Effect of Repeated Heat-Pressing on Marginal and Internal Fit of Lithium Disilicate Glass Ceramic Crowns after Thermo-Mechanical Fatigue

Abstract

Purpose: To evaluate the effect of repeated heat-pressing on marginal and internal fit of lithium disilicate glass ceramic crowns. Materials and Methods: A freshly extracted caries free human maxillary 1st premolar was prepared according to standardized preparation for all-ceramic crown restoration. The preparation was duplicated to produce thirty epoxy resin dies. The resin dies were divided into three groups (n=10) according to the number of heat-pressings of IPS e.max Press (Shade A2, LT) used for crowns construction. Group 1: Crowns constructed from freshly pressed ingots, Group 2: Crowns constructed from leftover repressed buttons for 1st time, and Group 3: Crowns constructed from leftover repressed buttons for 2nd time. The constructed crowns were cemented to their corresponding resin dies using adhesive resin cement, then samples were subjected to the thermo-mechanical fatigue with a ROBOTA chewing simulator. Each cemented ceramic crown was vertically sectioned bucco-lingually into 2 sections. Marginal, axial, and occlusal gaps were measured at seven defined points on each section using digital microscope. Data were tabulated and statistically analyzed using One-way ANOVA and Pearson’s correlation tests. The significance level was set at P<0.05. Results: The largest marginal and internal gap values were recorded in Group 1, while the lowest marginal and internal gap values were recorded in Group 3. Statistical analysis revealed that there were no significant differences in marginal and internal gaps between the tested groups (P<0.05). Conclusions: Repressing and thermomechanical fatigue have no significant effect on marginal and internal fit of IPS e.max Press crowns.