Comparison of etch-and-rinse and self-etch adhesives

Objectives: To compare bond strength and bond interface of etch-and-rinse and self-etch adhesives using different interface-preparation techniques. Methods: Human molars exposed fresh dentin surfaces were applied either an etch-and-rinse (3M Single Bond, SB) or a self-etch (Clearfil SE Bond, SE) adhesive respectively, then a block of composite resin was built up. The dentin surface before and after applying acid/primer was observed with SEM. The bond specimens were stored (distilled water 24 hours at 37℃), sectioned (0.9 mm² cross-sectional surface) and tested with Microtensile Tester (n=15) for tensile bond strength. To investigate bond interface, representative sectioned specimens were conditioned using the traditional interface-preparation technique (HCl+NaOC1) or a modified one (HCl+NaOC1+hyaluronidase) and then observed with SEM-EDAX. Results: After etching/priming, enlarged openings of dentinal tubule for SB and dentinal tubule openings with plugs for SE were shown. Significant difference in bond strength was observed between SB (35.50±6.40MPa) and SE (45.06±5.29MPa) (p<0.05). No obvious boundary between the hybrid layer (HL) and adhesive was observed for both adhesives. When conditioned only using HCl+NaOC1, SB showed tags of 8~45µm long consisting of both silicate and calcium. The calcium level of tags was higher on the pulp side. When using hyaluronidase additionally, the tags were shorter (10~15µm) and the calcium level was under detectable limit. SE showed shorter and less dense tags than SB. Calcium was detected in tags of SE whether or not additionally using hyaluronidase. Conclusion: Tags together with HL observed using the traditional interface-preparation technique were composed of both resin and dentin. SE may firmly chemical bond to dentin due to the detectable calcium in tags after thorough conditioning. SE showed shorter tags but higher bond strength than SB. This indicates that the quality of HL and tags may be critical to bond strength of dentin adhesives.