The effect of tooth preparation design on the breaking strength of Dicor crowns: 2.

Six maxillary first premolar tooth preparation designs for all-ceramic restorations were tested for their effect on the strength of Dicor crowns. Ten crowns were fabricated for each preparation design, and the breaking strengths were measured. Three finish line designs (1.2-mm shoulder with sharp axiogingival line angle, 1.2-mm chamfer, and 0.8-mm chamfer) and two total occlusal convergence angles (5 degrees and 15 degrees) were tested. All preparations possessed 2.0 mm of occlusal reduction. The average breaking strengths of the 10 Dicor crowns were compared to those of 10 metal ceramic control restorations. The three groups of restorations fabricated for preparations with 5 degrees of occlusal convergence were significantly weaker than those made for preparations with 15 degrees of convergence. The metal ceramic restorations were significantly stronger (247.45 kg) than the strongest Dicor crowns (56.2 kg).