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Lack of Neutralization of 10-MDP Primers by Zirconia May Affect the Degree of Conversion of Dual-cure Resin Cement

Abstract:

Objective: To assess the effects of different concentrations of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) included in experimental ceramic primers on the degree of conversion (DC) and microshear bond strength (μSBS) of a dual-cure resin cement, and on the acidity neutralization potential of zirconia (ZrO2) in comparison to hydroxyapatite (HAp). Methods: Experimental ceramic primers were formulated using 5 wt%, 10 wt%, 20 wt%, or 40 wt% 10-MDP as an acidic functional monomer and camphorquinone (CQ)/amine or 1-phenyl-1,2- propanedione (PPD) as a photoinitiator system. Clearfil Ceramic Primer (Kuraray Dental, Tokyo, Japan) was used as the commercial control. Micro-Raman spectroscopy was used to assess the DC of uncured and light-cured resin cements applied onto primer-treated ZrO2 surfaces. The μSBS and pH of primers were assayed in a universal testing machine and by a digital pH meter (Tec-3MP; Tecnal, Piracicaba, Brazil), respectively. Statistical analysis was performed by one-way analysis of variance (ANOVA) and Tukey's test (p<0.05). Results: DC was not affected until a concentration of 10% 10-MDP in CQ primer and 5% 10-MDP in PPD primer was reached, when compared with the positive control (p>0.05). Groups 10-MDP 5% in CQ and PPD primers showed the highest μSBS compared with the positive control (p>0.05); however, higher concentrations of 10-MDP induced significant DC and μSBS reduction (p<0.05). Hap neutralized 10-MDP primers, but ZrO2 provided higher acidity to the primers' pH. Conclusion: 10-MDP monomer should be used in low concentrations in ZrO2 primers to avoid reduction of the polymerization and bond strength of resin cement.