Purpose: to evaluate the effect of using different resin composite viscosities for elevation of deep cervical margins in maxillary premolars on the margin adaptation of CAD/CAM fabricated lithium disilicate ceramic overlays after exposure to thermomechanical aging.
Materials and methods: Thirty maxillary premolars were prepared for MOD indirect ceramic overlays with proximal box extends 2mm below the cementoenamel junction. Teeth were divided into 2 groups according to proximal box elevation (PBE): Control group (Group_C) (n=15); with No PBE and intervention group (n=15); which was subdivided into group I_F: mesial surface PBE with flowable composite and group I_B: distal surface PBE with bulk-fill flowable composite. All overlays were milled from lithium disilicate blocks and bonded to prepared cavities with dual cure adhesive resin cement. All samples were subjected to thermomechanical aging, then, marginal gap was evaluated with digital microscope.
Results: Two-way ANNOVA revealed that Group_C demonstrated the highest marginal gap values (42.78± 4.949 µm) before aging and (78.01± 5.767 µm) after aging, while, Group I_B demonstrated the lowest marginal gap values (39.97± 4.923 µm) before aging and (71.35± 10.29 µm) after aging, though the difference between all groups was non statistically significant.
Conclusions: Proximal box elevation under indirect ceramic overlays with either bulk-fill and flowable results showed comparable marginal sealing ability to direct bonding of ceramic overlays to cervical dentine. Thermomechanical aging significantly reduced the marginal adaptation, but, all tested restorations exhibited marginal quality within clinically accepted values.