Methods: Dentine blocks were prepared from extracted caries-free human premolars with a VC-50 slow-speed precision saw (Leco, Michigan). The dentine samples were divided into 8 groups (n=12 per group): (1) Water storage (control), (2) 9 % lactic acid (caries), (3) 0.5 M acetic acid (dietary), (4) 0.1 % phosphoric acid (dietary), (5) 0.3 % citric acid (dietary), (6) 10 % formic acid (laboratory), (7) 10 % ethylenediaminetetraacetic acid (EDTA) (laboratory) and (8) 10 % hydrochloric acid (gastric). Each sample was immersed in 10ml of acid solution for 14 days and refreshed every 24 hours. Demineralisation was terminated by alternating washes in 0.1 M cacodylate buffer and distilled water. Each of the 8 groups were divided into 4 assay subgroups (A-D): (A) Surface characterisation by scanning electron microscopy (SEM) (Inspect F-FEI, Oregon); (B) Micro-hardness testing (Mitutoyo HM, Illinois); (C) Hydroxyapatite content by X-ray diffraction (XRD) (Cu-STOE IP-PSD, Darmstadt); (D) Calcium and phosphorus levels by energy dispersive spectroscopy (EDS) (EDAX Genesis, Inspect F-FEI, Oregon).
Results: SEM analysis reveals a differential effect of the acids on the dentine structure with EDTA exposing more of the collagen matrix. Micro-hardness values range from 80 HV (control) to 160 HV (lactic acid). XRD and EDS confirm a differential loss of mineral content in all the acid-affected samples.
Conclusion: The structural integrity of dentine varies according to the nature of the demineralising acid.