Journal of Dental Research, Vol 74, 698-701, Copyright © 1995 by International & American Associations for Dental Research Online Journals
Problems associated with estimation of net calcium uptake during enamel formation using 45Ca
R. A. Moran, T. G. Deaton and J. W. Bawden
Department of Pediatric Dentistry, University of North Carolina, Chapel Hill, USA.
45Ca uptake in mineralizing tissues may occur by net Ca uptake or by
isotopic exchange. It is rarely possible to differentiate between these
effects, making interpretation of the findings difficult. Unfortunately,
this problem is not often considered, and 45Ca uptake is usually regarded
as representative of only net calcium uptake. The study reported here was
undertaken to estimate the extent to which 45Ca uptake in mineralizing
enamel is due to net Ca deposition or to isotopic exchange, and to consider
the implications. The enamel surfaces of the lower incisors of adult rats
were notched at the gingival line, and the eruption distance over 16 hours
was measured. This distance was used to establish the position of a
0.3-mm-wide increment of enamel at the beginning and end of the 16-hour
period, during which it passed through the early-maturation stage of enamel
formation. The rate of Ca uptake was determined by chemical assay. Other
rats were injected with 45Ca, mean plasma specific activity values for the
experimental period determined, and the rate of Ca uptake through the same
area of enamel formation was estimated. The estimates were from two- to
nearly ten-fold greater than those established by chemical assay,
indicating that from 50 to 90% of the 45Ca uptake occurred by isotopic
exchange. 45Ca uptake may indicate more about the labile state of Ca in
mineralizing enamel than about the rate of mineral deposition.
