Effect of a Water Rinse on ‘Labile’ Fluoride and Other Ions in Plaque and Saliva before and after Conventional and Experimental Fluoride Rinses

Abstract

Labile reservoirs are important in maintaining ion concentrations in oral fluids, especially after a fluoride dentifrice application, where a persistent increase in fluid fluoride can mitigate or reverse caries progression. In this study, the effect of experimental and conventional fluoride rinses on the in vitro and in vivo water–induced release of fluoride, calcium, phosphate, acetate and hydrogen ions from oral reservoirs was examined. At the start of each experiment, 13 subjects rinsed either with a conventional 228–ppm fluoride NaF rinse, a 228–ppm fluoride controlled–release rinse (CR rinse) or received no rinse. Sixty minutes later upper and lower molar plaque samples and 1–min saliva samples were collected. The subjects then rinsed with deionized water for 1 min, and 7 min later, a second set of samples was collected (in vivo study). Plaque fluid and clarified saliva were then recovered from samples by centrifugation, and the remaining plaque mass was sequentially extracted with water and acid to measure the water–extracted and total whole–plaque fluoride (in vitro study). All the samples were analyzed using microtechniques for pH, free calcium, phosphate, organic acids (plaque fluid) and fluoride (plaque fluid, centrifuged saliva and plaque extracts). Results showed that in vivo water rinsing decreased acetate and phosphate in plaque fluid, and fluoride in plaque fluid and saliva, but had no effect on plaque fluid pH. In vivo water rinsing, however, increased plaque fluid free calcium, apparently due to water–induced loss of calcium–binding ions. Water– or fluoride–rinse–induced changes in plaque fluid concentration were greater at the lower molar site, suggesting that rinse pooling may influence ion distribution. Before the water rinse, plaque fluid, saliva and whole–plaque total fluoride values were 1.7, 2 and 4 times higher after the CR rinse compared to the NaF rinse. Furthermore, the CR rinse deposited approximately 11 times more water–extracted fluoride compared to the NaF rinse, suggesting a ‘more efficient’ precipitation of ‘labile’ or ‘loosely bound fluoride’. The results presented here, and in previous studies, suggest the possibility of formulating effective fluoride dentifrices with a lower fluoride content than is currently in use.

Changes in Lactate and Other Ions in Plaque and Saliva after a Fluoride Rinse and Subsequent Sucrose Administration

“…The sucrose rinse was administered 1 h after a fluoride rinse because this was considered to be the shortest postfluoride rinse time that could be anticipated before a subsequent cariogenic attack, and because previous studies suggested that, for a short period of time, plaque ions may be depleted by the water component of the fluoride rinse [Vogel et al, 2001]. The controlled-release experimental fluoride rinse, which uses the controlled release of fluoride from the hydrolysis of Na 2 SiF 6 in the presence of CaCl 2 to enhance the deposition of fluoride in oral tissue [Vogel et al, , 2001Chow et al, 2000], was chosen for these experiments for the following reasons: (1) in agreement with the studies described in the introduction, a preliminary experiment using similar experimental conditions found no effect on lactic acid production with an NaF rinse [Vogel, unpubl.…”

“…The controlled-release experimental fluoride rinse, which uses the controlled release of fluoride from the hydrolysis of Na 2 SiF 6 in the presence of CaCl 2 to enhance the deposition of fluoride in oral tissue [Vogel et al, , 2001Chow et al, 2000], was chosen for these experiments for the following reasons: (1) in agreement with the studies described in the introduction, a preliminary experiment using similar experimental conditions found no effect on lactic acid production with an NaF rinse [Vogel, unpubl. data], and (2) compared with an NaF rinse, the experimental rinse produced a much higher concentration of plaque and plaque fluid fluoride and a greater release of fluoride when plaque was acidified [Vogel et al, 1992[Vogel et al, , 2001, suggesting that a positive effect might be observed. More importantly, the plaque fluid concentration of ions other than fluoride has been shown to be very similar after either an NaF rinse or the experimental controlled-release rinse so that the results found here should be similar to those obtained with a conventional NaF rinse [Vogel et al, , 2001.…”

“…data], and (2) compared with an NaF rinse, the experimental rinse produced a much higher concentration of plaque and plaque fluid fluoride and a greater release of fluoride when plaque was acidified [Vogel et al, 1992[Vogel et al, , 2001, suggesting that a positive effect might be observed. More importantly, the plaque fluid concentration of ions other than fluoride has been shown to be very similar after either an NaF rinse or the experimental controlled-release rinse so that the results found here should be similar to those obtained with a conventional NaF rinse [Vogel et al, , 2001. Finally, the fluoride concentration of the rinse, 12 mM (i.e., 228 ppm, here mM is used for the SI unit mmol/l), was chosen because it approximates current over-the-counter formulations and because it was used in these previous experiments.…”

“…The analysis procedures are very similar to those previously employed and are only summarized [Vogel et al, , 1997[Vogel et al, , 2001. Plaque fluid or centrifuged saliva samples were analyzed for free calcium and pH using microelectrodes.…”

“…Other complicating factors include the potential increase in oral clearance of fluoride and other cariostatic ions by diffusion: (1) into the water component of the sucrose rinse, (2) into saliva, due to a sucrose-mediated increase in salivary clearance and, in the case of fluoride, (3) into the cells at low pH. Recently, in vitro acidification and water-rinsing experiments [Vogel et al, 2001] were done to separately address some of these factors. The purpose of the current study was to examine the changes in fluoride, pH, lactate and mineral ions in plaque fluid and whole plaque (fluoride only) after a sucrose rinse given 1 h after a fluoride rinse, and to use the results of these previous studies (which are briefly described in the Methods section) to interpret our observations.…”