Effect of two axial wall height preparations on the retentive properties of full crowns using three different cements

This study evaluated how different tooth preparation heights and luting cements affected the retention of metallic full crowns. Tooth preparations were made on 60 extracted maxillary premolars with occluso-cervical heights of 4.0 or 5.0 mm. The nickel chromium (NiCr) metallic crowns in each group were subdivided randomly into three groups (n = 10); the samples in each group were cemented with either a self-adhesive resin cement, a conventional resin cement, or a zinc phosphate cement. Cementation was performed by applying 5.0 kg pressure in 50% relative humidity. Specimens were stored in 100% humidity at 37 degrees C for seven days, at which time they were subjected to a vertical tensile test with a universal testing machine at 0.5 mm/min. Data (Kgf) were analyzed by two-way ANOVA and Tukey's multiple comparisons tests (alpha = 0.01). There was a significant difference in mean force in the height preparations (P < 0.001) and in tensile strength (P < 0.001) among the resin cements. Regardless of the cement used, 5.0 mm high preparations showed significantly higher mean forces than the 4.0 mm high preparations. The self-adhesive resin cement showed significantly higher mean tensile strength than the conventional resin cement; the zinc phosphate cement displayed the lowest retention values. The self-adhesive resin cement displayed retention rates twice that of the zinc phosphate cement.