Journal of Dental Research, Vol 73, 1462-1469, Copyright © 1994 by International & American Associations for Dental Research Online Journals
The effect of supersaturation on apatite crystal formation in aqueous solutions at physiologic pH and temperature
K. Ishikawa, E. D. Eanes and M. S. Tung
National Institute of Dental Research, Bone Research Associate Program, National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
The importance of supersaturation in the dynamics of apatite precipitation
from aqueous solutions is well-established. To determine whether this
parameter has a comparable impact on the concomitant development of the
textural properties of this phase, such as crystal size and shape, we
investigated mineral accretion in synthetic solutions seeded with 0.67 g/L
apatite over a range of supersaturations at pH 7.4 and 37 degrees C. A dual
specific-ion electrode-controlled titration method was used to maintain the
seeded reactions under the following solution conditions: 1.0 to 1.8 mmol/L
Ca2+, 0.67 to 1.2 mmol/L total phosphate (PO4), Ca/PO4 (initial) = 1.5, 143
mmol/L KNO3, and 10 mmol/L HEPES. Samples were collected for chemical and
textural analyses when the seed apatite was reduced by new accretions to
1/2, 1/4, 1/8, 1/16, and 1/32 of the total solids in suspension. All new
accretions were found to be apatitic. At the lowest supersaturation,
accretion occurred primarily by growth of the seed crystals. However, at
the highest supersaturation examined, the crystals at the end of the
experiments were actually smaller, on average, than the original seeds,
even though the total mass increased 32-fold. The results suggest that
proliferation of new crystals supplanted growth of the seed crystals as
supersaturation was increased. The results also suggest that differences in
tissue fluid supersaturation may contribute to the large disparity in
dimensions between dentin and enamel apatite crystals.
