Effect of Deep Margin Elevation on CAD-CAM-Fabricated Ceramic Inlays

Objectives: To evaluate the effect of deep margin elevation on structural and marginal integrity of ceramic inlays.
Methods: Forty extracted human third molars were collected and randomly separated into four groups (n=10/group). Group 1 – Enamel margin group: the gingival margin was placed 1mm supragingival to the cemento-enamel junction (CEJ); Group 2 – Cementum margin group: gingival margin was placed 2mm below the CEJ; Group 3 – Glass Ionomer (GI) margin group: gingival margin was placed 2mm below the CEJ and then margin elevated with GI to the CEJ; Group 4 – Resin-Modified Glass Ionomer (RMGI) margin group: gingival margin was placed 2mm below the CEJ and then margin elevated with RMGI to the CEJ. Standardized ceramic class II inlays were fabricated with computer aided design-computer aided manufacturing (CAD-CAM), bonded to all teeth, and ceramic proximal box heights were measured. All teeth were subjected to 10,000 cycles of thermocycling (5°C/55°C) and then underwent 1,200,000 cycles of vertical chewing simulation at 50N of force. Ceramic restorations and marginal integrity were assessed with the Hirox digital microscope. Fisher's exact test (two-tailed) with adjusted p-values (p<0.05) and logistic regression were used for statistical analysis.
Results: Cementum margin group had a significantly higher ceramic fracture rate (90%) compared to other groups (10% in Enamel and GI margin groups, p=0.007; and 0% in RMGI group, p<0.001). Logistic regression showed that with increased ceramic proximal box heights, the probability of ceramic fracture increased dramatically.
Conclusions: Clinicians should consider deep margin elevation when margins are located deep subgingivally. There was no difference found between margin elevation with GI or RMGI. Increased heights of ceramic proximal box may lead to increased probability of ceramic fracture.