The impact of thickness differences to the breaking resistance of zirconia based infrastructure material

Ceramic restorations, due to their superb mechanical features and supported by metal infrastructure, are successfully used in both the posterior tooth failures as well es in the aesthetic restorations in the anterior region. However, it has disadvantages like reflection of the metal?s color on the gingiva, its formation of allergy, its corrosion and not to have light permeability in the anterior region. The increase in aesthetical concerns and the technological developments has creaated a usage area for different restorative systems in the tooth color that provides superb mechanical features made possible by the bio-comformable, metal infrastructure as an alternative to the metal-supported ceramic restoration (1, 2, 3). Researchers have tried to strenghten the infrastructure of the restoration by using different materials. With various techniques such as distribution of alumina with controlled crystallization, glass infiltration, usage of leucite or lithium disilicate cyrstalls ceramical infrastructures began to be strenghtened (1, 4, 5, 6, 7). However, with the ceramics produced by using these methods there was a limited success in fixed restorations only in the single kron in the frontal region and 3 (three) members (8). Due to increased need for aesthetics today full ceramic restorations in the posterior regions are also demanded by the patients. In the production of full ceramic restorations different system and materials are used. Full ceramic restorations are either formed of a single ceramic layer or of twolevel (a strong infrastructure ceramic that supports breakable veneer ceramic)systems (8, 9). Full ceramic materials have been alternatives to the metal-ceramic restorations due to their aestethical features close to the natural tooth strcuture, their chemical stability and bioconformities. But, since they exhibit low resistivity due to their breakability and against tensile stress, this limits the clinical applications of these materials. Till recently the usage of the entire ceramic systems was limited with the frontal part?s teeth, today, with the help of developed dental ceramics, it was possible to have application in the posterior teeth as well. When compared with the other ceramic systems zirconia has increased the reliability of full ceramic systems since it has a high v mechanical performance, resistivity, tensile resistance, chemical and dimensional stability(9, 10, 11, 12). Zirconia is the most appropriate ceramic that can resist against the high tensile stress that is formed especially at the multi-member bridges (13, 14, 15). Zirconia infrastructure even makes it possible to make full ceramic restoration in posterior partial dentation facts due to its superb mechanical features, and thus it has to be veneered with a feldispathic-structured ceramic due to its opaque appearance (3, 9, 16). Thus aesthetic restorations that are both resistive and also have translucency that looks like the natural tooth can be made. However, even if the translucency amount of the restorations with zirconia infrastructure is more when compared with the metal ceramic infrastructure, it is less when compared with the other full ceramic restoration samples. In the researches made; it is seen that in the zirconia-based infrastructural restorations infrastructure material thickness has affected the translucency amount a lot. It is determined that the thin usage of infrastucture material has led to an increase in the translucency amount .(17) Many researches were conducted with regard to the thickness amount of feldispathic porcelain that its processed on the zirconia infrastructure alternative. However, no study could be found that seeked an answer to the question of how the thinner usage of infrastructure material affected the bending resistivity. When the zirconia infrastructure material is used thin translucency increases, but how will it be affected from the decrease in bending resistivity. In the thesis study that is planned the aim is to determine the bending resistivity that the zirconia infrastructure material has at diffrent thicknesses. Key words : Dental ceramics, zirconia, thicknees, flexual strength.