A photoacoustic FTIRS study of the chemical modifications of human dentin surfaces: I. Demineralization

Acids are used to modify the structure and composition of dentin surfaces t o improve bonds formed with resins. The purpose of this work is to investig ate such chemical modifications using the surface-sensitive technique photo acoustic Fourier transform infrared spectroscopy (PA-FTIRS). Spectra of aci d-treated samples (citric, maleic, nitric, and phosphoric at pH = 1.0) were recorded at various time intervals. Analysis of these spectra indicates a gradual increase in sample surface area with treatment time. A decrease of the bands associated with calcium hydroxyapatite (HAP) and carbonate apatit e inherent to the mineral phase of dentin an also observed. A comparison of spectra of samples treated for 2 min with each acid also reveals that male ic and phosphoric acids remove more HAP than citric acid. We conclude that citric acid may cause the formation of precipitates at the etching front wh ich inhibit etching. (C) 2001 Elsevier Science Ltd. All rights reserved.