framework to simulate the closure of the vertical misfits (5, 25, 50, 100, 200, and 300 mu m) after tightening of the screws. Data were qualitatively evaluated using Von Mises stress given by the software. Results: The models showed stress concentration in cortical bone, corresponding to the cervical part of the implant, and in cancellous bone, corresponding to the apical part of the implant; however, in these regions few changes were observed in stress to the misfits studied. While in the bar framework, retaining-screw neck, and implant platform, a considerable stress increase proportional to the misfit amplification was observed. Conclusions: The different levels of vertical misfit did not considerably influence the static stress levels in the pen-implant bone tissue; however, the mechanical components of the overdenture-retaining bar system are more sensitive to lack of passive fit.20428028

Stress Distribution in Human Zygomatic Pillar Using Three-Dimensional Finite Element Analysis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)This paper aimed to analyze stress distribution in human zygomatic pillar during masseter muscle contraction using three-dimensional finite element analysis. A three-dimensional model and hemi facial skull were produced based on CT-scan data. An adult male skull with structural anatomy integrity was used as model. Muscles forces were applied at origin of elevator muscles and supports was applied at the occlusal surfaces at first and second molars to simulate a masticatory load and stimulate the zygomatic pillar. Supports were applied to the occlusal contacts. Symmetry conditions were placed at the mid-sagittal plane. For the top and back cutting plane, constraints were used. Equivalent Von-Mises Stress and Maximum Principal Stress analysis were performed from the stress fields along the zygomatic pillar. It was represented by stress concentration at the alveolar process, zygomatic bone, frontal and temporal process of zygomatic bone and superciliary arch. Stress line indicates distribution of stress from maxilla toward the frontal and temporal bone. The stresses occurred due to resultant occlusal forces is mainly supported by the zygomatic bone, non-uniformly distributed and predominantly through the zygomatic pillar. This study contributed to better understanding of stress distribution in zygomatic pillar to understand the influence of chewing on zygomatic pillar morphology and also be useful for clinical practice.31413861392Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Comparison of five different fixation techniques of sagittal split ramus osteotomy using three-dimensional finite elements analysis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The aim of this study was to compare the mechanical stress over hemimandible substrate and hardware after sagittal split ramus osteotomy (SSRO) fixed with five different techniques using three-dimensional (3D) finite element analysis. A 3D finite element model of a hemimandible was created and a 5 mm advancement SSRO was simulated on a computer model. The model was fixed with five different techniques: 3 linear 60 degrees screw arrangement; 3 linear 90 degrees screw arrangement; 3 inverted L screw arrangement; 1 conventional miniplate; and I locking miniplate with four monocortical screws. Load was applied until 3 mm displacement was reached and the results were compared with previous mechanical and photoelastic tests, thus analysing the mechanical stresses developed, in the proximity of miniplates and screws and within the fixation system itself. The maximum principal stress values demonstrate a lower mechanical stress rate in bone and in the fixation system with the inverted L arrangement, followed by the linear 90 degrees and linear 60 degrees arrangements. The locking miniplate/screw system presented lower maximum principal stress and better stress distribution compared with the conventional system. Under the conditions tested, the reversed L arrangement provided the most favourable stress dissipation behaviour.418934941Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq [141231/2008-4

A comparative evaluation of the hybrid technique for fixation of the sagittal split ramus osteotomy in mandibular advancement by mechanical, photoelastic, and finite element analysis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Objective. This study evaluated the mechanical characteristics and stress distribution of the hybrid technique fixation of the sagittal split ramus osteotomy. Study Design. In the mechanical test, 10 polyurethane replicas of human hemimandibles of each group were submitted to linear loading test. For the photoelastic evaluation, 3 hemimandible replicas of photoelastic resin were subjected to photoelastic analysis. In the finite element analysis, 3 computer models simulated the displacement and the results of maximum principal stress were analyzed. Results. The results of this study demonstrated that the fixation technique with 3 bicortical screws presented better mechanical resistance and stress distribution pattern when compared with the hybrid technique that, on the other hand, presents better results in comparison with a miniplate and monocortical screws. Conclusions. The results suggest that the hybrid technique increased the resistance and improved stress distribution of miniplate/monocortical screw fixation, maintaining most of the advantages of this technique. (Oral Surg Oral Med Oral Pathol Oral Radiol 2012;114(suppl 5):S60-S68)1145SS60S68Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq [141231/2008-4

Finite element analysis and fracture resistance testing of a new intraradicular post

Objectives: The objective of the present study was to evaluate a prefabricated intraradicular threaded pure titanium post, designed and developed at the Sao Jose dos Campos School of Dentistry - UNESP, Brazil. This new post was designed to minimize stresses observed with prefabricated post systems and to improve cost-benefits. Materials and and methods: Fracture resistance testing of the post/core/root complex, fracture analysis by microscopy and stress analysis by the finite element method were used for post evaluation. The following four prefabricated metal post systems were analyzed: group 1, experimental post; group 2, modification of the experimental post; group 3, Flexi Post, and group 4, Para Post. For the analysis of fracture resistance, 40 bovine teeth were randomly assigned to the four groups (n=10) and used for the fabrication of test specimens simulating the situation in the mouth. The test specimens were subjected to compressive strength testing until fracture in an EMIC universal testing machine. After fracture of the test specimens, their roots were sectioned and analyzed by microscopy. For the finite element method, specimens of the fracture resistance test were simulated by computer modeling to determine the stress distribution pattern in the post systems studied. Results: The fracture test presented the following averages and standard deviation: G1 (45.63 +/- 8.77), G2 (49.98 +/- 7.08), G3 (43.84 +/- 5.52), G4 (47.61 +/- 7.23). Stress was homogenously distributed along the body of the intraradicular post in group 1, whereas high stress concentrations in certain regions were observed in the other groups. These stress concentrations in the body of the post induced the same stress concentration in root dentin. Conclusions: The experimental post (original and modified versions) presented similar fracture resistance and better results in the stress analysis when compared with the commercial post systems tested (08/2008PA/CEP).20442743

Short fibre-reinforced composite for extensive direct restorations: a laboratory and computational assessment

OBJECTIVES: The objective of the study was to evaluate the effectiveness of a short fibre-reinforced composite (FRC) applied in combination with a conventional filler composite (CFC) on the fatigue resistance, fracture strength, failure mode and stress distribution, for restorations of premolars under two loading angles. MATERIAL AND METHODS: Thirty-two inferior premolars received extensive cavities with removal of the lingual cusp. Teeth were restored directly using 'FRC (EverX Posterior, GC) + CFC (G-aenial, GC)' or 'CFC only' and received two fatigue/fracture loadings at two different angles (0°/45°) (n = 8). Data were submitted to two-way ANOVA (α = 5 %) and Tukey test. Failure mode was analysed using SEM. Four 3D finite element (FE) models were constructed and static, linear and elastic analyses were performed. Maximum principal and von Mises stresses were evaluated. RESULTS: All specimens survived the mechanical fatigue simulation. No statistical difference in fracture resistance was recorded between FRC + CFC and CFC only, considering both loading angles (p = 0.115). However, the 0° loading showed a statistical significant higher strength than the 45° loading (p = 0.000). Failure mode analysis revealed more repairable fractures upon 0° loading, versus more root fractures (unrepairable) upon 45° loading. FE revealed a higher amount of stress upon 45° loading, with tensile stress being imposed to the lingual cervical area. CONCLUSION: The fracture strength was not increased using the FRC. Loading at a 45° decreased significantly the fracture resistance. CLINICAL RELEVANCE: The restoration of extensive cavities in posterior tooth is a challenge for the clinicians and the choice of the material that increases the fracture strength of tooth-restoration complex is required.status: publishe