2021 Volume 71 Issue 1 Pages 28-35
Surface pre-reacted glass-ionomer (S-PRG) filler has the ability to release mineral ions, such as aluminum (Al3+), borate (BO33-), fluoride (F-), silicate (SiO32-), sodium (Na+), and strontium (Sr2+). A three-way crossover trial using depth-specific analysis was conducted to estimate the enhancement of fluoride retention in oral biofilms when fluoride is applied at the same time as other mineral ions are released from experimental toothpaste containing S-PRG filler. Eighteen healthy participants wore in situ plaque-generating devices (a pair of 4-mm2 enamel slabs) on their upper molars, and biofilm was allowed to form for three days. A slurry of toothpaste containing S-PRG filler (ϕ 3µm, 5wt%) was filtered. This filtrate contained Al3+ (340.5ppm), BO33- (447.7ppm), Sr2+ (985.2 ppm), and F- (181.0ppm). Devices were removed twice each day, immersed in the filtrate for one minute, and reinserted at the same location. Thirty minutes after the final immersion, devices were collected and samples were serially sectioned, with 2 x 2-µm sections taken first, followed by 4 x 4-µm sections for separation into outer, middle, and inner-layered fractions (300µm thick). This procedure was repeated until the required thickness was obtained. Samples treated with filtrates containing F- and Sr2+ (PC) or F- (NC) without S-PRG filler extract served as positive or negative controls, respectively. Fluoride and the three other mineral ions extracted from the thicker sections were quantified using a fluoride-selective electrode and ICP-atomic emission spectroscopy, respectively. The results were corrected for the biomass volume estimated by area measurement of stained 2-µm sections. Mineral concentrations among the layers within the biofilm samples were analyzed by the Friedman test, and comparisons of mineral concentrations among the three groups were evaluated by the Kruskal-Wallis test. Concentrations of Al3+ and BO33- in the S-PRG group were significantly higher throughout the tissue than the PC and NC groups. Levels of Sr2+ in both the S-PRG and PC groups treated with solutions containing Sr2+ were significantly higher throughout the tissue than in the NC group. On the other hand, F- concentrations in the S-PRG group were significantly higher throughout the tissue than in the NC group, and significantly higher in the outer and middle layers than in the PC group, although the experimental and two control biofilms were treated with filtrates containing the same level of fluoride. The results suggest that toothpaste containing S-PRG filler promotes the retention of fluoride in biofilms.
