Thermogravimetric studies on sound and carious human enamel and dentin as well as hydroxyapatite

The present study was conducted to investigate the thermal behavior of human sound and carious enamel and dentin. The results were compared to those obtained for pure hydroxyapatite. The volatile decomposition products were identified by mass spectrometry. Solid decomposition products were analyzed by infrared (IR) spectrometry. For both normal and carious enamel, the differential thermogravimetry (DTG) curves revealed three peaks at about 90-100, 330, and 900 degrees C. Both normal and carious dentin revealed two common peaks in their DTG curves, at about 90-100 degrees C and 330 degrees C. An additional peak at 500-600 degrees C was observed in the DTG curve of carious dentin in air atmosphere. This peak completely disappeared in nitrogen (N2) atmosphere. About 11-12% of sound and carious enamel was volatilized in air. The values for sound dentin were 34% and for carious dentin 54% per weight, respectively. Enamel and dentin (apatite protein complex) decomposed at higher temperatures than pure hydroxyapatite in air. In N2 atmosphere, both enamel and dentin are more resistant to thermal decomposition than in air, because organic materials decompose easier in an oxidizing atmosphere than in an inert atmosphere.