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

摘要

Abstract Aim To characterize chemical degradation of the principal constituents of dentine after exposure to Na OC l 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% Na OC l for 2‐10?min; or 17% EDTA for 5‐1440?min. Powders larger than 75?μm were also sequentially exposed to Na OC l/ EDTA /Na OC l 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 Na OC l or EDTA , respectively. The data were analysed descriptively. Results Surface collagen fraction declined by ~40% within 2?min of Na OC l 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 Na OC l/ EDTA immersion yielded a 62?±?28?μm thick phosphate‐depleted surface. Sequential Na OC l/ EDTA /Na OC l treatment resulted in approximately 85?μm of collagen loss. Conclusions Data revealed the sequential depletion of collagen by Na OC l and apatite by EDTA in dentine, simultaneously exposing the other moieties. Alternate exposure to Na OC l and EDTA therefore enhances the depth of erosion.