Fluoride in plaque fluid, plaque, and saliva measured for 2 hours after a sodium fluoride monofluorophosphate rinse

Sodium monofluorophosphate (NaMFP) and sodium fluoride (NaF) are the two most common sources of fluoride used in currently marketed fluoride dentifrices. The purpose of this study was to investigate the effect of mouth rinses containing NaF or NaMFP on the concentrations of fluoride, or the MFP ion, in saliva, whole plaque, and plaque fluid. Twelve subjects abstained from tooth brushing for 48 h, fasted overnight, and then rinsed 1 min with 12 mmol/l (228 ppm [microg/g] F) NaF or NaMFP in the morning. Before the rinse and at 30, 60 and 120 min afterwards, upper and lower molar and premolar plaque samples and whole saliva samples were collected. Aliquots of plaque fluid and centrifuged saliva were obtained from these samples, and the whole plaque residue acid extracted. The F and MFP concentrations were then measured in these samples using ultramicro methods. For both rinses, a higher concentration of plaque fluid fluoride was found at lower molar sites while the reverse was true for the whole plaque fluoride. Furthermore, for both rinses, plaque fluid, whole plaque, but not salivary, fluoride concentrations were above baseline at 120 min. Following the NaMFP rinse, a substantial amount of unhydrolyzed MFP was found in plaque fluid and saliva. Although there was a very large range in these measurements, fluoride in plaque fluid (excluding fluoride in unhydrolyzed MFP) and whole plaque were significantly (p<0.05) greater after the NaF rinse at all time periods. In saliva, the NaF rinse produced a statistically significant greater salivary fluoride (excluding fluoride in unhydrolyzed MFP) only at 60 min. The lack of a clear correlation between these measurements and clinical studies suggest a novel mechanism may enhance the effectiveness of NaMFP dentifrices.     

Effect of a water rinse on 'labile' fluoride and other ions in plaque and saliva before and after conventional and experimental fluoride rinses

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 purpose of this study was to examine plaque and saliva composition after a fluoride rinse and subsequent sucrose application. Fifteen subjects accumulated plaque for 48 h, and then rinsed with a fluoride rinse based on 228 microg/g (ppm) Na2SiF6 and some received no rinse. After 60 min, upper and lower buccal molar plaque samples and 1-min saliva samples were collected. The subjects then rinsed with 10% g/g sucrose solution, and 7 and 15 min later, a second and a third set of samples were collected. Plaque fluid and clarified saliva were then recovered from these samples by centrifugation, and the remaining plaque acid extracted. The plaque fluid, centrifuged saliva, and plaque extract samples were then analyzed using micro techniques for pH, free calcium, phosphate, organic acids (plaque fluid and saliva only) and fluoride. Considering both the fluoride rinse and no-rinse groups, the most notable compositional changes in saliva 7 min after the sucrose rinse were pH -0.40 unit, free calcium 0.42 mM, lactate 5.2 mM, phosphate -1.3 mM, and fluoride 2.8 microM; while in plaque fluid, the corresponding changes were pH -1.59 unit, free calcium 1.5 mM, lactate 35 mM, phosphate -1.6 mM and fluoride -26 microM. After sucrose rinsing, undersaturation was found with respect to dicalcium phosphate dihydrate in saliva and plaque fluid and with respect to tooth enamel in some plaque fluid samples. Plaque fluid composition appeared to be strongly influenced by salivary clearance, diffusive loss of ions into the water phase of the rinse, and lower jaw pooling of the sucrose and fluoride components of the rinses. After the experimental rinse, the fluoride concentration in plaque fluid [86 +/- 22 mM (upper molar site), 162 +/- 150 mM (lower molar site)], saliva (26 +/- 18 mM), and whole plaque [99 +/- 97 microg/g (upper molar site), 197 +/- 412 microg/g (lower molar site)] was comparable to the values in previous studies using this rinse. These very high plaque fluid fluoride concentrations, compared with the 'no-rinse' samples, induced an approximately 0.3-unit increase in the plaque fluid pH 7 min after the sucrose rinse, a small decrease (approximately 20%) in lactate production and a modest increase in enamel saturation. Although these changes were all statistically significant, no correlation was found between the decrease in lactate concentration and plaque fluid fluoride, pH or whole plaque fluoride.     

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 intersubject variations in plaque-fluid distribution were observed, with the central incisors showing the 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.     

Fluoride tablet programs in healthy elderly subjects: distribution of fluoride in saliva and plaque with tablets in different sites

Based on root caries data and oral sugar clearance pattern, vestibular surfaces of upper incisors and lower molars may be regarded as risk areas along with the proximal surfaces. The aim of the present study was to use this information in improving fluoride tablet programs for the elderly. Six healthy elderly males with full dental arches took part. Flavored and unflavored tablets dissolved passively either under the tongue or in the vestibule close to the root caries risk areas. Salivary fluoride was determined at five to six intra-oral sites with a micro-sampling technique at intervals up to 10 min tablet use. Plaque samples were collected from single tooth surfaces before and after tablet use, and analyzed for total fluoride and total protein by micro-techniques. Salivary fluoride exposure to root caries risk areas was strongly increased when fluoride tablets were placed in the vestibule in these areas. The unflavored tablet gave higher fluoride retention in saliva than did the flavored brand. Plaque fluoride levels tended to be above baseline in the first couple of hours after tablet use, and then to decline. In the caries risk areas, at vestibular surfaces of lower posterior and upper incisor teeth, most of the fluoride taken up in plaque had been lost after 5 h and a bread meal, whereas in the non-risk areas it was largely retained. The study demonstrated that fluoride exposures to the vestibular caries risk areas can be strongly increased by placing fluoride tablets close to them. An unflavored tablet seemed to give higher exposures than a flavored one. The rapid loss of fluoride from plaque in slow clearance risk areas indicates that more than one daily treatment would be required for elderly caries risk subjects.     

The effect of salivary clearance of sucrose and fluoride on human dental plaque acidogenicity

Ten subjects rinsed with a 20% (0.58 M) sucrose solution with or without 0.2% NaF (905 parts/10(6) F-) added in two separate experiments. Saliva and plaque were collected before rinsing and after 2, 5, 10 and 30 min. Sucrose and fluoride concentrations in saliva and acid anion and fluoride concentrations in plaque were analysed. There was a statistically significant and positive correlation between the concentration of sucrose in the saliva 2 min after the rinse and the subsequent concentrations of lactate in plaque at 10 and 30 min after the rinse with sucrose alone but not in the presence of fluoride. Salivary fluoride concentrations during 2-30 min after the sucrose rinse were significantly correlated with plaque fluoride concentrations during the same time. The addition of fluoride to the sucrose rinse significantly inhibited lactate production.     

Effect in vitro acidification on plaque fluid composition with and without a NaF or a controlled-release fluoride rinse

Plaque fluid ion concentration changes, especially fluoride, in response to the pH decrease associated with a cariogenic episode are important components of the caries process. A "controlled-release" (CR) fluoride rinse, based on the controlled release of fluoride in the presence of calcium, has been shown to form large fluoride reservoirs in resting plaque. In this study, the in vitro acid-induced release of fluoride, and other ions, was examined in 48-hour-fasted plaque fluid from subjects (n = 11) who received no rinse, or who used a 228-ppm CR or NaF fluoride rinse 1 hr before being sampled. After collection, the plaque was centrifuged to yield plaque fluid, acidified (0.1 microL of 0.5 mol/L HCl per milligram plaque), and then re-centrifuged before a second sample was obtained. Although previous studies indicated a higher plaque fluid fluoride after the new rinse relative to NaF, no statistically significant difference was observed here. Average fluoride release after acidification (average pH, 5.2) was statistically greater following the use of the CR rinse (153 micromol/L) compared with the NaF rinse (17 micromol/L). No fluoride release was seen in the no-rinse samples. The pH, free calcium, phosphate, acetate, propionate, and buffer capacity were not affected by the different amounts of fluoride deposited in the plaque. However, following acid addition, an increase in free calcium and phosphate was observed, which was also independent of the rinse. The large release of fluoride following acidification suggests that the new rinse may provide an improved cariostatic effect.     

The inhibition of acid production in human saliva by monofluorophosphate.

Sodium monofluorophosphate (MFP) and NaF were compared for their ability to inhibit acid production in human saliva-glucose mixtures. Whole stimulated saliva was incubated at 37 °C with 2.5 per cent glucose in the presence of NaF (1.05 mmol/l) or MFP (initially 1.05 mmol/1 or neither (controls). Because MFP was gradually decomposed, releasing fluoride, further incubations were included in which increments of NaF were added to reproduce this increasing fluoride concentration. Acid production in the MFP incubations was less than in the controls and greater than in those containing equimolar NaF, but almost the same as in those in which added fluoride reproduced the release from MFP. This showed that the inhibition of acid production in the MFP incubations was due to the fluoride released and that the PO₃F^2? ion itself had little or no effect. The hydrolysis of MFP by salivary enzymes was greater at pH 7 than at pH 4. A direct effect on plaque microorganisms by MFP is an unlikely explanation for the cariostatic properties of MFP toothpastes.     

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.     

Use of an intra-oral model to evaluate 0.05% sodium fluoride mouthrinse in radiation-induced hyposalivation

The present study was undertaken to evaluate the effect of a twice-daily topical application of a 0.05% NaF mouthrinse on de- and remineralization in the oral cavities of subjects suffering from radiation-induced hyposalivation. Six subjects each wore a bonded intra-oral appliance containing a sound and a demineralized human enamel slab for four weeks. During that period, the subjects used 0.05% NaF rinses, twice daily, instead of the 1.1% NaF gel that had previously been a part of their preventive regimen. Salivary flow rates, plaque pH profiles following a 10% sucrose rinse, S. mutans and lactobacillus counts, fluoride clearance, and enamel microhardness were determined during the study. Sound enamel samples displayed no evidence of demineralization, and the previously demineralized enamel showed remineralization in the outer 50 microns in three of the six subjects. The results suggest that a twice-daily oral rinse with 0.05% NaF can prevent demineralization and enhance remineralization in subjects with radiation-induced hyposalivation.     

Distribution and kinetics of fluoride ions in the free aqueous and residual phases of human dental plaque.

24-h plaque samples from 97 dental students were studied. One minute after rinsing with 20 mM NaF, pH 7.80, the mean plaque fluid fluoride activity was 4.9 ± 0.8 mM and exceeded the control values at 2 h but not 3 h after rinsing. The total fluoride content in plaque residue followed a similar time course. The sodium concentration of plaque fluid, and the large decrease in potassium concentration of plaque residue indicated a short-term injury to the cellular elements. The increased fluoride content of the plaque residue could not be ascribed to mineral deposition. It was concluded that the presence of plaque during a rinse was advantageous because it reduced the fluoride ion activity at the enamel surface, which reduced CaF₂ formation, and it increased fluoride levels of the enamel environment up to 3 h after rinsing with 20 mM NaF.     

The influence of plaque on reaction mechanism of MFP and NaF in vivo

A modified Intra-oral Cariogenicity Test was used to study the influence of plaque on the reaction mechanism of sodium monofluorophosphate (MFP) or sodium fluoride (NaF) in either sound or demineralized enamel in vivo. Volunteer students, wearing mouth appliances holding enamel blocks, rinsed their mouths with MFP or NaF solution (1,000 ppm F-) three times a day. The amount of loosely-bound and acquired fluoride was determined after an experimental period of five days in plaque-covered, demineralized (PCD); clean, demineralized (CD); plaque-covered, sound (PCS); and clean sound enamel (CS). While no measurable loosely-bound fluoride could be found after MFP treatment, NaF caused deposition of a significant amount of alkali-soluble fluoride in all experimental groups. After MFP rinses, fluoride concentration in the enamel was increased in the following order: CS, PCS, CD, and PCD. After NaF treatment, demineralized enamel exhibited a higher fluoride acquisition when compared with sound enamel. Plaque had a minor effect on F- acquisition. It is concluded that demineralization of enamel enhances F- uptake from both NaF and MFP solutions. In the presence of plaque, F- acquisition was additionally increased only after MFP rinses in vivo.     

The diluting effect of saliva on the sucrose concentration in different parts of the human mouth after a mouth-rinse with sucrose

Saliva at four buccal sites [between the upper (UC) and lower (LC) central incisors, and between the upper (UM) and lower (LM) second premolar and first molar], and also whole saliva, was collected from 10 subjects at 0.5, 2.5, 5.5 and 10.5 min after a rinse with 10 ml of 0.3 mol/l sucrose solution. After 0.5 min, unstimulated salivary flow rate was inversely correlated with sucrose concentration in whole saliva (p less than 0.05). Sucrose concentration decreased faster at LC than at other sites. Sucrose dilution at UC and LC was inversely correlated (p less than 0.05) with salivary flow rate at times after 0.5 min. At 10.5 min, the sucrose concentration at all sites was significantly correlated (p less than 0.05) with the salivary flow rate.     

Fluoride concentrations in plaque, whole saliva, and ductal saliva after application of home-use topical fluorides [published eerratum appears in J Dent Res 1993 Jan;72(1):87]

It is now well-accepted that the primary anti-caries activity of fluoride (F) is via topical action. The retention of F in the mouth after topical fluoride treatment is considered to be an important factor in the clinical efficacy of F. The purpose of this study was to evaluate F levels in ductal saliva, whole saliva, and pooled plaque after treatment with topical F agents intended for home use. Ten consenting adults, mean (SD) age 31.0 (8.2) years, participated in all aspects of the study. Two days before each test, subjects received a professional tooth cleaning and subsequently abstained from all oral hygiene procedures to permit plaque to accumulate, and from the use of F-containing dental products. Treatments consisted of a placebo dentifrice (PD), fluoride dentifrice (FD; 0.24% NaF), fluoride rinse (FR; 0.05% NaF), and fluoride gel (FG; 1.1% NaF). Unstimulated whole saliva and pooled plaque were sampled at multiple points over a 24-hour period. In a separate experimental series, stimulated parotid saliva was sampled over a two-hour period after treatment. Fluoride levels generally followed the same pattern in whole saliva and pooled plaque samples, with FG > FR > FD > PD. Night-time F application resulted in prolonged F retention in whole saliva but not in plaque. Fluoride levels in parotid saliva were only slightly higher after F treatment and returned to baseline levels within two h. The results of this study indicate that the method of F delivery, the F concentration of the agent, and the time of application (daytime vs. night-time) are important factors influencing F levels in the mouth.(ABSTRACT TRUNCATED AT 250 WORDS)     

The buffer capacity of single-site, resting, human dental-plaque fluid

A carbonate equilibration method was used to measure the buffer capacity of resting plaque fluid collected from single buccal or interproximal sites of upper and lower first molars or anterior teeth. The maximum buffer capacity was 26 m-equiv./l at pH 7.1. The buffer contribution from the measured concentrations of phosphate and carbonate was calculated for each sample. These values were compared with the buffering actually measured and with that expected from organic acids, proteins, and amino acids at average values, as taken from reports in the literature. Relative contributions of buffer species at the average pH of the samples (6.86) were: 35 per cent phosphate, 10 per cent carbonate, 10 per cent protein, 10 per cent organic acids, 2 per cent amino acids, 30 per cent unidentified. There were no significant differences in the buffer capacities of samples originating from sites that differ in their accessibility to saliva. Buffering in resting plaque fluid is more than twice that in saliva and did not show differences correlated with the intra-oral location of the samples.     

Effect of toothpaste rinses compared with chlorhexidine on plaque formation during a 4-day period

Abstract Evidence suggests that brushing with a toothpaste may slow plaque reformation over 24 h. This study measured the effect of toothpaste alone on plaque regrowth over a 96 h period and compared the effect with water and the known antiplaque agent chlorhexidine. At 9 a.m. at the beginning of 7,4-day no oral hygiene periods, 10 volunteers were scaled and polished. Al 5 p.m. subjects brushed their own teeth with water until plaque free. Each subject rinsed for I min with 10 ml of a randomly allocated rinse. Rinsing was repeated at 10 a.m. and 10 p.m. on subsequent days. The rinses were water, chlorhexidine 0.2% or 3 g/10 ml slurries of toothpastes containing (1) monofluorophosphate(MFP), (2) monofluorophosphate + sodium fluoride (MFP+NaF) (3) monofluorophosphate + zinc citrate (MFP+ZCT) (4) stannous fluoride (SnF₂) (5) sodium fluoride (NaF). At 16, 24, 48 and 72 h plaque on the buccal surface of the upper and lower premolars, canines and incisors was scored by the Gingival Margin Plaque Index (GMPI) and gram films of plaque samples made. At 96 h plaque was recorded diagraromatically and areas of coverage measured visually (Debris Index) and by planimetry. Progressive plaque formation to a Gingival Margin Plaque Index of 100% at 72 h was observed for toothpaste and water rinses. For chlorhexidine the Gingival Margin Plaque Index at 72 h was 6%, At 96 h plaque areas were significantly less with toothpaste rinses compared with water. Chlorhexidine very significantly reduced plaque areas compared with toothpaste and water. The bacteriological assessment of smears revealed essentially similar plaque development during toothpaste and water rinses and was consistent with previous reports. However, with chlorhexidine the densities of organisms in the smears were greatly reduced. It was concluded that the small effect of toothpaste rinses on plaque accumulation compared with chlorhexidine would not alone represent a true antiplaque effect resulting in therapeutic benefit.     

Salivary fluoride levels following application of fluoride varnish or fluoride rinse

OBJECTIVES: This study examined the concentration of fluoride in whole saliva over time following the application of a fluoride varnish or a single rinse with a fluoride solution. METHODS: A two-period, two-treatment randomized cross-over experimental trial with a 2-week washout period was used with 16 adult subjects. In the first period, eight subjects rinsed once with a 0.05% NaF solution and 8 subjects had 5.0% NaF varnish applied to facial and lingual surfaces of 20 teeth. Stimulated whole saliva was collected at baseline, 5 and 15 min, 1, 2, 4, 8, 12, 24, 32, 48, 56, 72, 80, 96, 104 h. After the washout period each subject was switched to the other treatment and saliva was collected at the same intervals. Salivary fluoride content was measured with the micro-diffusion method. RESULTS: The NaF levels peaked at 5 min after application for both varnish (mean +/- SE 24.5 +/- 5.0 ppm) and rinse (3.2 +/- 0.8 ppm). Mean NaF levels returned to baseline, on average, within 2 h for the rinse and within 24 h for the varnish. The maximum fluoride levels were significantly greater (P < 0.01) with the varnish than with the rinse and remained above baseline levels for a longer duration. CONCLUSIONS: Salivary fluoride levels with the rinse returned to baseline, on average, in 2 h while they remained elevated for, on average, 24 h with the varnish. Salivary fluoride levels from the varnish were found to be comparable with those in previous studies for 1.1% neutral NaF.     

Fluoride in the oral environment

A predominant part of the cariostatic activity of fluoride is a function of its concentration in the fluid environment of the teeth. The fluoride exposure results in a slightly elevated steady-state level of fluoride in the oral fluids, primarily in saliva and plaque fluid. So far, however, little is known about the intra-oral fluoride concentration necessary to achieve a cariostatic effect at the site of action. Following fluoride intake, the fluoride remaining in the oral cavity is diluted by the saliva pool. The remaining fluoride may be found in several compartments in the oral cavity. It may be ionized in saliva, ionized in plaque (plaque fluid), bound in plaque, bound as calcium fluoride, bound to enamel, and bound to soft tissues. Fluoride is also distributed to the oral tissues and into the dental plaque by diffusion. It is well established that plaque, after fluoride exposure, becomes a fluoride reservoir which stores for some time and releases fluoride. The present review gives an insight into the important parameters that determine the disposition and fate of fluoride in the oral environment. To achieve in-depth understanding, and hence formulation of the optimal fluoride therapy, more information is needed to consolidate our understanding of the distribution, retention, and elimination of fluoride in the oral cavity. Such knowledge will form a better basis for providing our patients with more effective dental fluoride products and regimens.     

The effect of 0.2 per cent (48 mM) NaF rinses daily on human plaque acidogenicity in situ (Stephan curve) and fluoride content

Plaque acidogenicity (Stephan curves) and fluoride concentrations were measured in 40 subjects before and during a 1–2 month period of daily mouth-rinsing with 48 mM NaF. Plaque-fluoride concentration increased on average 12-fold during the rinsing period and there was also a small, but statistically significant (p < 0.025), average increase of 0.11 units in the pH minimum of the Stephan curve. This increase was slightly larger (0.20 units) for the group of 27 subjects whose pH minima prior to fluoride-rinsing were 5.7 or lower. Inclusion of 48 mM NaF in the sucrose rinse used to induce the Stephan curve for 4 subjects raised the average pH minimum by 0.70 units. The effect of fluoride rinsing on plaque acidogenicity and fluoride concentration was lost within 4–10 days of withdrawal of the rinse. It is concluded that a reduction in plaque acidogenicity may supplement the cariostatic action of fluoride on enamel solubility.     

Incidence of selected ureolytic bacteria in human dental plaque from sites with differing salivary access

Saliva is the main source of urea in the human mouth and may be responsible for the predilection of ureolytic bacteria for certain tooth sites. As a test of this hypothesis, the ureolytic bacteria, Haemophilus parainfluenzae, Actinomyces naeslundii, Actinomyces viscosus and coagulase-negative oral staphylococci, were enumerated in supragingival plaque from various sites in each of 10 subjects. The sites sampled included the maxillary and mandibular incisors (chosen because the lower incisors are more exposed to the submandibular-sublingual secretion than the upper) and the maxillary and mandibular molars (the upper molars being closer to the source of parotid saliva). After dispersion of the plaque samples in saline, subsamples of each suspension were plated on appropriate selective media and other subsamples were taken for nitrogen analysis to measure the amount of plaque sampled. H. parainfluenzae that used urea was present in the largest numbers, A. viscosus was next and A. naeslundii and coagulase-negative staphylococci were least. The staphylococci and H. parainfluenzae were more numerous from mandibular than from maxillary incisors and from maxillary than mandibular molars, a pattern which suggests that salivary access favours their selection. The numbers of A. viscosus and A. naeslundii were not related to salivary access: A. viscosus was most numerous from the maxillary incisors, possibly because this site is normally the most acidic of the four studied and A. viscosus is strongly acidogenic and aciduric; the incidence of A. naeslundii had no relationship with site.(ABSTRACT TRUNCATED AT 250 WORDS)