Effect of clenching on biomechanical response of human mandible and temporomandibular joint to traumatic force analyzed by finite element method.

PURPOSE: The purpose of the present study was to analyze the effect of clenching on the biomechanical response of human mandible and temporomandibular joint (TMJ) to traumatic force by the finite element (FE) method. MATERIAL AND METHODS: FE models of the mandible and the TMJ in resting and clenching positions were prepared. Distribution and magnitude of von Mises stress were analyzed by applying force as a point load in the symphyseal, canine, body and angle regions of the mandible. In addition, strain energy density (SED) at the articular disc and in posterior connective tissue of TMJ was analyzed. RESULTS: In the resting position, von Mises stress was mainly concentrated at the condylar neck and in the retromolar region of the mandible. In the clenching position, the stress at the condylar neck decreased in all loadings. The stress in the retromolar region similary decreased in the symphyseal, canine and body loading, respectively; however, higher stress was observed in the retromolar region on the loading side in the angle loading. High SED was generated at the articular disc and in posterior connective tissues of TMJ in the resting position. The SED in these tissues decreased in all loadings in the clenching position. CONCLUSIONS: Clenching generally reduces stress at the condylar neck and in the retromolar region of the mandible, and strain energy at the articular disc and in posterior connective tissue of TMJ by traumatic forces on the mandible; however, clenching induces greater stress in the retromolar region on the loading side by traumatic force to the angle region.

Biomechanical analysis of the strength of the mandible after marginal resection.

PURPOSE: This study investigated the biomechanical behavior of the mandible after marginal resection by tensile test in a human cadaveric mandible and finite element (FE) analysis. MATERIALS AND METHODS: Human cadaveric mandibular models after marginal resection were prepared with residual heights of 5, 10, and 15 mm. The strength in each of these mandibular models was examined by tensile testing. In addition, FE models of the mandible after marginal resection were prepared with residual heights of 5, 7.5, 10, 12.5, and 15 mm. Distribution and magnitude of von Mises stress were analyzed by applying bite forces of 151 N as a point load on the incisal region and 355.2 and 478.1 N on the premolar and molar regions on the nonresected and resected sides, respectively. At the molar region of the resected side, bite forces of 368.5 N and 286.9 N (80% and 60%, respectively, of 478.1 N) were also applied. RESULTS: On tensile testing, all cadaveric mandibular models were broken at the posterior resection corner. The tensile force was significantly larger in the model with a residual height of 15 mm compared with that of those with a 5- or 10-mm residual height. On FE analysis, von Mises stress was concentrated at the resection corner. The region of maximal von Mises stress concentration in FE models was consistent with that showing destruction on tensile testing. The relationship between the residual height and von Mises stress in the resection area was linear in models of the incisal, premolar, and molar loading on the nonresected side and quadratic in models of the premolar and molar loading on the resected side. The maximal von Mises stress in the resection area was highest during molar loading on the resected side under the present loading condition and exceeded the threshold for the development of pathologic fracture in the model with a residual height of around 10 mm or less. However, the maximal von Mises stress decreased in parallel with the reduction of bite force in the molar region of the resected side. CONCLUSIONS: The residual height and bite force are critical factors for the prevention of pathologic fracture of the mandible after marginal resection. Currently, a residual height of more than 10 mm and reduction of bite force are recommended to reduce the risk of fracture.

Biomechanical analysis of miniplate osteosynthesis for fractures of the atrophic mandible.

PURPOSE: The purpose of this study was to investigate the biomechanical behavior of miniplate osteosynthesis for fracture of the edentulous mandible with various degrees of atrophy by finite element (FE) analysis. MATERIALS AND METHODS: Three-dimensional FE models simulating various atrophic or nonatrophic edentulous mandibles were constructed. The models were divided into 3 groups based on the height: 20 mm, 15 mm, and 10 mm. A model 30-mm high was defined as a nonatrophic mandible. Fracture in the premolar region was simulated. Single or double miniplate osteosynthesis was assumed to fix the fracture. In each case, models of fractures with and without bone contact between bone fragments were prepared. A bite force of 62.8 N was applied in the FE models as a point load on the anterior point. RESULTS: There were no noticeable differences in compressive stress level in the bone around screws among the single miniplate models or double miniplate models with bone contact. Single miniplate models without bone contact showed markedly greater compressive stress than that of models with bone contact. The use of double miniplates showed a great influence on von Mises stress reduction in the miniplates. Without bone contact, greater interfragmentary displacements occurred; however, interfragmentary displacements were within the limit of not causing a malunion of the fractured bone in all models. CONCLUSION: Double miniplate fixation may be a reliable method for treating fracture of the atrophic mandible from a biomechanical viewpoint.

Ex vivo mechanical evaluation of carbonate apatite-collagen-grafted porous poly-L-lactic acid membrane in rabbit calvarial bone.

Appropriate mechanical recovery is an important parameter in successful restoration of skeletal defects. Carbonate apatite and type I atelocollagen mixture (CAp) was grafted on a porous poly-L-lactic acid (PLLA) membrane to produce a CAp bilayered PLLA membrane (CAp+PLLA). After implantation, regional mechanical change in the membrane was investigated in rabbit calvarial bone defects. Dynamic viscoelasticity and elastic modulus of the implanted specimen were measured after 2, 4, 8, 12, 16, 26, and 52 weeks. The modulus of the peripheral part was higher than that of the central part of the implanted area, whereas the central part demonstrated a gradual increase. This phenomenon indicates that regeneration initially occurs from the periphery of the calvarial bone. After 26 weeks, stiffness of the central part became similar to that of the periphery in the CAp+PLLA-implanted area. According to this result, measuring viscoelasticity of an implanted biodegradable material would be a useful method to determine degrees of regeneration and replacement of an implanted region.

Effect of clenching on biomechanical response of human mandible and temporomandibular joint to traumatic force analyzed by finite element method

Purpose: The purpose of the present study was to analyze the effect of clenching on the biomechanical response of human mandible and temporomandibular joint (TMJ) to traumatic force by the finite element (FE) method. Material and Methods: FE models of the mandible and the TMJ in resting and clenching positions were prepared. Distribution and magnitude of von Mises stress were analyzed by applying force as a point load in the symphyseal, canine, body and angle regions of the mandible. In addition, strain energy density (SED) at the articular disc and in posterior connective tissue of TMJ was analyzed. Results: In the resting position, von Mises stress was mainly concentrated at the condylar neck and in the retromolarregion of the mandible. In the clenching position, the stress at the condylar neck decreased in all loadings. The stress in the retromolar region similary decreased in the symphyseal, canine and body loading, respectively; however, higher stress was observed in the retromolar region on the loading side in the angle loading. High SEDwas generated at the articular disc and in posterior connective tissues of TMJ in the resting position. The SED in these tissues decreased in all loadings in the clenching position. Conclusions: Clenching generally reduces stress at the condylar neck and in the retromolar region of the mandible, and strain energy at the articular disc and in posterior connective tissue of TMJ by traumatic forces on the mandible; however, clenching induces greater stress in the retromolar region on the loading side by traumatic force to the angle region (AU)