Indirect posterior restorations are a frequently preferred option for restoring histomorphological and functional integrity in molar teeth with excessive tissue loss. However, large cavities in the indication of indirect restorations usually extend to the enamel-cementum junction (CEJ). This makes it difficult to seal with a rubber dam and to cement indirect restorations whose end margins extend below the gingival margin. As a less invasive and practical alternative approach, deep margin elevation (DME) emerges as a technique that makes the impression and cementation stages of indirect restorations easy and predictable. However, there is no consensus on the applicability of the DME technique or material selection. This study is aimed to investigate the bond strength of two different types of resin cements to composites with different application techniques used in DME with CAD/CAM blocks. Composite resin CAD/CAM block (Grandio Blok; VOCO) will be evaluated as indirect restorative material, and two different resin bulk-fill composites (Sonic Fill 3, Kerr; VisCalor Bulk, VOCO) with different application techniques will be evaluated as DME material. By selection of two different adhesive cement systems, the effect of using self-adhesive cement (Bifix SE; VOCO) and dual-cure üniversal resin cement (Bifix QM; VOCO) on bond strength will be compared.

80 discs from each bulk-fill composite group and 160 samples will be prepared by cross-sectioning from a resin-based composite CAD/CAM block (Grandio Block). Bulk-fill composite discs will be divided into two subgroups and surface treatment will be done with tribochemical silica coating (CoSiLab, Velopex) in order to increase the bond strength to one group, and no surface treatment will be applied to the other group. The surfaces of the samples obtained from CAD/CAM blocks will be treated with Al2O3. Samples will be exposed to thermal cycling (5-55C, 10000 cycles) 24 hours after cementation of the composite discs and CAD/CAM materials completed with dual-cure universal and self-adhesive resin cement in accordance with the manufacturer's instructions. The shear bond strength of the resin cement between the block and the resin composite will be measured by applying a load on a universal tester (AGS-X Universal, Shimadzu) until failure occurs. The type of failure will be determined using a stereomicroscope (Leica MZ 75, Leica Microsystems). The roughening pattern created by tribochemical silica coating and surface preparation with Al2O3 on the bulk-fill composite and CAD/CAM block surface will be evaluated by a Scanning Electron Microscope (SEM).