To examine the ultrastructure of bonding to occlusal enamel fissures using phosphoric acid etching in combination with a pit and fissure sealant (Clinpro Sealant), a total-etch single-bottle adhesive (One-Step) followed by the fissure sealant, and two single-step self-etch adhesives (Adper Prompt and Xeno III) followed by the fissure sealant.
Sections of bonded enamel fissures retrieved from specimens bonded in vivo were polished, and rinsed with phosphoric acid to bring surfaces into relief. They were examined, first under non-dehydrated conditions with field emission-environmental SEM, to evaluate the marginal integrity of the bonds. The same specimens were then re-examined under dehydrated conditions with conventional SEM to capture more detailed ultrastructural features. Extent of resin penetration into etched enamel was further evaluated by TEM examination of sections taken from undemineralized unstained bonded specimens. These sections were further examined after HCl demineralization and staining.
All occlusal fissure walls examined were lined with remnant aprismatic enamel. Full penetration of resins into the bottom of the fissures, and gap-free interfaces were not observed in any of the specimens, irrespective of whether total-etch or self-etch adhesives were used with the sealant. Phosphoric acid did not penetrate well into the fissures and although hybridization of the etched aprismatic enamel was observed with or without the use of the total-etch adhesive, etching was inconsistent and gaps were frequently observed. Entrapment of bacteria within the fissure walls was frequently seen. The more aggressive self-etch adhesive Adper Prompt created etching in aprismatic enamel that approached that of phosphoric acid etching. The moderately aggressive self-etch adhesive Xeno III produced 1 mm thick hybrid layers in the aprismatic enamel fissure wall.