published_or_final_version / Dentistry / Master / Master of Dental Surgery

published_or_final_version / Dentistry / Master / Master of Dental Surgery

Submitted in full compliance with the requirements for the Master of Health Science Degree: Dental Technology, Durban University of Technology, Durban, South Africa, 2017. / Background Shade matching is a challenging aspect of aesthetic dentistry (Vichi et al., 2011). For a long time, aesthetically pleasing prostheses have been achieved using the porcelain-fused-to-metal crown whereby the metal is masked with an opaque layer and then consecutive layers of veneering ceramic are built up (McLean, 1979). The growing popularity of all-ceramic restorations has created a need for an understanding of its colour characteristics in preference to porcelain fused to metal restorations. The study aims to assist dental technicians in making a more informed decision when choosing an all-ceramic system in terms of colour stability. Objectives The objectives were to identify colour changes of the zirconia after each firing cycle and defining if there are any microstructural changes in the zirconia cores after subsequent firing. Methods This is a quantitative study with a sample size of eighteen which was used for each experimental group. Green state zirconia blocks from Cercon (Dentsply DeguDent, USA), Lava (3M ESPE,USA), and Zirkon Zahn (Zirkonzahn Gmbh, Bruneck, Italy) were trimmed, finished and sintered to a final thickness of 0.5mm according to the manufacturers’ instructions. Each sample group was obtained directly from the manufacturer. In each group, nine specimens were shaded and nine were unshaded. The colour of each specimen was recorded before being exposed to firing cycles. This data formed the control group. All specimens were subjected to three firings and spectrophotometer reading. After each firing, SEM analysis was done after one and three firings. There was a total of thirty six specimens x three firings; n = 108. The raw data for the statistical analysis was obtained from the spectrophotometer readings recorded after the firings (n=108). The data of the study was analyzed using the SPSS version 22.0. The data were compared among the three groups using Pearsons chi square tests, where the data of the firings were measured as a binary or nominal variable, and using t-tests where a measured normally distributed variable was compared. The general linear model (GLM) looked at combinations of the variables and their effects on the dependant variable. The Multivariate tests table indicates the actual result of the one-way MANOVA. Results The Cercon results for both the control and experimental groups reveal the same result patterns and was maintained before and after firing. Lava also revealed the same results before and after firing, however, the cores in the control group differed in colour. The Zirkon Zahn system proved to be the least stable in colour. Conclusion This study supports the hypothesis that colour differences would occur relative to the number of firings for shaded zirconia. It can be concluded that Cercon displayed the most stable results in terms of colour. The acumen gained in this study may better assist dental technicians in their selection of an all-ceramic zirconia system. / M

CAPES / A técnica de clareamento dentário tem sido uma das modalidades estéticas mais utilizadas na atualidade, em prol da busca do "sorriso branco". No entanto, a escolha da técnica, agente clareador e freqüência de utilização do mesmo têm de ser feitas de forma adequada para evitar danos ou alterações na estrutura dental. Este trabalho teve por objetivo avaliar os efeitos dos clareadores na estrutura dental. Foram selecionados 90 dentes de humanos, para preparo de 6 grupos de 15 dentes cada, que foram transformados em 90 corpos-de-prova para os testes. As amostras foram submetidas a testes de microdureza Vickers e análise de impedância, ante e após cada uma das 3 sessões de clareamento realizadas. Foram utilizados 6 tipos diferentes de clareadores disponíveis comercialmente para serem aplicados em consultório ou administrados pelo paciente (caseiro). Os resultados obtidos mostram que, se for considerado os valores médios das microdurezas ante e após a última sessão de clareamento, nas amostras 1 a 60, que foram submetidas aos clareadores utilizados em consultório, foi observada uma diminuição de aproximadamente 2 % na microdureza. Já nas amostras 61 a 90, que foram submetidas aos clareadores caseiros, a diminuição na microdureza foi de aproximadamente 24%. O dados foram analisado-se o teste One-way ANOVA e os resultados mostraram-se significativos para os testes de microdureza realizados com as amostras nas quais foram aplicados os clareadores do tipo caseiro. Os resultados obtidos no trabalho permitem concluir que o uso indiscriminado de clareadores pode provocar danos à estrutura dental. / Techniques for teeth whitening have been largely used as aesthetic procedures. However, the choice of the bleaching agent, the method and the frequency that it will be applied to the patient has to be done properly in order to avoid damage or changes to the tooth structure. This study aimed to evaluate the effects of bleaching techniques on tooth structure. It was selected 90 samples of human teeth to be evaluated considering the Vickers microhardness and impedance analysis, before and after the use of bleaching techniques. The samples were divided into 6 groups of 15 teeth each and 6 different types of commercially available bleaches to be applied at dental offices or at home were used in the tests. The results have shown a decreasing of approximately 24 % in the microhardness after the use of bleaching agents at home (samples 61-90), and only 2 % for those used at dental offices (samples 1-60). The data were analysed using the One-Way ANOVA and the statistical analysis for the Vickers microhardness after the use of bleaching agents at home have shown significant results. Thus, it was possible to conclude that the indiscriminate use of bleaching agents can damage the tooth structure. / 5000