Optimizing filler content in an adhesive system containing pre-reacted glass-ionomer fillers

Objectives. (1) To evaluate the optimal concentration of the calcium type pre-reacted glass-ionomer (PRG-Ca) fillers in experimental light-activated adhesives for bonding to tooth substrates and fluoride release; (2) to evaluate the polymerization reactivity of these experimental filled adhesives; and (3) to examine the ultrastructure of the resin-dentin interface bonded with the commercial version of this self-etching adhesive (Imperva Fluoro Bond, Shofu Inc., Kyoto, Japan). Materials and methods. PRG-Ca fillers were prepared from the acid-base reaction of calcium type fluoroaluminosilicate glass with poly(acrylic acid) in water. Different experimental light-cured adhesives were prepared, with 0-57 wt% PRG-Ca fillers and 3 wt% aerosil silica incorporated in a resin matrix. Twenty-four hours shear bond strengths to bovine enamel and dentin were assessed using the adhesive with/or without accelerated aging. The cumulative amount of fluoride released from the cured adhesives and differential scanning calorimetry (DSC) measurements were also conducted. 180-grit SiC paper polished human dentin disks were treated with Imperva Fluoro Bond that contains 17 wt% PRG-Ca fillers and prepared for TEM examination. Results. Increase in PRG-Ca filler content of experimental adhesives was highly correlated with the decrease in bond strengths to dentin (r = -0.96 to -0.99), the increase in cumulative fluoride release, (r = 0.97) and the decrease in polymerization energy (cal/g) of the adhesives (r = -0.99) (p < 0.001). A PRG-Ca content of 17wt% provided optimal bond strength to enamel and dentin after accelerated aging and fluoride release. TEM showed that salt-like matrices were present around the hydrogels and remnant glass cores of the PRG-Ca fillers. The commercial self-etching primer completely dissolved the smear layer and formed 2 μm thick hybrid layers in intact dentin. Significance. The use of silanized PRG-Ca fillers provides good adhesion and a source of fluoride release in a commercially available self-etching adhesive system.