| Aim: It is well known that the force acting on teeth and prostheses is dynamical and has closely correlated with time of action. However, there are still rare studies using the dynamic to the biomechanics of stomatology. It, therefore, is necessary to apply dynamics to the study on biomechanics of stomatology. The purpose of this study is attempted to introduce dynamics study to stomatology, primarily the analysis of teeth vibration and fatigue measurement of fixed prostheses.Methods: (1)Based on the 3-D model of maxillary central incisor tooth created by 3D Max, a 3-D finite element model was generated firstly by using computer aided engineering (CAE) software. The parameters of material properties and boundary conditions were then given in according to different parts of tooth. (2)The densities of the fresh drawn teeth were measured according to male and female teeth, anterior and posterior teeth, crown and root of teeth, respectively.(3)By using the finite element method (FEM) software, the vibration of 3-D finite element model of maxillary central incisor tooth was analyzed. (4)Based on the principle of natural frequency measurement tostomatology, an instrument for natural frequency measurement of teeth was developed by using micro-piezoelectric accelerometer. The eigenfrequencies of total teeth of the adults were also investigated. (5)To measure the fatigue life of porcelain fused metal (PFM) restorations, an instrument was developed in this study. The force and the frequency of the instrument having been calibrated, the fatigue lifes of anterior and posterior, crown and fixed bridge PFM restorations were assessed.ResuIts:(1)The 3-D finite element model was successfully generated by CAE software. As the information has not been lost theoretically during the process of modeling, the similarity of model may be guaranteed. (2)The density of human teeth is approximately among 1.20-1.40+103kg/m3. The density of crown is higher than that of root with significant difference. There are no significant statisticlly differences between the densities of teeth in male and female, anterior and posterior teeth. (3)Crown's vibration is dominantly present during teeth vibration. The first four orders of vibration are the major parts, which the corresponding frequencies are 879.65 Hz, 1286.76 Hz, 1827.21 Hz, 2087.59 Hz, respectively. Their modes of vibration are the whole tooth vibrate along its axis, swing mainly by the crown in labiolingual direction, twist in accordance to its axis and swing mainly by the crown in mesiodistal direction. (4)The vibrations of teeth are consisted of many modes. The most important modes are the first of four orders, the frequencies of which distribute between 600 Hz and 2300 Hz. There is no significant statisticlly difference between the eigenfrequencies of same teeth on each side. The eigenfrequencies of teeth in female are higher than that in male without statisticlly difference. The gradation of eigenfrequencies of different tooth in same order has some rules. (5)There isonly fatigue wear appeared on the surface of functional area analyzed by low magnificent stereoscopic zoom microscopy after simulating mastication 20 years. However, there are some microscopic cracks by scanning electric microscopy (under 20m on anterior teeth restorations and 30-50m on posterior teeth restorations), indicating that PFM restorations may last 20 years even longer by using normal masticatory force.Conclution: (1)The 3-D finite element model can be generated by CAE software. (2)The tissue structure may play an important role in the density of teeth. (3)The modal analysis may be applied in the study of the teeth during being acted by masticatory force. (4)The frequencies of teeth may correlate with its volumes and supporting conditions by periodontium. (5)PFM restorations, which not only have excellent biocompatibility and esthetics, but also have good character of resistance to fatigue, can be used as perpetual prostheses.The present results suggest that applying dynamics to the...
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