An FTIR study on the setting mechanism of resin-modified glass ionomer restoratives.
OBJECTIVE
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 x 4 x 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 carboxylate yields compared to their irradiated analogues. Non-irradiated specimens from Vitremer had the highest carboxylate yield and a curing efficiency of approximately 50% residual double bonds.


CONCLUSIONS
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 carboxylate salt yields. This study demonstrated an experimental model for identification and characterization of the acid-base reaction in water-containing resinmodified glass ionomer restoratives.
Kakaboura
A
A
Research Center for Biomaterials, Athens, Greece.
Eliades
G
G
Palaghias
G
G
D000136:Acid-Base Equilibrium; D000180:Acrylic Resins / Q000737:chemistry; D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry*; D008027:Light; D011108:Polymers / Q000737:chemistry; D012044:Regression Analysis; D019279:Resin Cements / Q000737:chemistry*; D012117:Resins, Synthetic / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared
D000180:Acrylic Resins; D003188:Composite Resins; D005609:Free Radicals; C079765:Fuji II LC cement; D005899:Glass Ionomer Cements; C081144:Photac-Fil; D011108:Polymers; D019279:Resin Cements; D012117:Resins, Synthetic; C081982:VariGlass VLC; C084550:Vitremer