Effects of a newly designed HEMA-free, multi-purpose, single-bottle, self-etching adhesive on bonding to dental hard tissues, zirconia-based ceramics, and gold alloy

This study investigated the bonding effectiveness of newly designed self-etching adhesives to four types of adherends —enamel, dentin, zirconia, and gold (Au) alloy. Five experimental adhesives were prepared, which contained 3.0–5.0 wt% 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA) or 6-methacryloyloxyhexyl 3-phosphonopropionate (6-MHPP), 3.0 wt% 4-acryloyloxyethoxycarbonylphthalic acid (4-AET) or 17.0 wt% 4-methacryloyloxyethoxycarbonylphthalic acid (4-MET), 0–0.5 wt% 6-methacryloyloxyhexyl 6,8-dithiooctanoate (6-MHDT) or 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT), and varying contents of Bis-GMA, dimethacrylate monomers, water, acetone, and a photoinitiator system. After 2,000 times of thermal cycling, shear bond strengths (SBSs) between a resin composite (Beautifil II, Shofu Inc., Japan) and the four adherends, bonded using the experimental adhesives, were measured at 1.0 mm/min. No statistically significant differences in SBS for bonding to ground enamel, dentin, sandblasted zirconia and Au alloy (p>0.05) were found between experimental adhesives which contained 6-MHPA and/or 6-MHPP, 4-MET or 4-AET, 6-MHDT and/or 10-MDDT, Bis-GMA, and dimethacrylates. An adhesive layer of less than 5.0 μm thickness, by scanning electron microscopy observation, revealed strong adhesion to the four adherends. Therefore, the newly designed multi-purpose, self-etching adhesive strongly adhered to all the four adherend materials tested.