An FTIR study on the setting mechanism of resin-modified glass ionomer restoratives

Abstract

Objectives. An experimental method was used to assess the glass ionomer and resinous character in three “dual-cure” (Fuji II LC, Photac-Fil, Variglass) and a “triple-cure” (Vitremer) resin-modified glass ionomer restoratives to evaluate their acid-base and free-radical setting mechanisms.Methods. Four groups (A-D) of three specimens (5 × 4 × 1 mm) were prepared from each material and subjected to the following treatments: A: mixing; B,C: mixing, 60 s irradiation, 20 min dark/dry storage; and D: mixing, 20 min dark/dry storage and then 60 s irradiation. Micro-multiple internal reflectance FTIR spectroscopy was used to determine: 1) the curing efficiency of the products immediately after irradiation; 2) the effect of irradiation 20 min after dark/dry storage on the curing efficiency; and 3) the extent of the acid-base reaction on irradiated and non-irradiated specimens after 20 min dark/dry storage.Results. The curing efficiency immediately after irradiation was determined from the percentage of residual double bonds which ranged from 33–50% for these materials. Irradiation after 20 min dark/dry storage significantly reduced curing efficiency in all the products, except Variglass. The latter showed no acid-base reaction under the conditions of this study. Non-irradiated specimens after the dark storage period demonstrated higher car☐ylate yields compared to their irradiated analogues. Non-irradiated specimens from Vitremer had the highest car☐ylate yield and a curing efficiency of ∼50% residual double bonds.Significance. Photopolymerization seemed to greatly reduce the acid-base reaction during the early setting stages of resin-modified glass ionomer restoratives. The free-radical formation rates are slower than those achieved by chemically initiated polymerization, but they produce adequate conversion and high car☐ylate salt yields. This study demonstrated an experimental model for identification and characterization of the acid-base reaction in water-containing resin-modified glass ionomer restoratives.