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.