جستجوی مقالات مرتبط با کلیدواژه "آنالیز اجزای محدود" در نشریات گروه "پزشکی"

Short implants are used in the posterior mandible where the bone is insufficient. In these cases, the clinical crown is often made to match the level of the occlusal. As a result, the length of the lever arm and the stress of the implant complex, as well as the surrounding bone, are increased leading to the biomechanical problems. The purpose of this study was to evaluate dynamically the effect of increasing crown height space on the maximum stress induced in the abutment screw and the surrounding bone of the short dental implants in the posterior mandible using finite element analysis. Mandibular bone resorption in the posterior region, second premolar with three-crown lengths of 8.8, 11.2, and 13.6, two implants of 4 and 8 mm, two abutments, and two abutment screws were modeled using Solidworks software in this laboratory experimental study. In addition, Abacus software was used to the dynamic reconstruction of screw tightening and external load at an angle of 75.8 degrees with the occlusal plane. The stress values were calculated for the screw, abutment, fixture, and bone. In both 4- and 8-mm implants, the increased vertical height of the crown decreased the stress on the abutment screw and increased the stress on the abutment and fixture. For a 4-mm implant, the stress to the abutment screw at all three heights was less than 8 mm. At all heights, the stress values to the abutment and the fixture were more than 8mm for the 4-mm implant. The increased vertical height of the crown resulted in an increase in compressive and tensile stress in the surrounding bone for both 4-mm and 8-mm implants. The magnitude of these stresses in the 4-mm implant was more than 8 mm.   Increased vertical height of the crown and crown-to-implant ratio reduced the stress on abutment screws as the weakest member of the implant. However, it probably increased the failure due to fatigue in the abutment and fixture as well as bone resorption.

This study was performed to investigate the distribution of stress in indirect resin restorations of class II MOD cavities for obtaining the optimum wall angle and also the effect of axiopulpal angle bevel using 3D finite element analysis (FEA).
Material & A three-dimensional model of normal mandibular first molar and three class II cavity models with different wall angles were created. Also, all models were examined with axiopulpal angle bevel. The vertical occlusal force of 100 N was applied. The characteristics of all materials were defined as isotropic and elastic and, with the aid of a linear analysis; the distribution of stress and the maximum stress created in each model were obtained in mega-Pascal scale. T test was used for statistical of data.
The maximum stress in the simulated normal tooth was 24.63 MPa. Distribution of stress indicates the accumulation of pressure in the center and the furcal region of the first molar, as well as the cusps in the occlusal region. In beveled model of 95-degree angle, maximum stress was 24.90 MPa with a decrease of 0.05 maximum stress compared to the non-beveled model. In the cutting angle of 97.5, the maximum stress was 24.85 in the no-bevel model to the maximum stress of 24.80 in the model compared with axiopulpal angle bevel, which showed achieved a decrease of 0.05 in the maximum stress. At the cutting angle of 100, the maximum stress of 25.30 was in the no-beveled model comparing to maximum stress of 25.20 in the model with axiopulpal angle bevel, which showed red action of MPA.
Considering the limitations of such software studies, it seems that according to the results, the best treatment result is at angle of 97.5. Axiopulpal angle bevel reduces the maximum stress in the restoration and reduces the chance of failure

In post-core crown restorations, the use of prefabricated composite posts concentrate stress at the cervical region and the use of metal posts (prefabricated and customized posts) concentrates stress at the interfaces. Fiber reinforced composite posts (FRCs) with oval cross-section (oval posts) were proposed for post-core crown restorations to reduce the stress levels at the cervical region. The aim of the present study was to investigate the impact of oval cross-section composite posts on stress distribution of premolar with oval-shaped canal by using three-dimensional (3D) finite element analysis.
An extracted premolar tooth was mounted, sectioned, and photographed to create a 3D model. The surrounding tissues of the tooth, periodontal ligament, as well as cortical and trabecular bones were modeled. Seven taper posts with two different cross-section geometries (circular and oval shapes) were modeled, as well. Then, the effect of post geometry, post material (carbon fiber and fiberglass), and cement material were investigated by 3D finite element analysis and the stress distribution results were compared.
In all the models, the highest stress levels of the dentin were accumulated at the coronal third of the root, and the highest stress levels at the bonding layers were accumulated at the cervical margin. Narrow circular posts induced the highest stress levels, whereas the stress levels were reduced by using thick oval posts. Application of elastic cement reduces the stress at the bonding layers but increases stress at the dentin.
Finite element analysis showed that prefabricated oval posts are superior to traditional circular ones. The use of cement with low elastic modulus reduces the risk of debonding but raises the risk of root fracture.

because of problems associated with dentures nowadays implant supported overdentures are used widely. Despite the high success of implants, implant failure remains a major challenge. Implant overload is a factor for cortical bone loss and implant failure. This study, evaluated 3 designs used in overdentures with three implants, using finite element analysis for their stress distribution. Using finite element method, a geometrical model of the mandible was produced with CT data and three ITI implants were placed at the midline and at the first premolar teeth. All conditions were simulated using finite element software. Three treatment bar-ball, bar and ball were considered to support the overdenture. Maximum von Mayzz stress levels were compared for all attachments and supporting bone and mandibular flexure attachment was compared in different designs. Results showed that the greatest amount of stress on the bone was around the upper thread and the neck of the implants. Attachment of the ball and the bar-ball induced the greatest and the least amounts of stress to the bone around the implants respectively. The maximum stress could be seen on the ball attachment in the bar-ball design. The maximum amount of the movement was show in bar-ball attachment. According to the results, the bar-ball treatment plan with reducing the stability of over denture will reduce the stress around the bone of implant and ball treatment plan with increasing bone stress around the implant will increse the stability of overdenture.

Despite the high success rate, implant-supported prostheses fail in some cases. Control of the applied forces is an important factor determining the success or failure of implants. Complete understanding of the biomechanical principles in implant-supported prostheses is necessary for offering an appropriate custom-made treatment plan for each patient and reducing the risk of functional complications. Finite element analysis is a quantitative method for the assessment of force distribution in complex structures. This study sought to compare the effect of different framework materials on stress distribution in bone supporting implants using three-dimensional finite element analysis. In this in-vitro study, a three-dimensional model of bone was obtained using Cone Beam Computerized Tomography (CBCT). Using CATIA V5R20 (Dassault Systemes, France) software, a NobelReplace tapered implant (Nobelpharma Co., Gothenburg, Sweden) measuring 13 mm in height and 4.3 mm in diameter was virtually inserted in the anterior maxilla. A titanium abutment, ZOE cement and superstructure with different frameworks (Ag-Pd, Ni-Cr, and fiber-reinforced composite) were designed. Force was applied in an amount of 178 N at three angulations of zero, 30 and 45° relative to the implant axis and the maximum von-Mises stress and maximum strain were calculated for cortical and trabecular bone. Changing the framework material caused a small change in level of stress and strain and their distribution pattern. By increasing the angulation of the applied force, amount of stress and strain in the implant-supporting bone increased. Maximum stress and strain were applied at 45° angulation. At zero degree angulation, maximum stress in the cortical bone was 17.326 MPa with Ni-Cr framework, 17.383 MPa with Ag-Pd and 17.321 MPa with fiber-reinforced composite. In loading at 30° angulation, maximum stress in the cortical bone was 136.95 MPa with Ni-Cr framework, 136.03 MPa with Ag-Pd framework and 136.18 MPa with fiber-reinforced composite framework. In loading at 45° angulation, maximum stress in the cortical bone was 161.37 MPa with Ni-Cr, 161.21 MPA with Ag-Pd and 160.4 MPawith fiber-reinforced frameworks. The difference between framework materials with higher and lower strengths in amount and pattern of cortical stress and strain distribution was insignificant

The All-on-4 design with its significant advantages is an appropriate model in reconstruction of edentulous mandible. Evaluation of stress and strain distribution in this model is necessary for better judgment. The purpose of this FEA study was to measure stress and strain distribution on peri-implant bone in All-on-4 design in edentulous mandible. Three dimensional finite element model of human mandible was simulated according to data from CT-Scan of a cadaver. The model of 4×13.5 mm Nobel Biocare implant was simulated. Posterior implants were inserted in 452 inclination and anterior implants were parallel and vertical. Implants were splinted with a titanium bar and an acrylic superstructure was then simulated around the bar. Vertical loads of 178 N and 300 N were applied at incisor and left first molar positions, respectively. After meshing, defining boundary conditions and materials properties, analysis was performed with the aid of ABAQUS. Maximum Von-Mises stress of 38.9 MPa during anterior loading was located in peri-implant bone of anterior implants but maximum strain was observed in peri-implant bone of posterior implants. In posterior loading, maximum stress (77.3 MPa) was in peri-implant bone of posterior implant which was next to the place of load insertion. Maximum strain was found in the same area. During posterior loading, significant amount of strain was observed in peri-implant bone of posterior angulated implant. As a result, there was a possibility of resorption in this area. During anterior loading, detected stress and strain was absolutely favorable.

This study was designed to evaluate the stress distributions of different post materials in radicular dentine for providing a useful clinical guideline. In this experimental study, 5 three - dimensional models of maxillary central incisors were simulated by using ANSYS software and Finite Element Method. The models included: 1) Stainless Steel post 2) Titanium post 3) Carbon fiber post 4) Glass fiber post, and 5) Quartz fiber post. A composite core and PFM crown was constructed for all samples. Each model contained gingival, cortical and spongy bone, PDL and gutta-percha as well. All specimens were subjected to a compressive load at 45-degree angle to its long axis with a constant intensity of 100N. In all models there were two stress concentration sites: 1- a point between middle third and cervical third of the root and 2 - the cervical edge of the root. The amount of stresses between middle and the cervical third of fiber reinforced posts were nearly 1 MPa greater than those of the metallic ones. Compared to other materials, the metallic posts caused less stress in the radicular dentin and therefore are recommended for clinical use. Among fiber reinforced posts, Quartz fiber post showed the lowest stress peak.