Impact of Thermal Aging on Marginal Adaptation in Lithium Disilicate CAD/CAM Crowns with Deep Proximal Box Elevation

BACKGROUND This computer-aided design and computer-aided manufacturing (CAD/CAM) study aimed to evaluate the effects of thermocycling on deep margin elevation relocation of subgingival cavity outlines in 80 molar teeth using advanced lithium disilicate ceramic. MATERIAL AND METHODS Eighty mandibular molar teeth were prepared for deep margin elevation below the cementoenamel junction. The following types of restorations were subsequently applied to each group: glass ionomer filling, bulk-fill flowable resin composite, bioactive resin composite, and nanohybrid resin composite. Full-coverage crowns with standardized preparation and a shoulder finish line were prepared to receive CAD/CAM-milled advanced lithium disilicate crowns. Samples were examined at 6 equidistant points via digital microscope on each proximal surface at the restoration-tooth and crown-restoration interfaces before and after thermocycling for 15 000 cycles. Data were analyzed using one-way analysis of variance, at a level of significance of 0.05. RESULTS The vertical marginal gap was significantly higher after aging and was the highest for glass ionomer filling, 9.091 (±1.147) and 9.936 (±6.376) µm, followed by nanohybrid resin composite, 3.59 (±1.03) and 3.87 (±0.97) µm, bioactive resin composite, 3.17 (±0.81) and 2.59 (±0.21) µm, and bulk-fill flowable resin composite, 1.89 (±0.60) and 2.42 (±0.64) µm, at the cervical and apical interfaces, respectively. CONCLUSIONS Thermocycling significantly changed the marginal adaptation of all restorative materials. Highest values for marginal adaptation were recorded in the glass ionomer filling group, followed by nanohybrid composite and bioactive resin groups, whereas lowest values were recorded among the bulk-fill flowable resin composite group at cervical and apical interfaces.