The Preliminary Study Of Reliability Of Ceramic Crown In The Situation Of Maximal Forces Of Mastication And Oral Temperature

Ceramic technic is a new method in prosthodontics.It has been developed in recent years. Ceramic crown shows favorable biocompatibility, esthetic attribute and translucency. More and more dentists and patients draw attention to ceramic crown. But one of it's defects is lower strength and higher brittleness.Reliability is the ability that the object can finish regulated function in regulated condition and regulated time.Since the constant changes of oral temperature,the maximal forces of mastication are different,there are stochastic factors in physical and geomagical parameters in tooth tissure and denture materials and in the course of denture manufacturing.So it is difficult to simulate the condition by using former experimental method.But the method of reliability based on probability can be applied to calculate.Reliability is one of the most important index of products. Many designing and manufacturing departments pay more attention to reliability as much as performance index of products. It has been applied in almost all the industrial departments. It is a new method in prosthodontics.The stochastic three-dimensional finite element model of mandibular first molar based on probability was established by Three Dimensional Sensing System, Geomagic,UG and Ansys scientific calculation software. The theory of Stress-strength interference was applied in the preliminary research of reliability of ceramic crown. The research calculated the reliability of ceramic crown in different oral circumstances such as changes of temperature or the maximal force of mastication. The results were shown below:1) The stochastic three-dimensional finite element model of mandibular first molar based on probability was established.It included 5 parts: ceramic crown, adhesive layer, abutment, periodontal membrane and alveolar bone. The model was divided into 32360 nodes and 186296 elements.The point which was scanned by 3DSS was more successive and precise.In addition the software could establish model quickly. This skill could be a new scientific method in oral biomechanics.2) In the situation of test 2,in the condition of maximal forces of mastication with loading areas 49.322×10-6m2,there were maximal pressed and drawn stress in the mesio-cervical part of tooth.The reliability was 99.99%;In the condition of maximal forces of mastication with loading areas 5×10-6m2,there were maximal pressed and drawn stress in the loading part of tooth.The reliability was 86.86%.3)In the condition of test 3,whether the temperature increased or decreased,the change of oral temperature can influence the thermal stress of ceramic crown.And the maximal thermal stresses were in the lingual-cervical margins.In the condition of maximal forces of mastication with loading areas 49.322×10-6m2 and oral temperature varied from 37℃to 60℃and from 37℃to 0℃, there were maximal pressed and drawn stress in the mesio-cervical part of tooth.The reliability was 99.99%,Compared with condition 1 of test 2,the reliability was not changed.In the condition of maximal forces of mastication with loading areas 5×10-6m2 and oral temperature varied from 37℃to 60℃, there were maximal pressed and drawn stress in the loading part of tooth.The reliability was 87.7%,Compared with condition 2 of test 2,the reliability was increased; In the condition of maximal forces of mastication with loading areas 5×10-6m2 and oral temperature varied from 37℃to 0℃, there were maximal pressed and drawn stress in the loading part of tooth.The reliability was 81.59%,Compared with condition 2 of test 2,the reliability was decreased.In the condition of maximal forces of mastication,the ceramic crown was more liable to be destroyed in the condition of decreasing oral temperature than in the condition of increasing oral temperature.