In-Vitro Evaluation of the Spacer Setting and Type of Cement Effect on Margin Fit and Internal Adaptation of CAD/CAM Crowns

Abstract

Background: The longevity of restorations is influenced by multiple factors, including the internal adaptation and marginal fit. The cement must escape from the space between the tooth preparation and the crown in order to completely seat the restoration on the preparation. The challenge of expressing excess cement from the occlusal aspect of the preparation during cementation may lead to a larger marginal gap which may result in cement dissolution, caries, and plaque accumulation. Objective: The objective of the study is to evaluate the margin fit and internal adaptation of zirconia crowns fabricated with a chairside CAD/CAM workflow with different amounts of internal relief and different types of cement. Material & Methods: A master zirconia crown preparation was made on a typodont tooth and scanned to print 72 models. The models were divided at random between the test groups. Each printed model was scanned with a CEREC PrimeScan (software verion 5.2.9) to design a zirconia crown for each model. Models were differentiated by groups using different spacer settings that were chosen in the design phase prior to crown milling (150 μm, 120 μm, 90 μm). Each crown was cemented to its respective model with either self-adhesive resin cement (RC) or a resin modified glass ionomer cement (RMGIC). Each cemented crown was sectioned with a diamond saw and examined under a measuring microscope to measure the cement space was measured under the microscope from the marginal, axial, and occlusal wall. Results: Both types of cements had a smaller margin gap at a 120 μm spacer setting compared to 150 μm and 90 μm. Margins were significantly different between RC and RMGIC with all chosen spacer setting. Conclusions: The 120 μm spacer setting resulted in the smallest marginal gap for both RC and RMGIC. All the chosen spacer settings (90 μm, 120 μm, and the 150 μm) resulted in marginal gaps within the clinically acceptable marginal discrepancy (less than 120 μm) with both types of cement (RC and RMGIC). Modifying the spacer setting when using either RC and RMGIC is not indicated relative to the resulting margin fit.