Tooth Stress Research Articles

Effect of Tooth Surface Modification on the Load Sharing and Strength of Offset Face Gear Drive with Spur Involute Pinion

Load sharing is one of the main factors that determine gear strength. In this paper, Tooth Contact Analysis (TCA) and Loaded Tooth Contact Analysis (LTCA) have been performed to investigate the effect of tooth surface modification on the contact ratio, load sharing and strength of an orthogonal offset face gear drive with spur involute pinion. The results indicate that the contact ratio of 2.0 or higher could be achieved. The maximum load carried by single tooth and bending stress are significantly reduced when appropriate tooth surface modification is applied to the orthogonal offset face gear drive.

Computational Tooth Root Stress Analysis of Crossed Beveloid Gears with Small Shaft Angle

It is known that tooth bending failures are directly caused by the stress state at the tooth root or fillet regions of the gear teeth. In this study, the geometric and manufacturing of the fillet and root of crossed beveloid are investigated and a computational tooth stress prediction model is setup applying exact geometry-based mesh theory. The dominate fillet and root design parameter and load were examined in the loaded tooth contact analysis to analyze root stresses.

Using occlusal wear information and finite element analysis to investigate stress distributions in human molars

Simulations based on finite element analysis (FEA) have attracted increasing interest in dentistry and dental anthropology for evaluating the stress and strain distribution in teeth under occlusal loading conditions. Nonetheless, FEA is usually applied without considering changes in contacts between antagonistic teeth during the occlusal power stroke. In this contribution we show how occlusal information can be used to investigate the stress distribution with 3D FEA in lower first molars (M(1)). The antagonistic crowns M(1) and P(2)-M(1) of two dried modern human skulls were scanned by μCT in maximum intercuspation (centric occlusion) contact. A virtual analysis of the occlusal power stroke between M(1) and P(2)-M(1) was carried out in the Occlusal Fingerprint Analyser (OFA) software, and the occlusal trajectory path was recorded, while contact areas per time-step were visualized and quantified. Stress distribution of the M(1) in selected occlusal stages were analyzed in strand7, considering occlusal information taken from OFA results for individual loading direction and loading area. Our FEA results show that the stress pattern changes considerably during the power stroke, suggesting that wear facets have a crucial influence on the distribution of stress on the whole tooth. Grooves and fissures on the occlusal surface are seen as critical locations, as tensile stresses are concentrated at these features. Properly accounting for the power stroke kinematics of occluding teeth results in quite different results (less tensile stresses in the crown) than usual loading scenarios based on parallel forces to the long axis of the tooth. This leads to the conclusion that functional studies considering kinematics of teeth are important to understand biomechanics and interpret morphological adaptation of teeth.

Three-dimensional finite element analysis of effect of root canal taper and post on tooth stress distribution

To evaluate the effect of root canal taper and post on tooth stress distribution. Three-dimensional finite element models of human mandibular first molar with root canals prepared with 35# K file, ProTaper and Profile were established. The tooth were restored with fiber-resin, stainless steel and silver amalgam posts respectively. A vertical load on tooth occlusal surface was simulated. Marc software was used to analyze and calculate the stress distributions in the tooth restored with three kinds of different root canal posts, especially the in the cervical part and root. Different tapered root canals had no obvious influence on stress distribution in all three different posts. Stress distribution of stainless steel post located at the cervical and middle part of distal root, the highest Von-Mises stress was about 45 MPa. Stress distribution of silver amalgam post located at the orifice of root canal and pulp fundus, the highest Von-Mises stress was about 16 MPa. Stress distribution of fiber-resin post had no obvious stress concentration. Fiber-resin post is the most ideal root canal post. Stainless steel post causes remarkable stress concentration in the root, which may raise the possibility of root fracture.

Finite element analysis of strength and adhesion of cast posts compared to glass fiber-reinforced composite resin posts in anterior teeth

Previous studies on the strength of teeth restored with posts have not resolved the controversy as to which post systems provide the greatest strength and longevity. The purpose of this study was to compare the strength of teeth restored using cast posts with those restored using glass fiber-reinforced composite resin posts and to evaluate the bond strength of the posts to dentin. The investigation was conducted by using finite element analysis, combined with the application of contact elements. Three-dimensional (3-D) models of the maxillary central incisors were generated: IT, an intact tooth; CC, a tooth with a ceramic crown; FP, a tooth restored with an FRC (glass fiber-reinforced composite resin) post; CPAu, a tooth restored with a gold alloy cast post; and CPNi, a tooth restored with an NiCr (nickel chromium alloy) cast post. Each model was subjected to vertical and oblique loads with a force of 100 N. To evaluate the strength of the restored tooth, ceramics, and composite resin, the modified von Mises failure criterion was used, the Tsai-Wu criterion for FRC, and the von Mises criterion for gold and NiCr alloy. The equivalent stresses found in the tested models were compared with the tensile strength of the respective materials. Contact stresses in the luting cement-dentin interface were calculated. The maximum mvM (modified von Mises failure criterion) stresses in the dentin of the teeth restored with FRC posts were reduced by 21%, and in those restored with cast NiCr posts, stresses were reduced by 25% when compared to the stresses in the intact tooth. The equivalent stresses in metal posts were several times higher than in FRC posts, but did not exceed the tensile strength of the materials. The highest mvM stress in the luting resin cement around the FRC post was 55% higher than in the luting resin cement around the metal post, under an oblique load. In the ceramic crown, which covered the composite resin post and core, the highest mvM stress was 30.7 MPa, whereas with the metal post and core, it was 23 MPa. Cast metal posts resulted in lower stresses in the dentin of the restored teeth than did FRC posts. Irrespective of the material, the equivalent stresses in the posts did not exceed their tensile strength. Lower stresses were present in the luting cement and the cement-dentin interface around cast posts than around FRC posts. In the ceramic crown supported by a metal post and core, the stresses were lower than those observed in the crown supported by a composite resin core foundation.

Effects of orthodontic mini-implant position in the dragon helix appliance on tooth displacement and stress distribution: a three-dimensional finite element analysis

191 Assistant Professor, Professor, Division of Orthodontics, Department of Dentistry, School of Medicine, Ewha Womans University. Visiting Scholar, Division of Orthodontics, Department of Dentistry, University of Nebraska Medical Center. Former Student, Department of Orthodontics, Graduate School of Clinical Dentistry, Ewha Womans University. Associate Professor, Division of Orthodontics, Department of Dentistry, College of Medicine, The Catholic University of Korea, St. Mary’s Hospital. Associate Professor, Department of Orthodontics, University of Ulsan College of Medicine, Asan Medical Center. Associate Professor, School of Mechanical and Automobile Engineering, Kunsan National University. Corresponding author: Youn-Sic Chun. Division of Orthodontics, Department of Dentistry, School of Medicine, Ewha Womans University, 911-1 Mok-dong, Yangcheon-gu, Seoul 158-710, Korea. +82 2 2650 5114; e-mail, yschun@ewha.ac.kr. Received August 27, 2010; Last Revision October 22, 2010; Accepted October 25, 2010. DOI:10.4041/kjod.2011.41.3.191 Effects of orthodontic mini-implant position in the dragon helix appliance on tooth displacement and stress distribution: a three-dimensional finite element analysis

Calculation of the bending stresses of involute teeth with longitudinal surface modification

The results of the simulation of the deformation mode in the root of the teeth of cylindrical involute gears under the action of a concentrated force are given. It is the first step in determining the bending strength of involute teeth in the case that at least some of them (those in a pinion or in a gear) have a longitudinal surface modification providing for a contact that is a point one from the theoretical point of view and local from the practical point of view. The investigations have been performed using the finite-element model developed in an ANSYS environment. Taking into account the effective (equivalent) stresses responsible for damaging the material of the teeth, the volume factor of the shape of the tooth has been reduced to a form that makes it possible to use the bending durability limits specified for ordinary (unmodified) teeth of involute gears with a theoretically linear contact, which enter the working stresses for estimating the bending resistance.

Study on Mechanism of Tap Breakage in Low Frequency Torsional Vibration Tapping

Early breakage of tap often occurs when tapping on difficult-to-cut materials with the method of low frequency torsional vibration tapping, which decreases the technological effect and restricts its application. The effect of impact load on tap breakage in vibration tapping was analyzed, and the stress state in tap teeth was simulated by FEM, on this basis, it is concluded that too large tensile stress in tap teeth is the main cause of early breakage of tap. To reduce the tensile stress and enhance the shock resistance of tap teeth, the tap should be ground to minor negative rake angle. Experiments showed that the failure mode of grinded taps changed to wear, and thereby the service life of tap was prolonged significantly.

A 3D FEM Methodology for the Full-Scale Air Hammer Bit, Teeth and Rock Contact Analysis

In order to reveal the physical mechanism of air hammer drilling process, using the finite element methods (FEM), a three-dimensional (3D) contact model of full-scale bit, full-scale teeth and rock is established by using free meshing method. We use a Mohr-Coulomb type material model to describe when and how rock fails, and a triangular wave to replace the stress wave. Using the finite element analysis software (ANSYS), the 3D contact analysis of the bit, teeth and rock is carried out. The results show that: aggressive tensile failure may be primarily responsible for rock breakage in air hammer drilling, while compressive failure (or shear failure) may only contribute as a minor player; the distribution of the fragmentation dents can be used to verify the rationality of tooth arrangement; the larger tooth-hole stress of the outside rows mainly responses for the bit failure, while the larger tooth stress of the inside rows contributes as a secondary factor. The results are further calibrated with a series of field applications and research results.

풍력발전기용 기어트레인의 특성에 관한 연구

Gear trains are combined with the planetary gear units and helical gear units. It is known that the combination type is decisive to the system performances of the transmissions. In this paper, within the commonly used range of the design requirements for medium and large scaled (1~8 MW) wind turbines, the transmission characteristics of the typical layouts of the gear train are investigated. According to the international standard by ANSI/AGMA/AWEA 6006-A03, the gear boxes are basically designed and compared with respect to the system lifes of 99% reliability, total weight, the power densities, overall diameter/length and the maximum stresses of the gear teeth. With these comparison works, the characteristics of the layouts of gear trains are discussed.

Biomechanical Stress Analysis of Mandibular First Permanent Molar; Restored with Amalgam and Composite Resin: A Computerized Finite Element Study.

Normal mastication with its varying magnitude and direction generates considerable reactionary stresses in teeth and their supporting tissues. The structure of the human tooth and its supporting tissues is a complex assemblage of materials of varied mechanical properties. The finite element method (FEM), a modern technique of numerical stress analysis, has the great advantage of being applicable to solids of irregular geometry and heterogeneous material properties and therefore ideally suited to the examination of structural behavior of teeth. The mandibular first permanent molar is one of the earliest permanent teeth to erupt in the oral cavity and hence most prone to caries. The purpose of the present study was to construct a two-dimensional FE model of the mandibular first permanent molar and its supporting structures, using a FE software called NISA II-Display III, EMRC, USA to study the following:• To compare stress distributions patterns when a modeled Class I Cavity was restored with dental amalgam and composite resin.• To compare the stress distributions pattern when the load was applied to different to locations, i.e.: At the mesial cusp tip, and at the center of the occlusal surface.Both amalgam and composite resin showed similar stress distribution pattern, however, the magnitudes of stresses generated in the tooth restored with composite resin were higher. Thus, amalgam is a better restorative material in distributing stresses.

Rating of Spur Gear Strength Using Photoelasticity and the Finite Element Method

Problem statement: Toothed gears are some of the most used machine elements for motion and power transmission between rotating shafts. Thi s fact induces the need for improved reliability an d higher endurance, which require precise and clear k nowledge of the gear tooth stress field during meshing. Approach: This study considered the calculation of maximum s tress at gear tooth root when the meshing gears are loaded at their most unfavora ble contact point (highest point of single-tooth contact-HPSTC), using both numerical and experimental methods. Finite Element Method (FEM) is used for the numerical stress analysis and photoela sticity is applied for the experimental investigati on of the stress field. Results: The experimental results of the maximum dimensionless stress derived from the photoelasticity experiments are compared t o the respective theoretical stress results of the finite element analysis. Conclusion: It was found that the deviation between the result s of the applied methods falls between reasonable limits whereas it rises with increasing number of teeth of the large gear.

Load Sharing On Spur Gear Teeth And Stress Analysis When Contact Ratio Changed

The present research work concentrates on the effect of contact ratio change on the stresses generated on meshing gear teeth. Many cases of contact ratio (1.6, 1.7, 1.8, 1.9 & 2.0) have been studied. In each case the value and location of load were determined on the involute profile of meshing tooth. Also the angular position of this tooth for critical loading condition (at the instant when the generated root stresses at the maximum state). (Ansys) programming using F.E.M have been applied for stress analysis on gear model. From this study it is clear that, the highest contact ratio resulted in the lowest generated tooth stresses (i.e. the highest load carrying capacity). This depends on the value, location and direction of load applied on tooth involute. Keywords : Spur gear, Contact ratio, Load sharing, Stress analysis

Virtual analysis of stresses in human teeth restored with esthetic posts

The use of intra-radicular posts for rebuilding of damaged teeth is a normal practice in contemporary dentistry. However, dental roots restored with posts are subjected to the risk of failure under occlusal loads, particularly in cases of small dentin thickness. This study adopted the finite element analysis to compare the elastic stress distribution in simulated endodontically treated maxillary central incisor restored with two different esthetic posts, a ceramic post and a prefabricated fiber glass post. Under masticatory load, the shear stress and von Mises equivalent stress were determined for the different regions of the two models. The results demonstrated that stress concentrations occurred mainly in the cervical dentin in the prefabricated fiber glass post model. The ceramic post model presented stress concentration in a region limited to the proper post adjacent to its apical end, thus preserving the root dentin.

Determining the flexural stress concentration factor for gear teeth taking into account elastic deformations and errors in manufacture and assembly of gearing elements

Results of theoretical studies aimed at determining the flexural stress factor in toothed gears taking into account the contact pressure concentration due to elastic deformations and errors in manufacture and assembly of gearing elements are presented. Universal formulas for the flexural stress concentration factor in gear teeth are obtained. These formulas make it possible to calculate flexural stresses in gear teeth and toothed couplings. Diagrams of variations in the flexural stress concentration factor over the tooth length in the presence of misalignment are plotted.

Combining structural–thermal coupled field FE analysis and the Taguchi method to evaluate the relative contributions of multi-factors in a premolar adhesive MOD restoration

The aim of this study was to determine the relative contribution of changes in restorative material, cavity dimensions, adhesive layer adaptation, and load conditions on the biomechanical response of an adhesive Class II MOD restoration during oral temperature changes. A validated finite-element (FE) model was used to perform the structural-thermal coupled field analyses and the Taguchi method was employed to identify the significance of each design factor in controlling the stress. The results indicated that thermal expansion in restorative material amplified the thermal effect and dominated the tooth stress value (69%) at high temperatures. The percentage contributions of the load conditions, cavity depth, and cement modulus increased the effect on tooth stress values 46%, 32%, and 14%, respectively, when the tooth temperature was returned to 37 degrees C. Load conditions were also the main factor influencing the resin cement stress values, irrespective of temperature changes. Increased stress values occurred with composite resin, lateral force, a deeper cavity, and a higher luting cement modulus. The combined use of FE analysis and the Taguchi method efficiently identified that a deeper cavity might increase the risk of a restored tooth fracture, as well as a ceramic inlay with a lower thermal expansion, attaining a proper occlusal adjustment to reduce the lateral occlusal force and low modulus luting material application to obtain a better force-transmission mechanism are recommended.

Finite Element Method Analysis of the Stress Distribution to Supporting Tissues in a Class IV Aramany Removable Partial Denture (Part I: The Teeth and Periodontal Ligament)

Special care is required in the fabrication of a Class IV Aramany removable partial denture (RPD) in order to minimize the stress distribution to supporting tissues. Using the finite element method, the aim of this study was to analyze the distribution stress to supporting tissues when a Class IV Aramany RPD is worn. Three RPD designs with circumferential cast retainers were examined in this study. These varied in retainer configuration which included: buccal retention and palatal reciprocation (P1); palatal retention and buccal reciprocation (P2); and buccal and palatal retention (P3). The stress distribution in models using the Von Mises criteria was analyzed for each RPD design when placed under a 53N load from three different directions that included: vertical to the posterior teeth of the RPD (F1); at a 33 masculine angle to the posterior teeth of the RPD (F2); and vertically on the anterior teeth of the RPD (F3). The maximum stress in teeth (91.3 Mpa) was generated when a 53N force was applied vertically from anterior teeth of RPD (F3) using buccal and palatal retention (P3). The maximum stress (0.494 Mpa) in the periodontal ligament (PDL) was also generated under the same conditions using the F3 load on the P3 design. In all three directions of force application RPDs with buccal and palatal retention induced more stress in the tooth and the PDL with the maximum stress generated when the force was applied vertically to the anterior teeth. The axis of rotation can be changed by altering the RPD design as well as the direction and amount of force applied to the teeth.

Analytical Wear Model of a Gerotor Pump without Hydrodynamic Effect

The contact stress in a gerotor pump is addressed in this paper because the gerotor pump cannot be adjusted for wear. The first part of this paper presents a simple and exact rotor profile equations of the gerotor pump. In the second part of this paper, an explicit formula to avoid undercut in the inner-rotor of the gerotor pump is proposed by examining the minimum radius of curvature of the inner-rotor tooth profile on the convex section. It is found that undercut does not occur so long as the minimum value of the radius of curvature on the convex section is not less than zero. Next, the contact stresses without hydrodynamic effect between the inner and outer-rotors are evaluated through the calculation of the Hertzian contact stress in the rotor teeth. Based on the above results, we finally present the wear characteristics of pHVs factor, which is proportional to the wear rate, between the rotors of the gerotor pump under quasi-static and dry contact conditions.

Contact problems of a trochoidal-gear pump

The aim of the approach of this paper is to characterise contact stress of a trochoidal-gear set when it works as part of the hydraulic machine. It is important to know that the contact stress forces in a trochoidal-type machine is important because the machine cannot be adjusted for wear. The main difficulty in calculating the contact forces is to determine the forces that are transmitted through each contact point. Since there are many points of contact, at any instant, the problem is statically indeterminate. The first part of this paper presents a simplified analytical model of a trochoidal-type machine when friction at the contact points is neglected. From this study, the performance of the gear set is evaluated through the calculation of the normal maximum contact stress in the gear teeth. Then the second part of the paper presents a finite element model of the same machine. The analysis of both models is for quasi-static conditions. An experimental approach using a prototype model of the gear set provides the maximum contact stress on a pair of teeth through photoelasticity measurement techniques of the same machine. The results from the two models and the experimental work are compared and important conclusions are drawn and discussed.

Computational modeling of specific biological structures behavior

Biomechanical experimental studies are often a subject of interest to many researchers. The results of such investigations give a full insight of complex structural behavior under loading, visualize potential material weaknesses and evaluate if mechanical factors play a substantial role in the pathogenesis of the lesions of the investigated biological structure. The use of FEM enables most of the researchers to abandon the experimental animal models and expand the investigation on computational models, analyzing stress and strain distribution as an indicator of structural biomechanical behavior. The aim of this paper was to present computational modeling of any (human or animal) intact tooth behavior under loading and evaluate the intact tooth stress and strain distribution pattern. For the investigation to be carried out a mathematical model of an intact tooth had to be created. The difference in stress concentration, when masticatory forces are acting lateraly comparing to the ones acting vertically, can be attributed to the basic mechanical principle of leverage which states that forces concentrate at or near the fulcrum. When subjected to lateral loading, tooth with its root acts as a simple lever that fulcrums near the cervical region. This paper offers the new approach in veterinary dental scientific research. Once when a mathematical model is made, it is possible by changing the parameters to investigate different clinical situations. With increasing popularity of veterinary dentistry, the FEM/computational analyses could became a useful tool in biomechanical veterinary dental research due to its noninvasiveness.