Three-dimensional Finite Element Study Of All-ceramic Crowns With Different Occlusion Relationship

With the rapid development of modern society, there is a growing demand for aesthetics. As a branch of medicine, combined with aesthetics, Prosthodontics becomes more and more important. In the Prosthodontics clinical practice, many patients need to receive cosmetology anterior restorative. At present, for the cosmetic restoration of anterior prosthesis, PFM, porcelain veneers and all-ceramic crowns are mainly used. However, PFM crown being made of metal materials has many shortcomings, such as bad light transmittance, electrochemical corrosion problem, and allergy and so on. Therefore, all-ceramic restoration system has become the current focus both at home and abroad. With similar color and translucency to natural teeth, excellent biocompatibility, excellent corrosion resistance and good abrasion resistance, all-ceramic restorations have been more and more popular. However, the wise use is limited by the all-ceramic's strong brittle and easy fold. With the ongoing study of high-strength ceramic, all-ceramic restoration is increasingly applied in the clinic. However, with the new all-ceramic materials available, the dentists also encountered a new problem, that is, with different occlusion relationship, the selection and restoration design of all-ceramic material. There are many methods to research the strength influence of different all-ceramic crown materials and repair design. Because of its high reproducibility, the three dimensional finite element in biomechanics avoids the impacts of differences in individual factors in the clinic trials. It is preferred by many scholars and becomes one of the important research methods. Throughout the study, the three-dimensional finite element mechanical model is the basic and key point. It directly relates to the outcomes, so how to design the model, by which means and which methods to choose are essential. More and more researches are concerned about how to set up three-dimensional finite element model.Some factors influence on all-ceramic crowns strength. Many scholars have researched many factors about the application of the three-dimensional finite element method, from different neck shape, degree of polymerization of different wall-axis, different cut-side thickness of the binder, and have achieved some valuable results. However, because the occlusion relationship of each patient is different, loading points of all-ceramic crowns are also different. At present, it is rare to use the three-dimensional finite element method to analysis different occlusion relationship impacting on all-ceramic crowns. There is no uniform standard about materials selection of all-ceramic crown with different occlusion relationship in the clinic. From the perspective of the differences of occlusion relationship, this research discusses the changes of stress distribution of all-ceramic crowns with the normal occlusion or the deep overbite malocclusion.Objective: Analysis the stress distribution in all-ceramic dental crown restoration system of the maxillary central incisor; study the influences of different occlusion mode on all-ceramic dental crowns in and on the edge; aim to provide biomechanics supports for its clinical practice design.Methods: With non-contact laser scanning and three dimensional measuring, built a three-dimensional finite element model of all-ceramic dental crown restoration system of the maxillary central incisor with different occlusion situations; on the different points of all-ceramic dental crown surface imitating different occlusion situations load, the finite element analysis software--Ansys11.0 was used to analysis the stress distribution of all-ceramic crowns restoration system.Results:1 In different loading conditions, the stress distributions on all-ceramic crown with different materials were concentrated in the surrounding of loading point. When the loading point was same, the Von-Mises stress distribution of the groups as follows were similar:all-ceramic with different materials, the prepared tooth, root of teeth, pericementum, cementum and alveolar bone. It is obviously difference when the loading point was different.2 The extreme value points of the four material all-ceramic crowns: Empressâ… ,Empressâ…¡,In-Ceram Alumina and In-Ceram Zirconia in normal occlusion were in proper order: 442.533Mpa, 437.094Mpa, 442.675Mpa, 413.305Mpa. In the deep overbite malocclusion the values were: 521.837Mpa, 535.279Mpa, 595.984Mpa, 550.367Mpa. There were significantly difference of extreme value in different occlusion groups; but in different ceramic material groups, the difference of extreme value was not significantly.3 When the occlusion relationships were same, the Von-Mises stress distributions in the edges of the four material all-ceramic dental crowns were similar, but the value were obviously difference in different materials. In-Ceram Alumina stress was the strongest, and the stress of Empressâ… was the smallest in both occlusion groups. In the different occlusion situations, the Von-Mises stress distribution on the edge of all-ceramic dental crown was different significantly. When it was normal occlusion, it was the same that the labial stress is stronger than the lingual stress. It was opposite when it is deep overbite malocclusion.Conclusions:1 The finite element method (FEM) is a convenient and effective way in oral biomechanical study.2 We study stress in all-ceramic crown of the maxillary central incisor in the normal occlusion and deep overbite malocclusion situation by FEM, the stress distributions is obviously different on the prepared tooth, adhesive, cementum, pericementum, and alveolar bone. The high stress distribution of the prepared tooth and the adhesive is at the loading point surrounding. In normal occlusion, the high stress distribution area of the cement, pericementum, and alveolar bone is situated on the point of 1/3 neck of the tooth root, whereas, it is in the 1/3 tooth root when deep overbite malocclusion.3 In the different occlusion relationships, the high stress distribution are to be concentrated in the loading point surroundings.4 In normal occlusion, the extreme stress area is in the labial edge, which would in palatine edge in deep overbite malocclusion.5 Using glassion as the cementum, the stress of deep overbite malocclusion is stronger than that of normal occlusion.