Four-year water degradation of a resin-modified glass-ionomer adhesive bonded to dentin

Glass-ionomers are auto-adhesive to tooth tissue through combined micro-mechanical and chemical bonding. How much each of the two bonding components contributes to the actual bonding effectiveness is, however, not known and there is not much information available on long-term stability. The objective of this study was to assess the bonding effectiveness of a resin-modified glass-ionomer adhesive to dentin after 4 yr of water storage. Fuji Bond LC (GC) was applied without (i) and with pretreatment using (ii) a polyalkenoic acid conditioner and (iii) a 37.5% phosphoric acid etchant. The etchant was used to exclude any chemical interaction with hydroxyapatite. The micro-tensile bond strength (muTBS) to dentin decreased significantly over the 4 yr period in all three experimental groups. After 24 h and 4 yr, the lowest muTBS was recorded when dentin was not pretreated. The highest muTBS was obtained following polyalkenoic acid pretreatment, although this was not significantly different from specimens that were pretreated using phosphoric acid. Pretreating dentin with phosphoric acid intensified micromechanical interlocking at the expense of chemical bonding potential to hydroxyapatite. Nevertheless, correlating the muTBS data with failure analysis through scanning electron microscopy and transmission electron microscopy indicated that combined micro-mechanical and chemical bonding involving pretreatment with the polyalkenoic acid conditioner yielded the most durable bond.