Abstract
Statement of problemDuring the trial placement of zirconia restorations, contamination of the bonding surface is inevitable. Although cleaning methods for contaminated surfaces have been described, a method of preventing saliva contamination of the bonding surface of zirconia restorations is lacking. PurposeThe purpose of this in vitro study was to investigate an ethyl cellulose coating as an evaluation agent to mitigate the effects of saliva contamination on the bond strength of zirconia restorations. Material and methodsExperimental groups representing different cleaning methods of tetragonal yttria-stabilized tetragonal zirconia polycrystal (4Y-TZP) surfaces were investigated for shear bond strength with a resin luting agent, and the failure mode was analyzed. The 9.0×7.0×5.0-mm zirconia blocks (n=72) were assigned as follows: Group N: uncontaminated control; Group CU: contaminated with saliva, followed by ultrasonic cleaning with ethanol; Group CI: contaminated with saliva, followed by application of a zirconia cleaner; Group PCW: preapplication of a zirconia primer, contaminated with saliva, followed by cleaning with water spray; Group ECU: precoating with the ethyl cellulose agent, contaminated with saliva, followed by removal of the agent in an ultrasonic bath with ethanol. Each group was divided into 3 subgroups (immediate, short-term aging, and long-term aging), and the shear bond strength was measured (n=24). To analyze the bonding surface characteristics, the contact angle was measured (n=5). The surfaces of the zirconia specimens in each experimental group were evaluated by using a field emission scanning electron microscope (n=5). Time-of-flight secondary ion mass spectroscopy was used for the chemical analysis of the conditioned surfaces (n=3). A 2-way analysis of variance (ANOVA) with main effect model for shear bond strength results and a 1-way ANOVA for contact angle data were performed as statistical analysis, followed by the Bonferroni post hoc test (α=.05). ResultsThe shear bond strength was significantly higher in the ECU group than in the groups with the other cleaning methods (P<.05). After the removal of ethyl cellulose with ethanol, the contact angle and surface topography were found to be similar to those of the control group, and no saliva contaminants were identified in the spectroscopy analysis. ConclusionsCoating with ethyl cellulose may protect the bonding surface of zirconia restorations from salivary contamination better than cleaning a contaminated surface.
Highlights
The intaglio surface of the restoration is inevitably contaminated with saliva, blood, gingival crevicular fluid, and silicone evaluation paste during the trial placement procedure, and saliva contamination has been shown to be the main cause of reduced bond strength.[9,10]
The phosphate component of oral fluid and the acid etchant has a high affinity for zirconia, potentially leading to interference with the chemical reaction between the bonding surface and adhesive molecules such as 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP).[11,12]
Residual organic contaminants compromise the quality of adhesion between the tooth and the restoration, which may negatively affect its longevity.[10,13,14]
Summary
The purpose of this study was to determine whether coating the zirconia surface with a thin film of EC before the trial placement procedure would protect it from deleterious effects produced by direct contact with saliva contaminants
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