Materiais para modelagem: avaliação dos tempos de presa, das resistências à tração e compressão e das partículas (MEV)
Abstract
Este trabalho comparou os tempos de presa inicial e final e as resistências à tração diametral e compressão de gessos utilizados em odontologia (natural, sintético e reforçado com resina). Os ensaios mecânicos foram realizados nos tempos de 1h e 24h após a manipulação, sendo os resultados submetidos à análise estatística (Anova two way, Tuckey P < 0,05). As partículas foram analisadas em microscópio eletrônico de varredura, procurando-se estabelecer correlações com as propriedades avaliadas. Observou-se que o gesso natural possui propriedades mecânicas superiores e maior tempo de presa que os demais. As partículas do mesmo material se apresentaram maiores que as dos outros gessos, sendo as do gesso reforçado com resina as menores de todas. Conclui-se que há relação direta entre o tamanho das partículas e as propriedades avaliadas, como pode ser observado, por exemplo, para o gesso natural (maiores partículas e maiores valores nos testes realizados).
UNITERMOS: gesso; modelos; resistência à compressão; resistência a tração; microscopia eletrônica de varredura.
SUMMARY
This study compared the initial and final setting times and the diametral tensile and compressive strengths of dental plasters (natural, synthetic and resin-reinforced). The mechanical assays took place 1h and 24h after mixing, and the results were submitted to statistical analysis (Anova two way – Tukey with a level of significance of 95%). The particles were analyzed by scanning electron microscopy, aiming to establish correlations with the assessed properties. The natural plaster showed superior mechanical properties and a higher setting time than the others. The particles and crystals of the natural plaster were larger than that of the other plasters, and the resin-reinforced plaster had the smallest of them all. We conclude there is a straight correlation between particle size and the assessed properties, as we observed, for instance, for the natural plaster (larger particles and greater values on the tests).
UNITERMS: Dental stone, model, compressive strength, tensile strength, scanning electron microscopy.
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