Reinforcement of Fiber-reinforced Composite Crowns with Variant Margin Designs

Fiber-reinforced composite restorations provide excellent esthetics; however, little is known regarding the influence of margin design on marginal accuracy and breaking strength for this type of crown. This study evaluated the effect of variations in tooth preparation design on the marginal accuracy and breaking strength of fiber-reinforced composite crowns. Three metal dies with a total convergence of 5-degrees and different margin designs (0.5-mm light chamfer, 1.0-mm deep chamfer, and 1.0-mm shoulder) were prepared. Sixty standardized crowns (FibreKor) were made on duplicated base metal alloy dies (n=20 for each margin design). Marginal accuracy was stereoscopically evaluated by measuring the distances between each of four pairs of indentations on the crowns and on the dies. The specimens were then compressively loaded to failure dies using a universal testing machine. The data were analyzed with 1-way ANOVA followed by Ryan-Einot-Gabriel-Welsch multiple-range test (α =.05). Analysis of marginal accuracy and breaking strength disclosed a statistically significant difference for tooth preparation design (P<.001). The marginal adaptation of preparations with the 0.5mm light chamfer (66 μm) and 1.0-mm deep chamfer (69 μm) were significantly better than preparations with a shoulder finish line (92 μm) (P<.001). The fracture strength of the preparations with the 0.5-mm light chamfer (15.8 MPa) and 1.0-mm deep chamfer (15.1 MPa) were significantly greater than those of the preparations with the 1.0-mm shoulder (13.7 MPa) (P<.001). Marginal accuracy of fiberreinforced crowns was adversely affected by tooth preparation design. The marginal gaps were greater for the shoulder margin specimens than in the light or deep chamfer margin specimens. However, the fracture strength of the chamfer margins specimen was greater than that of the shoulder margin