DENTIN DEMINERALIZATION - EFFECTS OF DENTIN DEPTH, PH AND DIFFERENT ACIDS

Objectives. This investigation sought to determine: 1) if dentin demin eralization rates are proportional to acid concentration for demineral ization in phosphoric acid (10% or 1.76M, 0.025M, 0.0001M, with pH=0.9 5, 2.0, 4.0 respectively); 2) if the etching characteristics are indep endent of dentin depth; and 3) if the etching characteristics for phos phoric acid were comparable to those for citric acid over a similar pH range. Methods. Highly polished dentin disks from freshly extracted, non-carious, third molars were prepared with a reference layer. Sample s were prepared from either superficial or deep coronal dentin. The sa mples were etched for periods of up to 30 min using phosphoric acid so lutions (pH = 0.95, 2.0, 4.0) in a wet cell of an atomic force microsc ope (AFM). Depth changes with respect to the reference layer were dete rmined for the intertubular and peritubular dentin to quantify structu ral changes. The results were compared with similar studies using citr ic acid (pH = 1.0, 2.15 or 3.4). Etching characteristics were statisti cally compared using 2-way repeated measures ANOVA at p < 0.05 and the Tukey's multiple comparison test. Results. The relation between time and recession for peritubular dentin was initially linear. The intertu bular dentin recession started rapidly but then reached a plateau with in a very short interval for etching solutions at pH = 2.0 and 4.0. At the highest concentration, the recession decreased with time, but a c lear plateau was not established. There was no statistical difference between peritubular etching rates of superficial and deep dentin surfa ces with phosphoric acid at any concentration. There was also no diffe rence in the intertubular dentin recession at the location of the plat eau that depended on dentin depth. Etching rates increased dramaticall y with decreased pH for both phosphoric and citric acids, but were hig her for citric acid than for phosphoric acid.Significance. The BFM all owed quantification of changes during etching of we dentin. Peritubula r dentin etching rates increased with decreasing pH, as expected, but changes were not linear and were different for the two acids studied o ver a similar pH range. Intertubular dentin surface recession was smal l and plateaued for low concentrations, The peritubular etching rate a nd intertubular dentin recession did not depend on dentin depth.