Acidic pH weakens the bonding effectiveness of silane contained in universal adhesives

Objectives. Some silane-containing universal adhesives were introduced that a separate ceramic primer was unnecessary to glass-ceramic bonding because of incorporated silane. We aimed to investigate the effectiveness of silane in universal adhesives with acidic media. Methods. A functional gamma-methacryloxypropyltrimethoxysilane (gamma-MPTS) was used, and its pH value was adjusted to 2.7 by adding hydrochloric acid (HCl) or 10-methacryloxydecyl phosphate (MDP). The prepared acidic silane solutions after 2 h or 10 d storage were characterized by Fourier transform infrared spectroscopy (FTIR), H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy. Micro-shear bond strength (mu SBS) was used to evaluate the bonding performance of glass ceramics. Two silane-containing and two silane-free universal adhesives were included. Field-emission scanning electron microscopy fractography analysis was also performed. Results. FTIR, H-1 and C-13 NMR revealed that the hydrolysis of gamma-MPTS and the selfcondensation reaction of silanol groups occurred over time under acidic conditions (HCl or MDP solution). This reaction formed the siloxane oligomers. For glass-ceramic bonding, the ii,SBS of acidic silane after 10 d storage was lower than that of silane stored for 2 h storage (p < 0.05), although the difference among the ii,SBS of the four universal adhesives were nonsignificant (p > 0.05). Additionally, cohesive failure was the main fracture pattern of universal adhesive bonding. Significance. The effectiveness of silane contained in low pH universal adhesives can be weakened by dehydration self-condensation and consequently became unstable. For the enhancement of glass-ceramic bonding efficiency with universal adhesives, a separate ceramic primer was recommended. (C) 2018 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.