The Effect of Recementation on Crown Retention

Purpose: THe object of this study was to evaluate retention of complete cast crowns cemented with different luting cements and to dtermine whether recommended castings are as retentive as when initially placed. Materials and Methods: Thirty standardized Rexillium III complete crowns were made on extracted human molar teeth prepared with a modified milling machine using conventional laboratory techniques. The crowns were randomly assigned into three groups according to the luting cement used: zinc phosphate (Fleck's, Mizzy) adhesive r esin (Panavia-EX, J. Morita), and glass-ionomer (Ketac-Cem, Aplicap, ESPE-Premier Sales). Retention was evaluated by measuring the tensile force required to dislodge the crowns from tooth preparations with an Instron testing machine after thermocycling (1,500 cycles between 5 degrees C and 55 degrees C with 1-minute dwell times). Subsequently, the tooth preparations were scraped clean and polished with flour of pumice (prophylaxis paste), and the fitting surfaces of the artificial crowns were ultrasonically cleaned and air abraded using 50-um alumin um oxide powder prior to recementation. Results were subjected to two-way analysis of variance and Tukey's Studentized Range test. Results: The analysis showed the highest mean retention for cast crowns cemented with Panavia-EX cement (314 N), but teh difference was not statistically significantly different from crowns cemented with glass-ionomer cement (307 N). However, crowns cemented with zinc phosphate cement (233 N) had significantly lower values (P 0.05). Restorations recemented with zinc phosphate had significantly lower retention (190 N) than their initial cementation (P 0.05). Conclusions: Panavia-EX and glass-ionomer cements yeilded the highest initial and recementation retentive strength, with values almost 32% higher than those obtained with zinc phosphate cement during the initial cementation and 59% higher than zinc phosphate for recementation. Zinc phosphate cement exhibited significantly lower retention for the initial and second trial of cementation.