FLUORIDE-INDUCED ENHANCEMENT OF DIFFUSION IN STREPTOCOCCAL MODEL PLAQUE BIOFILMS

It has been demonstrated that fluoride decreases the calcium-binding a ffinity of Streptococcus mutans and approximately doubles the calcium- binding capacity. To investigate the effect of this mechanism on calci um mobility in plaque, Ca-45 flux was measured from a condensed films of S. mutans into tracer-free solution. Bacteria were suspended in pH 7.0 or 5.0 buffer including 0, 5, 10, 15 or 20 mmol/l Ca2+ carrier, wi th or without 5 mmol/l F- and with Ca-45 and H-3-inulin. The appearanc e of Ca-45 and H-3-inulin in carrier-containing but initially tracer-f ree buffer was measured and extracellular fraction (V-e) and bound cal cium were calculated. As the ratio (R) of bound to free Ca2+ approache d zero at high [Ca2+], the measured diffusion coefficient (D-r(e)) app roached the effective diffusion coefficient (D-e), such that: D-r(e) = D-e/(1+R). Fluoride increased the rate of calcium diffusion by a redu ction in the binding affinity. This work demonstrates that fluoride si gnificantly increases mobility in plaque; this may increase the rate a t which calcium is transported between plaque and an underlying lesion and so promote remineralization. This mechanism could also increase t he penetration of bacteriocides and suggests a novel method for biofil m treatment.