Purpose: To investigate the effects of nanozirconia fillers conditioned with 10-methacryloyloxydecyl dihydrogen phosphate (MDP) with or without zirconium hydroxide precoating on bending strength, Vickers hardness, and translucence of dental resin composites. Methods: We obtained nanozirconia fillers coated with different concentrations of Zr(OH) 4 using wet-chemical synthesis. We analyzed coating quality by observing electron-diffraction patterns using transmission electron microscopy. We conditioned zirconia fillers, with or without prior Zr(OH) 4-coating, using MDP-containing primers and evaluated the formation of chemical bonds using nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS). We then performed three-point bending-strength tests, Weibull analysis, Vickers hardness, and translucence-parameter analysis with or without addition of different concentrations of zirconia using untreated zirconia fillers as controls. Results: We achieved desirable Zr(OH) 4 coating using 5 mmol/L zirconium chloride. NMR and XPS analysis detected stronger Zr-O-P peaks on MDP-conditioned zirconia fillers with prior Zr(OH) 4-coating compared with MDP-conditioned fillers alone, suggesting that MDP bonding with zirconia was enhanced by zirconium hydroxide. Our three-point bending-strength tests revealed that increasing levels of untreated zirconia fillers decreased the three-point bending strength of the resin composites, while MDP-conditioned zirconia fillers with or without prior Zr(OH) 4 coating improved three-point bending strengths. Adding 5 wt% and 7.5 wt% MDP-conditioned zirconia fillers with prior Zr(OH) 4 coating achieved the highest three-point bending strength. Furthermore, addition of zirconia fillers decreased the translucence of silica-based resin composites. Conclusion: MDP conditioning with prior Zr(OH) 4 coating is recommended for treating nanozirconia fillers of resin composites.

PURPOSEThe aim was to study the masking ability of high-translucency monolithic zirconia and provide guidance in selecting resin luting cements in order to mask discolored substrates.MATERIALS AND METHODS160 high-translucency zirconia specimens were divided into 32 groups depending on their thickness and shades. Using five shades of try-in paste, the specimens were luted onto the sub strates (Co-Cr, precious-metal, opaque porcelain-sintered Co-Cr, opaque porcelain-sintered precious-metal, and 5M3-shade zirconia). All CIELAB color parameters were measured and statistically analyzed.RESULTSZirconia shade and thickness and try-in paste shade affected CIELAB color parameters (P=.000) in different substrates groups, and there were interactions among these factors (P=.000). All five try-in paste shades can be chosen to achieve ΔE values of zirconia with 1.2 – 1.5 mm for masking dark-tooth-like 5M3-shade and zirconia with 1.5 mm for masking precious-metal groups < 2.6. Only suitable try-in paste shades were used, can ΔE values that less than 2.6 be achieved when applied translucent monolithic zirconia with 0.7–1.0 mm for masking dark-tooth-like 5M3-shade and zirconia with 0.7 – 1.2 mm for masking precious-metal groups.CONCLUSIONChoosing suitable resin cement shades is necessary for high-translucency monolithic zirconia to achieve ideal masking ability (ΔE < 2.6) on the dark-tooth.

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The bonding performance of a glycerol phosphate dimethacrylate (GPDM)-based, two-step, self-etch (SE) adhesive was experimentally compared to that of 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based universal adhesives in different application modes for enamel bonding. Microtensile bond strength (μTBS) for adhesives bonded to enamel was measured initially (24 h water storage) and after 10 000 thermocycles plus water storage for 30 days. A GPDM-based, two-bottle, two-step, self-etch adhesive (Optibond Versa, OV) and three one-bottle MDP-based universal adhesives, one self-etching (Tetric N Bond Universal, TNBU) and two with etch-and-rinse (E&R) processing (Single Bond Universal (SBU); Clearfil Universal Bond Quick (CUBQ)), were tested. Scanning electron microscopy (SEM) evaluated nanoleakage at the bonding interfaces. A profilometer determined roughnesses of enamel surfaces after phosphoric acid etching, OV priming, or TNBU conditioning. SEM observed the corresponding surface morphology. NMR and X-ray photoelectron spectroscopy (XPS) characterized chemical bonding in hydroxyapatites (HAps) conditioned with the adhesives. Etch-and-rinse samples had significantly stronger bonding than self-etch samples ( p < 0.05) irrespective of aging. The μTBS values for initial and aged OV were significantly higher than those of TNBU ( p < 0.05). Aging did not significantly decrease μTBS for any sample except TNBU ( p < 0.05), but it significantly aggravated nanoleakage. Etch-and-rinse processing resulted in less nanoleakage than self-etching; the OV samples leaked less than TNBU, both before and after aging. Phosphoric acid etching achieved the highest enamel surface roughness, followed by OV primer. Ca–O–P bonds in hydroxyapatite conditioned with TNBU, SBU, and CUBQ were confirmed by NMR, which showed similar results to XPS observations of conditioned hydroxyapatite powders except OV primer. The GPDM-based, two-step, self-etch adhesive can provide higher micromechanical retention potential, bond strength, and durability than the MDP-based universal adhesive in self-etch mode but lower performance than the MDP-based universal adhesive in etch-and-rinse mode. None of the tested adhesives could avoid nanoleakage after aging.

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