Methods: One clinician placed 100 CAD/CAM lithium disilicate crowns. The preparation had shoulder margins with a rounded internal line angle and a minimum of 1.5 mm occlusal and 1.2 mm axial reduction. A CEREC 3 unit (Sirona Dental) was used to fabricate the monolithic crowns. After milling the crowns were fired under vacuum to complete the crystallization process; crowns were etched with 4.9% HF acid and silanated. The first 62 crowns were cemented with either a self-etching bonding agent and resin cement (ML = MultiLink Automix; Ivoclar Vivadent) or a self-adhesive resin cement (EC = Experimental Cement; Ivoclar Vivadent). The remaining 38 crowns were introduced later in the study and were cemented with a self-adhesive, light-cured resin cement (SP = SpeedCem; Ivoclar Vivadent).
Results: Tooth sensitivity was evaluated by report to cold stimulus. Mild sensitivity was reported on 15% of the teeth at 1 week. All sensitivity resolved by 4 weeks. The crowns were evaluated by two examiners using a modified USPHS rating. There was no difference in the gingival and plaque indexes between test and control teeth. The percent alpha scores were above 95% for color match at all recall intervals and remained at 100% for margin adaptation, caries, and crown fracture for both groups after four years. Percent alpha scores for margin discoloration at four years were 70% (ML) and 82% (EC) and remained at 100% for SP after one year. No surface chipping has been identified on any of the crowns. Two crowns cemented with EC debonded at 13 and 20 months, respectively.
Conclusions: The lithium disilicate crowns have performed well at 4 years. This study was supported by a grant from Ivoclar Vivadent.
Keywords: Adhesion, CAD/CAM, Ceramics and Clinical trials