Ultramorphological evaluation of the dentin acid-base resistant zone of two-step self-etching systems after long-term storage in water.

PURPOSE: To evaluate the morphological changes in the acid-base resistant zone (ABRZ) at the resin/dentin interface after long-term storage in water. MATERIALS AND METHODS: Two-step self-etching adhesive systems, Clearfil SE Bond (SE) and Clearfil Protect Bond (PB) (Kuraray Medical) were used. Human dentin disk sandwiches with resin composite were prepared, sectioned, and embedded in epoxy resin. The specimens were stored in water for 1 day, 1, 3 or 6 months, and then subjected to demineralizing solution and 5% NaOCl. The specimens were finally sectioned again, polished, argon-ion etched, and observed with SEM. RESULTS: The outer lesion (OL) thickness at 1 day ranged from 10 to 15 µm but increased to approximately 30 µm after 6 months, suggesting gradual loss of dentin stored in water. A lower electron density was noted in the adhesives at the locations that were exposed to water. The ABRZs were observed clearly in all groups; the thickness of the ABRZ at the mid-point of the OL gradually decreased with time for SE. For PB, the thickness was stable up to 1 month, but decreased after 3 months. The bottom of the ABRZ in SE formed a right angle with dentin; in contrast, in PB, it sloped down toward dentin with a broadening bottom. CONCLUSIONS: Water storage resulted in changes both in the dentin substrate and the adhesive layer. An ABRZ was observed beneath the hybrid layer after long-term storage in water in both SE and PB. The ABRZ was thicker and relatively more stable in PB, probably due to fluoride release.

Effect of functional monomers in all-in-one adhesive systems on formation of enamel/dentin acid-base resistant zone.

This study aimed at evaluating the effect of functional monomers in all-in-one adhesive systems on formation of acid-base resistant zone (ABRZ) in enamel and dentin. Experimental adhesive systems containing one of three functional monomers; MDP, 3D-SR and 4-META were applied to enamel or dentin surface and light-cured. A universal resin composite was then placed. The specimens were subjected to a demineralizing solution (pH 4.5) and 5% NaClO for acid-base challenge and then observed by SEM. The ABRZ was clearly observed in both enamel and dentin interfaces. However, enamel ABRZ was thinner than dentin ABRZ in all adhesives. Morphology of the ABRZ was different between enamel and dentin, and also among the adhesives. Funnel-shaped erosion was observed only in the enamel specimen with the 4-META adhesive. The formation of enamel/dentin ABRZ was confirmed in all adhesives, but the morphology was influenced by the functional monomers.