Effect of Plaque Mineralization on Experimental Dental Caries

Abstract

A urea-MFP mineralizing solution increased the average concentration of calcium in artificial plaque in 5 subjects from 7.6 to 219 μg/mg protein, but the concentration fell to 59.6 μg/mg protein during subsequent cariogenic glucose exposures. The concentration of phosphate rose from 5.4 to 107 μg/mg protein and then fell to 32.7 while fluoride rose from 0.008 to 7.62 and then fell to 4.27 μg mg protein. Following the cariogenic challenges, enamel beneath mineralized plaque showed an average increase in Knoop diamond indentation length of 4.3 μm (compared to 25.01 μm beneath unmineralized plaque) and no radiographic evidence of demineralization. Enamel softening was inversely related to the amount of mineral in the overlying plaque. When the maintenance was high, the development of experimental caries was virtually eliminated. Common ion suppression of enamel dissolution is the most likely explanation for the caries-protective effect.

Therapeutic Modifications to the Mineral Ion Composition of Dental Plaque

“…Epidemiological evidence for an in verse relationship between plaque miner als and caries [Ashley and Wilson, 1977;/4gu.«et al, 1976;Schamschula et al, 1978] has recently been supported by experi mental evidence [Pearce, 1982]. Calcium, phosphate and fluoride deposited in plaque from this mouth rinse would thus be expected to have significant beneficial effects.…”

“…Individual variation in this activity has not been reported but is likely since the MFPase activity of indi vidual salivas differs markedly [Pearce and Jenkins, 1977], Other factors of possi ble importance in mouth-rinse response include the varying nucleating ability of plaque [Eilberg et al, 1973] and the sub ject's diet. Sugar exposures decrease plaque mineral [Pearce, 1982] and must be assumed to have influenced plaque miner al accumulation in this study.…”

“…Substantial increases are present 16 h after the final solution expo sure, indicating that the mineral ions are not free to diffuse out of the plaques. A proportion is liberated, however, when the mineralized plaque is exposed to ferment able carbohydrate [Pearce, 1982], The min eral ions are thus conserved, and released only when they can exert their greatest benefit. Increased concentrations of solu ble calcium and phosphate, arising in plaque fluid as the pH declines with sugar fermentation, will lower the 'critical pH' for enamel dissolution [Dawes and Jen kins, 1962], a factor of the greatest import ance in maintaining the integrity of enam el.…”

“…The mechanism has been fully de scribed elsewhere [Pearce. 1981[Pearce. , 1982, A preliminary trial in a group of school children showed that the in vivo use of a mouth rinse based on this principle could raise the average concentration of cal cium, phosphate and fluoride in natural plaque [Pearce and Schamschula, 1982], suggesting that mineralization was not depiendent on the peculiar properties of arti ficial plaque grown on intra-oral appli ances.…”

Comparative Reduction of Enamel Demineralization by Calcium and Phosphate in vitro

“…In principle, the chemical properties of this interface can be altered to decrease the cariogenic challenge originating from the metabolism of the oral flora. Several agents have been advanced as constituents of mouthwashes to minimize enamel demineralization, for example, lactate dehydrogenase [Higham and Edgar, 1991], urea and fluoride [Pearce, 1982[Pearce, , 1984Pearce and Nelson, 1988;Pearce et al, 1991], calcium phosphate [Stralfors, 1964;Rankine et al, 1989], calcium lactate [van der Hoeven, 1985;Shrestha et al, 1982;van der Hoeven et al, 1989;Kashket and Yaskell, 1992], calcium glycerophosphate [Bowen, 1972;Grenby and Bull, 1975;Sidi and Wilson, 1991] …”