Effect of an Experimental Primer Solution on Bonding to Resin Blocks

<p> Purpose: This study investigated the bonding of resin cement to hybrid resin blocks using an experimental primer solution. The combined use of silane coupling and sandblasting was also investigated.</p><p> Methods: Shofu Block HC Hard (SH; Shofu) as a CAD/CAM hybrid resin block and an experimental non-filler type resin block with no filler (NF) were prepared and used in the experiments. Adherends (14×12×2 mm) and specimens (3×3×3 mm) were prepared using either SH or NF. The conditioning of each surface after sandblasting was: HC primer treatment (HC group), 4% silane compounded experimental primer solution (HC+SI group), experimental 4% silane coupling agent (SI group), and no treatment (NT group). After each treatment, the adherend surface and specimen surface were bonded using Block HC Cem (Shofu). After curing, the samples were immersed in 37°C water for 24 h, followed by 5,000 thermal cycles (n=6). A shear bond test was performed using a universal tester and the obtained data was statistically analyzed using one-way analysis of variance (ANOVA) and Tukey’s test. The fractured surface was observed under a scanning electron microscope. To investigate the penetration of HC into the matrix resin, an NF specimen (14×12×3 mm) was prepared, HC was applied to the surface of the specimen and the sample was kept standing for 10 min, after which it was analyzed using a laser Raman microscope.</p><p> Results: There was no significant difference in the bonding strength in each group after immersion of SH and NF in water for 24 h, but after thermal cycling, the bonding strength was significantly higher in the HC and HC+SI groups compared to the SI and NT groups. In addition, no difference was noted after thermal cycling in the HC and HC+SI groups compared with that after 24 h immersion in water. Laser Raman spectroscopic analysis implied the possibility of 4-5 μm superficial penetration of HC into the matrix resin. Thus, when using the experimental primer solution, a high bond strength might be obtained due to the synergistic effect of penetration into the matrix resin and chemical bonding to the filler although further study is needed to clarify the function of the experimental primer solution.</p><p> Conclusion: Within the limitations of this study, the experimental primer solution possibly enhanced the bonding to resin blocks.</p>