| Objective:The main purpose is to study the relationship between the variation of concentration strain stresses and the shape/depth of wedge-shaped defects of diseased tooth from the viewpoints of biomechanics. Also, the variation and distribution of concentration strain stresses of tooth body and the restoration under different force states after we restore the defects with different materials are studied. The biomechanical properties and its relationship with the stress distribution of dental tissues are also analyzed. The relationship between the occlusal loading factors and the occurrence, developing and future influences of wedge-shaped effects are discussed. The study can provide the theoretical evidence for the clinical treatment and help to choose restorative materials.Methods:By using the Mimics (Mimics Materialise's interactive medical image control system) based on the mandibular canine's original ASCII STL data provided by the Ulm University of Germany, the three-dimensional finite element model of selenodont and triangle wedge-shaped defects by the depth of 1mm,1.5mm, and 2mm. The stress distribution under various of occlusal loads are analyzed in ANSYS finite element analyzing software. The Von-mises stress distributions under different forces with different restorative materials which are amalgam, composite resin, and glass ionomer cement are also studied in detail.Results: 1. The stress concentration occurs in different wedge-shaped defects. The strongest stress area is in the apex of defects. The maximum stress value (SMX) is increasing with the depth of wedge-shaped defects. Especially, the stress concentration in triangle-shaped defects is more obvious than in selenodont-shaped defects, and the deeper of the triangle-shaped defects, the bigger of the SMX value in the selenodont-shaped defects.2. The SMX under horizontal loading and 45 degree oblique loading are all bigger than the SMX under vertical loading.3. The SMX occurs at the edge of the restoration of the three kinds of restorative materials. By restoring the amalgam and glass ionomer cement, the SMX value of the restoration will decrease with the increasing of the wedge-shaped defects depth. But with the restoring of composite resin, the SMX value has no significant change according to different depth of the wedge-shaped defects.4. With the restoration of the three kinds of materials, the SMX in diseased dental issues is similar to the SMX in normal dental issues. The stress concentration in the defect's area is decreased significantly. Different from the restoration with glass ionomer cement and composite resin, the SMX of the restoration with amalgam occurs in the restoration material other than in the dental issues, and the SMX value is the biggest.Conclusions:1. The model can emulate all kinds of physiological and pathological situation in clinic, and more research works can be done by finite element analysis base on it.2. The stress concentration occurs at the apex of wedge-shaped defects, and it's more obviously for the sharp wedge-shaped defects than for the smooth wedge-shaped defects.3. The deeper of the wedge-shaped defects, the more obvious of the stress concentration will occur, and the tooth body will be damaged faster.4. With the restoration of the wedge-shaped defects, the stress concentration in dental issues will be decreased significantly, so the restorative treatment should be done as earlier as possible. 5. From the viewpoint of biomechanics, the effect of restoration with glass ionomer cement and composite resin is better than that with amalgam. Especially for the small volume of wedge-shaped defect, it's not suitable for the restoration with amalgam.6. The occurrence, development of wedge-shaped defects, and the long term curative effect of restoration all have great relationship with the traumatic occlusal loadings and over occlusal loadings. The treatment of traumatic occlusal should be paid more attention to.
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