Effect of a retention groove on the shear bond strength of dentin-bonded restorations

Statement of problem. With the increasing use of minimally invasive restorations, effective adhesion becomes more important. Applying mechanical retention to a flat dentin surface might improve the adhesion of ceramic and composite resin restorations. Purpose. The purpose of this in vitro study was to evaluate the effect of a groove in a flat dentin surface on the bond strength of various restorative materials. Material and methods. Dentin specimens of bovine teeth were prepared with or without a groove. Identical disks were fabricated from direct composite resins (Filtek Supreme XTE [FS] and Clearfil AP-X [AP]) and indirect ceramics (Vita Mark II [VM] and IPS E.max CAD [EM]). These materials were bonded directly or cemented adhesively to the dentin specimens. Shear bond strength was tested with a universal testing machine. Finite element analysis (FEA) models of the test arrangement were made to further analyze the stress distribution. Results. VM (no groove, 5.1 +/- 3.0 MPa; groove, 8.7 +/- 1.5 MPa) and EM (no groove, 11.4 +/- 3.7 MPa; groove, 17.7 +/- 5.2 MPa) showed significant effect of a groove on the shear bond strength. FS (no groove, 18.6 +/- 4.9 MPa; groove, 16.3 +/- 4.3 MPa) and AP (no groove, 25.8 +/- 3.8 MPa; groove, 24.2 +/- 7.2 MPa) showed no significant effect of a groove. For the composite resins, the retention groove increased the shear stress along the dentin-restoration interface, and debonding at the contact surface started at lower load values than for the specimens without a groove. Conclusions. Application of a groove to a flat dentin surface improved the shear bond strength for ceramic restorations. For direct composite resin restorations, exhibiting a lower elastic modulus, a groove had no significant effect on the shear bond strength, while it increased the shear stress along the dentin-restoration interface for composite resin.