Cavity surface interaction with resin-modified glass ionomer: Surface morphology, interface adaptation, tooth demineralization and fluoride uptake

Secondary caries is the major reason most commonly cited for dental restoration failure and replacement. On the other hand, fluoride containing restorative materials have demonstrated a variable degree of secondary caries reduction. Among them is the resin-modified glass ionomer (RMGI), which has well-documented in vitro cariostatic effects. These beneficial effects however, may be critically determined by the mode of cavity surface treatment involving smear layer treatments and adhesive liner application.; Six cavity surface treatment modalities were studied. These were: maintenance of the smear layer (no treatment), partial removal of the smear layer (polyacrylic acid, PAA), total removal of the smear layer (phosphoric acid, H3PO4), and with or without adhesive liner application (Scotchbond Multi-purpose, SMP).; The results of the SEM indicated distinct surface topographies produced by the various treatments of the smear layer on the enamel and dentin surface of the cavity preparation. Also an improved margin adaptation and enhanced interfacial characteristics between RMGI and enamel or dentin were obtained by phosphoric acid etching of the cavity surface with or without adhesive liner application. PLM and MRG clearly revealed the ability of RMGI to inhibit secondary caries at the enamel and root margins despite the aging process used. Total removal of the smear layer by acid etching reduced the subsequent demineralization area, demineralization depth, and mineral loss in the enamel and dentin adjacent to RMGI restoration. This effect was more evident on the root than on the enamel secondary caries. EPMA supported PLM and MRG findings showing more fluoride uptake with phosphoric acid etching. In contrast, application of an adhesive liner prior to the placement of the RMGI restoration reduced its caries inhibition effects as well as the fluoride-uptake by adjacent tooth structure.; Phosphoric acid cavity surface treatment presumably increased the effective surface area available for adhesion, ions exchange, and fluoride diffusion. Therefore, the cariostatic effects of resin-modified glass ionomer on secondary caries revealed by this in vitro study are most likely a combination of fluoride release and unique bonding mechanisms. (Abstract shortened by UMI.)...