Journal of Dental Research, Vol 66, 1742-1747, Copyright © 1987 by International & American Associations for Dental Research Online Journals
The ultrastructure of human dental enamel heat-treated in the temperature range 200 degrees C to 600 degrees C
J. Palamara, P. P. Phakey, W. A. Rachinger and H. J. Orams
Department of Physics, Monash University, Clayton, Victoria, Australia.
Heating enamel in the temperature range 200 degrees C to 600 degrees C
resulted in poor crystal packing due to void formation, permanent change in
the sign of its birefringence (from negative to positive) in some areas,
and an altered crystal morphology. Transmission electron microscopy of
enamel heated in the temperature range 200 degrees C to 400 degrees C
revealed that the distinction between the positively birefringent regions
and the negatively birefringent regions (which were present up to 350
degrees C and occasionally up to 400 degrees 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 degrees C, and above this all of the enamel was positively
birefringent and opaque. Large remineralized crystals of beta-tricalcium
phosphate (beta-TCP) phase (whitlockite) were initially formed at 400
degrees C, and their size and number increased at 500 degrees C and above.
Both the greater solubility of beta-TCP crystals and the increased surface
area due to the presence of voids would increase the rate of
demineralization of heat-treated enamel.
