C.M. Carey

In vivo Fluoride Concentrations Measured for Two Hours After a NaF or a Novel Two-solution Rinse

The concentrations of fluoride in various samples from the oral environment were measured at timed intervals after a novel rinse or a NaF rinse, both containing a total of 12 mmol/L (228 ppm) fluoride. The novel rinse consisted of two solutions mixed just before application: Part A contained calcium chloride and sodium acetate; part B contained a hydrolyzable source of fluoride (sodium hexafluorosilicate) and sodium phosphate. Samples were obtained as follows: Single-site plaque-fluid samples were obtained by centrifugation of first-molar plaque; pooled whole-plaque samples were collected from second molars; centrifuged, pooled whole-saliva was collected by vacuum. All samples were analyzed by micro-analytical methods. Results showed that, compared with NaF, the two-solution rinse produced significantly higher salivary fluoride concentrations, plaque-fluid fluoride concentrations, and acid-extractable fluoride in the whole plaque by factors of about 4, 2, and 6, respectively, at 120 min. The results of this study suggest that the new rinse may provide a greater cariostatic effect at the same fluoride dosage than does a NaF rinse.

Ca Pre-rinse Greatly Increases Plaque and Plaque Fluid F

Previous studies demonstrated that a Ca pre-treatment greatly increases salivary F from a subsequent NaF rinse. This study examines if these increases are found in plaque and plaque fluid F. Thirteen individuals accumulated plaque before rinsing with: (1) 12 mmol/L NaF (228 μg/g F), (2) 150 mmol/L Ca rinse, or (3) the Ca rinse followed by the F rinse. One hr later, plaque samples were collected, the plaque fluid was recovered, and the plaque residues were extracted 5 times with pH 6.8 or pH 4.8 buffers, and then by acid. The F in each extract after the Ca rinse/F rinse greatly exceeded the corresponding F from the NaF rinse. Consequently, the Ca rinse/F rinse increased the total plaque F and the plaque fluid F by 12x and 5x, compared with the NaF rinse alone. These and the previous salivary results suggest that a Ca pre-treatment may increase the cariostatic effects of topical F agents.

Increased Overnight Fluoride Concentrations in Saliva, Plaque, and Plaque Fluid after a Novel Two-solution Rinse

Recent studies showed that salivary, plaque-fluid, and whole-plaque fluoride were significantly higher 120 min after subjects rinsed with a novel two-solution rinse than after they rinsed with a NaF rinse of the same fluoride concentration. In this study, the persistence of these increases was investigated overnight, a period of time that is more clinically relevant. Improved analytical techniques for the ultramicro determination of whole-plaque and plaque-fluid fluoride from the same sample are also described. Thirteen subjects abstained from toothbrushing for 48 hrs and rinsed for 1 min with a 12 mmol/L (228 ppm) NaF or the two-solution rinse before bedtime. Samples were then collected the following morning before breakfast: (1) Saliva samples were either clarified by centrifugation or acid-extracted with 1 mol/L HClO4; and (2) single-site molar plaque samples were centrifuged to obtain plaque fluid and/or extracted with 1 mol/L HC1O4. Results showed that, compared with NaF, the two-solution rinse produced significantly higher fluoride concentrations in all samples: The concentration of fluoride in whole plaque and whole saliva following the new rinse exceeded concentrations found after the NaF rinse by factors of three and four, respectively, while in plaque fluid, the two-solution rinse produced about a two-fold increase over NaF values, which were near baseline levels. This increase, however, was only about 20% in centrifuged saliva. The increases in saliva and especially in plaque-fluid fluoride after the two-solution rinse indicate a greater remineralization potential, while the enhanced fluoride reservoirs found in plaque overnight after this rinse constitute a reserve that may release fluoride into the plaque fluid over an extended period of time.

Distribution of Fluoride in Saliva and Plaque Fluid after a 0.048 mol/L NaF Rinse

An ultramicro method has recently been described for measurement of plaque-fluid fluoride concentration (Vogel et al., 1990a). This method was used: (1) for exploration of the variation in fluoride concentration of plaque fluid collected from the same buccal tooth sites following a 0.048 mol/L NaF (0.2%) rinse, and (2) for examination of the distribution of fluoride in plaque fluid and saliva within one hour after this rinse. Results indicated an average coefficient of variation (CV) of 31% for plaque-fluid fluoride in triplicate samples recovered simultaneously from the buccal-proximal region of two teeth after the rinse. This was similar to the CV found for plaque-fluid fluoride from the same sites after separate administrations of the rinse. A strong linear correlation was found between salivary and plaque-fluid fluoride at 30 and 60 min after rinse administration, showing that plaque-fluid fluoride is influenced by the concentration of salivary fluoride after administration of this rinse. Plaque-fluid fluoride concentrations were higher than that in saliva at baseline, 30, and 60 min. Very large inter-site and inter-subject variations in plaque-fluid distribution were observed, with the central incisors showingthe slowest clearance. These variations suggest that an examination of plaque-fluid fluoride from specific tooth regions may be essential for understanding the effects of fluoride on the site-specificity of caries.

Composition of Plaque and Saliva Following a Sucrose Challenge and Use of an a-tricalcium-phosphate-containing Chewing Gum

Calcium phosphate concentrations in plaque, plaque fluid, and saliva play an important role in caries prevention. In this study, we used a microanalytical technique to examine the anticaries potential of a 2.5% (mass fraction) a-tricalcium-phosphate-fortified experimental gum by measuring the pH, free and total calcium, and total phosphate in plaque fluid, whole plaque, and saliva, and centrifuged saliva from 14 subjects who (1) accumulated plaque for 48 hours, (2) fasted overnight, (3) rinsed for 1 min with sucrose, and (4) chewed a control or experimental gum for 15 min. From these data, the hydroxyapatite (HAp) ion activity products (IAPHAp) of saliva and plaque fluid were calculated as a measure of tooth mineral saturation. Results, compared with those of the control gum, show significant increases in pH and in free calcium and phosphate concentrations in plaque fluid and saliva when the experimental gum was chewed following sucrose ingestion. These increases result in a rise in fluid saturation with respect to tooth mineral that, for plaque fluid, nearly cancels the decrease seen with the control gum after the sucrose rinse. This suggests that the experimental gum may be more effective than a conventional gum in ameliorating the cariogenic effects of sucrose. Similar statistically significant increases were also seen in the total calcium content of the plaque fluid, centrifuged saliva, whole saliva, and whole plaque, and in the total phosphate of whole plaque and whole saliva. These results suggest that the deposition of a mineral reservoir in plaque and saliva by the experimental gum may help resist future cariogenic challenges.

Micro-analysis of Plaque Fluid from Single-site Fasted Plaque

Despite the site-specific nature of caries, nearly all data on the concentration of ions relevant to the level of saturation of plaque fluid with respect to calcium phosphate minerals or enamel are from studies that used pooled samples. A procedure is described for the collection and analysis of inorganic ions relevant to these saturation levels in plaque fluid samples collected from a single surface on a single tooth. Various methods for examining data obtained by this procedure are described, and a mathematical procedure employing potential plots is recommended.

Fluoride Release from a Resin-modified Glass-ionomer Cement in a Continuous-flow System: Effect of pH

Fluoride is added to many dental restorative materials, including glass-ionomer cements, for the specific purpose of leaching fluoride into the surrounding tissues to provide secondary caries inhibition. During the caries process, an acidic environment attacks the dental tissues as well as the glass-ionomer cement. We hypothesized that pH significantly affects the rate of release of fluoride from the glass-ionomer cement. A continuous-flow fluoride-measuring system that monitors the amount of fluoride released over time was used to determine the release of fluoride from a resin-modified glass-ionomer cement (KetacFil®). The results show that the release rate began with a fast burst of fluoride which quickly diminished to low levels in 3 days. Under neutral pH conditions, the rate of fluoride release at 72 hrs was significantly slower than at pH 4.

Remineralization Effects of a Two-solution Fluoride Mouthrinse: An in situ Study

Results from previous studies show that a two-solution fluoride (F) rinse is significantly more effective than a NaF rinse of the same F content of 250 μg/g (ppm) in remineralizing enamel and root lesions in an in vitro cyclic de- and remineralization model. In the present study, the two-solution rinse and two NaF rinses with F contents of 250 ppm and 1000 ppm were evaluated in an intra-oral remineralization model. Caries-like lesions were formed in the enamel of extracted human molars with the use of a pH 4 demineralizing solution. Thin sections of the enamel (~ 120 μm) containing lesions were prepared, and the mineral contents of the lesions were assessed by quantitative microradiography. With the cut surfaces protected by nail varnish, 3 enamel specimens were mounted with wax in the lingual areas of a removable mandibular appliance. The study used a randomized, crossover design with seven subjects. In each of the 3 legs of the study, subjects wore the appliances continuously except when eating, drinking, and brushing their teeth. Twice daily (after breakfast and before bedtime), the subjects received a one-minute rinse with 20 mL of (1) 250-ppm-F NaF rinse, (2) 1000-ppm-F NaF rinse, or (3) 228-ppm-F two-solution F rinse. At the end of the 14-day experimental period, the sections were retrieved, and the mineral contents of the lesions were again assessed quantitatively. The results show that both the 1000-ppm-F NaF and 228-ppm-F two-solution rinses produced a greater (p < 0.05) remineralization than did the 250-ppm-F NaF rinse. The remineralization produced by the two-solution rinse was not statistically different (p > 0.05) from that produced by the NaF rinse with 4x the F content (1000 ppm F).

Micro-analysis of Mineral Saturation Within Enamel During Lactic Acid Demineralization

In this study, the physicochemical factors responsible for caries-like lesion propagation were investigated by means of a micro-analytical system used to study the fluid within a lesion during a simulation of the decay process. Four 500-μm-thick serial sections prepared from a single human molar were mounted between glass plates with only the natural surface of the tooth exposed. Microwells were then drilled into sound and pre-existing carious regions of the section through one of the plates. These microwells were then filled with fluid under mineral oil, and after a week of equilibration, the natural surface of the section was exposed to a lesion-producing fluid. The concentrations of calcium, phosphate, and hydrogen ions of the fluid in the wells were then followed as a function of time as the lesion advanced. The results of this study, in which lactic acid was used to demineralize enamel, were consistent with those previously reported (Vogel et aL, 1987a): The solution within the lesion remained saturated during the acid attack. Differences in initial mobilities of the calcium and phosphate and other ions, a result of the permselectivity of the enamel, increased the concentrations within the lesion and permanently changed the ratio of these ions in the lesion solution. Based on these results, we suggest that the ionic permselectivity of tooth enamel can have a profound effect on the transport of mineral from a caries lesion.

Composition of Plaque and Saliva Following use of an α-Tricalcium-phosphate-containing Chewing Gum and a Subsequent Sucrose Challenge:

Previous studies demonstrated that the chewing of a 2.5% (mass fraction) α-tricalcium-phosphate-fortified (a-TCP) experimental chewing gum released sufficient calcium and phosphate to eliminate any fall in the tooth mineral saturation of plaque fluid after a sucrose rinse (Vogel et al., 1998). In contrast, the chewing of a conventional sugar-free gum did not eliminate this decrease in saturation. The purpose of this study was to examine if the release of ions from plaque calcium-phosphate pools induced by this gum could provide protection during subsequent exposure to cariogenic conditions. Fourteen subjects accumulated plaque for 48 hrs, fasted overnight, chewed a control or experimental gum for 15 min, and subsequently rinsed 1 min with a mass fraction 10% sucrose solution. Before gum chewing, and at 7 min and 15 min afterward, whole plaque, plaque fluid, and salivary samples were obtained and analyzed by micro-analytical techniques. Additional samples were collected and analyzed at 25 min (7 min after the sucrose rinse). Although the results confirmed the deposition of large amounts of calcium and phosphates in plaque seen in the previous study, only a small increase was seen in plaque-fluid-free calcium and phosphate before sucrose administration. This suggests that few of the mineral ions were mobilized under non-cariogenic conditions. However, 7 min after the sucrose rinsing, an increase in these concentrations was seen which, based on hydroxyapatite ion activity product calculations, indicated a decrease in the driving force for demineralization compared with that seen with the control gum. These results suggest that the chewing of the experimental gum deposits a labile mineral reservoir in plaque that can resist a subsequent cariogenic challenge.