The influence of sodium hypochlorite and EDTA on the chemical composition of dentine

Abstract

Aim To characterise changes in the chemical composition of dentine after exposure to sodium hypochlorite and ethylenediaminetetracetic acid (EDTA) using ATR‐FTIR and Raman spectroscopy.Methodology Crown dentine was acquired from recently extracted molars stored in formal‐saline (group A) or saline and frozen at −2oC (group B); it was then ground and sieved into a range of particle sizes. Samples from both groups (n = 5 each) were analysed with FTIR to investigate the influence of storage medium and to assign FTIR spectral peaks for collagen, carbonate, phosphate. As no differences were found, the samples were pooled for subsequent experiments. Ten samples of particle size range 38–75 μm were used to study the effect of mass ratio of NaOCl (2.5%): dentine over 5–10 min. Thirty samples of all sizes were reacted with 2.5% sodium hypochlorite at 1:0.5 (dentine:NaOCl) mass ratio for 2–10 min; EDTA (n = 90) for 5–1440 min; NaOCl for 10 min followed by EDTA for 10 mins (n = 30); the latter samples were further exposed to NaOCl for 10 min after obtaining FTIR spectra.Results FTIR spectra from the surface of the particles (~1.5 μm depth) were obtained for all the samples and Raman spectra (40 μm depth) were obtained for one sample each reacted either with NaOCl or EDTA. Spectral peak assignment was confirmed by previous data. Storage media had no effect on outcome measures used. The dentine:NaOCl ratio influenced collagen depletion. NaOCl affected the collagen FTIR peaks, mostly in the first 2–4 min, but only influenced the phosphate and carbonate peaks slightly. EDTA affected the phosphate:collagen peaks, which reduced over time, whilst the collagen peak values showed an increase. The two solutions (NaOCl and EDTA) used alternately, respectively increased collagen or phosphate peaks depending on the final solution used.Conclusions These series of investigations confirmed that sodium hypochlorite depletes the organic content of dentine and EDTA depletes the inorganic content. Used alternately, they have the ability to progressively degrade dentine structure.