Effect of the combined zirconium dioxide surface treatment on the shear bond strength of a veneering ceramic to zirconium dioxide

Background. Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) is used as a core material in all-ceramic restorations. The delamination and chipping of a veneering ceramic are the most common complications in the case of zirconia-based restorations. Objectives. The aim of the study was to investigate the effect of the combined treatment of the zirconium dioxide (ZrO2) surface (airborne-particle abrasion with liner application) on the shear bond strength (SBS) of a veneering ceramic. Material and methods. Thirty pre-sintered ZrO2 cuboidal specimens (VITA YZ (R) HT) were sub-divided into 3 groups: group C consisted of 10 specimens without treatment at the sintering stage; group SZ(1) consisted of 10 specimens treated with airborne-particle abrasion (50-micrometer paricles of aluminum oxide - Al2O3; Korox (R) 50), and then coated with a 0.1-millimeter liner (IPS e.max (R) Ceram ZirLiner) after sintering; group SZ(2) consisted of 10 specimens treated with airborne-particle abrasion (50-micrometer particles of Al2O3), and then coated with a 0.2-millimeter liner after sintering. Ceramic veneers (IPS e.max Ceram Dentin) were then applied using the layering technique. After that, the SBS tests were conducted. Results. The results showed that the combined treatment of the ZrO2 surface significantly affected SBS (p < 0.01). The highest mean value was shown in group C (12.441 +/- 2.284 MPa), followed by group SZ(2) (7.889 +/- 0.794 MPa), whereas the lowest mean value was observed in group SZ(1) (5.580 +/- 0.843 MPa). Conclusions. The combined treatment of the pre-sintered ZrO2 surface significantly reduced the SBS of a veneering ceramic. However, the combined surface treatment with a liner thickness of 0.2 mm significantly enhanced the SBS of a veneering ceramic compared to the same combined treatment but with a liner thickness of 0.1 mm.