Comparison of luting cements for minimally retentive crown preparations

Objective: The purpose of this study was to compare the retentive strengths of resin, glass-ionomer, and zinc phosphate cements under adverse conditions. Method and materials: Thirty extracted teeth were mounted and prepared in their long axis. The axial wall height was 3 mm and the convergence angle was 28 degrees. These conditions increased the role of the cement and decreased the role of the preparation in providing retention of the casting. The axial surface area was determined. Copings were fabricated with a ring aligned in the long axis to facilitate removal of the crown. They were cemented with a resin cement, a glass-ionomer cement, or a zinc phosphate cement. A block randomization scheme was used to assign cements so that the mean surface areas of the teeth were equivalent in all groups. The copings were loaded in tension, and the amount of force required to remove the coping was recorded. The stress required to remove the coping was calculated. Results: The mean stress required to remove the copings was 9.4, 5.0, and 3.1 MPa for the resin, glass-ionomer, and zinc phosphate cements, respectively. Conclusion: The resin cement group was significantly stronger than both the glass-ionomer cement and the zinc phosphate cement groups. The glass-ionomer cement was significantly stronger than the zinc phosphate cement.