The decomposition of forming, maturing, and mature enamel was studied between room temperature and 1,000 degrees C by powder X-ray diffraction and infrared absorption methods. In mature dental enamel, carbonate decomposition proceeds relatively fast until 500 degrees C and at a slower rate beyond it. In forming and maturing enamel, decomposition is faster and is completed around 800 degrees C. The formation of beta-Ca3(PO4)2 is observed in dental enamel at 500 degrees C. At 1,000 degrees C, the apatite phase in forming and maturing enamel transforms almost completely to beta-Ca3(PO4)2, whereas in mature enamel, even at 1,000 degrees C, only partial decomposition occurs. Infrared results show the appearance in dental enamel of (1) A-type carbonate at room temperature and in the 500-900 degrees C range, in addition to the commonly observed B-type carbonate, and (2) intermediate CO2 molecules during carbonate decomposition (200-500 degrees C).