Journal of Dental Research, Vol 70, 1230-1234, Copyright © 1991 by International & American Associations for Dental Research Online Journals
Effects of salivary film velocity on pH changes in an artificial plaque containing Streptococcus oralis, after exposure to sucrose
L. M. Macpherson and C. Dawes
Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Canada.
Results from a computer model suggest that following exposure of dental
plaque to sucrose, the rate of clearance of acids from plaque into the
overlying salivary film will be greatly retarded at low film velocities.
This was investigated with an in vitro technique in which artificial plaque
containing S. oralis cells was exposed to 10% sucrose for one min. The pH
at the proximal (P) and distal (D) undersurfaces of the plaque (0.5 or 1.5
mm thick) was then monitored during the passage of a 0.1-mm-thick film of a
sucrose-free solution over the surface. Over the range of salivary film
velocities that have been estimated to occur in vivo (0.8-8 mm/min), lower
minimum pH values and increased times for the pH to recover toward
neutrality occurred at the lower salivary film velocity. Lower pH values
were also reached with the 0.5- than with the 1.5-mm-thick plaque. P/D pH
gradients, with a lower pH distally, developed at film velocities of 0.8
and 8 mm/min, and the gradients were much more pronounced at the lower
velocity. No P/D pH gradients developed when the film velocity was 86.2
mm/min. Incorporation of dead S. oralis cells into the plaque at
percentages up to 57% reduced the extent of the pH fall and prolonged the
recovery of the pH toward neutrality. The results support the prediction
that, other factors being equal, plaque located in regions of the mouth
with low salivary film velocity will achieve pH values lower than those of
plaque of identical dimensions and microbial composition located in areas
where salivary film velocity is high.
