Acquired acid resistance of enamel by silica thin film coating

Objective: If the tooth surface is covered with a colorless transparent silica thin film, it can be expected to prevent caries. Previously we have reported that the rapid silica thin film coating method on enamel surface*. The purpose of this study was to examine the effectiveness of the silica coating method on acid resistance of enamel. Methods: 10% of preceramic polymer perhydropolysilazane (PHPS; AZ Electronic Materials, Tokyo, Japan) solution was used. Finely finished bovine enamel slabs (7 x 7 mm) were divided into two groups; silica thin film coated group and non-treated control group (n=5). PHPS was applied on the enamel surface and 40ml of 3 % hydrogen peroxide solution was dropped onto the PHPS-coated surface. PHPS was converted to silica by CO₂ laser (Opelaser-03S, Yoshida, Tokyo, Japan) irradiation for 1 min. All specimens were covered with nail varnish except for a window of 3mm diameter and immersed in 0.1 mol/l hydrochloric acid solution for 30 minutes. The measurement of dissolved calcium ion concentration from the enamel surface was determined quantity spectrophotometrically by a colorimetric assay based on the Arsenazo III reaction at a wavelength of 660nm. The data were analyzed statistically by One-way ANOVA and Tukey's test at p<0.01. Results: After the acid resistance test, the mean calcium concentrations that dissolved into the hydrochloric acid of the silica film coated and control group were 0.03 mmol/l and 1.89 mmol/l respectively. The silica film coated group was showed significantly lower concentration of calcium compared with the control group. Conclusion: It was suggested that the silica thin film coating method is promising to create a firm acid resistant layer on tooth enamel surface. * Tanaka T et. al., abst # 271, IADR-CED with NOF & ID congress in Munich, 9-12 Sept. 2009