Estimated depth of apatite and collagen degradation in human dentine by sequential exposure to sodium hypochlorite and EDTA: a quantitative FTIR study.

AIM: To characterize chemical degradation of the principal constituents of dentine after exposure to NaOCl and EDTA using Infrared Spectroscopy (ATR-FTIR). METHODOLOGY: Ground dentine particles, from extracted permanent human molars, were passed through sieves of 38 to 1 000 µm to provide six size ranges. Portions (250 mg) of each size range were reacted with 5 mL of 2.5% NaOCl for 2-10 min; or 17% EDTA for 5-1440 min. Powders larger than 75 µm were also sequentially exposed to NaOCl/EDTA/NaOCl each for 10 min. All experiments were repeated five times. Reacted and unreacted powders were washed and dried. Particles larger than 75 µm were then reground. FTIR spectra of unground and reground reacted particles enabled assessment of particle surface versus bulk chemistry, respectively, plus estimation of reaction depth. Changes in the ratio of the 1 640 cm-1 collagen: 1 010 cm-1 phosphate peak height or its inverse were obtained. These were used to estimate surface and bulk fraction reacted and thus depth to which collagen or phosphate was reduced following immersion in NaOCl or EDTA, respectively. The data were analysed descriptively. RESULTS: Surface collagen fraction declined by ~40% within 2 min of NaOCl exposure, and plateaued at ~60% between 6-10 min. Bulk spectra showed average depth of collagen loss at 10 min was 16 ± 13 µm. Ten minute EDTA exposure caused ~60% loss of surface phosphate. Average depth of phosphate loss was 19 ± 12 µm and 89 ± 43 µm after 10 and 1 440 min EDTA immersion, respectively. Sequential NaOCl/EDTA immersion yielded a 62 ± 28 µm thick phosphate-depleted surface. Sequential NaOCl/EDTA/NaOCl treatment resulted in approximately 85 µm of collagen loss. CONCLUSIONS: Data revealed the sequential depletion of collagen by NaOCl and apatite by EDTA in dentine, simultaneously exposing the other moieties. Alternate exposure to NaOCl and EDTA therefore enhances the depth of erosion.