Effect of hydroxyapatite morphology and quaternary ammonium polymer co-inclusion on bond strength, cytotoxicity, and cell morphology of self-etching adhesive

Abstract This study aimed to obtain and evaluate hydroxyapatites (HAp) as nanoparticles and nanorods for use in self-etching adhesive. The effect of co-inclusion of a multifunctional quaternary ammonium methacrylate polymer (QAMP) on their mechanical, cell viability, and morphological properties was also investigated. Hydroxyapatite nanoparticles (HApP24 and HApP36) and nanorod-shaped hydroxyapatite (HApR14) were characterized by XRPD, SEM-FEG, and FTIR spectroscopy. HApP24, HApP36, HApR14, and HApR14 + QAMP were added to Clearfil™ SE Bond. Microtensile bond strength (μTBS), cell viability (MTT method), and cell morphology (SEM) of these adhesives were studied. Characterization data confirmed that hydroxyapatites were successfully synthesized. Significant decrease μTBS was achieved for Clearfil™ SE Bond + HApP24 (p = 0.031) and Clearfil™ SE Bond + HApP36 (p = 0.008) when immediate (IM) and 12 months (12 M) were compared. No statistical difference (p > 0.05) was achieved when six months (6 M) and 12 M results of μTBS were compared for Clearfil™ SE Bond + HApR14. Clearfil™ SE Bond + QAMP, Clearfil™ SE Bond + HApR14 + QAMP, and Clearfil™ SE Bond presented no significant difference comparing storage periods. Lower cell viability was achieved when HApP24 and HApP36 were included to Clearfil™ SE Bond. Co-inclusion of QAMP + HApR14 into Clearfil™ SE Bond improved (p = 0.049) the viability of cells when compared to Clearfil™ SE Bond. SEM micrographs of fibroblast-like cells demonstrated consistent results with cell viability. This is the first report that hydrothermal nanorods of HAp and QAMP are co-included into adhesive system for providing remineralizing and antimicrobial properties at the same time as they kept bond stability.