Advances in Dental Research, Vol 3, 249-257, Copyright © 1989 by International & American Associations for Dental Research
Ultrastructure of spindles and tufts in human dental enamel
J. Palamara, P. P. Phakey, W. A. Rachinger and H. J. Orams
A transmission electron microscope (TEM) study was made of spindles and
tufts as identified in the light microscope, from samples prepared by
selected-area argon-ion-beam thinning. Spindles in human dental enamel were
found to be continuous with dentinal tubules across the dentin-enamel
junction (DEJ) and usually appeared at the DEJ as electron-lucent, empty
channels nearly circular in cross-section. The spindles were found to cross
prism boundaries, branched rarely, and some were occasionally found to be
occluded or partially occluded with small needle-like crystals
(approximately 5 nm width and approximately 70 nm length), granular
material (approximately 1.5 nm diameter) and/or amorphous material. Near
the DEJ, the majority of spindles had a diameter less than 2 microns, while
in the prismatic enamel away from the DEJ, spindles with a diameter greater
than 2 microns were generally found. Spindle varicosity was characterized
by an enlargement of their diameter. Tufts started at the DEJ and were not
associated with dentinal tubules. Two types of ultrastructure were observed
in the TEM: (i) disrupted regions of enamel incorporating large voids (up
to approximately 0.1 microns in diameter), or, more commonly, (ii) channels
within the enamel occluded or partially occluded, with small needle-like
crystals and granular and/or amorphous material similar to that found in
the enamel spindles. It was concluded that spindles and tufts represent
areas of hypomineralization with increased void volume and partial
remineralization.
