Convergence angle, occlusal reduction, and finish line depth of full-crown preparations made by dental students

Objective: To measure the convergence angle, incisal/occlusal clearance, and finish line depth, which indicate the amount of axial reduction of full metal-ceramic crown preparations made by final-year dental students. Method and materials: A total of 157 preparations were assessed. Convergence angle and finish line depths were measured by Tool Maker Microscope, while crown height was measured using a digital caliber. Results: The mean convergence angle, faciolingually and mesiodistally, was 22.4 and 25.3 degrees, respectively. The mean for molars was statistically significantly greater than that for other teeth. The incisal/occlusal reduction ranged from 1.8 to 2.2 mm and averaged 2 mm. Buccal shoulder finish line depth averaged 0.86 mm, and mean chamfer finish line depth was 0.74 mm lingually, 0.7 mm mesially, and 0.66 mm distally. The buccal shoulder for mandibular anterior teeth was significantly smaller than for other teeth and averaged only 0.45 mm. Conclusion: The mean convergence angle was clinically acceptable. However, shoulder depth was less than the recommended depth of 1.0 to 1.5 mm for metal ceramic crowns. Incisal/occlusal reduction was clinically adequate to provide enough structural durability and color matching.