The polymerization shrinkage of composite resins may affect negatively the clinical outcome of the restoration. Extensive research has been carried out to develop new formulations of composite resins in order to provide good handling characteristics and some dimensional stability during polymerization. The purpose of this study was to analyze, in vitro, the magnitude of the volumetric polymerization shrinkage of 7 contemporary composite resins (Definite, Suprafill, SureFil, Filtek Z250, Fill Magic, Alert, and Solitaire) to determine whether there are differences among these materials. The tests were conducted with precision of 0.1 mg. The volumetric shrinkage was measured by hydrostatic weighing before and after polymerization and calculated by known mathematical equations. One-way ANOVA (<FONT FACE=Symbol>a</font > or = 0.05) was used to determine statistically significant differences in volumetric shrinkage among the tested composite resins. Suprafill (1.87±0.01) and Definite (1.89±0.01) shrank significantly less than the other composite resins. SureFil (2.01±0.06), Filtek Z250 (1.99±0.03), and Fill Magic (2.02±0.02) presented intermediate levels of polymerization shrinkage. Alert and Solitaire presented the highest degree of polymerization shrinkage. Knowing the polymerization shrinkage rates of the commercially available composite resins, the dentist would be able to choose between using composite resins with lower polymerization shrinkage rates or adopting technical or operational procedures to minimize the adverse effects deriving from resin contraction during light-activation.

Este estudo avaliou o efeito de diferentes métodos de acabamento e polimento sobre a rugosidade superficial de resinas compostas. Dois sistemas para polimento, e sete marcas comerciais de resinas compostas foram avaliados e comparados. Um total de 126 espécimes confeccionados em uma matriz de aço inoxidável foram divididos em três grupos. No grupo 1, seis amostras de cada material foram polimerizadas sob a pressão de uma tira de poliéster. Os demais espécimes receberam acabamento seqüencial de pontas diamantadas finas e extrafinas. Após o acabamento, as amostras do grupo 3, foram polidas com os discos de óxido de alumínio, de abrasividades média, fina e extra-fina e jatos de água intermitentes. Os resultados mostraram não haver diferença estatisticamente significante nos valores médios de rugosidade de superfície (Ra, µm) entre o grupo 1 (tira de poliéster) e o grupo 2 submetido ao acabamento com as pontas diamantadas e o grupo 3 com pontas diamantadas e polidos com discos de óxido de alumínio (p>0.05). A análise estatística revelou diferenças de níveis de rugosidade entre as superfícies resinosas quando receberam somente o acabamento com as pontas diamantadas. As tiras de poliéster, como era esperado, produziram as superfícies mais lisas em todas as resinas, embora os resultados não têm estatisticamente diferenças daqueles encontrados nas superfícies polidas com os discos de óxido de alumínio.

This study evaluated the effect of surface finishing methods on the average surface roughness of resin composites. Seven composites and two polishing systems were used. One hundred and twenty-six conical specimens of each material were prepared in stainless steel molds against a polyester strip. Forty-two of them remained intact and were used as controls. Each half of the remaining samples was polished with either diamond burs or diamond burs + aluminum oxide discs. The results showed no statistical difference in average surface roughness (Ra, µm) between the polyester strip and aluminum oxide discs (p>0.05). However, finishing with diamond burs showed a statistically higher average roughness for all composites (p<0.05). Statistical differences were detected among materials (p<0.05) in the use of diamond burs.

Trinta e sete amalgamadores considerados novos e usados, de cinco marcas comerciais, foram avaliados comparando-os em relação à freqüência de oscilação e à sua possível influência no "creep" do amálgama. Não existiu diferença significante para o número de revoluções por minuto. O pistilo permitiu uma trituração mais eficiente e rápida, ocasionou o aumento da temperatura de trituração e proporcionou um amálgama de menor "creep".

Thirty seven used and new amalgamators of five different commercial brands were compared for the frequency of oscillation they produce in order to verify a possible relationship between frequency and creep of the amalgam. No significant differences in frequency were observed; yet the use of the pestle alone allowed a quicker, more efficient trituration under increased temperature, and it produced an amalgam with lower creep.