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According to the results of the statistical and microscopic analyses, 400 mJ Er:YAG laser energy or air abrasion can be used to obtain micromechanical retention prior to luting; however, air abrasion is the most effective surface treatment method.

This study aimed to evaluate the surface changes caused in zirconia by different surface treatments and the influence of the surface treatment and cement selection on bonding to zirconia under aging. Sintered zirconia specimens were divided into five groups (n = 31) based on the surface treatment, namely, control, air abrasion, silica coating, laser and air abrasion + laser. After surface treatment, surface roughness and microscope analyses were performed on one specimen of each group. Composite cylinders were then bonded to conditioned ceramics using RelyX U100 (RXU), Clearfil Esthetic Cement (CEC) and Panavia F (PF) (n = 10). After 24 h, the bonded specimens were subjected to thermal cycling (6,000 times), and then, a shear bond strength test was conducted. The roughness values were analysed using Kruskal-Wallis and Mann-Whitney U tests, and the bond strengths were analysed by two-way analysis of variance and Duncan's test. The relationship between the roughness and the bond strength was determined by Spearman's correlation analysis. Specimens subjected to surface treatments were rougher than the control specimen (p < 0.000). However, there were no significant differences between the air abrasion and air abrasion + laser groups and the silica coating and laser groups. Specimens treated with laser showed lower bond strengths irrespective of the resin cement used. CEC and/or PF showed higher bond strengths than RXU for each surface treatment group. No significant relationship was observed between the roughness and the bond strength. The results of this study showed that all the surface treatments, except for laser irradiation, were suitable for treating zirconia ceramics. Cement selection was found to be more important than surface treatment, and phosphate monomer-containing cements were suitable for cementing zirconia.

The purpose of this study was to investigate the surface morphology and roughness of zirconia after different surface treatments. Eighty sintered zirconia specimens were divided into four groups (n = 20) according to the surface treatments received: no treatment, erbium:yttrium-aluminum-garnet (Er:YAG) laser irradiation (400 mJ, 10 Hz, 4 W, 100 MPS, distance: 1 mm), tribochemical silica coating with 30 μm aluminum oxide (Al(2)O(3)) modified by silica, and air abrasion with 110 μm Al(2)O(3) particles. After the surface treatments, the surface roughness (Ra in μm) of the specimens was evaluated using a surface texture measuring instrument. Surface morphology of a specimen from each group was evaluated with atomic force microscope (AFM) and scanning electron microscope (SEM) analyses. The surface roughness values were statistically analyzed by the Kruskal-Wallis and Mann-Whitney U tests (p = 0.05). All of the surface treatments produced rougher surfaces than the control group (p < 0.005). While there were no significant differences between the surface roughness of laser and silica groups (p > 0.05). SEM and AFM analyses revealed changes in surface topography after surface treatments, especially in the laser group with the formation of rare pits and in the silica and air abrasion groups with the formation of microretentive grooves. According to the results of the statistical and microscopic analyses, all of the surface treatments can be used for roughening zirconia prior to cementation; however, air abrasion is the most effective surface treatment to obtain micromechanical retention.

PURPOSEThis study investigated the influence of surface conditioning procedures and repeated firings on monoclinic content and strength of zirconia before cementation.MATERIALS AND METHODSSintered bar-shaped zirconia specimens were subjected to no surface treatment (control), air abrasion, or grinding (n=21). Their roughness was evaluated using a profilometer, and microscope analysis was performed on one specimen of each group. Then, 2 or 10 repeated firings (n=10) were executed, the monoclinic content of specimens was analyzed by X-ray diffraction, and a three-point flexural strength test was performed. Surface roughness values were compared using one-way analysis of variance (ANOVA) and Tukey honestly significant difference (HSD) tests, the monoclinic content values were tested using Kruskal-Wallis and Mann-Whitney U tests, and the flexural strength values were tested using two-way ANOVA and Tukey HSD tests (P=.05). Spearman's correlation test was performed to define relationships among measured parameters.RESULTSSurface-treated specimens were rougher than untreated specimens and had a higher monoclinic content (P<.005), and the relationship between roughness and monoclinic content was significant (P<.000). Neither surface treatment nor firing significantly affected the flexural strength, but Weibull analysis showed that for the air-abraded samples the characteristic strength was significantly lower after the 10th firing than after the 2nd firing.CONCLUSIONAfter firing, a negligible amount of monoclinic content remained on the zirconia surfaces, and rougher surfaces had higher monoclinic contents than untreated surfaces. Multiple firings could be performed if necessary, but the fracture probability could increase after multiple firings for rougher surfaces.

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