| Recently, with the increasingly need of aesthetic among dentists and patients, all-ceramic crown metarils like zircoina become indentified and widely used. Excellent aesthetic property, high strength and the usage of CAD/CAM, show its' strong vitality and application prospect. Although glass ceramics have excellent aesthetic property, the high fragility restrict its' usage. However, the use of zircoina solve this problem in clinic working. With the qualities of high strength and high toughness, Zircoina Can be applied to any area of the oral and be a perfect substitute for metal materials for repair treatment.But in the clinical application process, this new all ceramic crown also exposed a number of problems, such as the collapse of porcelain, internal crown fracture, microleakage, and compared with the metal ceramic crown, it has a high risk of clinical collapse porcelain. The occurrence rate of 10 years literature review of the collapse porcelain was 25%, which was in a very high level of failure. ZrO2 all ceramic crown collapse occurred at the time after used in 2-3 years later. The collapse of porcelain in zircoina is different from other glass ceramics.Therefore, this study focus is on the bonding performance and the influencing factors of the interface between the ZrO2 ceramic and veneer porcelain.Related factors are complex from the current domestic and foreign research, but one of the key factors is the veneer porcelain lack of sufficient internal crown support, the elastic modulus,coefficient of thermal expansion and fracture toughness does not match between ZrO2 and veneer porcelain.The residual stress and the applied load on the veneer porcelain layer may be an important reason for the occurrence of the collapse of porcelain. At present, the combined mechanism of ZrO2 and veneer porcelain is not very clear, and it will be a great help to master the mechanism of the interface bonding of the new materials for the development of new materials and good structural design.Low temperature aging will reduce the bending strength of 3Y-TZP ceramics has become the consensus of researchers at home and abroad.Studies have also found that the surface of the 3Y-TZP ceramic monoclinic was increased with the increase of time after low temperature aging, but the bending strength was not significantly changed.This phenomenon can be explained with two aspects:first, the amount of monoclinic phase change is too small, only in the material surface, does not reached the decline degree of bending strength of 3Y-TZP ceramic.Two, the volume expansion of the t-m phase transformation will form a compressive stress layer on the surface of 3Y-TZP ceramic, which can counteract the harm of the micro cracks on the surface of 3Y-TZP ceramics to resist the bending strength, and it is beneficial to improve the bending strength.But also need to further study the effect of low temperature aging on bending strength of 3Y-TZP ceramic and its mechanism.Taking 3YS-E as the experimental material, we have studied the influence law and mechanism of the low temperature aging on the bending strength of 3 Y-TZP ceramics, which has important significance for the long-term success rate of 3 Y-TZP ceramics in the oral cavity.The results obtained are quite clear in response to the time of ZrO2 substrate crack and surface treatment of double layer porcelain has important guiding significance,(a)The relationship between surface monoclinic phase content and the degree of phase transition:T-M phase transition from the 3Y-TZP ceramic surface to the interior after low temperature aging. When the phase transition depth is more than X-ray penetration depth, the content of the monoclinic phase was kept constan after XRD measured, and the fact that the phase change is still expanding inside the material.(b)The fracture process of the phase change layer produced by low temperature aging is mainly intergranular fracture mode., the wear crystal fracture is the main part in the area of the phase transition. Wear crystal fracture need more energy than intergranular fracture mode.Therefore, the phase change layer is easy to produce micro cracks in the bending process, and the bending strength of 3 Y-TZP ceramics is destroyed.(c)Effect of low temperature aging on two aspects of flexural strength:The volume expansion and surface compressive stress of the phase transformation can reduce the crack and the hole of the 3Y-TZP ceramic surface when the content of monoclinic phase is low, and improve the bending strength of 3Y-TZP ceramic;When low temperature aging produces a larger amount of surface monoclinic phase,due to the existence of a large number of micro defects in the phase change layer, grain boundary strength was lower than that of the non aged region, the phase change layer is dominated by intergranular fracture, and it has a destructive effect to the flexural strength of 3Y-TZP ceramics.Zirconia is more and more used in the clinical treatment as the substrate material.Because of its excellent biological safety, can be comparable with the strength of the metal and excellent aesthetic simulation results get the favor of the majority of patients and physicians. But there are some problems in the current machinable zirconia materials, such as sintering process cumbersome and machinability of the material is poor.The most prominent is the sintering shrinkage rate is bigger than others, and sintering crystallization process requires special high temperature sintering furnace, and the temperature control program is complex,when sintering longbridge unit more than 4 are easily deformed,which leads to lower precision and even clinical failure.This study is based on the uniform inclusion of nano alumina and boron nitride particles in the sub micron 3Y-TZP particles, Phase analysis and mechanical property test are used to this new composite ceramic in order to obtain the best material ratio with high strength and toughness. The shrinkage and irregular shape changes after sintering were avoided. So as to improve the precision of the restorations, simplify the production process, shorten the treatment cycle, so that it can be better applied to the work of dental prosthesis. |
PDF Full Text Request