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Efeitos do zircónio no desgaste em dentes naturais
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Advisor(s)
Abstract(s)
O zircónio típico e, que serve de referência como material cerâmico em dentisteria, é o 3Y-TZP, pelas excelentes propriedades mecânicas. No entanto revela-se relativamente opaco em relação a outras cerâmicas, como o caso do dissilicato de lítio. Zircónio mais translucido tem surgido no mercado, com mais conteúdo em ítrio, que resulta numa estabilização parcial ou total da fase cúbica, mas com piores propriedades mecânicas. É o caso de 4Y-TZP e 5Y-TZP que, respetivamente e numa abordagem teórica, terão 4 e 5 mol%. O envelhecimento do zircónio caracteriza-se por ser uma transformação da fase tetragonal para monolítica, quando sujeito a temperatura moderada e ambiente húmido e que conduz à redução da resistência, aumento da rugosidade e consequente aumento da atrição. O zircónio 3Y-TZP, por conter mais fase tetragonal é mais suscetível ao processo de envelhecimento. Das várias formas de tratamento de superfície, como sejam o polimento, o acabamento com brocas, o jateamento com alumina e o tratamento térmico não se revelaram efetivos na prevenção deste tipo de envelhecimento. Das formas de acabamento, a que se manifesta como a mais vantajosa é o polimento, que segundo os estudos provoca menos desgaste em dentes oponentes. O zircónio 4Y e 5Y- TZP, considerados de 3ª geração, se por um lado apresentam uma considerável diminuição das suas propriedades mecânicas, por outro lado resultaram em melhorias consideráveis na translucidez. Apesar de não conseguirem níveis de translucidez equivalentes ao dissilicato de lítio, como as suas propriedades mecânicas são melhores, conseguem-se confecionar restaurações capazes de suportar o stress em função com menor espessura, sendo por essa razão mais conservadores em termos de preparação dentária e apresentando-se como uma boa alternativa a restaurações em dissilicato de lítio.
The typical zirconium, which is a reference in ceramic materials in dentistry, is 3Y-TZP, due to its excellent mechanical properties. However, it is relatively opaque in contrast to other ceramics, such as the case of lithium disilicate. More translucent zirconia has appeared on the market, with more yttrium content, which results in partial or total stabilization of the cubic phase, but with worse mechanical properties. This is the case of 4Y-TZP and 5Y-TZP, which, respectively and in a theoretical approach, owes 4 and 5 mol%. The LTD of zirconium stands out for being a transformation of the tetragonal to monolithic phase, when subjected to moderate temperature and humid environment, which leads to a reduction in strength, an increase in roughness and a consequent increase in attrition. The 3Y-TZP, because it contains more tetragonal phase, is more susceptible to the aging process. Of the various forms of surface treatment, such as polishing, ground, sandblasting and heat treatment have not proved effective in preventing this type of aging. Of the finishing forms, the one that manifests itself as the most advantageous is polishing, which according to studies causes less wear on opposing teeth. Zirconium 4Y and 5Y-TZP, considered to be 3rd generation, if on the one hand has a decrease in its mechanical properties, on the other hand have resulted in considerable improvements in translucency. Although they are not able to achieve translucency of lithium disilicate, as their mechanical properties are better, it is possible to make restorations for function and stress with less thickness, and for this reason they are more conservative in terms of dental preparation and presents as a alternative to lithium disilicate.
The typical zirconium, which is a reference in ceramic materials in dentistry, is 3Y-TZP, due to its excellent mechanical properties. However, it is relatively opaque in contrast to other ceramics, such as the case of lithium disilicate. More translucent zirconia has appeared on the market, with more yttrium content, which results in partial or total stabilization of the cubic phase, but with worse mechanical properties. This is the case of 4Y-TZP and 5Y-TZP, which, respectively and in a theoretical approach, owes 4 and 5 mol%. The LTD of zirconium stands out for being a transformation of the tetragonal to monolithic phase, when subjected to moderate temperature and humid environment, which leads to a reduction in strength, an increase in roughness and a consequent increase in attrition. The 3Y-TZP, because it contains more tetragonal phase, is more susceptible to the aging process. Of the various forms of surface treatment, such as polishing, ground, sandblasting and heat treatment have not proved effective in preventing this type of aging. Of the finishing forms, the one that manifests itself as the most advantageous is polishing, which according to studies causes less wear on opposing teeth. Zirconium 4Y and 5Y-TZP, considered to be 3rd generation, if on the one hand has a decrease in its mechanical properties, on the other hand have resulted in considerable improvements in translucency. Although they are not able to achieve translucency of lithium disilicate, as their mechanical properties are better, it is possible to make restorations for function and stress with less thickness, and for this reason they are more conservative in terms of dental preparation and presents as a alternative to lithium disilicate.
Description
Dissertação para obtenção do grau de Mestre no Instituto Universitário Egas Moniz
Keywords
Zircónio Monolítico Contorno total Degradação baixa temperatura