Effect of the number of thermocycles on microleakage of resin composite restorations Efeito do número de ciclos térmicos na microinfiltração de restaurações de resina composta

Thermocycling simulates, in vitro, thermal changes that occur in the oral cavity. The aim of this study was to evaluate the influence of the number of cycles on microleakage. Class V cavities (1.5 mm deep, 3 mm in height and 3 mm in width) were prepared in bovine teeth, restored with a Single Bond/Z250 restorative system (3M/ESPE) and then divided into five groups of ten teeth each: group 1 was not thermocycled (control group), and groups 2, 3, 4 and 5 were thermocycled 500, 1,000, 2,500 and 5,000 times, respectively (5o-55o 2oC, 15 s dwell time). The teeth were immersed in 0.5% basic fuchsin aqueous solution for 24 h, sectioned and the sections with the highest degree of microleakage were selected, scanned and the extent of dye penetration was measured by the ImageTool program. The results submitted to one-way ANOVA showed no significant differences between the groups (p > 0.05). The averages of microleakage values in millimeters were: group 1 (3.92); group 2 (3.13); group 3 (4.48); group 4 (4.33) and group 5 (3.42). Thus, it was concluded that there is no relation between the increase of the number of cycles and the increase in microleakage. DESCRIPTORS: Dental leakage; Composite resins. RESUMO: A ciclagem térmica tem por objetivo simular, in vitro, as mudanças térmicas intra-orais que ocorrem clinicamente. Sendo o seu efeito bastante discutido, o presente trabalho tem como objetivo avaliar a relação da ciclagem térmica e o número de ciclos na infiltração marginal. Foram confeccionadas cavidades classe V com dimensões de 3 mm de altura, 3 mm de largura e 1,5 mm de profundidade, em dentes bovinos. Os dentes foram restaurados com o sistema Single Bond/Z250 (3M/ESPE) e, então, divididos em 5 grupos de 10 dentes cada: grupo 1 (controle) sem ciclagem; grupos 2, 3, 4 e 5 com 500, 1.000, 2.500 e 5.000 ciclos, respectivamente (5o-55o 2oC, 15 segundos por banho). A seguir, os dentes foram seccionados e analisados em microscópio com 100 X de aumento para a escolha da fatia mais infiltrada, que foi escaneada e quantificada pelo programa ImageTool. Os dados submetidos ao teste ANOVA a um critério não apresentaram diferença significante (p > 0,05), resultando em valores médios de infiltração em milímetros: grupo 1 (3,92), grupo 2 (3,13), grupo 3 (4,48), grupo 4 (4,33) e grupo 5 (3,42). A análise dos dados permitiu concluir que não há relação entre o aumento do número de ciclos e o aumento da infiltração marginal. DESCRITORES: Infiltração dentária; Resinas compostas. 337 Restorative Dentistry *PhD Students; ***PhD, Professor – Department of Operative Dentistry, Endodontics and Dental Materials, Bauru School of Dentistry, University of São Paulo. **MSc, Health Science Institute, Paulista University, Goiânia. INTRODUCTION The development of dental materials and operative techniques over the last few years and a better understanding of dentin substrate characteristics has provided a significant decrease in the marginal microleakage of restorations. However, resin composites present polymerization shrinkage and different linear coefficients of thermal expansion from the tooth. These factors affect the clinical performance of resin composite restorations by disrupting the adhesive interface, resulting in microleakage. Additionally, in the oral cavity the restorations are subjected to both thermal and mechanical stress that also contribute to the increase of marginal microleakage. Microleakage tests are the most frequently used laboratory tests to study the mechanisms that may minimize, or eliminate, the leakage around dental restorations. Although the clinical relevance of the leakage tests does not always correlate precisely with the clinical situation, a microleakage test is a