Improvement in the Bonding of Y-TZP by Room-temperature Ultrasonic HF Etching.

PURPOSE: To investigate the effects of room-temperature etching with hydrofluoric acid (HF) in the presence and absence of ultrasonic irradiation on the bonding of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) to resin. MATERIALS AND METHODS: Y-TZP specimens were etched with 40% HF at room temperature for different time periods (2, 5, 10, 15, 30, 60, and 90 min) with and without ultrasonic exposure. The surface roughness, micromorphology, dimensions, and phases of the treated Y-TZP specimens were evaluated by atomic force microscopy (AFM), scanning electron microscopy (SEM), digital caliper measurement, and x-ray diffraction, respectively. The HF etching conditions that resulted in the most drastic Y-TZP surface morphology and highest roughness values were used to prepare specimens for shear bond strength (SBS) testing; the effect of thermocycling on SBS was also examined. Alumina-sandblasted Y-TZP specimens were used as the control. RESULTS: The Y-TZP surfaces etched with HF without ultrasonic exposure for 30, 60, and 90 min and those surfaces ultrasonically etched with HF for 10 and 15 min were severely etched, although their dimensions were not changed by etching. Monoclinic-phase zirconia was observed only in the alumina-sandblasted Y-TZP specimens. Surface roughening from HF etching for 30 min and ultrasonic etching for 10 min resulted in higher mean SBS compared to roughening with alumina sandblasting. CONCLUSION: Ultrasonic etching with 40% HF at room temperature for 10 min may be used as an alternative roughening method for improving the bonding of Y-TZP.

Chemical affinity of 10-methacryloyloxydecyl dihydrogen phosphate to dental zirconia: Effects of molecular structure and solvents.

OBJECTIVES: To examine whether solvents and changing the molecular structure of 10-Methacryloyloxydecyl dihydrogen phosphate (10-MDP) affect its chemical affinity to Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP). METHODS: The present work investigated the chemical affinity between Y-TZP and 10-MDP dissolved in different solvents (acetone/ethanol/water or mixture) using X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and thermodynamic calculations. Shear bond strength (SBS) tests were used to evaluate the influence of different solvents on 10-MDP bonding. In addition, several phosphate ester monomer variants were created by changing the 10-MDP molecular structure. Changes included extending/shortening the spacer chain-length, and installing hydroxyl or carboxyl groups as side chains at different positions along the spacer chain. The thermodynamic parameters of the complexes formed between the 10-MDP variants and tetragonal zirconia were evaluated. RESULTS: The acquired data indicated that solvent is necessary for the formation of Zr-O-P bonds between 10-MDP and Y-TZP. Solvents affected the chemical affinity of 10-MDP to Y-TZP; acetone facilitated the best bonding, followed by ethanol. Changing the molecular structure of 10-MDP affected its chemical affinity to Y-TZP. The variants 15-MPDP, 12-MDDP, 6-hydroxyl-10-MDP and 6-carboxy-10-MDP all exhibited higher thermodynamic stability than 10-MDP when coordinated with tetragonal zirconia. In contrast, 2-MEP, 5-MPP, 10-hydroxyl-MDP, 10-carboxy-MDP, 5,6-dihydroxyl-10-MDP and 5,6-dicarboxy-10-MDP exhibited lower thermodynamic stability. SIGNIFICANCE: 10-MDP coordinates with zirconia through dissociating in solvents. Changing the molecular structure of 10-MDP theoretically affects its chemical affinity to Y-TZP.

Effect of 10-Methacryloxydecyl Dihydrogen Phosphate Concentration on Chemical Coupling of Methacrylate Resin to Yttria-stabilized Zirconia.

PURPOSE: To test the hypothesis that the concentration of 10-methacryloxydecyl dihydrogen phosphate (MDP) in zirconia primers has no effect on the chemical bonding efficacy of methacrylate resins to yttria-stabilized tetragonal zirconia (Y-TZP). MATERIALS AND METHODS: Shear bond strength testing was performed to evaluate the efficacy of experimental primers containing 5, 10, 15, 20 or 30 wt% MDP (5M, 10M, 15M, 20M, 30M) in improving composite-zirconia bond strength. Bonding without use of MDP-containing primer served as the negative control (Ctr0). Bonding with a commercially available MDP-containing primer served as the positive control (CtrM). Thermogravimetric analysis (TGA), inductively coupled plasma-mass spectrometry (ICP-MS), x-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR), and computational simulation of infrared spectra were used to confirm the formation of Zr-O-P bond between MDP and Y-TZP. RESULTS: Results derived from TGA, ICP-MS, XPS, and FT-IR suggested that MDP chemically bonded with Y-TZP. Simulation of IR data supported the FT-IR results. There was a higher concentration of phosphorus on the 10M-conditioned Y-TZP surface when compared with the other groups, suggesting bettter formation of Zr-O-P bond in the 10M group. Shear bond strengths were significantly lower for group 5M (p < 0.05), compared to groups 10M to 30M, which were not significantly different from one another (p > 0.05). CONCLUSIONS: MDP improves resin bonding of zirconia through the formation of Zr-O-P bonds with zirconia. 10 wt% MDP appears to be the most optimal concentration for synthesizing zirconia primers for resin bonding.

Dipentaerythritol penta-acrylate phosphate - an alternative phosphate ester monomer for bonding of methacrylates to zirconia.

The present work examined the effects of dipentaerythritol penta-acrylate phosphate (PENTA) as an alternative phosphate ester monomer for bonding of methacrylate-based resins to yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and further investigated the potential bonding mechanism involved. Shear bond strength testing was performed to evaluate the efficacy of experimental PENTA-containing primers (5, 10, 15, 20 or 30 wt% PENTA in acetone) in improving resin-Y-TZP bond strength. Bonding without the use of a PENTA-containing served as the negative control, and a Methacryloyloxidecyl dihydrogenphosphate(MDP)-containing primer was used as the positive control. Inductively coupled plasma-mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) were used to investigate the potential existence of chemical affinity between PENTA and Y-TZP. Shear bond strengths were significant higher in the 15 and 20 wt% PENTA groups. The ICP-MS, XPS and FTIR data indicated that the P content on the Y-TZP surface increased as the concentration of PENTA increased in the experimental primers, via the formation of Zr-O-P bond. Taken together, the results attest that PENTA improves resin bonding of Y-TZP through chemical reaction with Y-TZP. Increasing the concentration of PENTA augments its binding affinity but not its bonding efficacy with zirconia.

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

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.

Effects of multiple firings on the low-temperature degradation of dental yttria-stabilized tetragonal zirconia.

STATEMENT OF PROBLEM: The clinical failure of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) substrates may be attributed to their susceptibility to low-temperature degradation (LTD). The acceleration of LTD by multiple veneering firings of Y-TZP remains poorly understood. PURPOSE: The purpose of this in vitro study was to evaluate the effects of different numbers of veneering firing cycles on the LTD of Y-TZP. MATERIAL AND METHODS: Ninety bar-shaped specimens were cut from a machinable Y-TZP block and fully sintered. The Y-TZP bars were divided into 3 groups; each group received 1, 3, or 5 veneering porcelain firing cycles. Specimens from each firing cycle (n=10) were then subjected to hydrothermal aging in an autoclave sterilizer for 10 or 20 hours to accelerate the LTD of Y-TZP. Specimens without hydrothermal aging served as the control. XRD was used to characterize phase transformations. The flexural strength and surface Vickers hardness of the 9 subgroups were investigated, and scanning electron microscopy was used to characterize the fractured surface morphology. RESULTS: Hydrothermal aging increased the monoclinic phase, although increased hydrothermal aging time provided no additional effects. Veneering firings did not enhance the influence of hydrothermal aging on phase transformation. No statistical significance was found among the 9 groups in terms of flexural strength or surface Vickers hardness (P>.05). CONCLUSIONS: Additional veneering porcelain firing cycles do not accelerate the LTD of Y-TZP.

Comparison of resin bonding improvements to zirconia between one-bottle universal adhesives and tribochemical silica coating, which is better?

OBJECTIVES: To evaluate the bonding of resin-cement to yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) via silica coating followed by silanization, and three one-bottle universal adhesives, with or without prior conditioning using a zirconia primer. METHODS: Y-TZP specimens (n=160) were conditioned by tribochemical silica coating and silanization (CS), or alumina sandblasting with one of the following MDP containing adhesives or primers: Z-Prime Plus™ (zirconia primer, ZP), Single Bond Universal™ (SU), Clearfil Universal Bond™ (CU) or All-Bond Universal™ (AU). Additionally, some specimens (ZPSU, ZPCU and ZPAU) received Z-Prime Plus™ followed by one of the three adhesives. After 24h water storage and "aging" (20,000 thermocycles plus additional 40-day water storage), shear bond strength (SBS) was measured. Fourier-transform infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) were employed for characterization of the chemical bonds between the primer/adhesives and the zirconia. Thermodynamic calculations were used to examine the hydrolytic stability between the MDP-zirconia chemical bonds and the SiO2-silane chemical bonds. RESULTS: The CS and ZPCU groups showed higher SBS than the other six groups. There were no significant pairwise differences amongst ZP, SU and ZPSU, or amongst ZP, AU and ZPAU. Aging led to significantly decreased SBS for all groups except CS and ZPCU. There was no statistically significant interaction between surface treatment and aging. XPS determined the chemical bonds between MDP and zirconia. FTIR showed similar shifts in characteristic phosphate peaks for all the primer and/or adhesive groups. Result of thermodynamic calculation showed that equilibrium constant of SiO2-silane system is much larger than the one of MDP-tetragonal phase zirconia system. SIGNIFICANCE: The application of one-bottle universal adhesives after alumina sandblasting is an alternative to tribochemical silica coating with silanization for bonding to zirconia, while bonding between resin and Y-TZP is more susceptible to hydrolysis when zirconia primer or one-bottle universal adhesive is used.

Effects of Acid Treatment on Dental Zirconia: An In Vitro Study.

The aim of this study was to evaluate the effects of hydrofluoric (HF) acid, acetic acid, and citric acid treatments on the physical properties and structure of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) at ambient temperature. In total, 110 bar-shaped zirconia specimens were randomly assigned to 11 groups. The specimens in the control group (C) received no surface treatment, while those in the Cage group were hydrothermally aged at 134°C and 0.2 MPa for 20 h. Ten specimens each were immersed at ambient temperature in 5% and 40% HF acid for 2 h (40HF0), 1 day (5HF1, 40HF1), and 5 days (5HF5, 40HF5), while 10 each were immersed at ambient temperature in 10% acetic acid and 20% citric acid for 7 (AC7, CI7) and 14 days (AC14, CI14). X-ray diffraction (XRD) was used to quantitatively estimate the monoclinic phase. Furthermore, flexural strength, surface roughness, and surface Vickers hardness were measured after treatment. Scanning electron microscopy (SEM) was used to characterize the surface morphology. The Cage group specimens exhibited an increased monoclinic phase and flexural strength. Furthermore, 40% HF acid immersion decreased the flexural strength and surface hardness and deteriorated the surface finish, while 5% HF acid immersion only decreased the surface hardness. All the HF acid-immersed specimens showed an etched surface texture on SEM observations, while the other groups did not. These findings suggest that the treatment of Y-TZP with 40% HF acid at ambient temperature causes potential damage, while treatment with 5% HF acid, acetic acid, and citric acid is safe.