Effect of the crown preparation margin and die type on the marginal accuracy of fiber-reinforced composite crowns.

AIM The objective of this laboratory investigation was to determine the effect of different preparation designs (light chamfer, deep chamfer, and shoulder) and die-making materials (stone and epoxy) on the resulting margin misfit for fiber-reinforced composite crowns using a measuring microscope. METHODS AND MATERIALS Sixty standardized FibreKor crowns were made on stone and epoxy resin dies (n=30 each) duplicated from three metal master dies representing complete crown tooth preparation with a total convergence of 5 degrees . For each die group, three of the tooth preparation designs were established in relation to the type of finish line (n=0 each) as follows: Group A (0.5-mm light chamfer finish line); Group B (1.0-mm deep chamfer finish line); and Group C (1.0-mm shoulder finish line). Marginal accuracy was evaluated by measuring the distances between each of four pairs of indentations on the crowns and on the dies with a Nikon measuring microscope. RESULTS Analysis of seating measurements with parametric analysis of variance and Tukey's Studentized Range (HSD) disclosed a statistically significant difference for both tooth preparation design and die material (p< 0.001). However, the interaction effect was not significant (p=0.9073). The least marginal opening value was for FibreKor crowns made on epoxy resin dies with a light chamfer finish line (57 microm), but the difference was not statistically significantly different from crowns made on epoxy resin dies with a deep chamfer light chamfer finish line (61 microm). However, crowns made on epoxy resin dies with a shoulder finish line (81 microm) had significantly higher values (p< 0.05). FibreKor crowns made on stone dies with the shoulder finish line (95 microm) had statistically higher marginal opening values (p< 0.05). The least marginal opening value was for crowns made on stone dies with a light chamfer finish line (66 microm), but the difference was not statistically significantly different from crowns made on stone dies with a deep chamfer light chamfer finish line (70 microm). CONCLUSIONS Significant differences were found among the die material used for the shoulder margin design. However, there was no significant difference between light chamfer and deep chamfer margin designs for both die materials.