Evaluation of the Marginal Fit of Three Margin Designs of Resin Composite Crowns Using CAD/CAM

Objectives: The purpose of this study was to examine the ability of the newly introduced resin composite blocks for CAD/CAM to reproduce three different crown finish lines, namely a shoulder, a 45 degree bevel and a chamfer. Materials and Methods: Three duplicate models of a lower phantom molar tooth were fabricated and prepared for a full-coverage crown with a marginal finish of a shoulder, a 45 degree bevel or a chamfer. Each model was then duplicated ten times (n=10) and all duplicates were scanned in the CEREC Scan^TM (Sirona). A crown restoration was designed using the CEREC 3^TM software. The material used for the crowns was Paradigm MZ100^TM(3M/ESPE). Each crown was cemented onto its original model using a silicone impression material (Aquasil^TM LV, Dentsply) under a standardised loading condition (40N for 3 min). The crowns, with the set silicone polymer film still attached, were removed from the models. The silicone polymer film was detached from the crown using a contrasting impression material (Aquasil^TM putty, Dentsply). Buccal, lingual, mesial and distal sections of the silicone impressions were produced and the marginal gaps of the crowns were measured using a traveling microscope at x30 magnification. Results: The crowns did not show any signs of marginal chipping, irrespective of the margin design. The average marginal gap for each group was: Bevel Group 105±40mm, Shoulder Group 91±31mm and Chamfer Group 94±39 mm. One-way Anova showed that the results were not significantly different. Conclusions: The marginal fit of Paradigm MZ100^TMresin composite crowns, whether with a shoulder, a chamfer or a bevel, is within the range of clinical acceptance when using the CEREC Scan^TM. Acknowledgement: We are grateful to 3M/ESPE for the donation of the resin composite blocks.