Abstract
Specular reflectance Fourier transform infrared (SR-FTIR) spectroscopy was used to study the setting reaction of dental resin-modified glass ionomer (RMGI) restoratives as a function of curing depth and postirradiation time. Two light-cure and one tri-cure RMGI materials were selected and used according to the manufacturers’ instructions. Samples were prepared by filling the mixed materials into custom-made molds and then light-irradiating using a dental curing light. The degree of conversion and the extent of acid-base reaction of the materials at different depths (0, 1, 2, and 4 mm) and postirradiation times (10 min, 1 day, and 7 days) were determined using SR-FTIR spectroscopy in conjunction with the Kramers-Kronig (K-K) transformation. The setting reaction was also investigated using microhardness measurements. The results showed that the depth of cure increased over time by the continuous acid-base reaction rather than photopolymerization or chemical polymerization. Microhardness tests seemed less suitable for studying the setting reaction as a function of postirradiation time, probably due to softening from the humidity. Analysis using specular reflectance in conjunction with the K-K algorithm was an easy and effective method for monitoring the setting reaction of dental RMGI materials.
Highlights
Dental glass ionomers (GIs) are water-based materials that set by an acid-base reaction between a polyalkenoic acid and fluoroaluminosilicate glass [1, 2]
There is still limited experimental and clinical information available concerning the setting reaction of resinmodified glass ionomer (RMGI) restorative materials as a function of curing depth and postirradiation time. In this in vitro study, we investigated the monomerto-polymer conversion and the acid-base reaction of three commercial RMGI restoratives at different depths and postirradiation times using an optical microscope connected to an Fourier transform infrared (FTIR) spectrophotometer
The filled RMGI material was irradiated for 40 s by placing the end of the light guide of a dental light-curing unit (Elipar TriLight, 3 M ESPE, Seefeld, Germany; standard mode) onto the top of the polyester strip so that the light could transmit through the polyester strip over the material (n = 6) [10]
Summary
Dental glass ionomers (GIs) are water-based materials that set by an acid-base reaction between a polyalkenoic acid and fluoroaluminosilicate glass [1, 2]. A previous Fourier transform infrared (FTIR) spectroscopy study demonstrated that the visible light-curing process, for either light- or tricure RMGIs, greatly reduces the salt formation (acid-base reaction) rate during the early setting stages, which is likely due to rapid polymer network formation [7]. Another FTIR study showed that the acid-base reaction is greatly delayed in RMGIs compared to conventional GIs [11]. It was assumed that each measured microhardness value reflects the surface hardening by the contribution of both the polymerization reaction and acid-base reaction at a specified depth and postirradiation time
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