Investigating the impact of different cleaning techniques on bond strength between resin cement and zirconia and the resulting physical and chemical surface alterations.

ABSTRACT

PURPOSE: To evaluate the effect of cleaning methods and thermocycling on the micro-tensile bond strength between resin cement and contaminated zirconia and to characterize the physicochemical alterations at the zirconia surface resulting from contaminants and subsequent application of cleaning methods. MATERIALS AND METHODS: Thirty-two alumina air-abraded zirconia blocks were divided into eight groups (i) uncontaminated control followed by methacryloyloxydecyl dihydrogen phosphate (MDP) primer (G-Multi Primer) application (CON). In groups ii-viii, the blocks were contaminated with saliva and silicone disclosing agents, followed by cleaning as follows (ii) MDP primer applied, followed by contamination (GMP1); (iii) MDP primer applied before and after contamination (GMP2); (iv) cleaning with alumina air-abrasion (APA); (v) cleaning with sodium hypochlorite (NaOCl); (vi) cleaning with Ivoclean (IVC); (vii) cleaning with ZirClean (ZC); and (viii) cleaning with Katana Cleaner (KC). After cleaning, the zirconia blocks in groups iv-viii were applied with MDP primer. The blocks in each group were cemented together with resin cement (G-Cem Linkforce). Subsequently, each bonded zirconia block was sectioned using a water-cooled diamond saw into microsticks (1 × 1 × 9 mm3). Micro-tensile bond strength was measured after either 24 h or 10,000 thermal cycles (n = 20/subgroup). Data were analyzed using two-way analysis of variance (ANOVA), followed by one-way ANOVA, and Tukey's post-hoc test. The contact angle measurements, energy dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared (FTIR) spectrometer were used for physiochemical evaluation. RESULTS: After 24 h of water storage, the highest bond strength was observed in the CON, NaOCl, APA, and GMP2 groups. After thermocycling, the bond strength significantly decreased in all groups except the GMP2 group, which maintained the highest bond strength. Commercial ceramic cleaning agents (IVC, ZC, and KC groups) exhibited lower bond strengths than the CON groups in both aging conditions. CONCLUSIONS: The application of MDP primer before and after contamination is a promising cleaning protocol for removing saliva and silicone disclosing agent contaminants from zirconia surfaces. This approach achieved the highest bond strength and maintained it even after artificial aging through thermocycling.