Relationship of margin design for fiber-reinforced composite crowns to compressive fracture resistance.

摘要

PURPOSE: Fiber-reinforced composite restorations provide excellent esthetics; however, little is known regarding the influence of margin design on marginal fit and fracture resistance for this type of crown. This study evaluated the effect of variations in tooth-preparation design on the marginal fit and compressive fracture resistance of fiber-reinforced composite crowns. MATERIALS AND METHODS: 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 fit was stereoscopically evaluated by measuring the distances between each of the four pairs of indentations on the crowns and on the dies. The specimens were then subjected to a compressive fracture-loading test using a universal testing machine. The data were analyzed with one-way analysis of variance (ANOVA) followed by Ryan-Einot-Gabriel-Welsch multiple-range test (alpha = 0.05). RESULTS: Analysis of marginal fit and fracture resistance disclosed a statistically significant difference for tooth-preparation design (p < 0.001). The marginal adaptation of preparations with the 0.5-mm light chamfer (66.2 mum) and 1.0-mm deep chamfer (69.7 mum) was significantly better than preparations with a shoulder finish line (92.8 mum) (p < 0.001). 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) was significantly greater than those of the preparations with the 1.0-mm shoulder (13.7 MPa) (p < 0.001). CONCLUSIONS: Marginal fit of fiber-reinforced 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 margin specimens was greater than that of the shoulder margin specimens.