Finishing tooth-colored restorations in vitro: an index of surface alteration and finish-line destruction

Many studies have evaluated the surface characteristics of finishing and polishing instruments on different restorative materials using two- and three-dimensional models based on mechanical and optical techniques. However, only limited data are available regarding the problem of marginal causing detectable surface alterations such as scratches or grooves may also cause marginal damage. This study aimed to correlate the smooth-surface polishing efficacy of different instruments with their potential for destructive effects on restoration margins and enamel finish lines. An index was created that will help to evaluate future polishing instruments and select suitable ones for different clinical situations. A planar inlay system with a 100 microm wide defined gap was simulated in vitro. Pre-fabricated ceramic (n = 40) and composite blocks (n = 40) were connected to bovine enamel without luting material. After standardized pre-polishing, mean surface roughness and marginal quality were assessed using a profilometer and scanning electron microscopy (SEM). Enamel and restorative surfaces were colored, and subsequently prepared using one of 10 different finishing and polishing instruments. Four specimens per instrument and material were evaluated, resulting in eight interfaces for each test group. Surface roughness (Ra) and marginal quality (expressed as the percentage fracture-free margin) were measured and compared statistically using unpaired t-tests and two-way ANOVA, respectively. The level of significance was set at 0.05 Eight-micrometer diamond burs and 40-fluted tungsten carbide finishers produced smoother surfaces and less finishing-line destructions than the other instruments under evaluation. The index values developed will prove helpful in evaluating and selecting appropriate instruments.