Effect of Two Self-Adhesive Cements on Marginal Adaptation and Strength of Esthetic Ceramic CAD/CAM Molar Crowns

Purpose: This study evaluated the effects of adhesive cements on marginal adaptation and fracture resistance of ceramic molar crowns. Materials and Methods: Seventy-five extracted maxillary molars were selected. The occlusal morphology of 15 molars (control) was scanned and transferred to the crowns in the test groups by CAD/CAM. Sixty molars received full-coverage crown preparations with 6-degree axial taper, 1.0-mm shoulder, and 2.0-mm occlusal reduction. They were assigned to four groups, and pulpal pressure was simulated. The 15 crowns in each test group were seated with resin-based self-adhesive cements, Rely-X (RX) and Multilink (MS), one multistep bonded adhesive luting composite resin, Variolink (VL), and glass-ionomer cement, Ketac Cem (KC). Test and control molars were subjected to thermal and mechanical fatigue stress (TMS: 12,000 x 5 degrees C to 50 degrees C; 2.4 million x 49 N) for 18 days in a masticator. Marginal adaptation ["continuous margin%" (CM%)] of the crowns was determined by scanning electron microscopy (200x). Finally, molars were occlusally loaded until fracture in a testing machine, and fracture load (N) was recorded. Marginal adaptation and strength data were statistically analyzed. Results: TMS significantly (p < 0.001) reduced CM% in all groups. After TMS, CM% at the cement-dentin interface was significantly (p < 0.001) higher for RX than for all other cements. At the crown-cement interface both self-adhesive cements MS and RX had significantly better CM% than VL (p < 0.05) and KC (p < 0.001). Fracture resistance of natural untreated molars was significantly (p < 0.001) higher than that of experimental crowns. Fracture resistance of RX cemented crowns was significantly (p < 0.05) higher than that of other crowns. Occlusal morphology significantly influenced fracture resistance (p < 0.05). Conclusions: Self-adhesive cement RX offers a valid alternative to multistep resin-based luting composite with respect to marginal adaptation to dentin and fracture resistance. The latter is also influenced by occlusal morphology, necessitating careful monitoring of occlusal contacts.