Sodium monofluorophosphate degradation by oral streptococci, plaque and saliva

Interindividual differences in degradation of sodium monofluorophosphate by saliva in relation to oral health status

The enzymatic degradation of sodium monofluorophosphate by whole saliva in patients with differing oral health status was compared Ten patients each with good or poor oral health were selected. Assessment of oral health status included indices of the amount of dental plaque, caries experience and counts of Streptococcus mutans and lactobacilli. Whole-saliva samples were collected under standardized conditions and monofluorophosphatase (MFPase) activity was measured in 2-ml saliva samples during 2 h of incubation at 37 C with 1 ml of monofluorophosphate solution (equivalent 31.5 mmol/1 F). MFPase activity was found in all the saliva samples. The values ranged from 0.6 to 17.8 nmol F/ml saliva per min. High MFPase activities correlated well with large amounts of plaque with the D component of the DMFT index and with high counts of salivary S. mutans and lactobacilli. The results show a wide range of MFPase activity in individuals and a statistically significant correlation (p < 0.05) between high MFPase activity and poor oral health status.

The diffusion and enzymic hydrolysis of monofluorophosphate in dental plaque

Although the ability of dental plaque to hydrolyze sodium monofluorophosphate (MFP) has been known for some time, its effect on the F- concentration at the plaque-enamel interface is undefined. We have determined enzyme kinetic values for MFP hydrolysis and diffusion coefficients so that the penetration and degradation of MFP in plaque can be modeled by computer. The KM and Vmax values for natural human plaque were 1.77 mmol/L and 41.4 nmol/min/mg protein, respectively, at pH 8.0. At pH 6.0, the Vmax was lower, 15.6 nmol/min/mg, but KM was not significantly different. Competitive inhibition by orthophosphate gave a Ki of 4.55 mmol/L. The diffusion coefficient for MFP in artificial plaque was 1.91 x 10(-6) cm2/sec. When these data were used for mathematical modeling of the effects of rinsing with MFP and F- solutions, compared with an equivalent NaF application, the concentration of F- from MFP was lower at the inner surface of plaque, and the peak occurred later. Both pH and plaque thickness had a marked effect on the amount of MFP that could penetrate: At pH 8.0, almost none reached the inner surface of a 1-mm-thick plaque intact. At pH 6.0, however, more MFP was able to penetrate, due to lower MFPase activity. While MFP diffusion is inherently slower than that of F-, enzymic degradation increases the gradient for inward diffusion. If the conventional view that MFP in toothpaste acts as a source of F- is true, then MFP toothpaste should be formulated to optimize MFPase activity in dental plaque.