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O objetivo do presente estudo foi avaliar o desenvolvimento das tensoes de polimerizacao de um composito resinoso restaurador ao longo das primeiras 24 horas apos a fotoativacao, segundo dois metodos de analise da propagacao de trincas. A influencia do armazenamento em agua sobre a magnitude das tensoes tambem foi avaliada. O grau de conversao (GC) e o modulo de elasticidade (E) do composito foram determinados nos diferentes tempos de observacao. As hipoteses nulas do trabalho foram: 1) tensao de polimerizacao, GC e E nao variam de forma significativa ao longo do periodo de observacao; 2) os dois metodos de analise de propagacao de trincas fornecem resultados semelhantes; 3) os valores de tensao nao sao influenciados pelo meio de armazenamento. Foram confeccionados discos de vidro de soda-cal com 2 mm de espessura, diâmetro externo de 12 mm, com perfuracao central de 4 mm de diâmetro. Os discos foram aleatorizados em tres grupos. Em um deles, os discos foram restaurados (Charisma Diamond, Heraeus Kulzer) e, apos os tempos de 10 min, 1, 2, 4, 8 ou 24 horas (n=10), os especimes receberam quatro indentacoes Vickers, (9,8N por 20s) a 500m da margem da cavidade. O segundo grupo passou pelo mesmo processo, porem os discos ficaram armazenados em agua antes de serem indentados. Em seguida, o comprimento das trincas e a diagonal da indentacao foram mensurados em microscopio optico. A tensao residual no vidro foi calculada de acordo com a norma 4-01 (The Society of Materials Science, JSMS, Japao). No terceiro grupo, os discos foram indentados e armazenados em dissecador por 24h antes de serem restaurados. As trincas foram medidas antes e apos(AU) a restauracao, nos mesmos tempos descritos acima, e a tensao calculada de acordo com a formula descrita por Yamamoto et al. (Dent Mater, 2009). O GC foi determinado por espectroscopia no infra-vermelho proximo (n=3). O E foi obtido atraves do teste de dobramento em tres pontos (n=10). Os dados foram submetidos a ANOVA/Tukey (=0,05) e analise de regressao. A tensao de polimerizacao, assim como o GC e o E tiveram seus valores aumentados ao longo do tempo. O GC aumentou 28% entre 10 minutos e 24 horas, para o E houve um aumento de 1,7 GPa para 6,3 GPa entre 10 minutos e 24 horas. A tensao de polimerizacao aumentou 40% entre 10min e 24h para a norma 4-01 e 51% para o metodo do Yamamoto et al. O meio de armazenamento foi estatisticamente significativo ate o tempo de 4 horas. Portanto, a primeira hipotese foi rejeitada. A segunda e a terceira hipotese podem ser apenas parcialmente rejeitadas.(AU) The objective of this study was to evaluate composite resin restoration polymerization stress development over the first 24 hours after polymerization, according to two methods of analysis of crack propagation. The influence of water storage on the magnitude of the stresses was also evaluated. The degree of conversion (DC) and modulus of elasticity (E) of the composite were determined at various time points. The null hypotheses of this study were: 1) The polymerization stress, DC and E do not change significant throughout the observation period, 2) the two methods of analysis of crack propagation provide similar results, 3) the stress values are not influenced by storage medium. Disks were made of soda-lime glass with 2 mm thickness, 12 mm in outside diameter with central bore of 4 mm in diameter. The perforations were treated with hydrofluoric acid and silane. The discs were randomized into three groups. In one of them, the discs were restored (Charisma Diamond, Heraeus Kulzer), and, the times after 10 min, 1, 2, 4, 8 or 24 hours (n = 10), the specimens received four Vickers indentations (9.8 N for 20 s) at 500m cavity margin. The second group went through the same process, but the discs were stored in water prior to being indented. Then, the length diagonal of the indentation and crack was measured in an optical microscope. The residual stress in the glass was calculated according to standard 4-01 (The Society of Materials Science, JSMS, Japan). The third group of discs were treated similarly, indented and(AU) stored in a desiccator for 24 hours before being restored. The cracks were measured before and after the restoration following the same time, and the stress calculated according to the formula described by Yamamoto et al. (Dent Mater, 2009). The DC was determined by near-infrared spectroscopy (n = 3). The E was obtained through the bend test conducted at three-points. Data were subjected by ANOVA / Tukey test ( = 0.05) and regression analysis. The polymerization stress, as well as DC and E values were increased over time. GC increased 28% between 10 minutes and 24 hours, and for an increase of 1.7 GPa to 6.3 GPa between 10 minutes and 24 hours. The polymerization stress increased 40% between 10 min and 24 hours to the standard 4.1 and 51% for the method of Yamamoto et al. The storage medium was statistically significant at the time of 4 hours. Thus, the first hypothesis was rejected. The second and third hypothesis may only be partially rejected.(AU)

Desenvolvimento de tensões de polimerização determinado através do método da propagação de trincas