Acid Production In Plaque Research Articles

Antimicrobial Effect of Silver Ionised Water Prepared with the Sintering Coating Method—Effect on Acid Production in Plaque

Purpose: To investigate the effect of silver ionised water on acid production in plaque. Methods: After injecting 0.5 mL of silver ionised water (concentration: 5 ppm) produced with the sintering coating method in the sensor part of the pH metre, plaque collected from the oral cavity by one platinum loop was mixed in. Immediately after that, a 5% sucrose solution (1 g/20 mL) was added and the pH was continuously measured for 30 minutes at 1-minute intervals (A). Similarly, silver ionised water was mixed with 5% sucrose solution in the same way as in (A) at 3 (B), 5 (C), 10 (D) and 15 minutes (E) after plaque contamination. The pH was measured at 1-minute intervals. The pH of the purified water containing no silver ionised water mixed with plaque and sugar solution at the same time was measured and used as a control. Each experiment was conducted three times, and the pH measured every minute was compared as a percentage of the pH at the beginning of the measurement (100%). Results: Analysis of variance of the repeated measurements to determine the effect of silver ionised water on the decrease in pH revealed a main effect of silver ionised water and an interaction between time and group [F(1.302,20.826) = 39.145, p < 0.01]. Multiple comparisons using Dunnett’s method showed a significant decline in the rate of decrease in pH from B to E as compared with that in the control (p < 0.01). Conclusion: Silver ionised water was found to inhibit the acid production in plaque.

Inhibitory Effects of Nitrite on Acid Production in Dental Plaque in Children.

To assess the inhibitory effects of nitrite on plaque acidogenicity and its relationship with caries experience. Plaque (2 μl) was collected from 76 children (age 5.8 ± 2.6 years, dmft 2.9 ± 3.5, DMTF 0.6 ± 1.4) and mixed with nitrite solution (final concentration = 0.63 mM) or distilled water (control). The initial pH (pH-0) of each sample was measured using a portable pH meter. The samples were incubated for 10 min, then their pH (pH-1) was measured again. Next, glucose (final concentration = 0.67%) was added to the samples, which were then incubated for a further 10 min before their pH was assessed for a third time (pH-2). The pH-0, pH-1, and pH-2 values of the control samples were 7.25 ± 0.16, 6.07 ± 0.44, and 5.11 ± 0.48, respectively, and those of the nitrite-treated samples were 7.26 ± 0.16, 6.37 ± 0.45, and 5.34 ± 0.48, respectively. The pH-1 and pH-2 values of the nitrite-treated samples were higher than those of the control samples (p < 0.005). Greater plaque acid production was associated with stronger inhibition of plaque acid production by nitrite (p < 0.005). No relationship was detected between the inhibition by nitrite and caries experience. Nitrite inhibited both endogenous and exogenous plaque acid production. Nitrite inhibited acid production more markedly in plaque that exhibited greater acid production, suggesting that nitrite might be effective at preventing caries, as it contributes to pH homeostasis in plaque by countering excess acidification.

English

The high cariogenicity of all black cola drinks is recognized by all oral health care professionals. It has been proven that black cola drinks pose a threat to the integrity of tooth structure. Despite the presence or absence of artificial sweeteners in cola drinks, both regular and diet soft drinks still contain phosphoric and citric acid, which contributes to the total acidic challenge potential on enamel. Fourteen children (8 to 15 years of age) were recruited with DMFT +deft &le;3. Subjects were instructed to stop brushing 48 h prior to the appointment. Plaque samples collected and dissolved in the test beakers having 1 ml of double distilled water and pH was determined immediately inherent pH of the test drinks was measured. Five minutes after the consumption of each drink, the plaque sampling was done. The pH was recorded after 10, 20, 30, 40 and 60 min of the post consumption period. All the test drinks dropped the plaque pH below the critical pH indicating that the entire four carbonated beverage were capable of causing dissolution of enamel. That all carbonated beverages have virtually the same effect on acid production in plaque and thus are equally erosive. &nbsp; Key words: Diet coke, regular coke, diet pepsi, regular pepsi, pH, saliva.

Scientific Opinion on the substantiation of a health claim related to “non fermentable” carbohydrates and maintenance of tooth mineralisation by decreasing tooth demineralisation pursuant to Article 13(5) of Regulation (EC) No 1924/2006

Following an application from Roquette Frères, submitted for authorisation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006 via the Competent Authority of France, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver an opinion on the scientific substantiation of a health claim related to Nutriose® which should replace “fermentable carbohydrates” in foods or beverages in order to obtain the claimed effect, i.e. maintenance of tooth mineralisation by reducing tooth demineralisation. From the information provided, the Panel noted that the main characteristic of carbohydrates which is relevant to the claimed effect is the rate and amount of acid production resulting from their fermentation by saccharolytic bacteria in the oral cavity. This Opinion applies to “non-fermentable” carbohydrates, which should replace “fermentable” carbohydrates in foods or beverages in order to obtain the claimed effect. The Panel considers that maintaining tooth mineralisation by reducing tooth demineralisation resulting from acid production in plaque caused by the fermentation of carbohydrates is a beneficial physiological effect. The Panel concludes that a cause and effect relationship has been established between the consumption of foods/beverages containing “fermentable” carbohydrates at an exposure frequency of four or more times daily and an increased tooth demineralisation, and that the consumption of foods/beverages containing “non-fermentable” carbohydrates instead of “fermentable” carbohydrates may maintain tooth mineralisation by decreasing tooth demineralisation. In order to bear the claim, “fermentable” carbohydrates should be replaced in foods or beverages by “non-fermentable” carbohydrates, so that consumption of such foods or beverages does not lower plaque pH below 5.7 during and up to 30 minutes after consumption, and does not lead to dental erosion.

Probiotics and dental caries

Caries is one of the most common infectious diseases in the world. Dental caries can be defined as destruction of the tissues of the tooth by bacterial fermentation of dietary carbohydrates. In this respect, some bacteria are considered more caries-promoting than others, as an example Streptococcus mutans. A common feature for caries-promoting bacteria is that they are acidogenic and aciduric. The most common bacteria used as probiotics, lactobacilli and bifidobacteria, are, in theory, caries-promoting. They are excellent acid producers, they tolerate low pH-values, and they are frequently found in caries lesions. Since probiotics can be consumed several times a day and they are even given to infants, it is essential to know that they are safe. All studies so far indicate that probiotics have rather beneficial than adverse effects on the caries risk. The best-studied probiotics Lactobacillus rhamnosus GG (LGG), Lactobacillus reuteri, and Bifidobacterium lactis BB-12 (BB-12) colonize poorly the oral cavity of adults (1–3). A recent study shows that BB-12 administered to infants twice a day showed poor retention to the teeth and oral mucosa of the infants (4). Transient colonization reduces the possible risks for oral health. Little is known about the effects of the above probiotics on the composition of the oral flora. Short-term consumption of LGG, L. reuteri, and BB-12 have in some studies reduced counts of S. mutans (5, 6). Also, the amount of dental plaque (biofilm on the teeth) has been reduced by some probiotics. Dental plaque is not only a caries risk factor but also associated with periodontal diseases. A recent study showed that consumption of LGG and L. reuteri did not result in an increase in the plaque acid production potential, an important virulence factor of plaque (7). There are only a few studies in which occurrence of caries has been studied in connection with consumption of probiotics. Nase et al. (5) found that LGG milk reduced caries occurrence in 3–4-years-old children. Milk with L. rhamnosus LB21 and fluoride reduced caries occurrence in school children (8). Reversals of root caries lesions were studied with L. rhamnosus LB21 milk w/wo fluoride – in that study, not only the fluoride-containing milks but also the probiotic milk had beneficial effects on root caries (9). Recently, caries occurrence was studied in 4-years-old children who had received BB-12 twice a day during infancy. The administration of the probiotic did not increase the caries occurrence (Taipale et al., unpublished results). Clearly, long-term clinical studies with the disease occurrence as the primary outcome measure are needed to establish beneficial versus adverse effects of probiotics on oral health. Optimally, ‘old’ probiotics with proven benefits for general health could be also be used to benefit dental health. (Published: 18 June 2012) Citation: Microbial Ecology in Health & Disease 2012, 23 : 18582 - http://dx.doi.org/10.3402/mehd.v23i0.18582

Metabolomic Effects of Xylitol and Fluoride on Plaque Biofilm in Vivo

Dental caries is initiated by demineralization of the tooth surface through acid production from sugar by plaque biofilm. Fluoride and xylitol have been used worldwide as caries-preventive reagents, based on in vitro-proven inhibitory mechanisms on bacterial acid production. We attempted to confirm the inhibitory mechanisms of fluoride and xylitol in vivo by performing metabolome analysis on the central carbon metabolism in supragingival plaque using the combination of capillary electrophoresis and a time-of-flight mass spectrometer. Fluoride (225 and 900 ppm F−) inhibited lactate production from 10% glucose by 34% and 46%, respectively, along with the increase in 3-phosphoglycerate and the decrease in phosphoenolpyruvate in the EMP pathway in supragingival plaque. These results confirmed that fluoride inhibited bacterial enolase in the EMP pathway and subsequently repressed acid production in vivo. In contrast, 10% xylitol had no effect on acid production and the metabolome profile in supragingival plaque, although xylitol 5-phosphate was produced. These results suggest that xylitol is not an inhibitor of plaque acid production but rather a non-fermentative sugar alcohol. Metabolome analyses of plaque biofilm can be applied for monitoring the efficacy of dietary components and medicines for plaque biofilm, leading to the development of effective plaque control.

Scientific Opinion on the substantiation of a health claim related to calcium‐containing fruit juices and the reduction of tooth demineralisation pursuant to Article 14 of Regulation (EC) No 1924/2006

Following an application from FrieslandCampina submitted pursuant to Article 14 of Regulation (EC) No 1924/2006 via the Competent Authority of The Netherlands, the Panel on Dietetic Products, Nutrition and Allergies was asked to deliver an opinion on the scientific substantiation of a health claim related to acidic calcium-containing fruit juices and the reduction of tooth demineralisation. The scope of the application was proposed to fall under a health claim referring to reduction of disease risk. The Panel considers that the food, acidic calcium-containing fruit juices and comparative products, conventional fruit juices (not containing added calcium), are sufficiently characterised. The Panel considers that reducing tooth demineralisation resulting from erosive potential of a food is a beneficial physiological effect, provided that it is not accompanied by tooth demineralisation resulting from acid production in plaque through the fermentation of carbohydrates. A total of 37 pertinent studies were identified by the applicant, including observational studies, reviews, intervention studies on the erosive potential of fruit juices and other acidic drinks with and without added calcium in situ, in vitro studies on the erosive potential of acidic drinks with and without added calcium, and an animal study on the effect of calcium added to acidic drinks on dental erosion. The Panel notes that the potential of fruit juices with and without added calcium for demineralisation of dental enamel by acid production in plaque as a result of sugar fermentation was not assessed in any study. The Panel considers that the potential of fruit juices with and without added calcium for demineralisation of dental enamel, including the possible effects of both acids and sugars, has not been assessed appropriately. The Panel concludes that a cause and effect relationship has not been established between the consumption of acidic calcium-containing fruit juices in replacement of fruit juice without added calcium and the reduction of tooth demineralisation.

Scientific Opinion on the substantiation of a health claim related to sugar free chewing gum and neutralisation of plaque acids which reduces the risk of dental caries pursuant to Article 14 of Regulation (EC) No 1924/2006

Following an application from Wrigley GmbH submitted pursuant to Article 14 of Regulation (EC) No 1924/2006 via the Competent Authority of United Kingdom, the Panel on Dietetic Products, Nutrition and Allergies was asked to deliver an opinion on the scientific substantiation of a health claim related to sugar-free chewing gum and neutralisation of plaque acids which reduces the risk of dental caries. Sugar-free chewing gum is sufficiently characterised. The Panel considers that plaque acid neutralisation might be a beneficial physiological effect in the context of reducing the risk of caries. The applicant identified a total of 47 publications as being pertinent to the health claim. In weighing the evidence, the Panel took into account that many human studies of sugar-free chewing gum consumption were consistent in showing neutralisation of plaque acid, that almost all clinical trials on sugar-free chewing gum consumption showed a reduction in caries incidence, and that there was strong evidence supporting the biological plausibility for the effect. The Panel concludes that a cause and effect relationship has been established between the consumption of sugar-free chewing gum and plaque acid neutralisation and a reduction in incidence of caries. Plaque acid production may contribute to increased risk of caries. In order to obtain the claimed effect, 2–3 g of sugar-free chewing gum should be chewed for 20 minutes at least three times per day after meals. This quantity and pattern of use of chewing gum can easily be included within a balanced diet.

Plaque formation and lactic acid production after the use of amine fluoride/stannous fluoride mouthrinse

The aim of this study was to determine the effects of 3 wk of daily rinsing with amine fluoride/stannous fluoride (AmF/SnF(2)) mouthrinse on plaque formation at buccal and interproximal sites, and on the acid production in plaque, in a randomized clinical trial with 30 participants. The amount of plaque was scored according to Turesky's modification of the Quigley and Hein index. Plaque samples were collected, before and after sucrose rinsing, from the buccal and interproximal surfaces of upper (pre)molars at two baseline visits and on days 2 and 7 after the discontinuation of 3 wk of daily rinsing. Metabolic acid ions were determined by capillary electrophoresis. The results at baseline showed higher lactic acid concentrations in resting interproximal plaque than in buccal plaque, and a higher acid production in response to sucrose challenge in buccal plaque than in interproximal plaque. After 3 wk of use of the AmF/SnF(2) mouthrinse, no significant differences in plaque scores were observed, and the alleged reduction in acidogenicity of dental plaque was not significant on the second day after the last mouthrinse. We conclude that 3 wk of use of AmF/SnF(2) rinse once daily does not result in a reduction of plaque formation or in a reduction of sucrose metabolism in buccal and interproximal plaque after discontinuing the rinse.

Effects of Various Rinsing Protocols after the Use of Amine Fluoride/Stannous Fluoride Toothpaste on the Acid Production of Dental Plaque and Tongue Flora

The aim of this clinical study was to evaluate the effect of various rinsing protocols on oral acid production 6 h after tooth brushing with an amine fluoride/stannous fluoride (AmF/SnF₂) toothpaste. After a 14-day period of using F-free toothpaste, 30 participants followed three experimental protocols each, followed by F-free washout periods in a randomized crossover trial. They used AmF/SnF₂ toothpaste twice daily for 1 week, and after brushing, they either rinsed with tap water, omitted the post-brush rinse, or rinsed with an AmF/SnF₂ mouthwash. In the F-free washout periods, the participants brushed their teeth without further instructions. Six hours after the last brushing (± rinsing) of each period, subjects rinsed with 10 ml 10% sucrose solution for 2 min. A tongue film sample and a buccal plaque sample were taken 4 and 8 min after the sucrose challenge, respectively. Metabolic acid ions were determined by capillary electrophoresis. The results show that (1) omitting the post-brush water rinse did not reduce the production of lactic, acetic or minor acids in plaque, nor on the tongue, and that (2) the additional use of AmF/SnF₂ mouthwash after brushing reduced the acid production in plaque and tongue samples for at least 6 h. The distributions of acids produced in the plaque or tongue samples were not statistically different between experimental periods. It is concluded that an increase in the antimetabolic effect of AmF/SnF₂ toothpaste in between two daily brushing exercises is not achieved by omitting the post-brush water rinse. The additional use of AmF/SnF₂ mouthwash after brushing is effective in reducing the acid metabolism in dental plaque and tongue flora.

The effect of a 2% zinc citrate, 0.3% Triclosan dentifrice on plaque acid production following consumption of a snackfood

A) To assess plaque lactate production following consumption of three foods (cake, chocolate/caramel bar, sweetened coffee), and B) To measure the effect of a fluoride dentifrice containing 2% zinc citrate and 0.3% Triclosan on plaque lactate and pH drop following consumption of cake. A) 10 subjects completed the first study. Plaque samples taken before and at 8,15 and 30 minutes after eating. Samples were analysed for lactate via Capillary Electrophoresis. B) 30 subjects completed the second study. Plaque samples were taken before and after cake and use of test dentifrice or no treatment control. Plaque pH and lactate content were assessed. A) Plaque lactate levels increased after all three foods; peak lactate levels occurred 8 minutes after eating. B) Plaque lactate concentrations after eating cake were 39.2mM for the control treatment and a significantly lower value, 23.6mM, for the test 2% zinc citrate, 0.3% Triclosan dentifrice. After food challenge, pH values were 5.53 for the no treatment group and a significantly higher value of 5.79 for the test dentifrice group. A toothpaste containing 2% zinc citrate, 0.3% Triclosan can significantly reduce plaque lactate generation and pH drop induced by cake, compared to no treatment control.

Cheese with naturally decorated rind

The number of non-sugar sweeteners that are approved for use in foods and drinks is increasing and manufacturers are using these as alternatives to cariogenic sugar. These non-sugar sweeteners are generally classed as non-cariogenic. The most frequently used non-sugar sweetener is sorbitol, and concern has been expressed that the oral flora may adapt to sorbitol so that it looses its ‘safe for teeth’ property. The purpose of this review is to describe the mechanisms whereby oral microorganisms, and mutans streptococci in particular, might metabolize sorbitol and to summarize published research into changes in plaque acid production and changes in plaque flora after exposure to sorbitol. Finally, the possibility that some groups of people may be especially ‘at-risk’ from adaptation of oral microorganisms to sorbitol is considered. It is concluded that frequent or long-term use of sorbitol is unlikely to present any increased risk of dental caries in normal people, but that frequent use of sorbitol may present a small cariogenic risk in people with low salivary flow.

Saliva Stimulation and Caries Prevention

The protective role of saliva is demonstrated by the rampant caries seen in human subjects with marked salivary hypofunction, and in desalivated animals. In normal cases, however, the relationship between saliva flow and coronal or root caries experience is doubtful, and to examine the concept that stimulation of saliva might have protective effects against caries, one must look beyond a simple correlation between caries and flow rate. Protective properties of saliva which increase on stimulation include salivary clearance, buffering power, and degree of saturation with respect to tooth mineral. These benefits are maximized when saliva is stimulated after the consumption of fermentable carbohydrates, by reducing the fall in plaque pH leading to demineralization and by increasing the potential for remineralization. Plaque acid production is neutralized, and experimental lesions in enamel are remineralized, when gum is chewed to stimulate saliva after a carbohydrate intake. The pH-raising effects are more easily explained by the buffering action of the stimulated saliva than by clearance of carbohydrates. The remineralization action depends upon the presence of fluoride. These findings suggest that the protective actions of saliva can be mobilized by appropriate salivary stimulation, and that in addition to established procedures such as tooth cleaning and fluoride regimens, eating patterns which lead to saliva stimulation to increase the potential for saliva protection might be included in recommendations for caries prevention. Confirmation of this concept in clinical tests is required.

フッ化ナトリウム配合歯磨剤の口腔内動態に関する研究

Although fluoride has been widely used for caries prevention in various ways, attention is now being paid to the use of toothpaste containing fluoride for caries control.The inhibition of decalcification and the remineralization of initial carious lesions should be promoted by the continuous presence of fluoride derived from toothpaste in dental plaque and saliva.In this study, I assessed the effects of toothpaste containing 100 or 250 ppmF- as NaF on the fluoride level in the oral environment, on selected organic acids in plaque, and on the number of bacteria in plaque.The results obtained were as follows:1) Fluoride concentration in both plaque and saliva was increased significantly by the use of fluoride-containing toothpastes (p<0.05).2) With 250 ppmF- toothpaste the fluoride concentration in plaque and saliva was higher than that obtained when 100 ppmF- tooth paste was used. However, these levels decreased to almost the original levels after 60 minutes. Therefore, the oral clearance of fluoride is apparently rapid.3) Acid production in plaque was inhibited significantly by the use of fluoride-containing toothpastes (p<0.001).4) When the 250ppmF- toothpaste was used for 5 days, the bacterial number in plaque tended to decrease.5) These data suggest that fluoride-containing toothpaste could prevent caries incidence even at a concentration as low as 100 or 250 ppmF-.

Sorbitol Adaptation of Dental Plaque in People with Low and Normal Salivary-secretion Rates

Caries-related bacteriological and biochemical factors were studied in 12 persons with low and 11 persons with normal salivary-secretion rates before and after a four-week period of frequent mouthrinses with 10% sorbitol solution (adaptation period). After the adaptation period, an increase in total numbers of sorbitol-fermenting bacteria and mutans streptococci was found in plaque samples from both groups. The pH drop in dental plaque in situ after a mouthrinse with sorbitol was more pronounced after the adaptation period, especially in the group with the low salivary-secretion rate. Increased acid production in plaque from sorbitol was also observed in the two groups in vitro. The composition of the fermentation end-products was affected by the sorbitol exposure. It is suggested that in subjects with diminished natural protection against caries development, such as patients with low salivary-secretion rate, a cariogenic potential of sorbitol should be considered when this polyol is included in products that might be used frequently.

Oral disposition of triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) delivered from a dentifrice.

This paper reports measurements of oral retention and intra-oral distribution of triclosan in man after use of an antiplaque toothpaste slurry containing this antibacterial. Determinations of triclosan were made by high-performance liquid chromatography. It was shown that 38% of the triclosan in a 1-gramme dose of toothpaste (0.50%, w/w triclosan) and 62% of a 3-gramme dose was retained. Triclosan was detected and measured in plaque and this antibacterial was also present in saliva. Levels of approximately 20–30 μg triclosan/ml of saliva were measured 5 min after toothpaste use and these had fallen to approximately 3–4 μg/ml 2 h later. A significant inhibition of plaque acid production is shown to follow use of the antiplaque dentifrice.

The role of sugar in the aetiology of dental caries. 3. The physiochemical evidence.

Frequency and pattern of consumption and food characteristics may modify the response in vivo of the acidogenic organisms in plaque to sugary foods, leading to changes in plaque pH. The relationship between plaque acid production and caries is confirmed by plaque pH studies in subjects with contrasting levels of caries, and by production of caries-like lesions in enamel exposed to acid in vitro, although the relationship may be modified by alternative modes of demineralization, by remineralization processes, and by inhibitors of tooth dissolution. Epidemiological and animal studies indicate that sucrose is the major source of readily fermentable carbohydrate in the diet, and that starch, although potentially acidogenic, is normally consumed in a way which does not give rise to the initiation of high caries levels. Sucrose may act specifically in favouring the development of a cariogenic plaque flora, but its principal role is non-specific, as an ubiquitous dietary substrate for acid production.

Inhibition of dental plaque acid production by the salivary lactoperoxidase antimicrobial system.

Resting human whole saliva inhibited acid production by glucose-stimulated, homologous plaque. The degree of inhibition of plaque acid production correlated positively with the concentration of hypothiocyanite (OSCN-) ions in saliva. Supplementation of saliva with an appropriate combination of thiocyanate and hydrogen peroxide resulted in a significant increase in the concentration of OSCN- ions and in more effective inhibition of plaque acid production. In most cases, the inhibition was complete when the supplements were added directly to saliva-plaque mixtures. Acid production resumed when the inhibitory effect of OSCN- was reversed by addition of thiols. Among the oral defense factors, the salivary lactoperoxidase system seems to play an important role by producing highly reactive antibacterial products (including OSCN-) which can regulate bacterial metabolism in the human mouth. The concentration of OSCN- in normal human whole saliva seems to be just below the threshold level required for plaque inhibition. Therefore, enhancement of this system in vivo may be effective in the regulation of plaque acid production.

Oral starch degradation and its influence on acid production in human dental plaque.

Enzymatic hydrolysis of starch by salivary α-amylase, its time dependence and influence on plaque acid production was investigated. Analysis of the composition of starch digests was performed with gel filtration chromatography. Wheat starch in solution, in bread and in biscuit was hydrolyzed rapidly mainly to maltose, maltotriose and limit dextrins. In vivo enzymatic degradation of wheat starch caused marked drops in interdental plaque pH to 4.75 measured by intraoral plaque pH telemetry, most probably as the result of the fermentation of low molecular weight maltodextrins by plaque bacteria. On this basis starch may contribute to cariogenesis.

Thiol groups and reduced acidogenicity of dental plaque in the presence of metal ions in vivo.

Metal ions are known to influence the cariogenicity of dental plaque. Inhibition of acid metabolism in plaque may be of importance in this respect. Metal ions inhibit the acidogenicity of dental plaque to a different extent and it has been suggested that an enzyme inhibition based on oxidation of thiol groups may explain this observation. The aim of the present study was to evaluate the significance of oxidation of thiol groups in the inhibition of acid production in plaque by silver, tin and zinc salts. Nine subjects with 3-d sucrose induced plaque received topical applications of the metal ions. Cysteine or glutathione, which are known to reverse thiol oxidations, were then applied in one side of the mouth. Plaque pH measurements, in the presence of sucrose, were performed prior to and up to 2 h after treatment. The results showed that the acid production inhibited by the metal ions was reactivated by cysteine or glutathione. Iodoacetamide and p-chloromercuribenzoate were also shown to inhibit acid formation in dental plaque. The high affinity silver, tin and zinc have for SH groups, the observed inhibitory effect of these metals, the reactivation of the metabolism by monothiols and the fact that organic sulfhydryl reagents inhibit acid formation in plaque indicate that oxidation of thiol groups may be the mechanism by which these metals exert their effect.