Effects of honeycomb surfaces on bond strength to zirconia fabricated with 3-dimensional printing.

STATEMENT OF PROBLEM: In dental applications, the bonding ability of zirconia to resin remains a significant limitation to its broader clinical use. The microstructures on its surface can improve bonding strength, but the effects of honeycomb structures remain unclear. PURPOSE: The purpose of this study was to evaluate the effects of surface honeycomb structures on the bond strength to zirconia fabricated with advanced customized jetting (ACJ) technology, a 3-dimensional printing method. MATERIAL AND METHODS: Honeycomb structures with varying depths (60, 80, and 100 microm) and widths (100, 200, and 300 microm) were designed on the surfaces of zirconia specimens (test groups). Zirconia specimens with smooth surfaces (controls) were polished and airborne-particle abraded. Each set of specimens was divided into 2 subgroups (n=20) based on the presence or absence of 10-methacryloxydecyl dihydrogen phosphate (MDP). Surface roughness (Sa) was measured by using an optical profiler. The specimens were bonded to cylindrical resin with resin cement. Shear bond strengths (SBSs) were measured by using a universal mechanical testing machine. Fracture modes were observed under a stereomicroscope. The Shapiro-Wilk test was used to assess the normality of the data distribution. The Levene test was used to evaluate the homogeneity of the variance of data. Differences in SBS between the groups were analyzed by using 3-way analysis of variance and the least significant difference test for normally distributed data or the Kruskal-Wallis test with Bonferroni correction for nonnormally distributed data (alpha=.05). RESULTS: Among all surface designs, the groups with a depth of 100 microm and a width of 300 microm exhibited the highest Sa (15.34 microm). The SBSs of the subgroup treated with MDP were significantly higher than those of the subgroup without MDP (P<.05). In addition, in subgroups without MDP treatment, significant differences were found between controls (7.11 +/-2.4 MPa) and test groups, with that featuring honeycomb structures of 100 microm depth and 300 microm width showing the highest SBS (11.38 +/-2.0 MPa), representing a 60.6% improvement in bond strength. In addition, in the MDP treatment group, statistically significant differences were observed between both the group with structures of 100 microm depth and 200 microm width (14.73 +/-2.6 MPa) and that with structures of 100 microm depth and 300 microm width (16.39 +/-3.0 MPa) and controls (12.50 +/-2.3 MPa) (P<.05). The test group with the highest SBS of these 2 groups exhibited a 31.1% improvement. Adhesive failure and mixed failure were the predominant fracture modes in the subgroups without MDP, whereas cohesive failure and mixed failure were observed in the subgroups with MDP. CONCLUSIONS: The incorporation of honeycomb structures on zirconia surfaces combined with MDP treatment can significantly improve the SBS to zirconia. The depth and width of these honeycomb structures influence the SBS.