A study evaluated the effect of different instruments used to finish resin composite restorations in terms of marginal integrity. The study, published by Maresca, et al in the Journal of Esthetic and Restorative Dentistry, used 75 bovine incisors that were embedded in epoxy resin; the facial enamel was ground and polished to 1,200-grit. In each incisor a standardized cavity was prepared 3 × 3 mm, 2 mm deep), and the cavities were restored using a 2-step total-etch adhesive (Single Bond, 3M ESPE) and a hybrid resin composite (Filtek Z250, 3M ESPE) in a single increment. Each restoration was mechanically polished to 1,200-grit. The specimens were divided into random groups based on finishing technique as follows: (1) positive control (1200-grit paper), (2) negative control (regular-grit diamond), (3) fine cross-cut laminated burs, (4) straight-cut laminated burs, (5) spiral-cut laminated burs, and (6) finishing diamonds. The straight-cut burs, spiral-cut burs, and finishing diamonds were tested individually as fine, extra-fine, and ultra-fine, as well as sequentially as a series. All finishing procedures utilized a high-speed, water-cooled handpiece under 0.5 N pressure for 40 seconds. Margin gaps were systematically measured using a scanning electron microscope, and data were analyzed with one-way analysis of variance and Duncan test.
The study found that the negative control specimens produced the largest gaps, and the positive control specimens produced the smallest gaps. No statistically significant difference was noted between the finishing diamonds and the positive control. The negative control exhibited significantly larger gaps when compared with the other finishing instruments. When intermediate results were observed for cross-cut, straight-cut, and spiral-cut laminated burs, it was found that fine, extra-fine and ultra-fine finishing diamonds generated smaller gaps compared with laminated burs, but the differences were not always statistically significant. The authors of the study conclude that fine, extra-fine, and ultra-fine finishing diamonds used to finish composite restorations generated better marginal integrity when compared with carbide burs and regular-grit diamonds.
(Source: Journal of Esthetic and Restorative Dentistry, 2010, Volume 22, Issue 2, page 113, published online April 2, 2010)