Effects of dietary sucrose levels on pH fall and acid-anion profile in human dental plaque after a starch mouth-rinse

Identification of unknown acid-resistant genes of oral microbiotas in patients with dental caries using metagenomics analysis

Acid resistance is critical for the survival of bacteria in the dental caries oral micro-environment. However, there are few acid-resistant genes of microbiomes obtained through traditional molecular biology experimental techniques. This study aims to try macrogenomics technologies to efficiently identify acid-resistant genes in oral microbes of patients with dental caries. Total DNA was extracted from oral microbiota obtained from thirty dental caries patients and subjected to high-throughput sequencing. This data was used to build a metagenomic library, which was compared to the sequences of two Streptococcus mutant known acid-resistant genes, danK and uvrA, using a BLAST search. A total of 19 and 35 unknown gene sequences showed similarities with S. mutans uvrA and dnaK in the metagenomic library, respectively. Two unknown genes, mo-dnaK and mo-uvrA, were selected for primer design and bioinformatic analysis based on their sequences. Bioinformatics analysis predicted them encoding of a human heat-shock protein (HSP) 70 and an ATP-dependent DNA repair enzyme, respectively, closely related with the acid resistance mechanism. After cloning, these genes were transferred into competent Escherichia coli for acid resistance experiments. E. coli transformed with both genes demonstrated acid resistance, while the survival rate of E. coli transformed with mo-uvrA was significantly higher in an acidic environment (pH = 3). Through this experiment we found that identify unknown acid-resistant genes in oral microbes of patients with caries by establishing a metagenomic library is very efficient. Our results provide an insight into the mechanisms and pathogenesis of dental caries for their treatment without affecting oral probiotics.

Starch Combined with Sucrose Provokes Greater Root Dentine Demineralization than Sucrose Alone

Since there is no consensus about whether starch increases the cariogenic potential of sucrose, we used a validated 3-species biofilm model to evaluate if starch combined with sucrose provokes higher root dentine demineralization than sucrose alone. Biofilms (n = 18) composed by Streptococcus mutans (the most cariogenic bacteria), Actinomces naeslundii (which has amylolytic activity), and Streptococcus gordonii (which binds salivary amylase) were formed on root dentine slabs under exposure 8 ×/day to one of the following treatments: 0.9% NaCl, 1% starch, 10% sucrose, or a combination of 1% starch and 10% sucrose. Before each treatment, biofilms were pretreated with human whole saliva for 1 min. The pH of the culture medium was measured daily as an indicator of biofilm acidogenicity. After 96 h of growth, the biofilms were collected, and the biomass, bacteria viability, and polysaccharides were analyzed. Dentine demineralization was assessed by surface hardness loss (% SHL). Biofilm bioarchitecture was analyzed using confocal laser scanning microscopy. Treatment with a starch and sucrose combination provoked higher (p = 0.01) dentine demineralization than sucrose alone (% SHL = 53.2 ± 7.0 vs. 43.2 ± 8.7). This was supported by lower pH values (p = 0.007) of the culture medium after daily exposure to the starch and sucrose combination compared with sucrose (4.89 ± 0.29 vs. 5.19 ± 0.32). Microbiological and biochemical findings did not differ between biofilms treated with the combination of starch and sucrose and sucrose alone (p > 0.05). Our findings give support to the hypothesis that a starch and sucrose combination is more cariogenic for root dentine than sucrose alone.

Relationship among α amylase and carbonic anhydrase VI in saliva, visible biofilm, and early childhood caries: a longitudinal study

AIM

This longitudinal study investigated the relationship among early childhood caries (ECC), α amylase, carbonic anhydrase VI (CA VI), and the presence of visible biofilm, besides detecting if these variables could predict risk for ECC.

DESIGN

One hundred children were divided into two groups: caries group (n = 45) and caries-free group (n = 55). Visible biofilm on maxillary incisors was recorded, followed by caries diagnosis in preschoolers at baseline and at follow-up. Saliva samples were collected, and activities of CA VI and α amylase were determined. Data normality was assessed by Shapiro-Wilk test and then Mann-Whitney, Spearman correlation, and chi-square tests followed by multiple logistic regression analysis (α = 0.05, 95% confidence interval).

RESULTS

CA VI activity was significantly higher in saliva of children with caries (P ≤ 0.05), and α amylase activity was significantly higher in saliva of caries-free children (P < 0.0001). Children with α amylase activity in saliva lower than 122.8 U/mL (OR = 3.33 P = 0.042) and visible biofilm on maxillary incisors (OR = 3.6 P = 0.009) were more likely to develop ECC than caries-free children. A negative correlation between caries and α amylase activity was found (P = 0.0008).

CONCLUSIONS

The presence of visible biofilm and low salivary activity of α amylase may be considered risk predictors for ECC.

Effect of starch on the cariogenic potential of sucrose

Since in vitro and animal studies suggest that the combination of starch with sucrose may be more cariogenic than sucrose alone, the study assessed in situ the effects of this association applied in vitro on the acidogenicity, biochemical and microbiological composition of dental biofilm, as well as on enamel demineralization. During two phases of 14 d each, fifteen volunteers wore palatal appliances containing blocks of human deciduous enamel, which were extra-orally submitted to four groups of treatments: water (negative control, T1); 2 % starch (T2); 10 % sucrose (T3); and 2 % starch+10 % sucrose (T4). The solutions were dripped onto the blocks eight times per day. The biofilm formed on the blocks was analysed with regard to amylase activity, acidogenicity, and biochemical and microbiological composition. Demineralization was determined on enamel by cross-sectional microhardness. The greatest mineral loss was observed for the association starch+sucrose (P<0.05). Also, this association resulted in the highest lactobacillus count in the biofilm formed (P<0.05). In conclusion, the findings suggest that a small amount of added starch increases the cariogenic potential of sucrose.

Developments in dental plaque pH modelling

OBJECTIVES

The objectives of this review were to give a comprehensive account of the methods used to determine dental plaque pH over the last 50 years, to review how these methods have been used in dental cariology research and to give an update as to how dental plaque pH studies might be developed in the future.

DATA

Published, referred papers and abstracts of conference proceedings in the literature were reviewed.

SOURCES

A comprehensive search of the electronic databases PubMed and Medline, was undertaken. In addition, a hand search of the Index Denticus was done to identify relevant citations before 1966.

STUDY SELECTION

Relevant published literature in peer-reviewed publications was reviewed. No additional inclusion criteria were applied.

CONCLUSIONS

This comprehensive review gives an account of the background to, history of, relative merits and demerits of, applications of and future of dental plaque pH technologies.

Oral colonization and cariogenicity of Streptococcus gordonii in specific pathogen-free TAN:SPFOM(OM)BR rats consuming starch or sucrose diets

The significance of Streptococcus gordonii in dental caries is undefined, as is that of other alpha-amylase-binding bacteria (ABB) commonly found in the mouth. To clarify the ecological and cariological roles of S. gordonii our specific pathogen-free Osborne-Mendel rats, TAN:SPFOM(OM)BR, were fed either diet 2000 (containing 56% confectioner's sugar, most of which is sucrose) or diet 2000CS (containing 56% cornstarch, in lieu of confectioner's sugar) and inoculated with S. gordonii strains. Uninoculated rats were free of both indigenous mutans streptococci (MS) and ABB, including S. gordonii, as shown by culture on mitis salivarius and blood agars of swabs and sonicates of dentitions after weanlings had consumed these diets for 26 days. ABB were detected by radiochemical assay using [125I]-amylase reactive to alpha-amylase-binding protein characteristic of the surface of S. gordonii and other ABB. No ABB were detected (detection limit < 1 colony-forming units in 10(6) colony-forming units). Thus the TAN:SPFOM(OM)BR colony presents a 'clean animal model' for subsequent study. Consequently, S. gordonii strains Challis or G9B were used to inoculate weanling rat groups consuming either the high-sucrose diet 2000 or the cornstarch diet 2000CS. Two additional groups fed each of these diets remained unioculated. Recoveries of inoculants were tested 12 and 26 days later by oral swabs and sonication of the molars of one hemimandible of each animal, respectively. Uninoculated animals were reconfirmed to be free of ABB and mutans streptococci, but inoculated ones eating diet 2000CS had S. gordonii recoveries of 1-10% or, if eating diet 2000, 10-30% of total colony-farming units in sonicates. There were no statistically significant differences among the inoculated and uninoculated animal groups' caries scores when they ate the cornstarch diet. Lesion scores for sucrose-eating rats were, however, from 2.4-5.1-fold higher than for cornstarch-eating rats, P < 0.001, and were still higher if animals had been inoculated with either Challis (1.41-fold) or G9B (1.64-fold), than if uninoculated, both P < 0.001, so long as the rats ate the sucrose diet. Therefore, TAN:SPFOM(OM)BR rats do not harbour ABB or S. gordonii but can be colonized by S. gordonii. Colonization levels of S. gordonii on the teeth are higher in the presence of high sucrose than with high starch-containing diets. Caries scores are augmented by sucrose compared with starch, and are further augmented by S gordonii colonization. S. gordonii is thus cariologically significant in the presence of sucrose, at least in this rat.

Food starches and dental caries

Sucrose and starches are the predominant dietary carbohydrates in modern societies. While the causal relationship between sucrose and dental caries development is indisputable, the relationship between food starch and dental caries continues to be debated and is the topic of this review. The current view of dental caries etiology suggests that in-depth evaluation of the starch-caries relationship requires the consideration of several critical cariogenic determinants: (1) the intensity (i.e., the amount and frequency) of exposure of tooth surfaces to both sugars and starches, (2) the bioavailability of the starches, (3) the nature of the microbial flora of dental plaque, (4) the pH-lowering capacity of dental plaque, and (5) the flow rate of saliva. Studies of caries in animals, human plaque pH response, and enamel/dentin demineralization leave no doubt that processed food starches in modern human diets possess a significant cariogenic potential. However, the available studies with humans do not provide unequivocal data on their actual cariogenicity. In this regard, we found it helpful to distinguish between two types of situations. The first, exemplified by our forebears, people in developing countries, and special subject groups in more modern countries, is characterized by starch consumption in combination with a low sugar intake, an eating frequency which is essentially limited to two or three meals per day, and a low-to-negligible caries activity. The second, exemplified by people in the more modern societies, e.g., urban populations, is characterized by starch consumption in combination with significantly increased sugar consumption, an eating frequency of three or more times per day, and a significantly elevated caries activity. It is in the first situation that food starches do not appear to be particularly caries-inducive. However, their contribution to caries development in the second situation is uncertain and requires further clarification. Although food starches do not appear to be particularly caries inducive in the first situation, the possibility cannot be excluded that they contribute significantly to caries activity in modern human populations. The commonly used term "dietary starch content" is misleading, since it represents a large array of single manufactured and processed foods of widely varying composition and potential cariogenicity. Hence, increased focus on the cariogenicity of single starchy foods is warranted. Other aspects of starchy foods consumption, deserving greater attention, include the bioavailability of starches in processed foods, their retentive properties, also in relation to sugars present (starches as co-cariogens), their consumption frequency, the effect of hyposalivation on their cariogenicity, and their impact on root caries. The starch-caries issue is a very complex problem, and much remains uncertain. More focused studies are needed. At present, it appears premature to consider or promote food starches in modern diets as safe for teeth.

A computer program for correlating dental plaque pH values, cH+, plaque titration, critical pH, resting pH and the solubility of enamel apatite

A computer program was written in Visual Basic (Microsoft) to calculate (a) the area between a plaque pH curve (as seen after a sucrose rinse) and either a resting pH (around pH 7) or a critical pH value (around 5.5) above at least parts of the pH curve; (b) the solubility of apatite at the pH values in plaque; (c) the area between the plaque pH solubility curve and the apatite solubility at the resting pH/critical pH; (d) the area between plaque cH+ curve and the cH+ value at resting pH/ critical pH; and (e) the area between a plaque pH curve and a cut-off pH value below the curve, e.g. pH 3. It was found that because both the cH+ and the solubility of apatite increased logarithmically with a pH drop, the two latter area functions (d, e) were basically different from those based directly on pH curves. Thus, pH changes around the resting pH value had little effect on areas calculated from concentrations of H+ and solubility. In contrast, a small pH change around pH 4 had a strong impact on both demineralization potential and areas based on cH+. Also, because of the logarithmic nature, demineralization potentials were generally large in comparison to remineralization potentials, a point that has hitherto received little attention.

Role of micro-organisms in caries etiology

The microbial etiology of dental caries is discussed in terms of the dynamic relationship among the dental plaque microbiota, dietary carbohydrate, saliva, and the pH-lowering and cariogenic potential of dental plaque. The evidence supports a concept of caries as a dietary carbohydrate-modified bacterial infectious disease. Its key feature is a dietary carbohydrate-induced enrichment of the plaque microbiota with organisms such as the mutans streptococci and lactobacilli which causes an increase of plaque's pH-lowering and cariogenic potential. The shift in the plaque proportions of these organisms appears to be related to their relatively high acid tolerance. A large body of evidence also supports a major effect of saliva on caries development. Integration of salivary effects with the concept of caries as a dietary carbohydrate-modified bacterial infectious disease suggests a broader concept which includes a major role of saliva in the regulation of the exposure of tooth surfaces to carbohydrate and of plaque acidity and, hence, the microbial composition and the pH-lowering and cariogenic potential of dental plaque. It is proposed that caries occurs preferentially in dentition sites characterized by a relatively high exposure to carbohydrate and diminished salivary effects. Some implications of this concept are discussed.

Effect of frequent consumption of starchy food items on enamel and dentin demineralization and on plaque pH in situ

The aim of this cross-over study was to determine the cariogenic potential of starchy food items as between-meal snacks. This was done by measuring demineralization of human enamel and dentin as well as the pH of dental plaque in situ. Eight volunteers with complete dentures carried two enamel and two dentin specimens, mounted in the molar regions of their mandibular prostheses. There were three test periods, each lasting for 21 days, followed in a randomized order: (1) consumption of starchy food products, 12-15 times a day, in addition to the normal diet (starch period); (2) consumption of sucrose products, 12-15 times a day, in addition to the normal diet (sucrose period); and (3) no addition of test products to the normal diet (control period). Both the starch and the sucrose diets increased the demineralization of enamel and dentin compared with the control period. However, only the sucrose period resulted in significant demineralization of dentin compared with the control period. The plaque pH, followed during 60 min after a one-minute mouthrinse with 10% sucrose, was lower at all time points after both the starch and the sucrose periods compared with the control period.

Salivary alpha-amylase: role in dental plaque and caries formation

Salivary alpha-amylase, one of the most plentiful components in human saliva, has at least three distinct biological functions. The enzymatic activity of alpha-amylase undoubtedly plays a role in carbohydrate digestion. Amylase in solution binds with high affinity to a selected group of oral streptococci, a function that may contribute to bacterial clearance and nutrition. The fact that alpha-amylase is also found in acquired enamel pellicle suggests a role in the adhesion of alpha-amylase-binding bacteria. All of these biological activities seem to depend on an intact enzyme conformation. Binding of alpha-amylase to bacteria and teeth may have important implications for dental plaque and caries formation. alpha-Amylase bound to bacteria in plaque may facilitate dietary starch hydrolysis to provide additional glucose for metabolism by plaque microorganisms in close proximity to the tooth surface. The resulting lactic acid produced may be added to the pool of acid in plaque to contribute to tooth demineralization.

The effect of increased mastication by daily gum-chewing on salivary gland output and dental plaque acidogenicity

The effect of increased mastication on plaque metabolism and salivary gland function was determined in 11 human subjects who chewed a sugarless gum for ten minutes of each waking hour for two weeks. Prior to and at the conclusion of the gum-chewing regimen, unstimulated whole saliva and 2% citric-acid-stimulated parotid saliva were collected. Flow rates, pH, and buffer capacity were determined on all saliva samples. In addition, parotid saliva was analyzed for protein concentration and the proteins further studied by SDS-PAGE. The plaque pH response to a 10% sucrose rinse was also measured before and after the regimen. Significant increases were observed in the pH and buffer capacity of unstimulated whole saliva as were similar increases in the flow rate, pH, and buffer capacity of stimulated parotid saliva. Protein concentrations and profiles remained unaffected. In addition, the resting plaque pH and minimum plaque pH reached after a sucrose challenge were both raised significantly, with a significant reduction in the cH area. The results of this study indicate that increased masticatory effort by frequent consumption of sugar-free chewing gum over a prolonged time period resulted in a functional increase in the output of stimulated parotid saliva, as well as in increases in pH and buffer capacity of whole and parotid saliva, which may help to reduce plaque acidogenicity.

Plaque fluid as a bacterial milieu

Studies of the extracellular, free concentrations of substrates, growth factors, inhibitors, and end-products of metabolism to which the intact plaque microflora is exposed in situ can assist in the understanding of factors controlling plaque pathogenicity. Information is becoming increasingly available from analysis of fluid separated by centrifugation of plaques collected at various intervals after an intra-oral pulse of dietary or experimental substrate, or different procedures or treatments having cariostatic potential. Such analytical results give more information than those obtained by analysis of aqueous or other extracts, because they yield values of substrate concentration representing those occurring at the bacterial cell surface. The largest body of information concerns extracellular levels of acid end-products of sugar catabolism in relation to food quality or sequence, and of amino acids and other products of nitrogen metabolism, in relation to studies of the detailed metabolic events of the Stephan curve, and of the demineralizing effect of the plaque environment. Areas where little information is available and which merit further study include plaque clearance of salivary and other components with anti-caries activity (e.g., antibodies, enzymes, fluorides, cations, other antimicrobials, etc.), and substrate concentrations to determine gradients for diffusion into and out of plaque.

The relationship between the biochemical composition of dental plaque from both approximal and free smooth surfaces of teeth and subsequent 3-year caries increment in adolescents

The biochemical composition of both types of plaque and the subsequent caries increment were investigated in 39 males aged 11-12 years at the time of plaque collection. The calcium concentration of free smooth-surface plaque was inversely related to both total and approximal 3-year DFS increment (p less than 0.01). A relationship between calcium concentrations in approximal plaque and subsequent caries was restricted to the 3-year increment on approximal surfaces (p less than 0.05). There was evidence for a direct relationship between caries increment and both magnesium and organic phosphorus concentrations in plaque on the free smooth surfaces only (p less than 0.05). In contrast, a direct relationship between total caries increment and both total and intracellular carbohydrate concentrations reached statistical significance for approximal plaque only (p less than 0.05). Regression analysis indicated that the combination of the calcium and inorganic phosphorus concentrations of free smooth-surface plaque and the intracellular carbohydrate concentrations of approximal plaque explained 40% of the variation in subsequent caries increment.

The effect of previous diet on plaque pH response to different foods

In this study we investigated the effect of previous diet on the response of plaque pH to three test foods. The study population consisted of 11 dental students. Plaque pH was measured, by means of the touch electrode method, on the first two upper molars. The study was conducted at two sessions, one week apart. Subjects followed a 48-hour high-sugar diet before the first test session and a 48-hour low-sugar diet before the second test session. During both 48-hour periods, students refrained from all oral hygiene practices and fluoride utilization. At each session, three foods were ingested at one-hour intervals: cola, beer, and chocolate bar. pH measurements at baseline and at selected times after food ingestion were recorded and analyzed. Multivariate analysis of variance revealed significant independent effects of food, previous diet, and their interaction on plaque pH. After the same foods were ingested, plaque pH response after a previous high-sugar diet was significantly more acidic than after a previous low-sugar diet.

The relationship between plaque pH, plaque acid anion profiles, and oral carbohydrate retention after ingestion of several 'reference foods' by human subjects

The primary aim of this study was to rank several reference foods (apple drink, caramel, chocolate, cookie, skimmed milk powder, snack cracker, and wheat flake) according to their plaque pH response as monitored in a panel of 12 volunteers by the plaque-sampling method for comparison with data previously reported with other methods used to assess cariogenicity potential. Secondary experiments (using subsets of the panel of subjects) were undertaken in an attempt to elucidate some of the reasons for the observed plaque pH changes. Oral carbohydrate retention was measured at a single time period after food use as total anthrone-positive carbohydrate material, and as specific acidogenic sugars by gas-liquid chromatography after gel-exclusion chromatography. The concentrations of acid anions in the plaque fluid after food consumption were measured by isotachophoresis eight min after food use. According to the plaque pH response, apple-flavored fruit drink and chocolate were the most acidogenic foods and skimmed milk powder the least acidogenic. There were significant correlations (p less than 0.05) between the plaque pH data and lactate-plus-acetate concentrations in plaque fluid, but the correlations between the pH data and any of the carbohydrate retention parameters were not significant.

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.

Degradation of starch and its hydrolytic products by oral bacteria

Selected strains of oral bacteria were analyzed for their ability to degrade wheat starch, maltose, maltotriose, and maltoheptaose. S. sanguis IUOM-11M and JC804, S. mutans 6715, S. salivarius IUOM-8, A. viscosus IUOM-62, and A. naeslundii ATCC 12104 degraded all four substrates. S. mutans NCTC 10449 degraded starch, maltose, and maltotriose, while A. viscosus ATCC 15987 degraded starch and maltose, and S. sanguis SS34 degraded only maltose. L. casei IUOM-14 did not degrade any of the substrates. Analysis of starch degradation products from S. sanguis IUOM-11M and A. viscosus IUOM-62 demonstrated oligosaccharides, maltose, and trace amounts of glucose for the former and oligosaccharides, maltotriose, and maltose for the latter. S. sanguis IUOM-11M alpha-glucosidase (EC 3.2.1.20) demonstrated a pH optimum of 6.5 and greatly enhanced activity from maltose-cultured cells as compared with cells cultured in glucose or fructose. The presence of fructose in the growth medium prevented this enhancement of activity by maltose. Maltose inhibited sucrose-dependent synthesis of S. sanguis IUOM-11M insoluble polysaccharide and both primer-dependent and primer-independent synthesis of soluble polysaccharide. Maltoheptaose inhibited primer-dependent but not primer-independent soluble polysaccharide synthesis. Several oral bacteria have the ability to hydrolyze starch and to degrade further the products to acidogenic substrates. These products may also inhibit sucrose-dependent synthesis of polysaccharides, which enhances the production of the acidogenic substrate fructose. The results add further support to the growing body of evidence suggesting that caries-promoting properties of starch may be expressed only when starch is present in diets containing sucrose.