Ultrastructural study of a glass ionomer-based, all-in-one adhesive

Objective: Reactmer Bond (Shofu Inc., Kyoto, Japan) is a glass ionomer (GI) based, tri-curable, all-in-one, filled adhesive. Both fluoroaluminosilicat e glass (FASG) and fully pre-reacted glass (F-PRG) are used as fillers. Thi s study examined the ultrastructure and elemental composition of resin-dent ine interfaces that were treated. with this adhesive. Methods: Dentine disks prepared from human third molars were abraded with e ither 600- or 60-grit SiC paper to create smear layers of different thickne ss. They were bonded using Reactmer Bond. Cryo-fraetured dentine surfaces d evoid of smear layers were also bonded by chemical-activation and GI reacti on without additional light-activation, or allowing the GI reaction to proc eed for I min before the adhesive was applied and light-activated. Undemine ralised and demineralised sections were processed for TEM examination and S TEM/EDX analysis. Results: Resin-dentine interface from specimens with smear layers consisted of a mineral-dense surface layer that resided on top of a partially demine ralised dentine. The partially demineralised zone was considerably, thicker in the 600-grit than the 60-grit specimens. In smear layer-free specimens that were cured by chemical-activation/GI modes. only, the surface layer co ncurred with the partially demineralised zone, and appeared as an electron- dense layer over the undemineralised intact dentine. Smear layer-free speci mens that were cured by the light-activation of the partially neutralised a dhesive contained incomplete amorphous surface layers only. Apart from coll oidal silica, FASG fillers were the predominant filler type within the resi n matrices. Peripheral hydrogel layers that contained electron-dense 'seeds ' were found around the FASG fillers. F-PRG fillers were only sparsely obse rved. In specimens that were laboratory demineralised with formic acid, pha se separation of the unstained resin matrices into electron-dense and elect ron-lucent domains occurred. Artefactual dendritic deposits were found with in the electron-dense domains. Conclusions: The presence of a surface interaction layer on top of a partia lly demineralised zone along the resin-dentine interface suggests that eith er a GI-type reaction or precipitation of insoluble carboxylate salts aroun d remnant apatite crystallites may occur when this single-step adhesive int eracts with dentine. Appearance of artefactual dendritic deposits suggests that continuous ion movement is possible within the hydrophilic portion of the resin matrix in this fluoride-releasing adhesive. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.