The Ultrastructure of Human Dental Enamel Heat-treated in the Temperature Range 200°C to 600°C

Abstract

Heating enamel in the temperature range 200°C to 600°C resulted in poor crystal packing due to void formation, permanent change in the sign of its birefizngence (from negative to positive) in some areas, and an altered crystal morphology. Transmission electron microscopy of enamel heated in the temperature range 200°C to 400°C revealed that the distinction between the positively birefringent regions and the negatively birefringent regions (which were present up to 350°C and occasionally up to 400°C) at the tooth's surface was due to the greater volume of intra- and inter-crystalline voids within the positively birefringent regions. There was a significant increase in void volume at 400°C, an..