Acid-base reaction and fluoride release profiles in visible light-cured polyacid-modified composite restoratives...

The aim of the study was to evaluate the extent of the acid-base reaction and F- release in Compoglass (Vivadent) and Dyract (Dentsply/DeTrey) restoratives.

For evaluation of the extent of the acid-base reaction, two groups of three specimens (7 mm x 5 mm x 1 mm) were prepared for each material. The first group was immersed in distilled water, while the second was kept in dark and dry conditions. Micro-MIR FTIR spectroscopy was used to determine the extent of the acid-base reaction on directly irradiated material surfaces immediately after irradiation and following water storage for 30 min, 3 d, 1, 2, 4, 8 and 12 wks. The in-depth extent of the acid-base reaction of the specimens stored in water for 4 weeks was studied by sequential spectra acquisition after removal of the uppermost 20, 70, 100, 240 and 400 microns layer by controlled grinding and 1 wk re-immersion in water of the 400 microns reduced specimens. For the F- release measurements, five disk-shaped specimens (10 mm x 1.5 mm) were prepared from each material and stored in distilled water. The amount of F- released for the storage periods reported above was measured using an ionometer with an F- electrode. Statistical analysis was performed by ANOVA, Scheffé's test and regression analysis.

Storage in water promoted the development of an acid-base reaction on directly irradiated surfaces which reached a saturation point after 4 weeks. Depth profiling of the 4 wk immersed specimens revealed high salt concentration at the uppermost 100 microns layer. Re-immersion in water for 1 week of the 400 microns reduced specimens increased the salt concentration again at the uppermost region. Statistically significant differences were found in the acid-base rates and the in-depth salt yields between the materials (p < 0.05). The fluoride release after a 1 week initial "bursting" period was stabilized below 2 mg l-1 (p > 0.05) in both products. No positive correlation was found between acid-base reaction and fluoride release.

The development of a carboxylate-rich surface layer on polyacid-modified composite restoratives after water storage may explain their lower wear resistance compared with resin composites. The dynamic nature of these surfaces may provide several advantages regarding their interaction potential with hard dental tissues and their anticariogenic properties, but also some disadvantages concerning the quality of the surface texture obtained.