Acids treatment modify enamel permeability.

Objectives: evaluate acids effect on enamel by Raman and IR spectroscopy. Enamel permeability detected by replica technique was correlated. Materials and Methods: twelve slices and powder of sound human enamel were prepared. Two treatments were investigated: 15 % hydrochloric acid (HCl) for 120 s and orthophosphoric acid (H3PO4) 37% for 30s. Raman spectra were recorded using a Bruker IFS66/FRA-106 FT-Raman spectrometer (Ćexc = 1064 nm). IR spectra were recorded on a Nicolet 5700 FT-IR spectrometer (diamond ATR accessory). Nine teeth were selected for replicas at baseline and after treatments. Polyvinylsiloxane impressions (Affinis, Coltene) were later cast in polyether impression material (Permadyne Garant; 3MESPE) and inspected by SEM. Results: Raman and IR spectroscopy showed that treatment with both hydrochloric and phosphoric acids induced a decrease in the carbonate: the relative intensity of the bands at 1075 cm-1 (Raman, B-type carbonate stretching mode), 1415 cm-1 (IR, B-type carbonate stretching mode) and 1540 cm-1 (IR, A-type carbonate stretching mode) decreased upon treatment. At the same time, both acids induced the formation of HPO42- ions, as revealed by the increase in relative intensity of the bands at 587 cm-1 (Raman) and 530 cm-1 (IR). Upon treatment with HCl, strong bands due to the organic component were observed in both Raman (2940, 1670, 1455, 1275-1248 cm-1) and IR (2950, 2920, 2850 cm-1) spectra. On the contrary H3PO4 decreased organic bands. SEM baseline replicas showed droplets. Replicas of H3PO4 treated enamel showed a strongly reduced permeability with no droplets detectable. Replicas of HCl 15% still showed droplets. Conclusions: a decrease of the organic detected bands, as resulted after H3PO4 treatment, could be related to a decreased permeability as well the increase of the organic matter by HCl maintained enamel permeability. Results suggested a correlation between the organic matter and enamel permeability.