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

Abstract

Aim

To characterise 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 to1000 μm to provide six size ranges. Portions (250 mg) of each size range were reacted with 5mL of 2.5% NaOCl for 2-10 minutes; or 17% EDTA for 5-1440 minutes. Powders larger than 75μm were also sequentially exposed to NaOCl/EDTA/NaOCl each for 10 minutes. All experiments were repeated 5 times. Reacted and unreacted powders were washed and dried. Particles larger than 75μm 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 1640 cm⁻¹ collagen: 1010 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 were reduced following immersion in NaOCl or EDTA, respectively. The data was analysed descriptively.

Results

Surface collagen fraction declined by ~40% within 2 minutes of NaOCl exposure, and plateaued at ~60% between 6–10 minutes. Bulk spectra showed average depth of collagen loss at 10 minutes 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 1440 minutes 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 moeity. Alternate exposure to NaOCl and EDTA therefore enhances the depth of erosion.

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