| In recent years, the popularity of zirconia ceramic restorations has been increased due to the excellent mechanical properties and biocompatibility of this high strength and toughness material, in combination with the CAD/CAM technology. Although superior in terms of fracture/fatigue resistance and long-term viability, zirconia material has a high refractive index and translucent colored porcelain is necessary to be veneered over the zirconia ceramic core to promote high aesthetics quality in dental restorations. However, clinical studies of veneered zirconia restorations indicated that chipping of the veneering porcelain and delamination between the veneering porcelain and zirconia frames were the main problems in the complicated stress surroundings during mastication. In clinical situation, the application of light-cured composite resin to repair directly the fractured zirconia restorations is more and more popular. However, bonding to zirconia ceramic still remains a challenge. Alternative mechanical and chemical surface treatments have been explored to improve micromechanical and chemical bonding. However, the application of these surface treatments is restricted when it refers to zirconia ceramic repairing in dental environment, and air-abrasion and the application of various ceramic primers are the relatively ideal choices. But in clinical situation, the choices of bonding agents and primers are abundant, and this research aims at the choices of appropriate zirconia ceramic surface treatments for ceramic repairing.Objective:In order to find appropriate zirconia ceramic surface treatments for ceramic repairing, the repairing procedure were simulated and the influences of different ceramic repairing bonding agents, ceramic primers and air-abrasion on resin bonding to zirconia ceramic were compared. The surface characteristics and the bonding interfaces were observed and analyzed. The bonding mechanism and effective instructions was explored for clinical application.Methods:100zirconia ceramic plates (12.5mm×15mmx2mm) were cut from Zirconia ceramic blocks and sintered. The bonding surfaces were polished on wet240-and320-grid silicon carbide paper.50of the specimens were air-abraded with50μm Al2O3particles and obtained as the air-abraded specimens. The rest zirconia plates were obtained as the polished specimens. Finally all the specimens were cleaned ultrasonically and air-dried.An Atom force microscope was used to image the zirconia ceramic surfaces.4samples of each surface treatment group (polished and air-abraded) were picked out and scanned over an area of20×20μm2. Various roughness parameters were calculated by an image processing and analysis software package. These include arithmetic mean surface roughness (Ra), root mean square division (Rq) and the maximμm peak-to-valley measurement (Rmax).All the zirconia ceramic specimens were divided into2supergroups (polished and air-abraded). According to the different application of the composite resins, bonding agents and ceramic primers, each supergroup was divided into5groups, and totally10groups were obtained. Four groups of the specimens untreated with any primer were obtained as control. The surface of each zirconia ceramic specimen was treated with or without one of primers, and then mildly air dried. One of the bonding agents was applied on the surface, and then gently air blown. The bonding agents were light-cured by a LED light unit. Transparent plastic modes were placed on the ceramic surface to control the bond area. Each composite resin was filled in the mode and light-cured. All the specimens were allowed to stand for30min at room temperature.The bonding interfaces of10samples from each group were observed by a Field Emission Scanning Electron Microscope at x10000magnification. The samples were invested in Epoxy resin and polished on the polishing machine until the bonding interface was flat and available for electron microscopy. The samples were gold coated and the bonding interfaces were observed.Every test group had10ceramic specimens with20bond test specimens, and they were divided into2subgroups of5ceramic specimens with10bond test specimens each. One of the two subgroups was stored in distilled water at37℃for24hours. The other subgroup was stored in distilled water at37℃for24hours and followed by5,000thermal cycles. The specimens were fixed in a special sample holder and placed in a universal testing machine. The resin columns were loaded up to failure at the interface parallel to the zirconia surfaces and the bond strengths were obtained. The failure mode of specimens was observed and analyzed by an optical microscope at×10magnification. The failure mode was classified as type Ⅰ (adhesive between ceramic and bonding agent/primer) and type Ⅱ (mixed failure).Statistical analysis was performed using SPSS18statistical software. The bond strength of each group was analyzed through three-way ANOVA followed by comparison of means with Tukey’s test were applied in order to compare the bond strength of all the groups (p<0.05).Results:AFM analysis of the zirconia surface showed that air-abrasion could significantly increase the surface roughness comparing with polishing procedure (p<0.05). The cracks and grooves caused by the polishing procedure were effectively removed by air-abrasion and a rougher and more homogeneous zirconia surface was available for resin bonding.According to ANOVA, the differences among the experimental groups were significant (p<0.05). Among all the experimental groups, SE Bond applied group without any primer on the air-abraded zirconia ceramic, presented the highest bond strength value (23.038±3.945MPa). Among the SE Bond applied groups, before and after thermal cycles, there were no significant differences between the primer groups and the controls. In contrast, among the Heliobond applied groups, before and after thermal cycles, the bond strength of the Metal/Zirconia Primer applied groups was significantly higher than the Monobond-S groups and the controls (p<0.05). All the air-abrasion treated groups showed significant higher bond strength than the corresponding polished groups (p<0.05).The bonding interface FE-SEM microscopy photographs showed that the bonding agent/primer-zirconia interfaces and the primer-zirconia interfaces. The interfaces of the SE Bond applied groups were firmer than the Heliobond groups. Obvious cracks could be observed in the Heliobond applied groups.Before thermal cycle, mixed failures were observed in SE Bond applied groups, in which SE Bond was applied on the polished or air-abrasion treated zirconia surface with or without the primer, and residual resin could be observed. Meanwhile, all the other groups were performed type Ⅰ failure mode. After5000thermal cycles, type Ⅰ failures were observed in all the test groups.Conclusions:1. Air-abrasion significantly improved the surface roughness and wetting behavior of zirconia ceramic and resin zirconia bond.2. Compared with Heilobond,10-MDP-containing bonding agent, SE Bond, was more recommended to repair fractured zirconia restorations when luting composite resin.3. Metal/Zirconia Primer combined with air-abrasion could significantly improve the resin ceramic bond. Clearfil Porcelain Bond Activator (CPBA) and Monobond-S (MS) was ineffective for the increase of bond strength. But we couldn’t deny the effect of CPBA for the increase of bond durability. The application of MS was negative for bond durability. |
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