Effects of proximal grooves and abutment height on the resistance of resin-cemented crowns in teeth with inadequate resistance: An in vitro study.

BACKGROUND The resistance form is a key factor for a successful crown fabrication. This in vitro study evaluates the effects of proximal grooves and abutment height on the resistance of single cast crowns in molars with inadequate resistance. METHODS Sixty extracted human molars were prepared to possess 20° of total occlusal convergence for single crown fabrication. All of the prepared teeth were divided into six groups and prepared according to three axial heights (2, 3, and 4 mm) with or without preparing a pair of proximal grooves. Alloy metal copings of 5% titanium were casted and cemented. A self-adhesive modified-resin cement was used for cementation. A lateral dislodgement test was performed with an increasing external force applied at a 45° angulation on a universal testing machine. The force required to dislodge the crown from the tooth or to break the core was recorded. RESULTS Proximal grooves increased the dislodgement resistance in groups with an abutment height of 4 mm, whereas adding grooves made no significant differences in resistance in groups with abutment heights of 2 and 3 mm. The 2 mm groups exhibited worse performance than the other groups, whether they had proximal grooves or not. CONCLUSION An abutment height of 3 mm provided adequate resistance for single cast crowns when self-adhesive modified-resin cement was used. Preparing a pair of proximal grooves on abutments shorter than 4 mm had no significant influence on the resistance.