Bacterial factors of cariogenicity (literature review).

OBJECTIVE: Introduction: According to the 2003 WHO report, dental caries affects from 60% to 90% of school-age children and adults that makes it one of the most common diseases worldwide. The aim was to systematize data about the modern conception of plaque formation and role of microorganisms in its development. PATIENTS AND METHODS: Materials and methods: Biblosemantic, 50 medical literature sources were systematically reviewed as the material for the research. RESULTS: Review: According to Miller's theory, oral microorganisms can decompose dietary carbohydrates into acids, which in turn dissolve the calcium phosphates found in the enamel, causing it demineralisation Along with Streptococcus mutans, nowadays some other bacteria as Streptococcus sorbinus, Lactobacillus spp. and Actinomyces spp. have been well studied as caries contributors. However, the disease is related to plaque-mediated, because a much larger number of normal oral microflora representatives are involved in creating favourable preconditions for its development. There are a lot of original research papers about a role of bacteria in caries decay but compositions and characters of oral microflora are changing nowadays. Therefore, authors show the main cariogenic bacteria and their factors of pathogenicity which create special conditions for caries lesions. Modern concepts of dental plaque formation and pathogenesis of plaque-assosiative diseases are presented according to the new actual dental research. A lot of attention is paid to the biochemical properties of cariogenic bacteria and chemical process in biofilm. Role of acid and alkali production by oral bacteria in caries decay are shown in this article. Moreover, mechanisms of bacterial acid-fast and acid-tolerance are presented. CONCLUSION: Conclusions: Analysis of literature demonstrates a lot of bacterial pathogenicity factors which play key role in caries development.

pH modulation and salivary sugar clearance of different chocolates in children: A randomized clinical trial.

BACKGROUND: Sugars that occur naturally in foods and those added in processed foods may act as the source for fermentable carbohydrates and may initiate caries process. Among all the foods consumed by children, chocolates form an important constituent. A wide variety of chocolates are available in the Indian market and very few studies have compared their acidogenicity and salivary sugar clearance. OBJECTIVES: To compare the acidogenicity and salivary sugar clearance of 6 different commercially available chocolates in the Indian market. MATERIALS AND METHODS: Thirty subjects aged 10-15 years were selected randomly from one of the available public schools in Nellore city. Six commercially available chocolates in the Indian market were divided into three groups, unfilled (dark and milk chocolate), filled (wafer and fruit and nuts chocolate), and candy (hard milk and mango-flavored candy) groups. Plaque pH values and salivary sugar clearance rates are assessed at baseline, 5, 10, 15, 20, and 30 min after consumption. All the data obtained were statistically evaluated using independent sample t-test and one-way ANOVA for multiple group comparisons. RESULTS: Mango-flavored candy had maximum fall in plaque pH and least fall in plaque pH was recorded with milk chocolate. Fruit and nuts chocolate had a maximum clearance of salivary sugar and least fall in the salivary sugar clearance was recorded with dark chocolate. When the plaque pH and salivary sugar clearance of all the chocolates were assessed, it was seen that the values were statistically significant at all the time intervals (P < 0.05). CONCLUSION: Dark chocolate had a high fall in pH and milk chocolate had low salivary sugar clearance which signifies that unfilled chocolates are more cariogenic than other chocolates. Even though mango-flavored candy had maximum fall in plaque pH, its salivary sugar clearance was high.

Metabolic activity of Streptococcus mutans biofilms and gene expression during exposure to xylitol and sucrose.

The objective of the study was to analyse Streptococcus mutans biofilms grown under different dietary conditions by using multifaceted methodological approaches to gain deeper insight into the cariogenic impact of carbohydrates. S. mutans biofilms were generated during a period of 24 h in the following media: Schaedler broth as a control medium containing endogenous glucose, Schaedler broth with an additional 5% sucrose, and Schaedler broth supplemented with 1% xylitol. The confocal laser scanning microscopy (CLSM)-based analyses of the microbial vitality, respiratory activity (5-cyano-2,3-ditolyl tetrazolium chloride, CTC) and production of extracellular polysaccharides (EPS) were performed separately in the inner, middle and outer biofilm layers. In addition to the microbiological sample testing, the glucose/sucrose consumption of the biofilm bacteria was quantified, and the expression of glucosyltransferases and other biofilm-associated genes was investigated. Xylitol exposure did not inhibit the viability of S. mutans biofilms, as monitored by the following experimental parameters: culture growth, vitality, CTC activity and EPS production. However, xylitol exposure caused a difference in gene expression compared to the control. GtfC was upregulated only in the presence of xylitol. Under xylitol exposure, gtfB was upregulated by a factor of 6, while under sucrose exposure, it was upregulated by a factor of three. Compared with glucose and xylitol, sucrose increased cell vitality in all biofilm layers. In all nutrient media, the intrinsic glucose was almost completely consumed by the cells of the S. mutans biofilm within 24 h. After 24 h of biofilm formation, the multiparametric measurements showed that xylitol in the presence of glucose caused predominantly genotypic differences but did not induce metabolic differences compared to the control. Thus, the availability of dietary carbohydrates in either a pure or combined form seems to affect the cariogenic potential of S. mutans biofilms.

Fermentative 2-carbon metabolism produces carcinogenic levels of acetaldehyde in Candida albicans.

UNLABELLED: Acetaldehyde is a carcinogenic product of alcohol fermentation and metabolism in microbes associated with cancers of the upper digestive tract. In yeast acetaldehyde is a by-product of the pyruvate bypass that converts pyruvate into acetyl-Coenzyme A (CoA) during fermentation. THE AIMS OF OUR STUDY WERE: (i) to determine the levels of acetaldehyde produced by Candida albicans in the presence of glucose in low oxygen tension in vitro; (ii) to analyse the expression levels of genes involved in the pyruvate-bypass and acetaldehyde production; and (iii) to analyse whether any correlations exist between acetaldehyde levels, alcohol dehydrogenase enzyme activity or expression of the genes involved in the pyruvate-bypass. Candida albicans strains were isolated from patients with oral squamous cell carcinoma (n = 5), autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) patients with chronic oral candidosis (n = 5), and control patients (n = 5). The acetaldehyde and ethanol production by these isolates grown under low oxygen tension in the presence of glucose was determined, and the expression of alcohol dehydrogenase (ADH1 and ADH2), pyruvate decarboxylase (PDC11), aldehyde dehydrogenase (ALD6) and acetyl-CoA synthetase (ACS1 and ACS2) and Adh enzyme activity were analysed. The C. albicans isolates produced high levels of acetaldehyde from glucose under low oxygen tension. The acetaldehyde levels did not correlate with the expression of ADH1, ADH2 or PDC11 but correlated with the expression of down-stream genes ALD6 and ACS1. Significant differences in the gene expressions were measured between strains isolated from different patient groups. Under low oxygen tension ALD6 and ACS1, instead of ADH1 or ADH2, appear the most reliable indicators of candidal acetaldehyde production from glucose.

A defined-multispecies microbial model for studying enamel caries development.

The aims of this study were to describe and validate an in vitro multispecies microbial biofilm model for caries development by evaluating the effects of varying medium concentration of sucrose (0.5 and 1.0%) and fluoride (0.4, 0.8 and 1.0 ppm F) in study 1, and calcium (1.0 and 2.0 mM Ca) in study 2. Defined-multispecies biofilms, formed by Lactobacillus casei, Streptococcus mutans, S. salivarius and S. sanguinis, were grown on the surface of salivary-pellicle-coated enamel slabs, with known baseline surface hardness; growth medium was changed daily. Counts of viable cells on biofilms and the percentage of surface microhardness change (%SMC), lesion depth (LD) and integrated mineral loss (IML) on enamel slabs were assessed after 4 days of biofilm formation under the tested conditions. Counts of viable cells on biofilms were significantly affected by sucrose, fluoride and calcium concentrations (p < 0.05). There was a decrease in %SMC in response to increased fluoride and calcium concentrations (p < 0.001). Lower IML (p < 0.001) and LD (p < 0.05) were found in the presence of 0.8 and 1.0 ppm F. A negative correlation was found between the response variables (%SMC, LD and IML) and fluoride and calcium concentrations. The results suggest that the microbial caries model developed was able to show distinct levels of caries inhibition in response to fluoride and calcium concentrations, corroborating clinical observations. An effect of sucrose concentration on caries development was found only in the presence of the lowest fluoride concentration.

pH of tooth surface in healthy adolescents at rest and after a glucose rinse: effect of 72 hours of plaque accumulation.

AIM: This study was performed to evaluate the effect of a glucose rinse and of plaque accumulation on pH of tooth surface in healthy adolescents with a device used in gastroenterology and never tested in the oral cavity. MATERIALS AND METHODS: Values of pH were monitored in 12 adolescents using a portable device (pH-day 2® Menfis, bioMedica S.r.l., Bologna, Italy) with a disposable antimonium electrode kept in contact with the interproximal surface of the upper molars for 40 minutes respectively before and after a one-minute rinse with 10 ml of a 10% glucose solution. The same procedure was repeated in the same subjects after 72 hours of plaque accumulation. RESULTS: The device tested resulted difficult to use on the tooth surface because of the size of the active part of the probe. The glucose rinse caused a statistically significant decrease of the mean pH, restrained in basal conditions (d = -0.16, p <0.05), clinically relevant after plaque accumulation (d = -1.24, p <0.05). Time in minutes of pH < 6 grew considerably only in case of combination of plaque accumulation and glucose rinse (d = 20.90, p <0.05). A Stephan's curve of drop and recover of the pH values was not recorded. CONCLUSIONS: The continuous recording of pH of natural plaque present on the tooth could represent an alternative to other techniques found in literature. More studies are necessary to verify the suitability of this new device for the monitoring of pH in the oral cavity.

Structural investigation of an extracellular polysaccharide produced by the cariogenic bacterium Streptococcus mutans strain UA159.

The structure of an extracellular polysaccharide EPS159 produced from sucrose by Streptococcus mutans UA159 was investigated through the main oligosaccharides obtained from partial acid hydrolysis, monosaccharide/methylation analysis, and 1D/2D (1)H NMR spectroscopy. The results showed that EPS159 contained terminal, 3-substituted, 6-substituted, and 3,6-disubstituted α-D-glucopyranose residues in a molar percentage of 14, 18, 54, and 14%. The backbone of EPS159 was composed of →6)Glcp(1→ residues, and about 20% of the →6)Glcp(1→ residues was substituted at 3-OH by →3)Glcp(1→ and/or Glcp(1→ residues to form side chains. A composite model of EPS159, that includes all identified structural features, was formulated: [Formula, see text:].

Relationship between gap size and dentine secondary caries formation assessed in a microcosm biofilm model.

Secondary caries can develop at the tooth-restoration interface, depending on the presence of a gap and its size, but this process could be inhibited by fluoride. The aim of this study was to assess the relationship between gap size and dentine secondary caries adjacent to composite resin (CR) or glass ionomer (GI) restorations, using a microcosm biofilm model in a constant depth film fermentor (CDFF). Dentine discs restored with CR (Z250) or GI (Vitremer) with gap sizes of 0, 50, 100, 180 or 250 microm were mounted on the CDFF. Microcosm biofilms were formed on the restored discs and daily subjected to 8 pulses of 10% sucrose solution. On the 18th day, dentine mineral loss and lesion depth around the restorations were determined by transverse microradiography. The effect of gap size was overall not statistically significant either with regard to mineral loss (p = 0.449) or lesion depth (p = 0.328), but greater mineral loss and lesion depth were found adjacent to CR than to GI (p < 0.001). However, Spearman correlation showed that mineral loss and lesion depth increased with gap size for CR (p < 0.001) but not for GI (p > 0.05). The findings support the conclusion that fluoride released from GI inhibits dentine demineralization adjacent to restorations, irrespective of gap width.

Chlorhexidine efficacy in preventing lesion formation in enamel and dentine: an in situ study.

BACKGROUND: Clinical studies on the caries-preventive properties of chlorhexidine mouthrinses are limited and the results are inconclusive. AIM: The aim of this study was to elucidate the contribution of a 0.2% chlorhexidine mouthrinse to the protection of enamel and dentine against demineralization. METHODS: In this randomized two-treatment, two-leg study 14 individuals wearing partial prostheses were enrolled. Sound enamel and dentine specimens were placed in situ for 4 weeks. Twice daily, a mouthrinse was performed with either chlorhexidine or saline (control) depending on the experimental group the participant was allocated to. After the experimental period, plaque samples were collected from the surface of the specimens and from natural tooth surfaces to assess the organic acid production upon a sucrose challenge. The specimens were analyzed for mineral loss by transversal microradiography. RESULTS: This study could not demonstrate a significantly better protection of enamel and dentine against demineralization by the chlorhexidine treatment compared to saline. No differences in acid production of plaque samples from the chlorhexidine-treated and control groups were observed. This result was also found for plaque samples originating from the natural tooth surfaces. CONCLUSION: Mouth rinsing with 0.2% chlorhexidine did not prevent demineralization of dentine and enamel in situ.

Salivary flow patterns and the health of hard and soft oral tissues.

BACKGROUND: This nonsystematic review summarizes the effects of saliva on some of the diseases affecting the hard and soft oral tissues. RESULTS: Saliva enters the mouth at several locations, and the different secretions are not well-mixed. Saliva in the mouth forms a thin film, the velocity of which varies greatly at different sites. This variation appears to account for the site specificity of smooth-surface caries and supragingival calculus deposition. Saliva protects against dental caries, erosion, attrition, abrasion, candidiasis and the abrasive mucosal lesions seen commonly in patients with hyposalivation. These effects are the result of saliva's being a source of the acquired enamel pellicle; promoting the clearance of sugar and acid from the mouth; being supersaturated with respect to tooth mineral; containing buffers, urea for plaque base formation, and antibacterial and antifungal factors; and lubricating the oral mucosa, making it less susceptible to abrasive lesions. CLINICAL IMPLICATIONS: For optimal oral health, people should keep food and liquids in the mouth as briefly as possible. The most important time for toothbrushing is just before bedtime, because salivary flow is negligible during sleep and the protective effects of saliva are lost. Chewing sugar-free gum or sucking on sugar-free candies stimulates salivary flow, which benefits hard and soft oral tissues in many ways.

Merenda escolar na promoção da saúde bucal: o potencial cariogênico dos alimentos / School meal in promotion of oral health: the cariogenic potential of food

Studies on school meals have increased in recent years in pursuit of strategies to offer food that serves not only to feed students, but also provide adequate physical and mental development, as well as promote general and oral health, emphasizing the prevention of caries. This article is a bibliographical review concerning works about foods and meals offered in schools, considering their cariogenic potential, as well as its role in the promotion of oral health. Carbohydrates, mainly the simple ones, are the nutrients of bigger impact on caries. However, an active bacterial flora is necessary to metabolize such nutrients in the mouth, which depends on the individual's oral hygiene. The variation in the cariogenic potential of different foods must also be considered, and this depends on the consistency, the way they are prepared and the period of time the food is adhered to the dental surface. Few studies on the cariogenic potential of meals served in schools were found in the literature. However, many foods offered present a great cariogenic potential. Some examples are cheese, bovine milk, rapadura (a Brazilian preparation of raw brown sugar in bars), some fruits, yoghurt and sugar. A lack of con cern about the damage of these foods to the dental health is observed. Some authors alert about the importance of making adjustments in school meals to preserve oral health and recognize that feeding programs must be joined to education about oral hygiene, control of the dental plaque, application of fluorides and permanent reinforcement of the educative task

Estudios sobre la merienda escolar han aumentado en los últimos años procurando estrategias para ofrecer una alimentación que sirva no apenas para saciar el apetito de los alumnos sino también para garantizar unadecuado desarrollo físico y mental, promoverla salud en general y en particular la prevención de la carie dentaria. Este trabajo es una revisión bibliográfica de los trabajos sobre alimentos y comidas ofrecidas en la merienda escolar em relación a su potencial cariogénico y su papelen la promoción de la salud bucal. Los carbohidratos, principalmente los de bajo peso molecular son los nutrientes de mayor impacto sobre la carie. Sin embargo, es necesario que haya una flora bacteriana activa para metabolizar tales nutrientes en la cavidad oral,lo cual está determinado por la higiene bucal.Es necesario considerar también la variación enel potencial cariogénico de los alimentos, que depende de la consistencia, modo de preparación y tiempo que el alimento permanece adherido ala superficie dental. La literatura presenta pocos estudios sobre la cariogenicidad de refeccionesservidas en la merienda escolar, pero muchos delos alimentos ofrecidos presentan gran potencial cariogénico: queso, leche bovino, algunas frutas, yogur y azúcar, sin observar alguna preocupación en relación a los daños de esta alimentación a la salud de los dientes. Algunos autores alertan para la importancia de realizar ajustes en la merienda escolar para contribuir apreservar la salud bucal, advirtiendo también que programas de alimentación deben estar unidos a la enseñaza de higiene bucal, control de la placa bacteriana, aplicación de fluoreto, con refuerzo permanente de la tarea educativa

Estudos sobre a merenda escolar vêm aumentando nos últimos anos com a busca de estratégias para oferecer uma alimentação que não sirva apenas para saciar a fome dos alunos, mas também para proporcionar um adequado desenvolvimento físico e mental, além de promovera saúde geral e bucal, com ênfase na prevenção da cárie. Este artigo refere-se a uma revisão bibliográfica realizada acerca de trabalhos referentes a alimentos e refeições oferecidos na merenda escolar quanto ao seu potencial cariogênico, bem como seu papel na promoção da saúde bucal. Os carboidratos, principalmente os simples, são os nutrientes de maior impacto sobre a cárie. No entanto, é necessário que haja uma flora bacteriana ativa para metabolizar tais nutrientes na cavidade oral, o que depende da higiene bucal do indivíduo. Deve-se considerar também a variação no potencial cariogênico dos alimentos, que depende da consistência, do modo de preparação e do tempo que o alimento fica aderido à superfície dentária. Foram encontrados na literatura poucos estudos sobre a cariogenicidade de refeições servidas na merenda escolar, porém, muitos alimentos oferecidos apresentam grande potencial cariogênico, a exemplo do queijo, leite bovino, rapadura, algumas frutas, iogurte e açúcar, e o que se observa é a inexistência de preocupação quanto aos prejuízos desta alimentação à saúde dos dentes. Alguns autores alertam para a importância de se realizarem ajustes na merenda escolar de forma a preservar a saúde bucal, e reconhecem que programas de alimentação devem estar unidos ao ensino de higiene bucal, controle da placa bacteriana, aplicação de fluoretos e reforço permanente da tarefa educativa

The role of sucrose in cariogenic dental biofilm formation--new insight.

Dental caries is a biofilm-dependent oral disease, and fermentable dietary carbohydrates are the key environmental factors involved in its initiation and development. However, among the carbohydrates, sucrose is considered the most cariogenic, because, in addition to being fermented by oral bacteria, it is a substrate for the synthesis of extracellular (EPS) and intracellular (IPS) polysaccharides. Therefore, while the low pH environment triggers the shift of the resident plaque microflora to a more cariogenic one, EPS promote changes in the composition of the biofilms' matrix. Furthermore, it has recently been shown that the biofilm formed in the presence of sucrose presents low concentrations of Ca, P(i), and F, which are critical ions involved in de- and remineralization of enamel and dentin in the oral environment. Thus, the aim of this review is to explore the broad role of sucrose in the cariogenicity of biofilms, and to present a new insight into its influence on the pathogenesis of dental caries.

Intra-oral acid production associated with eating whole or pulped raw fruits.

The hypotheses that raw fruits, whether whole or pulped, were cleared rapidly from the mouth and that the sugars in the whole and pulped fruits are fermented with equal efficiency to acids by the oral microflora were tested in this study. Groups of 7-9 adult subjects chewed 10 g of raw, whole or pulped fruit (apple, banana, orange, pear and pineapple) for 1 min and whole, unstimulated saliva samples were collected during the following 60-min interval. Each saliva sample was assayed for the concentrations of fruit-derived sugars (glucose, fructose and sucrose), fruit-derived acids (malic and citric) and acids which may be produced as a result of bacterial fermentation (acetic, lactic, formic and succinic). We found the fruit-derived sugars were rapidly cleared from the mouth (within 5 min). The major bacterially produced acids were lactic and succinic, which reached maximum concentrations in the 5-min sample. There was no significant difference, within a fruit, in the salivary levels of any of the sugars or acids between the raw whole or raw pulped forms. In light of these findings it seems unwise to assume that fruits may be consumed without consideration of their acidogenic potential.

Composition of dental plaque formed in the presence of sucrose and after its interruption.

Since dental plaque reservoirs of fluoride (F), calcium (Ca) and inorganic phosphorus (Pi) are susceptible to decreases in pH, this in situ crossover study was conducted to test the hypothesis that the low concentration of these ions in plaque, formed in the presence of sucrose, could be attributed merely to the fermentation of this sugar. Eleven volunteers wore palatal appliances containing 6 human enamel blocks during two stages. In each stage, the treatments were either 20% sucrose solution or distilled deionized water, which were dripped onto the blocks 8 times a day. After 28 days, in each stage, the dental plaque formed on two blocks was collected, the treatment was inverted and after a further 24 and 48 h, the biofilm formed was collected from the other blocks. The concentration of acid-soluble F, Ca and Pi, and the concentration of insoluble polysaccharide (IP) were determined in the dental plaque. Statistically lower concentrations of F, Ca and Pi, and a higher concentration of IP were found in the 28-day biofilm formed in the presence of sucrose than in its absence; after the treatment inversion the change in F, Ca and Pi was not statistically significant, but the IP concentration changed significantly. The hypothesis was rejected because change in concentration of F, Ca and Pi is not due to fermentation of the sucrose.

Composition of dental plaque formed in the presence of sucrose and after its interruption

Desde que os reservatórios de flúor (F), cálcio (Ca) e fósforo inorgânico (Pi) na placa dental são suscetíveis a quedas de pH, este estudo in situ cruzado foi conduzido para testar a hipótese de que baixas concentrações destes íons na placa, formada na presença de sacarose, poderiam ser atribuídas simplesmente à fermentação deste açúcar. Onze voluntários utilizaram dispositivos palatinos contendo seis blocos de esmalte dental humano durante duas fases. Em cada fase os tratamentos foram solução de sacarose a 20 por cento ou água destilada deionizada, que foram gotejadas sobre os blocos 8 vezes ao dia. Após 28 dias, em cada fase, a placa dental formada sobre dois blocos foi coletada, o tratamento foi invertido e após um tempo adicional de 24 e 48 horas, o biofilme formado foi coletado dos outros blocos. A concentração de F, Ca e Pi solúvel em ácido e a concentração de polissacarídeo insolúvel (PI) foram determinadas na placa dental. Concentrações estatisticamente menores de F, Ca e Pi, e uma concentração maior de PI foram encontradas no biofilme de 28 dias formado na presença de sacarose do que na sua ausência; após a inversão do tratamento a mudança no F, Ca e Pi não foi estatisticamente significante, mas a concentração de PI mudou significativamente. A hipótese foi rejeitada porque a mudança na concentração de F, Ca e Pi não é devida à fermentação da sacarose.

Intake of sweet foods and counts of cariogenic microorganisms in relation to body mass index and psychometric variables in women.

OBJECTIVE: As a part of the SPAWN (Stockholm Pregnancy and Women's Nutrition) study, the intake of sweet foods (habitual and pre-menstrual intakes) and the number of cariogenic microorganisms in saliva was analysed in relation to body mass index (BMI) and psychometric variables. DESIGN: A cross-sectional study. SUBJECTS: Three hundred and sixty-two women with a median BMI of 24.2 kg/m(2) (range 17.5-47.8) and 45 y of age (range 34-64). METHODS: A questionnaire of sweet food intake, salivary counts of mutans streptococci and lactobacilli and a self-rating scale on psychometric variables (CPRS-S-A). RESULTS: The number of mutans streptococci correlated with BMI (P<0.05), indirectly indicating a higher intake of sweet foods in obese women. The reported energy intake of sweet foods (more specifically the intake of chocolate), correlated with CPRS scores (P<0.01), indicating that women with more severe psychiatric symptomatology have higher intakes of sweet foods. CONCLUSIONS: This study suggests that women with higher CPRS score have higher energy intakes of sweet foods, indicating a possible link between mood regulation and the intake of sweet food. SPONSORSHIP: Karolinska Institute Research Funds.

A mixed-bacteria ecological approach to understanding the role of the oral bacteria in dental caries causation: an alternative to Streptococcus mutans and the specific-plaque hypothesis.

For more than 100 years, investigators have tried to identify the bacteria responsible for dental caries formation and to determine whether their role is one of specificity. Frequent association of Lactobacillus acidophilus and Streptococcus mutans with caries activity gave credence to their being specific cariogens. However, dental caries occurrence in their absence, and the presence of other bacteria able to produce substantial amounts of acid from fermentable carbohydrate, provided arguments for non-specificity. In the 1940s, Stephan found that the mixed bacteria in dental plaque produced a rapid drop in pH following a sugar rinse and a slow pH return toward baseline. This response became a cornerstone of plaque and mixed-bacterial involvement in dental caries causation when Stephan showed that the pH decrease was inversely and clearly related to caries activity. Detailed examination of the pH (acid-base) metabolisms of oral pure cultures, dental plaque, and salivary sediment identified the main bacteria and metabolic processes responsible for the pH metabolism of dental plaque. It was discovered that this metabolism in different individuals, in plaque in different dentition locations within individuals, and in individuals of different levels of caries activity could be described in terms of a relatively small number of acid-base metabolic processes. This led to an overall bacterial metabolic vector concept for dental plaque, and helped unravel the bacterial involvement in the degradation of the carbohydrate and nitrogenous substrates that produce the acids and alkali that affect the pH and favor and inhibit dental caries production, respectively. A central role of oral arginolytic and non-arginolytic acidogens in the production of the Stephan pH curve was discovered. The non-arginolytics could produce only the pH fall part of this curve, whereas the arginolytics could produce both the fall and the rise. The net result of the latter was a less acidic Stephan pH curve. Both kinds of bacteria are numerous in dental plaque. By varying their ratios, we were easily able to produce Stephan pH curves indicative of different levels of caries activity. This and substantial related metabolic and microbial data indicated that it is the proportions and numbers of acid-base-producing bacteria that are at the core of dental caries activity. The elimination of S. mutans, as with a vaccine, was considered to have little chance of success in preventing dental caries in humans, since, in most cases, this would simply make more room for one or more of the many acidogens remaining. An understanding of mixed-bacterial metabolism, knowledge of how to manipulate and work with mixed bacteria, and the use of a bacterial metabolic vector approach as described in this article have led to (1) a more ecological focus for dealing with dental caries, and (2) new means of developing and evaluating anti-caries agents directed toward microbial mixtures that counter excess acid accumulation and tooth demineralization.

Do we need to be concerned about dental caries in the coming millennium?

Dental caries continues to be a pubic health problem despite claims that 50% of schoolchildren are caries-free. There are widespread variations in the prevalence of caries worldwide. Caries lesions are the clinical manifestation of a pathogenic process that may have been occurring on the tooth surface for months or years. Acid production by bacteria embedded in a biofilm termed "dental plaque" is a key aspect of the pathogenesis of dental caries; nevertheless, the ability of micro-organisms to survive in a hostile acid milieu and the influence of fluoride and additional agents on this acid tolerance receive scant attention. Study of cariogenic micro-organisms largely has been limited to observations made on them in the planktonic state; clearly dental caries is essentially a surface phenomenon, and micro-organisms behave distinctively when grown on a surface. Although significant progress has been made in our understanding of the etiology, pathogenesis, and prevention of dental caries, it still remains a scientific and clinical enigma worthy of the attention of the best scientists.

Cariogenic potential of lactosylfructoside as determined by acidogenicity of oral streptococci in vitro and human dental plaque in situ.

The cariogenic potential of lactosylfructoside [O-beta-D-galactopyranosyl-(1-->4)-O-alpha-D-glucopyranosyl-(1<-->2)-beta-D-fructofuranoside] was estimated by experiments on oral streptococci in vitro and human dental plaque in situ. Lactosylfructoside was unable to support growth of the strains of Streptococcus mutans and S. sobrinus used in this study. However, it was able to support growth of strains of S. sanguis, S. mitis and S. oralis. Acid was produced rapidly by cell suspensions of S. oralis ATCC 10557 incubated with lactosylfructoside. Application of 5% w/v solution decreased the pH of human dental plaque. The minimum pH value was below 5.3. The results suggest that lactosylfructoside is as acidogenic as lactose and could be cariogenic if it is consumed frequently and retained for a long period in the mouth.

Remineralization of caries lesions extending into dentin.

Remineralization is one aspect of the overall process of tooth decay. However, it is primarily studied in shallow lesions. The aim of this study was to explore whether caries lesions in enamel and extending into the dentin can be remineralized. A single-section model was developed for the longitudinal and non-destructive monitoring of changes in enamel and dentin. Lesions at least 200 microm into dentin were formed in undersaturated acetate buffers. Next, the lesions were divided into groups (three treatment and one control) and remineralized. The treatments were: weekly immersion in 1,000 ppm fluoride, single treatment with methanehydroxybisphosphonate, and a constant level of 1 ppm fluoride. De- and remineralization was assessed by transverse microradiography. Remineralization was observed in enamel, but also in dentin, indicating that, deep into dentin, the pores become supersaturated to apatite formation. Treatments affected remineralization only in the outer part of enamel. Both findings are explained by a relatively fast diffusion of mineral ions, with precipitation being rate-limiting. The results suggest that dentin remineralization, underneath enamel, can be achieved and could possibly be used in clinical treatment strategies.