Thermal decomposition of developing enamel

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