Jamal Kashani

Stress distributions in maxillary central incisors restored with various types of post materials and designs

Different dental post designs and materials affect the stability of restoration of a tooth. This study aimed to analyse and compare the stability of two shapes of dental posts (parallel-sided and tapered) made of five different materials (titanium, zirconia, carbon fibre and glass fibre) by investigating their stress transfer through the finite element (FE) method. Ten three-dimensional (3D) FE models of a maxillary central incisor restored with two different designs and five different materials were constructed. An oblique loading of 100 N was applied to each 3D model. Analyses along the centre of the post, the crown-cement/core and the post-cement/dentine interfaces were computed, and the means were calculated. One-way ANOVAs followed by post hoc tests were used to evaluate the effectiveness of the post materials and designs (p=0.05). For post designs, the tapered posts introduced significantly higher stress compared with the parallel-sided post (p<0.05), especially along the centre of the post. Of the materials, the highest level of stress was found for stainless steel, followed by zirconia, titanium, glass fibre and carbon fibre posts (p<0.05). The carbon and glass fibre posts reduced the stress distribution at the middle and apical part of the posts compared with the stainless steel, zirconia and titanium posts. The opposite results were observed at the crown-cement/core interface.

Manufacturing of flexible surgical guide for fully edentulous patients

Despite efficiency of modern implantology, unplanned perforation and drill deviation could be happened during freehand placement. The aim of this study was to provide a methodology for fabricating dental surgical drill guide for fully edentulous patients while it was flexible in term of changing drill diameter. The data of patient consisted of bone anatomy and radio-opaque template obtained from computed tomography. Jawbone and radio-opaque template three dimensional models converted into a three dimensional modeling software by means of an image processing package. Based on jawbone anatomy and radio-opaque template, implantation plan and design of surgical guides were carried out in three dimensional software. Rapid prototyping technique was used to manufacture several surgical guides to be used in different drilling sequences. Finally stainless steel tubes were accommodated passage of drill. Sequential surgical guides were different only in terms of the metal tubes internal diameter. This provides the ability of changing diameter of the implant or drill after fabricating surgical guide.

Influence of the TMJ Implant Geometry on Stress Distribution

The purpose of this study was to investigate the influence of Temporomandibular Joint implant geometry on stress distribution in total reconstruction of temporomandibular joint. A three dimensional model of a lower jaw of a patient was developed from a Computed Tomography scan images. Anatomical curvature and flat contact surface of implant design and fixation screws were modeled. Two implanted mandibles were then compared by means of finite element analysis. The muscle forces for incisal clenching were applied. The equivalent stress resulted in contact surface region of the bone and implant and in fixation screw holes were investigated to evaluate the designs. In applied loading condition, The results showed that anatomical design of implant was more preferred and it will lead to long-term success of implant.

Design Analysis of TMJ Implant under Physiological Loading Condition

Equal channel angular extrusion (ECAE) is a severe plastic deformation (SPD) method for obtaining bulk nanostructured materials. The ECAE die consists of two equal channels that intersect at an angle, usually between 90。and 135。. In the present study, the plastic deformation behavior of copper during the ECAE process with 120o die was investigated. To analyze the deformation behavior and the related strain distributions in the specimen, the commercial FE code ABAQUS has been used. The properties of the materials are strongly dependent on the shear plastic deformation behavior during equal channel angular extrusion (ECAE), which is controlled mainly by die geometry, material properties, and the friction between billet and the die. The ECAE process for these conditions was explained using the two different friction conditions of 0.15 and 0.08 to all sliding surfaces. The effective strain by the theoretical equation is in good agreement with the FEM results.

Influence of Cancellous Bone Existence in Human Lumbar Spine: A Finite Element Analysis

The aim of this study was developed an accurate computational finite element model (FEM) to simulate biomechanical response of human lumbar spine under physiological functions. In reality, anatomical intricate structure of the spine and also complex deformation in the different defection situation, severe application of finite element analyses. During computational study complexity of finite element model intensify acquire precision results and frequently leads to analyses failure. In this study the importance of cancellous bone contribution during finite element analyses of lumbar spine has been evaluated. A finite element model of lumbar (L2-L3) was generated from Computer Tomography images. Complete disectomy simulated, single cage inserted and posterior instrumentation was added in order to providing sufficient stability. Stress distribution pattern on two different models of vertebral body was included cancellous bone and cortical shell, for the first model, or totally cortical bone, for the second model, were discussed under various loading situations. The FEM developed in this study demonstrated analogus model with the natural spine anatomy make differences between results, and accurate result will obtain when FEM was exactly similar as natural model. Therefore cancellous bone existence seems necessary in finite element analyses of spine.

Finite element analysis of different ferrule heights of endodontically treated tooth

Objective: To investigate the influence of ferrule height on the crown mechanical resistance and stress distribution through the root and luting cement to explain restoration lose and root fracture pattern. Material and methods: Threedimensional models of an adult maxilla and root of incisor tooth were developed from a Computed Tomography scan images. Periodontal ligament, luting cement, crown and custom post were reconstructed on the computer . A static load of 50N was applied to the crown at 70° to the occlusal plan. Results: Design with no ferrule had the most crown displacement and 2mm ferrule had the least. Also 2mm ferrule design had the lowest root and luting cement stress Conclusion: The study suggests that a ferrule increases mechanical resistance of crown. Furthermore, a ferrule decreases stress in dentin and luting cement; consequently, the fracture and losing restoration risk decline.

A new mechanical indentation framework for functional assessment of articular cartilage

The conventional mechanical properties of articular cartilage, such as compressive stiffness, have been shown to have limited capacity to distinguish visually normal from degraded cartilage samples. In this study, a new mechanical indentation framework for assessing functional properties of articular cartilage during loading/unloading, i.e. deformation and recovery, was established. The capacity of a ring-shaped indenter integrated with an ultrasound transducer to distinguish mechanically intact from proteoglycan-depleted tissue was investigated. To achieve this, normal and enzymatically degraded bovine osteochondral samples were subjected to loading/unloading while the response of the tissue at the middle was captured by ultrasound at the same time. The enzymatic degradation model was characterized by amount of proteoglycan content, glycosaminoglycan release and proteomic analysis. The mechanical response of a wider continuum of articular cartilage in the loaded area and its surrounding region was captured in this framework leading to investigate two parameters, L and TS, related to the surrounding tissue of the loaded area for functional assessment of cartilage. L is the distance between the ultrasound transducer and articular cartilage surface and TS is the transient strain of articular cartilage during loading and unloading. Classification Analysis based on Principal Component Analysis was used to investigate the capacity of the new parameters to assess the functionality of the tissue. Multivariate statistics based on Partial Least Squares regression was employed to identify the correlation between the response of the tissue in the indented area and its surrounding cartilage. The results of this study indicate that L during loading (deformation) can differentiate normal and mildly proteoglycan-depleted samples from severely depleted samples and L during unloading (recovery) can distinguish between normal and proteoglycan-depleted tissue. However, TS during deformation and recovery is unable to discriminate normal cartilage samples from proteoglycan-depleted tissue. The results also demonstrate a strong correlation between mechanical properties of the loaded area with the response of its surrounding cartilage during recovery. It is therefore concluded that L in this newly established framework can discriminate between normal and proteoglycan-depleted cartilage samples. However, more samples will be needed to verify the demarcation between samples degraded for varying amount of time.

Effect of Humeral Stem Shape on Displacement in Elbow Implant

The daily activities are restricted by elbow architecture changes which causes instability and pain. Total elbow arthroplasty is considered last way to relief pain and instability. Various stem cross sectional shapes are designed to reduce loosening of the cemented stemmed implants. The purpose of this study is to analyse the effect of three different humeral stem shapes on implant displacement. Computed tomography scan image was used to reconstruct humerus bone. A three dimensional model of elbow humeral component with three different stem shapes (rectangular, triangular with round edges and circular) with the same length were modelled to be inserted in the constructed bone. All materials were assumed linear, homogenous, elastic and isotropic. A 4 N.m torque was applied and displacement for each implant was analysed. The results of this study showed displacement is more for distal region compared with proximal region. It was also found that rectangular stem had more resistance to torsional loading in comparison with circular and triangular. The present study demonstrates that changing the stem shapes affects the implant displacement and consequently the implant loosening.

Simulation of Brittle Damage for Fracture Process of Endodontically Treated Tooth

The mechanics of brittle damage in porcelain of an endodontically treated maxilla incisor tooth was simulated using finite element method (FEM). For this purpose a very complex composite structure of endodontically treated tooth is simulated under transverse loading. Three dimensional (3D) model of human maxilla incisor tooth root was developed based on Computed Tomography (CT) scan images. Crown, core cement, resin core, dental post, post cement and dentin were created using SolidWorks software, and then the model was imported into ABAQUS-6.9EF software for nonlinear behavior analysis. This study utilizes finite element method to simulate onset and propagation of crack in ceramic layer (porcelain) by the cause of both tension and compression loading related to complexity of the geometry of tooth implant. The simulation has been done using brittle damaged model available in ABAQUS/Explicit in quasi-static load condition. The load-displacement response of whole structure is measured from the top of porcelain by controlling displacement on a rigid rod. Crack initiated at the top of porcelain bellow the location of the rod caused by tension damage at equivalent load of 590 N. Damage in porcelain accounts for up to 63% reduction of whole structure stiffness from the undamaged state. The failure process in porcelain layer can be described by an exponential rate of fracture energy dissipation. This study demonstrated that the proposed finite element model and analysis procedure can be use to predict the nonlinear behavior of tooth implant.