8 - Dentine Conditioners: Effect on Collagen Probed By Amide-III Peak Analysis

Abstract

To assess the extent of demineralization and changes in the collagen type I structure of dentine conditioned with various acids, by using the amide-III peak for analysis, which is not affected by the presence of water, as opposed to the commonly used Amide-I peak. Coronal dentin specimens (n=10/group) were analyzed by ATR-FTIR spectroscopy before and after conditioning (15 s for all) with 32% phosphoric acid (PA), 3% nitric acid (NA), 20% phytic acid (PT), 20% citric acid (CT) and 17% neutral EDTA (ED). The extent of demineralization (DM%) was measured from the PO 4 (1185-885 cm -1 ) / Amide-III (1370-1150 cm -1 ) peak area ratios, normalized against the native dentine specimens. The Amide-III peak was curve-fitted in four components assigned to α-helix (1285-1275 cm -1 ), β-turns (1255-1245 cm -1 ), random coils (1220-1210 cm -1 ) and β-sheets (1210-1200 cm -1 ) and the percentage subpeak areas were calculated relative to the total Amide-III peak. Statistical analysis was performed by one-way ANOVA (DM%) and t-test/Wilcoxon signed rank test for the curve-fitted components (α=0.05) The results of DM% were (mean/sd): PA: 89(3), NA: 95(2), PT:71(7), CT: 58 (8), ED: 25 (9) with a ranking of significant differences NA,PA>PT,CT>ED. Curve-fitting of the Amide- III peak revealed the following significant differences: Reduction in -helices and β-turns (PA); reduction in α-helices, β-turns and increase in β-sheets (NA); reduction in α-helices, β-turns and increase in random coils (PT); reduction in β-turns and an increase in β-sheets and random coils (CT) and increase in β-sheets and α-helices (ED) Amide-III peak may provide important information for the extent of demineralization and the collagen type I structure of acid etched dentine, without the water interferences considered in Amide-I analysis. The inorganic and phytic acids, with the highest demineralization, disorganized the α-helix and β-turn structures, citric acid adversely affected only b-turns, whereas ED was the least aggressive treatment.