Plaque Suspensions Research Articles

Effects of Nitrate and Nitrite on Plaque pH Decrease and Nitrite-Producing and -Degrading Activities of Plaque in vitro.

The purpose of this study was to investigate the effects of nitrate and nitrite on the pH-lowering activity of human plaque, the nitrite-producing and -degrading activities of human plaque, and their correlation. Nitrate and nitrite were added to human plaque suspensions collected from the buccal aspect of maxillary molars of patients visiting a general dental clinic, and changes in pH were measured with and without glucose addition. Nitrite-producing and -degrading activities were evaluated by adding nitrate and nitrite to the plaque suspension and measuring the increase and decrease in nitrite with Griess reagent, respectively. The addition of nitrate inhibited both endogenous and glucose-induced plaque pH-lowering. The addition of glucose enhanced the production of nitrite from nitrate by about 3.3-fold. The addition of nitrite also inhibited endogenous plaque pH-lowering, but the addition of glucose promoted nitrite degradation by only about 1.1-fold. Nitrite-producing activity was positively correlated with age, but not with nitrite-degrading activity. This study revealed that nitrite was produced from nitrate and inhibited the pH-lowering activity of human plaque, which may contribute to caries control. Both nitrite-producing and -degrading activities occurred in human plaque, but no correlation was found between them. Furthermore, nitrite production was enhanced by glucose metabolism, which may function as a self-regulatory mechanism (resilience) to prevent excessive acidification by glucose metabolism.

Rose Bengal incorporated to α-cyclodextrin microparticles for photodynamic therapy against the cariogenic microorganism Streptococcus mutans.

Rose Bengal@α-cyclodextrin (RB@α-CD) microparticles (μPs) were prepared and the RB inclusion in α-CD was experimentally demonstrated through infrared, UV-VIS absorption spectroscopy and cyclic voltammetry. The RB inclusion in α-CD was theoretically investigated using classical molecular mechanics calculations, the simulation results showing that RB can be included in both the narrow and wide apertures of the α-cyclodextrin ring with configurations exhibiting average binding energies of about 27 kcal mol-1. The prepared RB@α-CD microparticles were characterized through Scanning Electron Microscopy (SEM) and it was demonstrated that they are highly efficient in the photodynamic therapy against a Streptococcus mutans (the main bacteria of cariogenic dental plaque) suspension, as a concentration of RB@α-CD μPs 10 times smaller than the usual concentration of pure RB is still capable to produce significant antibacterial activity.

First Cultivation of Health-Associated Tannerella sp. HOT-286 (BU063)

Despite significant advances in recent years in culture-independent molecular microbiology methods, the detailed study of individual bacterial species still relies on having pure cultures in the laboratory. Yet, more than a third of the approximately 700 bacterial taxa found in the human oral cavity are as yet uncultivated in vitro. One such taxon, Tannerella sp. HOT-286 (phylotype BU063), is the focus of much interest since it is associated with periodontal health, while Tannerella forsythia, its closest phylogenetic neighbor, is strongly associated with periodontal disease. HOT-286, however, has remained uncultivated despite the efforts of several research groups, spanning over a decade. The aim of this study was to cultivate Tannerella sp. HOT-286. A heavily diluted sample of subgingival plaque was inoculated onto culture plates supplemented with siderophores (pyoverdines-Fe complex or desferricoprogen) or a neat plaque suspension. After 8 d of anaerobic incubation, microcolonies and colonies showing satellitism were passaged onto fresh culture plates cross-streaked with potential helper strains or onto cellulose-acetate membranes placed over lawn cultures of helper strains. Subcultured colonies were identified by 16S rRNA gene sequencing, and purity was confirmed by sequencing 20 clones per library prepared from a single colony. Three colonies of interest (derived from pyoverdines- and plaque-supplemented plates) were identified as Tannerella sp. HOT-286. The isolates were found to be incapable of independent growth, requiring helpers such as Propionibacterium acnes and Prevotella intermedia for stimulation, with best growth on membranes over “helper” lawns. A representative isolate was subjected to phenotypic characterization and found to produce a range of glycosidic and proteolytic enzymes. Further comparison of this novel “periodontal health-associated” taxon with T. forsythia will be valuable in investigating virulence factors of the latter and possible health benefits of the former.

The effect of blue light on periodontal biofilm growth in vitro.

We have previously shown that blue light eliminates the black-pigmented oral bacteria Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, and Prevotella melaninogenica. In the present study, the in vitro photosensitivity of the above black-pigmented microorganisms and four Fusobacteria species (Fusobacterium nucleatum ss. nucleatum, F. nucleatum ss. vincentii, F. nucleatum ss. polymorphum, Fusobacterium periodonticum) was investigated in pure cultures and human dental plaque suspensions. We also tested the hypothesis that phototargeting the above eight key periodontopathogens in plaque-derived biofilms in vitro would control growth within the dental biofilm environment. Cultures of the eight bacteria were exposed to blue light at 455 nm with power density of 80 mW/cm2 and energy fluence of 4.8 J/cm2. High-performance liquid chromatography (HPLC) analysis of bacteria was performed to demonstrate the presence and amounts of porphyrin molecules within microorganisms. Suspensions of human dental plaque bacteria were also exposed once to blue light at 455 nm with power density of 50 mW/cm2 and energy fluence of 12 J/cm2. Microbial biofilms developed from the same plaque were exposed to 455 nm blue light at 50 mW/cm2 once daily for 4 min (12 J/cm2) over a period of 3 days (4 exposures) in order to investigate the cumulative action of phototherapy on the eight photosensitive pathogens as well as on biofilm growth. Bacterial growth was evaluated using the colony-forming unit (CFU) assay. The selective phototargeting of pathogens was studied using whole genomic probes in the checkerboard DNA-DNA format. In cultures, all eight species showed significant growth reduction (p < 0.05). HPLC demonstrated various porphyrin patterns and amounts of porphyrins in bacteria. Following phototherapy, the mean survival fractions were reduced by 28.5 and 48.2% in plaque suspensions and biofilms, respectively, (p < 0.05). DNA probe analysis showed significant reduction in relative abundances of the eight bacteria as a group in plaque suspensions and biofilms. The cumulative blue light treatment suppressed biofilm growth in vitro. This may introduce a new avenue of prophylactic treatment for periodontal diseases.

Correlation of Dental Plaque Acidogenicity and Acidurance with Caries Activity – Perspectives of the Ecological Plaque Hypothesis

AbstractThe ecological plaque hypothesis for the aetiopathogenesis of caries implies a microbial shift towards a more acidogenic and aciduric dental plaque microflora, due to a frequent carbohydrate intake. Certain plaque bacteria exhibit metabolic activity, at a low pH. A correlation exists between the increased numbers of some aciduric bacterial species, e.g. mutans streptococci and lactobacilli, and caries activity. The aim of this study was to study the acidogenic (lactate production / mg plaque x min., at pH 7.0) and aciduric potential (lactate production at pH 5.5 / lactate production at pH 7.0) of dental plaque in relation to the caries activity. Samples of dental plaque were collected from fifteen caries free and fifteen caries active children. Plaque suspensions in Ringer’s solution containing 1% sucrose and buffered with 0.5 M MOPS (pH 7.0) or MES (pH 5.5) were incubated aerobically at 37 ºC for 10-20 min. The production of lactic acid in the suspensions was determined by an enzymatic assay. In caries free children, significantly lower acidogenic potential at both pHs were recorded than in caries active children. The highest difference between the groups was in the acidogenic activity at neutral pH. On the contrary, the aciduric potential was lower in the caries active group than in the caries free. Caries activity correlated with the acidogenic potentials of dental plaque at both pH 7.0 and 5.5. A new perspective of the ecological plaque hypothesis based on the increased catabolic ability of plaque is proposed.

Outcomes of revascularization treatment in immature dog's teeth

The purpose of the current study was to examine the success rate of a revascularization treatment protocol involving canal space disinfection using copious irrigation, a triantibiotic dressing, and induction of a blood clot matrix in immature dog's teeth. Thirty-six immature mongrel dog's teeth were divided into two experimental and two control groups. The experimental groups included a necrotic-infected group (n = 20) and a vital group (n = 10). In the group with the necrotic-infected teeth, periapical lesions were induced, and disinfection of the canals was carried out using copious irrigation and a triple antibiotic medication (metronidazole, ciprofloxacin, and tetracycline). Subsequently, the periapical tissues were irritated to initiate bleeding, producing a blood clot. A double seal of the coronal access was then placed. In the vital group, the pulp was aseptically removed before the canal was irrigated and periapical tissues irritated to induce bleeding. The same protocol as that used for the necrotic-infected group was used to seal the coronal access. In the positive control group (n = 3), after pulp removal, sterile sponges soaked in plaque suspension were placed in the pulp chambers of the teeth, after which the chambers were sealed. In the negative control group (n = 3), one untouched 1st premolar tooth in each dog was assigned and left to develop naturally. Radiographic and histological findings were evaluated at 3 and 6 months. Data analysis was performed using Fisher's exact test. The necrotic-infected group radiographically demonstrated apical healing and apical closure in 70% of the cases and thickening of the walls in 40% after 6 months. The vital group showed apical closure in 77% and thickened walls in 44% of the cases after 3 months. Histological findings confirmed the radiographic findings. No significant difference was observed between the two groups (P > 0.05). If necrotic-infected canals are effectively disinfected and treated according to the protocol, the ensuing revascularization response is similar to that of vital immature teeth.

Acid production in dental plaque after exposure to probiotic bacteria

BackgroundThe increasing interest in probiotic lactobacilli in health maintenance has raised the question of potential risks. One possible side effect could be an increased acidogenicity in dental plaque. The aim of this study was to investigate the effect of probiotic lactobacilli on plaque lactic acid (LA) production in vitro and in vivo.MethodsIn the first part (A), suspensions of two lactobacilli strains (L. reuteri DSM 17938, L. plantarum 299v) were added to suspensions of supragingival dental plaque collected from healthy young adults (n=25). LA production after fermentation with either xylitol or fructose was analyzed. In the second part (B), subjects (n=18) were given lozenges with probiotic lactobacilli (L. reuteri DSM 17938 and ATCC PTA 5289) or placebo for two weeks in a double-blinded, randomized cross-over trial. The concentration of LA in supragingival plaque samples was determined at baseline and after 2 weeks. Salivary counts of mutans streptococci (MS) and lactobacilli were estimated with chair-side methods.ResultsPlaque suspensions with L. reuteri DSM 17938 produced significantly less LA compared with L. plantarum 299v or controls (p<0.05). Fructose gave higher LA concentrations than xylitol. In part B, there were no significant differences in LA production between baseline and follow up in any of the groups and no differences between test and placebo were displayed. The salivary MS counts were not significantly altered during the intervention but the lactobacilli counts increased significantly in the test group (p<0.05).ConclusionLactic acid production in suspensions of plaque and probiotic lactobacilli was strain-dependant and the present study provides no evidence of an increase in plaque acidity by the supply of selected probiotic lactobacilli when challenged by fructose or xylitol. The study protocol was approved by The Danish National Committee on Biomedical Research Ethics (protocol no H-2-2010-112).Trial registrationNCT01700712

Experimental infective endocarditis induced by human supragingival dental plaque in rats

Human dental plaque is thought to contribute to disease, not only in the oral cavity but also at other body sites. To investigate the pathogenicity of dental plaque in tissues remote from the mouth, we examined the ability of human supragingival dental plaque to induce infective endocarditis (IE) in rats. In total, 15 out of 27 catheterized rats survived after intravenous injections with human supragingival dental plaque suspensions containing 3 x 10(6) colony-forming units (CFU) of bacterial cells. In surviving rats, infected vegetations were formed in all except one rat. The microbial composition of the infected vegetations was different from that of the respective dental plaque inocula, with Streptococcus oralis comprising the majority of the isolates. In rats affected with endocarditis, the aortic sinus was filled with fibrinous vegetation containing bacteria. Inflammatory cells infiltrated the aortic valve, the aorta adjacent to the valve, and the cardiac muscles. The inoculation of catheterized rats with a cell suspension of S. oralis isolate (5 x 10(6) CFU) was not lethal but capable of inducing endocarditis in all animals. The results suggest that if dental plaque were introduced into the bloodstream, it could serve as a potent source of bacteria causing IE in humans.

Marginal and subgingival plaque--a natural habitat of Tropheryma whipplei?

DNA of Tropheryma whipplei, the etiologic agent of Whipple's disease, has recently been detected in the saliva of healthy subjects. In this pilot study we searched for the habitat of T. whipplei within the oral cavity. Samples from different oral sites were obtained from periodontically healthy volunteers, patients with progressive periodontitis and Chinese subjects with necrotizing ulcerative gingivitis or gingivitis. Quantitative real-time PCR was performed using T. whippleispecific primers, human beta-globin-specific primers to control for tissue DNA extraction and PCR reaction and broad-range eubacterial primers to control for bacterial DNA extraction. T. whipplei specificity of multiple amplicons was confirmed by sequencing. The detection limit of the method was 10 ag of T. whipplei DNA, corresponding to one to five bacteria under reference assay conditions. T. whipplei was found in the oral cavity of four out of ten healthy individuals from hospital staff and in three out of nine periodontitis patients, but in none of the individuals from China. All positive samples derived from subgingival and gingival sulcus plaque containing between 10(3) and 5 x 10(5) cells ml(-1) of plaque suspension, whereas saliva, smooth surface plaque and samples from the tongue or cheeks were negative. Our results suggest that T. whipplei colonizes the human body via the oral cavity and that bacterial plaques of the gingival crevice and the gingival sulcus/pocket may serve as a natural primary habitat.

Comparison of Erythritol and Xylitol Saliva Stimulants in the Control of Dental Plaque and Mutans Streptococci

The effect of 2–month usage of saliva–stimulating pastils containing either erythritol or xylitol was studied in a cohort of 30 subjects assigned to the respective polyol groups (n = 15). The daily consumption level of both polyols was 5.2 g, used in 5 daily chewing episodes. The mean weight of total plaque mass (collectable during a standard period of 3 min from all available tooth surfaces) was reduced significantly in the xylitol–group, while no such effect was observed in the erythritol–group. This reduction in plaque mass was accompanied by a significant reduction in the turbidity readings (A₆₆₀) of aqueous plaque suspensions; no such effect was observed in the erythritol–group. However, plaque protein levels did not differ between baseline and endpoint in either polyol group. The plaque and salivary levels of Streptococcus mutans and plaque levels of total streptococci were reduced significantly in the xylitol–group, while no such effect was detected in the erythritol–group. However, either polyol regimen had no effect on plaque levels of S. sobrinus. The results suggest that systematic use of xylitol–containing saliva stimulants may be more effective in controlling some oral–hygiene–related and caries–associated parameters than similar use of erythritol–containing products. The results also speak for a special relationship between xylitol and S. mutans. However, owing to the great potential of erythritol as a caries–reducing agent – based on the tetritol nature of erythritol – the present laboratory results should be considered preliminary and subject to verifying clinical studies.

Abiotrophia species in early dental plaque.

The most characteristic traits that distinguish Abiotrophia strains from other streptococci are nutrient requirements, satellitism and pyrrolidonyl arylamidase activity. The presence of Abiotrophia strains was studied in early dental plaque formed on sucrose-containing and sucrose-free (glucose-containing) diets. The isolates were from 0- to 3-day dental plaque formed on the buccal surface of a lower premolar in six subjects. Identification of Abiotrophia strains was based on their pyrrolidonyl arylamidase activity. They were among the predominant cultivable microorganisms isolated from diluted suspensions of early dental plaque formed on both diets. Using biochemical tests without testing for pyrrolidonyl arylamidase activity, the Abiotrophia strains would be biochemically identified as Streptococcus mitis or unidentified streptococci, and many isolates first classified as unidentified streptococci were Abiotrophia strains. Generally, identifications using partial 16S rRNA sequences confirmed the identifications obtained biochemically. However, Abiotrophia elegans and Gemella strains were biochemically identified as Abiotrophia adiacens. Abiotrophia strains produce hydrogen sulfide, which may influence the metabolism and ecology of dental plaque and act as a virulence factor in periodontal disease. They are not able to grow on tryptic soy agar. In the present study, some S. mitis strains were not able to grow on mitis salivarius agar, and some Abiotrophia strains were able to grow on this medium. These observations indicate that the use of these media for estimation of total viable counts and number of streptococci introduces systematic error in studies of microorganisms in dental plaque.

Porphyromonas gingivalis, Prevotella intermedia and Bacteroides forsythus in plaque subjacent to bridge pontics

This study examined the distribution of P. gingivalis, P. intermedia and B. forsythus in plaque on metallic and porcelain pontics adjacent to healthy and inflamed mucosa. Subpontic plaque was collected from 33 inflamed and 31 healthy sites. Plaque suspension was incubated with specific rabbit antisera to P. gingivalis (FDC 381), P. intermedia (ATCC 25261) and B. forsythus (FDC 335), and the labelled cells disclosed with fluorescein-labelled goat-anti-rabbit IgG by indirect immunofluorescence microscopy. Mean proportions of P. gingivalis, P. intermedia, and B. forsythus at inflamed sites were 0.60+/-0.75, 2.48+/-2.28, and 0.44+/-0.64% respectively, and at healthy sites 0.21+/-0.43, 1.27+/-1.05, and 0.15+/-0.18% respectively. These differences were statistically significant. Almost all sites were positive for P. intermedia, whereas only 12/31 healthy and 21/33 inflamed sites were positive for P. gingivalis. 18/31 healthy and 28/33 inflamed sites were positive for B. forsythus. P. intermedia was recovered in higher proportions from metallic pontics adjacent to inflamed sites (MI) than healthy sites (MH) or porcelain pontics next to inflamed (PI) or healthy sites (PH). P. gingivalis is was recovered in higher proportions from MI than PH. We conclude that both the nature of the pontic material and the health status of the mucosa affect the composition of the associated microbiota.

Xylitol fermentation by human dental plaque.

The aim of the present study was to examine xylitol metabolism by dental plaque collected immediately after the use of xylitol gum. Plaque was collected from 12 individuals immediately before and after xylitol exposure. The effect on xylitol metabolism by dental plaque of a 3 d discontinuation of the xylitol exposure was also examined. Xylitol metabolism by the plaque suspensions was initiated by adding [14C]xylitol and analyzed by HPLC. The results showed increased xylitol metabolism after 11 wk of chewing xylitol-containing gum. The ability to metabolize xylitol was rapidly reduced after the discontinuation of the xylitol exposure. It is suggested that an induction of enzymes in one or more of the species of plaque bacteria may have caused this effect. Glucose metabolism, which also was studied in the plaque samples, was decreased after xylitol exposure, but increased again 3 d after cessation of the xylitol exposure. It is suggested that the reduced glycolysis was caused by accumulation of intracellular xylitol-5-phosphate in some plaque bacteria during the xylitol exposure.

Effect of xylitol‐containing chewing gum on sorbitol metabolism in dental plaque

The aim of the present study was to examine whether a long-term use of chewing gum with xylitol as the only sweetener would affect sorbitol metabolism in dental plaque. Ten test subjects used xylitol-sweetened chewing gum for 12 weeks. Plaque was collected at three occasions; 1) Control plaque; 2) Test plaque I: plaque collected after 12 weeks of chewing xylitol-containing chewing gum; 3) Test plaque II: sucrose-stimulated plaque collected 2 d after Test plaque I was collected. Plaque suspensions were incubated with [14C]sorbitol, and uptake of sorbitol and production of sorbitol metabolites were determined by HPLC. Plaque formation and sorbitol uptake were significantly reduced.

Retinal artery occlusion in rabbit eyes using human atheroma.

Previous animal models of central retinal artery occlusion using glass or latex embolic material may not simulate human disease. We have developed a rabbit model using human atherosclerotic material, which may be useful in developing embolus specific treatments, including thrombolysis or laser photodisruption. Fresh human atherosclerotic plaque was harvested from atherosclerotic human aorta by mechanical removal and suspension in normal saline. The suspension was agitated vigorously to produce small particles, which were separated into various sizes by filtration through mesh filters with specific pore sizes. The common carotid artery of the anesthetized rabbit was isolated by neck dissection and cannulated using a modified Seldinger technique. Suspensions of human atherosclerotic plaque were injected into the common carotid artery via this cannula. All animals were examined by slit lamp and fluorescein angiography before and after retinal artery occlusion. This model reliably produced retinal artery occlusion using human atherosclerotic plaque. Plaque particles less than 105 microns reliably produced branch retinal artery occlusion, while larger plaque particles less than 149 microns reliably produced central retinal artery occlusion. Sublingual nitroglycerin, at 0.1 mg/kg, intravenous verapamil, from 0.2 mg/kg to 2 mg/kg, and intracarotid urokinase given acutely in standard doses failed to cause reperfusion. This model will be very useful in the study and treatment of retinal vascular disorders as it may more closely simulate human disease over previous models using artificial embolic materials. Embolic specific treatment stategies, such as thrombolysis and laser photodisruption, may be further developed with this model.

The association of mutans streptococci and non-mutans streptococci capable of acidogenesis at a low pH with dental caries on enamel and root surfaces.

Coronal dental plaque from each of 12 caries-positive subjects (Group I) was pooled from "white spot" tooth surface areas and, separately, from sound surface areas; sound surface areas in each of 18 caries-free subjects (Group II) were sampled similarly. Two samples, one consisting of material from a root-surface lesion and another of plaque from a sound root-surface area, were obtained from each of another 10 subjects (Group III). The samples from Groups I and II were evaluated for: (1) pH-lowering potential in vitro with dispersed plaque suspensions, excess glucose supply, and a 60-minute test; (2) the levels of mutans streptococci (MS) and lactobacilli; and (3) the distribution of the predominant non-mutans streptococci (non-MS) according to their final pH in glucose broth; only microbial analysis was done for the Group III samples. The levels of the MS were generally positively associated with caries. A weaker positive association was found for the levels of those non-MS capable of acidogenesis at low pH (final pH < 4.4). The latter generally far outnumbered the MS in all types of samples. The levels of lactobacilli were nearly always very low. The pH-lowering potential (final pH and pH drop rate) was higher for plaque from "white spot" areas than for plaque from sound surface areas (Group I). The samples from caries-free subjects (Group II), however, exhibited a pH-lowering potential which was not significantly different from that of both types of samples from the caries-active subjects (Group I).(ABSTRACT TRUNCATED AT 250 WORDS)

Mutans Streptococci and Non-mutans Streptococci Acidogenic at Low pH, and in vitro Acidogenic Potential of Dental Plaque in Two Different Areas of the Human Dentition

Samples of human dental plaque were obtained from sound tooth surfaces in the lower anterior and upper posterior areas of each of 11 subjects with various degrees of caries experience. Both types of plaque were compared for: (1) their pH-lowering potential [pH at 10 and 60 min after sugar addition and the pH drop between 0 and 10 min (delta pH)] with an in vitro method involving dispersed plaque suspensions and excess glucose supply; (2) the proportions of mutans streptococci; and (3) the distribution of the predominant non-mutans streptococci according to their final pH in glucose broth. Compared with plaque from the lower anterior area, plaque from the upper posterior area exhibited a significantly higher pH-lowering potential, i.e., a lower pH at 10 and 60 min and a greater delta pH and significantly higher levels of mutans streptococci. The final pH values for the non-mutans streptococci exhibited a wide range from about 4.4 to over 5.0. The proportions of such organisms designated as capable of acidogenesis at low pH (final pH less than 4.6), whether expressed as a percentage of the total non-mutans streptococci or of the total plaque flora, were significantly increased in plaque from the upper posterior area. The proportions of non-mutans streptococci capable of acidogenesis at low pH in plaque from the upper posterior area were also significantly increased, with decreasing pH values at 10 and 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro Acidogenic Potential and Mutans Streptococci of Human Smooth-surface Plaque Associated with Initial Caries Lesions and Sound Enamel

Samples of human dental plaque were pooled from several "white spot" smooth tooth surface areas as well as from several clinically-sound tooth surface areas in each of 12 caries-positive college students. Each of the two samples from each subject was used for the determination of: (1) pH-lowering potential in vitro involving dispersed plaque suspensions, excess glucose supply, and a 60-minute test, and (2) the proportions of mutans streptococci and lactobacilli. When all subjects were considered, plaques from "white spot" areas, as compared with samples from sound surface areas, were characterized by significantly higher proportions of mutans streptococci, a lower starting ("resting") pH, a faster rate of pH drop between pH 6.0 and 5.0, and a lower minimum pH of the suspension; the lactobacillus proportions were generally very low in both types of plaques. For individual subjects, however, the proportions of mutans streptococci in plaque associated with "white spot" areas showed a wide range (0.001-10.0%), and samples with high as well as low levels of these micro-organisms could exhibit a high rate of pH drop and a low pH minimum. This suggests that, besides mutans streptococci and lactobacilli, other bacteria capable of acidogenesis at a low pH may contribute to the high pH-lowering potential exhibited by many plaques.

A rapid method for the enumeration of cultivable bacteria in dental plaque samples

A rapid method for estimating the number of cultivable bacteria in dental plaque samples was developed in which five fluorogenic substrates (4-methylumbelliferyl (4-MU)-α-glucoside, 4-MU-β-glucoside, glycyl-prolyl-7-amido-4-methyl-coumarin (-AMC), tyrosyl-AMC and prolyl-AMC) in 150 μl were incubated with 50 μl of dental plaque suspension. The increase in fluorescence measured at emission and excitation wavelengths of 380 and 460 nm correlated with the colony count per plaque sample. The rapid method allows the number of cultivable bacteria in plaque samples to be estimated and, with the choice of appropriate substrates, it should be useful for estimating the numbers of bacteria in other mixed populations.

Cariological Assessment of Leucrose [D-Glucopyranosyl-α(1→5)-D-Fructopyranose] as a Sugar Substitute

Leucrose [D-glucosyl-alpha(1----5)-D-fructopyranose] prepared by microbial-enzymatic transglycosidation from sucrose, is the first alpha(1----5)-linked disaccharide which possesses excellent nutritional properties with regard to metabolic utilization and is well tolerated. The aim of the present work was to assess its cariogenic potential. Yeast invertase was shown to be inhibited by leucrose in a noncompetitive way, while hydrogenated leucrose (leucritol) acted as an activator. Plaque polysaccharide forming glucosyltransferases from Streptococcus cricetus AHT were not influenced by leucrose, but by leucritol. Essentially no acid formation was observed after incubation of leucrose with suspensions of human dental plaque, S. mutans NCTC 10449, Lactobacillus casei LSB 132 and Actinomyces viscosus Ny 1 No. 30. Leucrose was a competitive inhibitor of the acid formation from sucrose by S. mutans NCTC 10449 at neutral pH. Furthermore, leucrose inhibited at neutral pH considerably the uptake of sucrose by S. mutans NCTC 10449. The uptake of fructose and maltose was also inhibited but that of glucose not at all. In Cara rats as the animal model, leucrose was compared to sucrose and to corn starch for its cariogenic potential. In sharp contrast to the group fed with 30% sucrose, caries scores of the 30% leucrose group were not significantly different from the starch group. pH telemetry with an indwelling electrode in man proved lueucrose to be 'safe for teeth' since plaque pH did not drop below pH 5.7. Leucrose is a novel noncariogenic disaccharide and thus represents a highly promising sugar substitute for caries prevention.