Journal of Dental Research, Vol 65, 1053-1056, Copyright © 1986 by International & American Associations for Dental Research Online Journals
A comparison of the potassium content and osmolality of plaque fluid and saliva, and the effects of plaque storage
G. H. Dibdin, R. P. Shellis and C. Dawes
Previous determinations of osmolality and potassium concentrations in
plaque fluid, much higher than those in saliva, suggest a restricted
exchange between the two, which must be reconciled with recent findings of
quite rapid diffusion in plaque. Possible reasons for the high values were
considered, and of these the effect of solute leakage from bacteria to the
plaque fluid during typical periods of storage was investigated. It was
also shown that the osmotic pressure of plaque fluid could be measured
quite accurately by vapor pressure osmometry on whole plaque samples
without the need for centrifugation. Samples of plaque, or plaque fluid
prepared by centrifugation at 12,000 g, were compared for osmolality or
potassium content with matched samples prepared from plaque stored chilled
or in liquid nitrogen. Saliva samples obtained just prior to plaque
collection were also analyzed. Freshly collected plaque from
overnight-fasted subjects had a plaque fluid osmolality of 156 +/- 35 as
compared with 98 +/- 23 mOs/kg for saliva. Potassium in plaque fluid from
freshly collected "mature" plaque was 40.6 +/- 5.1 as compared with 20.3
+/- 5.3 mmol/L for saliva, but for 1-2-day-old plaque from fasted subjects
it was significantly lower (30.4 +/- 5.6 mmol/L). These values for plaque
fluid are all much less than those previously found, and storage was found
to cause a marked increase (range, 35-100%). Centrifugation at 12,000 g
caused little change in plaque fluid osmolality but seemed to accelerate
the rate of increase during subsequent storage.
