Alkaline nanoparticle coatings improve resin bonding of 10-methacryloyloxydecyldihydrogenphosphate-conditioned zirconia

Abstract

Creating an alkaline environment prior to 10-methacryloyloxydecyldihydrogenphosphate (MDP) conditioning improves the resin bonding of zirconia. The present study evaluated the effects of four alkaline coatings with different water solubilities and pH values on resin bonding of MDP-conditioned zirconia. Two alkaline nanoparticle coatings were studied in particular. Thermodynamics calculations were performed to evaluate the strengths of MDP-tetragonal phase zirconia chemical bonds at different pH values. Zirconia surfaces with and without alkaline coatings were characterized by scanning electron microscope (SEM)/energy dispersive spectrometer and Fourier transform infrared spectroscopy; alkaline coatings included NaOH, Ca(OH) 2 , nano-MgO, and nano-Zr(OH) 4 . A shear bond strength (SBS) test was performed to evaluate the effects of the four alkaline coatings on bonding; the alkaline coatings were applied to the surfaces prior to conditioning the zirconia with MDP-containing primers. Gibbs free energies of the MDP-tetragonal zirconia crystal model coordination reaction in different pH environments were −583.892 (NaOH), −569.048 [Ca(OH) 2 ], −547.393 (MgO), and −530.279 kJ/mol [Zr(OH) 4 ]. Thermodynamic calculations indicated that the alkaline coatings improved bonding in the following order: NaOH > Ca(OH) 2 > MgO > Zr(OH) 4 . Statistical analysis of SBS tests showed a different result. SBSs were significantly different in groups that had different alkaline coatings, but it was not influenced by different primers. All four alkaline coatings increased SBS compared to control groups. Of the four coatings, nano-Zr(OH) 4 and -MgO showed higher SBS. Therefore, preparing nano-Zr(OH) 4 or -MgO coatings prior to conditioning with MDP-containing primers may potentially improve resin bonding of zirconia in the clinic.

<p>Surface Treatment Of Nanozirconia Fillers To Strengthen Dental Bisphenol A–Glycidyl Methacrylate–Based Resin Composites</p>

“…The increase in hydroxyl groups provided by zirconium hydroxide contributed to the improved chemical affinity of MDP for zirconia. 35 These findings are consistent with previous studies, suggesting that bonding of MDP and zirconia is enhanced by zirconium hydroxide. 29 Our NMR analysis also showed that prior Zr(OH) 4 coating positively impacted MDP bonding with zirconia.…”

“…Our NMR and XPS analyses indicated that Zr(OH) 4 enhanced bonding of MDP to zirconia, which is consistent with previous findings. 35 Moreover, previous experiments have shown that the addition of 10 wt% MDP-conditioned Zr(OH) 4 -coated zirconia does not significantly improve the flexural strength of resin composites. 22 In our study, we controlled the concentration of zirconium chloride used to avoid the influence of excess zirconium hydroxide on the properties of resin composites.…”

“…It creates an alkaline microenvironment that promotes the bonding of zirconia to matrix. 35 Therefore, we coated Zr(OH) 4 on the surface of zirconia in our experiments. We first verified that Zr-O-P bonds existed on the surface of MDP-conditioned zirconia fillers using XPS, suggesting chemical affinity of MDP to the zirconia filler surface, which provided zirconia fillers the capacity to be polymerized with bisphenol Aglycidyl dimethacrylate.…”

“…The 1 H MAS NMR spectrum ( Figure 3A and C) showed sharp narrow resonance at 6.1 ppm, 5.5 ppm, 4.2 ppm, 1.9 ppm, 1.7 ppm, and 1.4 ppm, attributed to the methacryloyloxy group of the MDP monomer. 35 The broad resonance at 5.0 ppm was attributed to the Zr-OH groups, which adsorbed water molecules from the hydrated surface layer around the zirconia particles. 28 Weak broad resonance around 6.0 ppm was attributed to OH-groups, including the P-OH bonds of MDP, 29 indicating that zirconia strongly interacts with MDP, even after acetone washes.…”

Chemical interaction mechanism of 10-MDP with zirconia

“…Pilo et al 22. and Qian et al 23. assessed the chemical bonding by Fourier transform infrared spectroscopy (FTIR).…”