Comparison of methods for monitoring changes in the pH of human dental plaque

Biofilm volume and acidification within initial biofilms formed in situ on buccally and palatally exposed bracket material

PURPOSE

Acidification by bacterial biofilms at the bracket/tooth interface is one of the most common problems in fixed orthodontic treatments, which can lead to white spot lesions (WSL) and caries. As lingual brackets were shown to exhibit reduced WSL formation clinically, the aim of this in situ study was to compare initial intraoral biofilm formation and acidification on bracket-like specimens placed buccally and palatally in the upper jaw as a possible cause for this observation.

METHODS

Intraoral biofilm was collected from splints equipped with buccally and palatally exposed test specimens, which were worn by 12 volunteers for a total of 48 h. The test specimens consisted of standard bracket material cylinders on top of a hydroxyapatite disc to represent the bracket/tooth interface. They were analyzed for three-dimensional biofilm volume and live/dead distribution by fluorescence staining and confocal laser scanning microscopy as well as for acidification by fluorescence-based pH ratiometry.

RESULTS

Similar general biofilm morphology with regard to volume and viability could be detected for buccally and palatally exposed specimens. For pH values, biofilms from both positions showed increased acidification at the bottom layer. Interestingly, the pH value at the top layers of the biofilms was slightly lower on palatally than on buccally exposed specimens, which may likely be due to anatomic conditions.

CONCLUSION

Based on the results of this study, initial intraoral biofilm formation and acidification is almost similar on the bracket material/biomimetic tooth interface when placed buccally or palatally in the upper jaw. As lingual brackets were shown to exhibit reduced WSL formation clinically, future studies should investigate further factors like bracket geometry.

Efficacy of Sub-Gingivally Delivered Propolis Nanoparticle in Non-Surgical Management of Periodontal Pocket: A Randomized Clinical Trial

Naturally sourced products like propolis are commonly employed for the non-surgical treatment of periodontal pockets. The use of nanoparticle formulations of these natural remedies has the potential to improve treatment outcomes. The aim of the present study was to evaluate the efficacy of sub-gingivally delivered propolis nanoparticles in the non-surgical management of periodontal pockets. Forty patients diagnosed with periodontitis presenting at least one periodontal pocket with a probing pocket depth between 4 and 6 mm were selected. Patients were randomly assigned into the control group (n = 20), which received scaling and root planing (SRP) and saline (SRP + Saline), and the test group (n = 20), which received SRP and sub-gingivally delivered propolis nanoparticles (PRO) into the periodontal pocket (SRP + PRO). The clinical parameters recorded were plaque index (PI), gingival index (GI), relative attachment loss (RAL), probing pocket depth (PPD), and bleeding on probing (BOP). They were assessed at baseline, one month, and three months post therapy. The results indicated that there was a significant improvement in clinical parameters (p < 0.05) in the test sites compared with the control sites at the end of the study. The gingival index at one month and three months was found to be significantly better in the SRP + PRO group than the SRP + Saline group, with a p value of <0.001. The BOP, PPD, and RAL showed significant improvement with the SRP + PRO group at the end of the 3-month follow-up with p values of 0.0001, 0.001, and 0.05, respectively. The subgingival delivery of propolis nanoparticles showed promising results as an adjunct to SRP in patients with periodontitis presenting periodontal pockets.

Assessment of Cariogenicity by pH-value Decrement of Plaque Solution with Four Infant Milk Formulas: An In Vitro Study

Introduction

People all over the world use a wide variety of infant formulas to nourish the infants. Recent studies demonstrated the high caries-inducing potential of infant formulas. This indicates a need for awareness toward the possible role of the infant formulas in the etiology of early childhood caries (ECC).

Aim

The present study was undertaken to evaluate and comparatively assess the change in plaque pH solutions after fermenting four commonly used infant milk formulas.

Materials and methods

This simple randomized study was carried out on 40 healthy children aged 4–6 years old. The children received full-mouth prophylaxis before examination. They were asked not to implicate oral hygiene for 24 hours and not to have anything at least 2 hours prior the study. Supragingival plaque from the buccal surface of posterior teeth was collected using a Hu-Friedy's curette. Four commonly used infant milk formulas were prepared and given to children for rinsing. The pH of plaque samples were measured at 30 and 60 minutes at 37°C.

Results

The present study showed that all of the four infant milk formulas decreased the mean pH values in plaque solutions significantly after 30 and 60 minutes of preparation.

Conclusion

Our results showed that the plaque pH varied in response to the oral rinsing with the various infant formulas and most of infant formulas were able to reduce the pH significantly below the pH before the rinse. Based upon this study further evaluation of the cariogenicity of infant formulas is recommended.

How to cite this article

Pandey A, Pathivada L, Kajapuram P, et al. Assessment of Cariogenicity by pH-value Decrement of Plaque Solution with Four Infant Milk Formulas: An In Vitro Study. Int J Clin Pediatr Dent 2022;15(3):263-266.

Rinsing with water for 1 min after milk formula increases plaque pH

PURPOSE

Parents find it challenging to follow recommendations to brush young children after feeds at night despite the increase caries risk. This study compared three clinical recommendations (dilution, rinsing and wiping) on plaque pH after formula consumption.

METHODS

Eighteen subjects were recruited. The five interventions with 2-week washout between visits included: Rinse with undiluted formula for 30 s (UF); rinse with 50% diluted formula for 30 s (DF); rinse with undiluted formula for 30 s, followed by rinsing with water for 1 minute (UF/R); rinse with undiluted formula for 30 s, followed by wiping (UF/W); rinse with 10% sucrose for 30 s as control (C). Plaque samples were collected at baseline, 2, 5, 10, 20 and 30 min after the intervention and pH measured using the plaque sampling method.

RESULTS

UF/R resulted in significantly smaller pH drops at 5, 10 and 20 min compared to UF. It also resulted in higher minimum pH (UF/R: 6.34 ± 0.36 Vs UF: 6.06 ± 0.40, p = 0.02), smaller maximum pH drop (UF/R: 0.63 ± 0.35 Vs UF: 0.90 ± 0.49, p = 0.03), smaller sum of change of hydrogen ion concentration (UF/R: 9.22 × 10^-7 ± 7.8 × 10^-7 Vs UF: 2.30 × 10^-6 ± 2.6 × 10^-6, p = 0.04), and smaller area under the curve (UF/R: 7.70 ± 5.44 Vs UF: 13.44 ± 9.44, p = 0.02). DF and UF/W did not result in any significant pH change compared to UF.

CONCLUSIONS

Of the three clinical recommendations, only rinsing with water for 1 min after undiluted formula reduced plaque acidogenicity. Teeth wiping with a moist cloth and 50% dilution of infant formula did not have an effect on plaque acidity.

Little Color, Little Flavor of Different kinds of Commercially Available Flavored Milk and their Consumption Effect on Salivary pH Value in Children: An In Vivo Study

Aim

This study aimed to compare the effect of different flavored kinds of milk on salivary pH value in 6 to 14 years old children.

Materials and methods

The impact of these different kinds of flavored milk on the salivary pH is evaluated between two groups of children, caries-active group (n = 35) constituted children who had decayed missing filled tooth (DMFT) ≥2, and the caries-free group (n = 35) constituted children who had DMFT = 0. Four different flavors of milk are taken for the study, and plain sweetened milk is chosen as the control baseline. The endogenous pH of the salivary samples is measured at baseline and after consumption of the flavored milk immediately and then at 5-, 10-, 15-, and 30-minute intervals. The results are statistically analyzed by using the paired t-test and analysis of variance (ANOVA).

Results

It is shown in the present study that caries-active group subjects had a more evident salivary pH fall than the caries-free group subjects which was statistically significant. For caries-active group, subject's salivary pH value took a longer duration to return to baseline pH as compared to caries-free subjects. However, salivary pH value is restored to standard/baseline value after 30 minutes for all the flavored milk taken in both groups; hence, their intake can be regarded safe for the oral environment.

Conclusion

It is concluded from the current study that the consumption of flavored milk can be considered as non-cariogenic for children.

Clinical significance

In the present study, the salivary pH fall in both caries-active and caries-free subjects was found above the critical pH level. Hence, all these flavored milk used in the study did not cause a threat to oral environment health as there was no significant decrease in salivary pH value so their consumption can be regarded as safe for children.

How to cite this article

Navit S, Agarwal S, Khan SA, et al. Little Color, Little Flavor of Different kinds of Commercially Available Flavored Milk and their Consumption Effect on Salivary pH Value in Children: An In Vivo Study. Int J Clin Pediatr Dent 2020;13(S-1):S87–S91.

Dental plaque pH in predicting caries relapse after general anaesthesia - an exploratory study

OBJECTIVES

Numerous caries risk assessment tools have been proposed in the literature, with few validated in preschool children especially those receiving oral rehabilitation under general anaesthesia (GA). Past caries experience, the best predictor thus far, may not be a reliable indicator after effective clinical intervention. Hence, this longitudinal study was aimed to explore the potential role of plaque pH in predicting future caries incidence after GA among preschool children.

METHODS

Oral examination, plaque pH measurements and questionnaire survey were performed, among pre-schoolers indicated for GA, at baseline (n = 92), 6-month (6M; n = 83), 12-month (12M; n = 79) and 24-month (24M; n = 66) recall visits after GA. Multivariable logistic regression and receiver-operating characteristic analysis were performed to evaluate the predictive value of models with plaque pH and past caries experience.

RESULTS

Individuals with low resting plaque pH at 6M and 12M were shown to be at high risk of 1-year caries incidence at 12M [relative risk (RR) 1.41, 95% confidence interval (CI) 1.09-1.48] and 24M (RR 1.61, 95% CI 1.22-1.73) recall visit, respectively. Moreover, plaque pH demonstrated a statistically significant predictive value in the 12M and 24M models (12M/24M: 85%/77%) compared with past caries experience, which was not a significant predictor in both models (both P > 0.05).

CONCLUSIONS

Plaque pH may be a promising prognostic and predictive marker for early identification of high-risk children undergoing oral rehabilitation under GA.

Acidogenic Potential of Plain Milk, Milk with Sugar, Milk with Cornflakes and Milk Cornflakes with Sugar: A Comparative Study

Aim

To compare the acidogenic potential of plain milk, milk with sugar, milk with cornflakes, and milk cornflakes with sugar by assessing the salivary pH.

Materials and methods

The study was carried out on 40 school children of 8 to 12 years; 20 boys and 20 girls were randomly selected. The salivary pH was assessed before and after the consumption of milk; milk and sugar; milk and cornflakes; and milk, sugar, and cornflakes. Baseline unstimulated saliva was collected in sterile plastic tube and the pH was recorded. The change in the salivary pH from the respective groups after consuming the test meal was recorded as follows: (1) after 5 minutes; (2) after 10 minutes; (3) after 15 minutes; (4) after 30 minutes; (5) 120 minutes. Statistical analysis was done using Statistical Package for the Social Sciences 18.0 (SPSS).

Results

The average baseline salivary pH among all the groups was 7.26. A fall in pH at 5 minutes was seen in all the four groups. However, at different time intervals 5, 10, 15, 30, and 120 minutes, the pH values between the groups showed a significant difference at p < 00.7, 0.005, 0.001, 0.010, and 0.028 respectively.

Conclusion

The fall in pH in all the groups was not significant to a limit of critical pH. Milk when added with sugar and/or cornflakes as a meal did not pose a threat as there was not significant decrease in pH.

How to cite this article

Bhat SS, Hegde SK, Bhat VS, Ramya KM, Jodalli PS. Acidogenic Potential of Plain Milk, Milk with Sugar, Milk with Cornflakes, and Milk Cornflakes with Sugar: A Comparative Study. Int J Clin Pediatr Dent 2016;9(3):218-221.

Ratiometric imaging of extracellular pH in bacterial biofilms with C-SNARF-4

pH in the extracellular matrix of bacterial biofilms is of central importance for microbial metabolism. Biofilms possess a complex three-dimensional architecture characterized by chemically different microenvironments in close proximity. For decades, pH measurements in biofilms have been limited to monitoring bulk pH with electrodes. Although pH microelectrodes with a better spatial resolution have been developed, they do not permit the monitoring of horizontal pH gradients in biofilms in real time. Quantitative fluorescence microscopy can overcome these problems, but none of the hitherto employed methods differentiated accurately between extracellular and intracellular microbial pH and visualized extracellular pH in all areas of the biofilms. Here, we developed a method to reliably monitor extracellular biofilm pH microscopically with the ratiometric pH-sensitive dye C-SNARF-4, choosing dental biofilms as an example. Fluorescent emissions of C-SNARF-4 can be used to calculate extracellular pH irrespective of the dye concentration. We showed that at pH values of <6, C-SNARF-4 stained 15 bacterial species frequently isolated from dental biofilm and visualized the entire bacterial biomass in in vivo-grown dental biofilms with unknown species composition. We then employed digital image analysis to remove the bacterial biomass from the microscopic images and adequately calculate extracellular pH values. As a proof of concept, we monitored the extracellular pH drop in in vivo-grown dental biofilms fermenting glucose. The combination of pH ratiometry with C-SNARF-4 and digital image analysis allows the accurate monitoring of extracellular pH in bacterial biofilms in three dimensions in real time and represents a significant improvement to previously employed methods of biofilm pH measurement.

Effect on oral pH changes and taste perception in 10-14-year-old children, after calcium fortification of a fruit juice

AIM

The aim was to determine the effect of calcium fortification of a commercially available mixed-fruit juice on oral pH changes and taste perception in a group of 10 to 14 year-old Indian children.

METHOD

A controlled, blinded, non-randomised clinical trial was adopted, consisting of a sample of 100 healthy children (DMFT <3; age 10-14 years), who were exposed to three test juices one by one [Group A: original fruit juice (control group); Group B: calcium-fortified fruit juice and Group C: calcium + vitamin D fortified fruit juice]. Oral pH, collection of saliva and plaque sampling was undertaken, before and after the juice exposure by each subject at 0, 1, 5, 15, 30 and 45 min. The respective pH was measured with a digital pH meter. For taste perception, a scoring system was used after exposure of the juices to the subjects in a blind manner. The statistical evaluation was done using one-way ANOVA for salivary and plaque pH and Kruskal-Wallis test for buffer capacity and taste perception.

RESULTS

There was a smaller drop in salivary and plaque pH (p < 0.5) and a significant reduction in perceived taste (p < 0.001) by the subjects after calcium modification of fruit juice.

CONCLUSION

The calcium-modified mixed fruit juices was less acidogenic compared with the unfortified juice, and hence will be less cariogenic and erosive towards teeth.

The effects of beverages on plaque acidogenicity after a sugary challenge

BACKGROUND

Caries prevention traditionally has emphasized the restriction of cariogenic foods and beverages, but it has placed less emphasis on how the choice, combination and sequence of consumed foods and beverages may help reduce plaque acidogenicity. The authors conducted a study to examine whether whole milk, 100 percent apple juice or tap water affect dental plaque acidity in people after a sugary challenge.

METHODS

Twenty adults participated in a randomized controlled crossover study. Participants consumed four combinations of foods: 20 grams of dry sugary Froot Loops (FL) (Kellogg's, Battle Creek, Mich.) cereal, 20 g of FL followed by 50 milliliters of milk (FL/milk), 20 g of FL followed by 50 mL of juice (FL/juice) and 20 g of FL followed by 50 mL of water (FL/water). The authors used a touch microelectrode to take plaque pH readings at the interproximal space just below the contact area between the maxillary premolars on both left and right sides at two and five minutes after FL consumption and at two to 30 minutes after milk, juice or water consumption.

RESULTS

Consumption of FL plaque pH (standard deviation [SD]) was 5.83 (0.68) at 30 minutes, whereas plaque pH (SD) in the FL/milk group was 6.48 (0.30), which was significantly higher than that for FL/juice (5.83 [0.49]) or FL/water (6.02 [0.41]) (P < .005) at 35 minutes.

CONCLUSION

Drinking milk after a sugary cereal challenge significantly reduced plaque pH drop due to the sugary challenge.

PRACTICAL IMPLICATIONS

When discussing the cariogenicity of foods and beverages with patients, dentists and other health care professionals should emphasize that the order of ingesting sugary and nonsugary foods is important and may affect their oral health.

pH gradient and distribution of streptococci, lactobacilli, prevotellae, and fusobacteria in carious dentine

OBJECTIVES

Caries process comprises acidogenic and aciduric bacteria that are responsible for lowering the pH and subsequent destruction of hydroxyapatite matrix in enamel and dentine. The aim of this study was to identify the correlation between the pH gradient of a carious lesion and proportion and distribution of four bacterial genera; lactobacilli, streptococci, prevotellae, and fusobacteria with regard to total load of bacteria.

MATERIALS AND METHODS

A total of 25 teeth with extensive dentinal caries were sampled in sequential layers. Using quantitative real-time PCR of 16S rRNA gene, we quantified the total load of bacteria as well as the proportion of the above-mentioned genera following pH measurement of each sample with a fine microelectrode.

RESULTS

We demonstrated the presence of a pH gradient across the lesion with a strong association between the quantity of lactobacilli and the lowest pH range (pH 4.5-5.0; p = 0.003). Streptococci had a tendency to occupy the most superficial aspect of the carious lesion but showed no correlation to any pH value. Prevotellae showed clear preference for the pH range 5.5-6.0 (p = 0.042). The total representation of these four genera did not reach more than one quarter of the total bacterial load in most carious samples.

CONCLUSION

We revealed differential colonization behavior of bacteria with respect to pH gradient and a lower than expected abundance of lactobacilli and streptococci in established carious lesions. The data indicate the numerical importance of relatively unexplored taxa within the lesion of dentinal caries.

CLINICAL RELEVANCE

The gradient nature of pH in the lesion as well as colonization difference of examined bacterial taxa with reference to pH provides a new insight in regard to conservative caries management.

The Stephan Curve revisited

The Stephan Curve has played a dominant role in caries research over the past several decades. What is so remarkable about the Stephan Curve is the plethora of interactions it illustrates and yet acid production remains the dominant focus. Using sophisticated technology, it is possible to measure pH changes in plaque; however, these observations may carry a false sense of accuracy. Recent observations have shown that there may be multiple pH values within the plaque matrix, thus emphasizing the importance of the milieu within which acid is formed. Although acid production is indeed the immediate proximate cause of tooth dissolution, the influence of alkali production within plaque has received relative scant attention. Excessive reliance on Stephan Curve leads to describing foods as "safe" if they do not lower the pH below the so-called "critical pH" at which point it is postulated enamel dissolves. Acid production is just one of many biological processes that occur within plaque when exposed to sugar. Exploration of methods to enhance alkali production could produce rich research dividends.

An assessment of the cariogenicity of commonly used infant milk formulae using microbiological and biochemical methods

Dental caries is an important dental public health problem and is the most prevalent oral disease among children in the world. The present study was undertaken to evaluate and comparatively assess the change in plaque and salivary pH after ingestion of various commercially available infant milk formulae, and also to evaluate and comparatively assess plaque and salivary samples for change in colony-forming units of Streptococcus mutans caused due to their ingestion. 36 children in the age group of 1-2 years were fed with infant milk formulae three times a day for 21 days and results quantified. The present study revealed a highly significant increase in the levels of colony-forming units of Streptococcus mutans in both the plaque and salivary samples when assessed at baseline and after a period of 21 days, with the t value being 11.92 for the plaque samples and 11.66 for the salivary samples. It was also observed that all the test samples produced significantly lower plaque pH values than pre-feed pH. Based upon this study, further evaluation of the cariogenicity of infant milk formulae is recommended.

Counteractive balancing of transcriptome expression involving CodY and CovRS in Streptococcus pyogenes

Streptococcus pyogenes (group A streptococcus [GAS]) responds to environmental changes in a manner that results in an adaptive regulation of the transcriptome. The objective of the present study was to understand how two global transcriptional regulators, CodY and CovRS, coordinate the transcriptional network in S. pyogenes. Results from expression microarray data and quantitative reverse transcription-PCR (qRT-PCR) showed that the global regulator CodY controls the expression of about 250 genes, or about 17% of the genome of strain NZ131. Additionally, the codY gene was shown to be negatively autoregulated, with its protein binding directly to the promoter region with a CodY binding site. In further studies, the influence of codY, covRS, and codY-covRS mutations on gene expression was analyzed in growth phase-dependent conditions using C medium, reported to mimic nutritional abundance and famine conditions similar to those found during host GAS infection. Additional biological experiments of several virulence phenotypes, including pilin production, biofilm formation, and NAD glycohydrolase activity, demonstrated the role that both CodY and CovRS play in their regulation. Correlation analysis of the overall data revealed that, in exponentially growing cells, CodY and CovRS act in opposite directions, with CodY stimulating and CovRS repressing a substantial fraction of the core genome, including many virulence factors. This is the first report of counteractive balancing of transcriptome expression by global transcription regulators and provides important insight into how GAS modulates gene expression by integrating important extracellular and intracellular information.

Characterization of mleR, a positive regulator of malolactic fermentation and part of the acid tolerance response in Streptococcus mutans

Background

One of the key virulence determinants of Streptococcus mutans, the primary etiological agent of human dental caries, is its strong acid tolerance. The acid tolerance response (ATR) of S. mutans comprises several mechanisms that are induced at low pH and allow the cells to quickly adapt to a lethal pH environment. Malolactic fermentation (MLF) converts L-malate to L-lactate and carbon dioxide and furthermore regenerates ATP, which is used to translocate protons across the membrane. Thus, MLF may contribute to the aciduricity of S. mutans but has not been associated with the ATR so far.

Results

Here we show that the malolactic fermentation (mle) genes are under the control of acid inducible promoters which are induced within the first 30 minutes upon acid shock in the absence of malate. Thus, MLF is part of the early acid tolerance response of S. mutans. However, acidic conditions, the presence of the regulator MleR and L-malate were required to achieve maximal expression of all genes, including mleR itself. Deletion of mleR resulted in a decreased capacity to carry out MLF and impaired survival at lethal pH in the presence of L-malate. Gel retardation assays indicated the presence of multiple binding sites for MleR. Differences in the retardation patterns occurred in the presence of L-malate, thus demonstrating its role as co-inducer for transcriptional regulation.

Conclusion

This study shows that the MLF gene cluster is part of the early acid tolerance response in S. mutans and is induced by both low pH and L-malate.

Characterization of the L-lactate dehydrogenase from Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a Gram-negative opportunistic pathogen and the proposed causative agent of localized aggressive periodontitis. A. actinomycetemcomitans is found exclusively in the mammalian oral cavity in the space between the gums and the teeth known as the gingival crevice. Many bacterial species reside in this environment where competition for carbon is high. A. actinomycetemcomitans utilizes a unique carbon resource partitioning system whereby the presence of L-lactate inhibits uptake of glucose, thus allowing preferential catabolism of L-lactate. Although the mechanism for this process is not fully elucidated, we previously demonstrated that high levels of intracellular pyruvate are critical for L-lactate preference. As the first step in L-lactate catabolism is conversion of L-lactate to pyruvate by lactate dehydrogenase, we proposed a model in which the A. actinomycetemcomitans L-lactate dehydrogenase, unlike homologous enzymes, is not feedback inhibited by pyruvate. This lack of feedback inhibition allows intracellular pyruvate to rise to levels sufficient to inhibit glucose uptake in other bacteria. In the present study, the A. actinomycetemcomitans L-lactate dehydrogenase was purified and shown to convert L-lactate, but not D-lactate, to pyruvate with a K_m of approximately 150 µM. Inhibition studies reveal that pyruvate is a poor inhibitor of L-lactate dehydrogenase activity, providing mechanistic insight into L-lactate preference in A. actinomycetemcomitans.

Biochemical and molecular characterization of a novel type of Mutanase from Paenibacillus sp. strain RM1: identification of its mutan-binding domain, essential for degradation of Streptococcus mutans biofilms

A novel type of mutanase (termed mutanase RM1) was isolated from Paenibacillus sp. strain RM1. The purified enzyme specifically hydrolyzed alpha-1,3-glucan (mutan) and effectively degraded biofilms formed by Streptococcus mutans, a major etiologic agent in the progression of dental caries, even following brief incubation. The nucleotide sequence of the gene for this protein contains a 3,873-bp open reading frame encoding 1,291 amino acids with a calculated molecular mass of 135 kDa. The protein contains two major domains, the N-terminal domain (277 residues) and the C-terminal domain (937 residues), separated by a characteristic sequence composed of proline and threonine repeats. The characterization of the recombinant proteins for each domain which were expressed in Escherichia coli demonstrated that the N-terminal domain had strong mutan-binding activity but no mutanase activity whereas the C-terminal domain was responsible for mutanase activity but had mutan-binding activity significantly lower than that of the intact protein. Importantly, the biofilm-degrading activity observed with the intact protein was not exhibited by either domain alone or in combination with the other. Therefore, these results indicate that the structural integrity of mutanase RM1 containing the N-terminal mutan-binding domain is required for the biofilm-degrading activity.

First molar eruption related to plaque acidogenicity in children of different socio-economic status

OBJECTIVE

The aim of this study was to evaluate the association between the eruption stage of the lower first permanent molar and dental plaque acidogenicity. Socio-economic status (SES), gender, and oral hygiene condition were also variables considered.

MATERIAL AND METHODS

230 children between 6 and 8 years of age were recruited from one public and one private primary school with different SES in Lima, Peru. Clinical examinations were performed to assess lower first permanent molar eruption stage, plaque acidogenicity, and oral hygiene condition. Bivariate associations were analyzed through chi-square tests and the variable interactions were analyzed through a hierarchical log-linear analysis with backward elimination.

RESULTS

21.8% of the population had highly acidogenic plaque, 34.3% acidogenic plaque, and 43.9% non-acidogenic plaque. Of the lower first permanent molars, 46.1% were fully erupted, whereas 53.9% were partially erupted. According to the final log-linear model, children with fully erupted molars and non-acidogenic plaque are less frequent in low than in high SES. Also, the frequency of children with partially erupted molars and acidogenic to highly acidogenic plaque is higher in males than in females. Finally, fully erupted molars and non-acidogenic plaque are more frequent in children with good hygiene than in children with moderate to poor hygiene.

CONCLUSIONS

Association between eruption stage of the lower first permanent molar and plaque acidogenicity was not significant in a bivariate context. However, in a multivariate context, socio-economic status, oral hygiene condition, and gender had an impact on the association between the two main variables.

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.

The haem pigment of the oral anaerobes Prevotella nigrescens and Prevotella intermedia is composed of iron(III) protoporphyrin IX in the monomeric form

The haem pigment of Porphyromonas gingivalis is composed of micro -oxo bishaem, [Fe(III)PPIX](2)O, but the nature of that generated by Prevotella species has not been established. Mössbauer, Raman and UV-visible spectrophotometry were used to characterize the haem pigment of Prevotella intermedia and Prevotella nigrescens. Mössbauer and Raman spectroscopy revealed the major haem species to be monomeric iron protoporphyrin IX, Fe(III)PPIX.OH (haematin). The terminal growth pH of both species on blood agar was between 5.8 and 6.0, which favours the formation and maintenance of monomeric Fe(III)PPIX.OH. Incubation of Pr. nigrescens and Pr. intermedia with oxyhaemoglobin at pH 6.5 resulted in formation of aquomethaemoglobin which was degraded to generate Fe(III)PPIX.OH which in turn became cell-associated, whilst incubation at pH 7.5 resulted in formation of [Fe(III)PPIX](2)O. It is concluded that both Prevotella species degrade oxyhaemoglobin to form [Fe(III)PPIX](2)O as an intermediate, which is converted to Fe(III)PPIX.OH through a depression in pH. The low pH encourages cell-surface deposition of insoluble Fe(III)PPIX.OH which would act as a barrier against oxygen and reactive oxygen species, and also protect against H(2)O(2) through its inherent catalase activity.

Acid-neutralizing activity during amino acid fermentation by Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum

Acid-neutralizing activity during amino acid fermentation by washed cells of Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum was studied. When the washed cells of these strains were anaerobically incubated in the presence of aspartylaspartic acid or glutamylglutamic acid for P. gingivalis, aspartic acid for P. intermedia and glutamic acid for F. nucleatum at an initial pH of 5.0 or 5.5, the pH of the incubation mixtures rose toward neutral. F. nucleatum had the highest acid-neutralizing activity, followed by P. intermedia and P. gingivalis. The P. intermedia and F. nucleatum cells were used to measure the amounts of base produced at a fixed pH of 5.0. These cells generated significant amounts of base at pH 5.0 along with the production of organic acids and ammonia from aspartic or glutamic acid. Acid-base balance theoretically calculated from the amounts of consumed substrate and end products implies that the acid-neutralizing activity was derived from the decrease in acidity during the fermentation of amino acid into organic acids and ammonia.

Effects of carbohydrate polymers applicable in saliva substitutes on the anti-Candida activity of a histatin-derived peptide

The effects of polymers applicable in saliva substitutes on the anti-Candida activity of the cationic antimicrobial peptide dhvar1 were investigated. Dhvar1 is a derivative of the 14 C-terminal amino acids of histatin 5. The effects of the following polymers were tested: uncharged hydroxyethylcellulose (HEC), negatively charged xanthan (XG) and three types of negatively charged carboxymethylcellulose (CMC) of identical mass but different degrees of carboxylic acid-group substitution (DS). The effects were tested at pH 4.0, 7.0 and 8.5 in a killing assay. HEC had no effect at any pH tested; XG and the three types of CMC caused a decrease in activity at increasing concentrations. Within the CMC group, inhibition increased slightly with increasing DS. These results suggest that the reduction in activity associated with these polymers is the result of electrostatic interaction between the positively charged peptides and the negatively charged polymers. In the absence of polymers, no effect of pH was found on the activity of dhvar1. In the presence of the charged polymers XG and CMC, lowering the pH from 7.0 to 4.0 resulted in a decrease of dhvar1 activity. It was concluded that, with respect to the retention of activity, HEC is the most appropriate polymer for use in combination with dhvar1. However, for use in saliva substitutes XG seems more suitable because of its rheological properties. If XG or CMC are to be used, their reductive effect on the anti-Candida activity of dhvar1 should be compensated for by increasing the peptide dose.

Fluoride and organic weak acids as respiration inhibitors for oral streptococci in acidified environments

Oxygen metabolism (respiration) of Streptococcus mutans GS-5 involving NADH oxidases, mainly of the H(2)O-producing type, was found to be acid sensitive, as was NADH oxidase activity of cell extracts. Respiration of intact cells in acidified media was also highly sensitive to fluoride, with a 50% inhibitory concentration of about 0.02 mM at pH 4. In contrast, NADH oxidases in cell extracts were fluoride insensitive. Fluoride inhibition of respiration of intact cells was related to weak-acid effects leading to enhanced proton permeability of cells, cytoplasmic acidification and resultant acid inhibition of NADH oxidases and glycolysis. Organic weak acids, such as indomethacin and benzoate, were also effective inhibitors. H(2)O(2) production by intact cells of Streptococcus sanguis NCTC 10904, a peroxide producer, was similarly inhibited by fluoride or organic weak acids in acidified media. Thus, weak acids act as respiratory inhibitors for oral streptococci indirectly by acidifying the cytoplasm rather than acting as direct inhibitors of NADH oxidases.

Inhibitory effect of sorbitol on sugar metabolism of Streptococcus mutans in vitro and on acid production in dental plaque in vivo

This study was conducted to find out whether sorbitol inhibits the sugar metabolism of Streptococcus mutans in vitro and the acid production in dental plaque in vivo. S. mutans NCIB 11723 was anaerobically grown in sorbitol-containing medium. The rate of acid production from sugars was estimated with a pH stat. The rate of acid production from glucose or sucrose was not changed at various concentrations of oxygen. By the addition of sorbitol to sugar, however, the acid production was decreased with increasing levels of oxygen. Intracellular NADH/NAD+ ratio and (dihydroxyacetone-phosphate+glyceraldehyde-phosphate)/3-phosphoglycerate ratio were high whenever the acid production was inhibited by sorbitol. Sorbitol also inhibited the acid production in dental plaque in vivo. These results suggest that the increased NADH/NAD+ ratio during sorbitol metabolism through the inactivation of pyruvate formate-lyase by oxygen inhibited glyceraldehyde-phosphate dehydrogenase and then the acid production of S. mutans and the one in dental plaque.

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.

Effects of pH on the glucose and lactate metabolisms by the washed cells of Actinomyces naeslundii under anaerobic and aerobic conditions

Effects of pH on the glucose and lactate metabolism by the washed cells of Actinomyces naeslundii genospecies 1 and 2 under anaerobic and aerobic conditions were studied. The rate of acid production from glucose was the highest at pH 7.0 and decreased as the pH lowered to 4.5, irrespective of atmospheric conditions. The anaerobic end-product in the absence of bicarbonate was mainly lactate, while in the presence of bicarbonate the rate of acid production increased 1.8-2.5 times with the production of formate, acetate and succinate in addition to lactate. Under aerobic conditions, the cells produced acids from glucose along with oxygen consumption and the end-product was mainly acetate. In contrast to the glucose metabilism, the cells produced base from lactate along with oxygen consumption. The rates of base production and oxygen consumption were the highest at pH 5.5. The end-products from lactate were acetate and pyruvate. These results indicate that oral actinomyces has a various activity of glucose and lactate metabolism at a wide range of environmental pH and suggest its flexibility in surviving in dental plaque, where the environmental factors fluctuate.

Acid tolerance and acid-neutralizing activity of Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum

The tolerance to acid and the acid-neutralizing activity of three important periodontopathic bacteria, Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum were studied. P. gingivalis strains grew only at neutral pH and did not utilize glucose, whereas strains of P. intermedia and F. nucleatum could grow under acidic conditions and increased their growth by utilizing glucose. P. gingivalis tended to raise the culture pH during growth. P. intermedia and F. nucleatum raised the culture pH during growth in the absence of glucose, while in the presence of glucose they decreased the pH. Resting cell suspensions of all the bacteria raised the pH in the presence of tryptone and casamino acids. Acid-neutralizing activity was confirmed by measuring base production at a fixed pH with a pH-stat. During neutralization, the cells produced cytotoxic substrates, ammonia and organic acids (butyric, isobutyric and isovaleric acids by P. gingivalis; isovaleric and succinic acids by P. intermedia; propionic and butyric acids by F. nucleatum). These findings suggest that deamination of amino acids into ammonia and organic acids occurs simultaneously with base production, resulting in acid neutralization. These results could partially explain the survival of P. intermedia and F. nucleatum in both supragingival and subgingival plaque and the apparent restriction of P. gingivalis to subgingival plaque. The former bacteria may aid in creation of an environment fostering colonization of subgingival plaque by P. gingivalis.

Effects of acidification on growth and glycolysis of Streptococcus sanguis and Streptococcus mutans

After carbohydrate intake, pH in dental plaque decreases rapidly and reaches about 4 within a few minutes. The acidification not only promotes demineralization of tooth surface but can also cause damage to bacteria in dental plaque. We, therefore, investigated the effect of acidification on the dental plaque bacteria Streptococcus sanguis and Streptococcus mutans. At pH 4.0 and 4.2, both growth and glycolytic activities in these streptococci were repressed. Prolonged acidification (for 60 min at pH 4.0) not only repressed both growth and glycolytic activities but also impaired them in S. sanguis cells with concomitant inactivation of the glycolytic enzymes, hexokinase, phosphofructokinase, glyceraldehydephosphate dehydrogenase and enolase. The impaired abilities of glycolysis and growth recovered following incubation at pH 7.0 for 80-90 min, and this was accompanied by reactivation of the glycolytic enzymes. On the other hand, these impairments were not observed in S. mutans cells exposed to prolonged acidification. These results indicate that the low pH frequently occurring in dental plaque may transiently impair streptococcal glycolysis and growth and that S. mutans is more durable to the acidification than S. sanguis.

Rapid procedure for acid adaptation of oral lactic-acid bacteria and further characterization of the response

Acid-adaptive responses could be induced readily in oral lactic-acid bacteria by growing them in batch cultures with excess sugar or more conveniently and rapidly by transferring cells to acidified growth media for the time required for biomass doubling. The response of Streptococcus mutans GS-5 was induced in a progressive rather than all-or-nothing way, and the extent of acid tolerance was inversely related to the pH of the inducing medium over a range from 8.5 to 5. The weak acids fluoride, acetate, or lactate did not measurably enhance acid adaptation, and so the response did not appear to depend primarily on changes in delta pH or the proton motive force across the cell membrane. Transcription and translation to form new proteins did appear to be necessary, as indicated by inhibition of adaptation by rifampin or chloramphenicol and by lack of adaptation by cells suspended in phosphate buffer at pH 5. Streptococcus salivarius and Lactobacillus casei were acid adapted by the rapid method, and the method appeared to be generally useful for oral lactic-acid bacteria. The rapid induction of the response in multiple oral lactic-acid bacteria suggests that it is of general importance for maintaining a diversity of organisms in the oral microbiota, which is regularly subjected to acid stresses.

Antimicrobial actions of fluoride for oral bacteria

Fluoride is widely used as a highly effective anticaries agent. Although it is felt that its anticaries action is related mainly to effects on mineral phases of teeth and on the process of remineralization, fluoride also has important effects on the bacteria of dental plaque, which are responsible for the acidification of plaque that results in demineralization. The results of recent studies have shown that fluoride can affect bacterial metabolism through a set of actions with fundamentally different mechanisms. It can act directly as an enzyme inhibitor, for example for the glycolytic enzyme enolase, which is inhibited in a quasi-irreversible manner. Direct action seems also to occur in inhibition of heme-based peroxidases with binding of fluoride to heme. The flavin-based peroxidases of many oral bacteria are insensitive to fluoride. Another mode of action involves formation of metal-fluoride complexes, most commonly AlF4-. These complexes are responsible for fluoride inhibition of proton-translocating F-ATPases and are thought to act by mimicking phosphate to form complexes with ADP at reaction centers of the enzymes. However, the actions of fluoride that are most pertinent to reducing the cariogenicity of dental plaque are those related to its weak-acid character. Fluoride acts to enhance membrane permeabilities to protons and compromises the functioning of F-ATPases in exporting protons, thereby inducing cytoplasmic acidification and acid inhibition of glycolytic enzymes. Basically, fluoride acts to reduce the acid tolerance of the bacteria. It is most effective at acid pH values. In the acidic conditions of cariogenic plaque, fluoride at levels as low as 0.1 mM can cause complete arrest of glycolysis by intact cells of Streptococcus mutans. Overall, the anticaries actions of fluoride appear to be complex, involving effects both on bacteria and on mineral phases. The antibacterial actions of fluoride appear themselves to be complex but to be dominated by weak-acid effects.

Urease activity in Streptococcus salivarius at low pH

Arginine metabolism to alkali by the arginine deiminase system in oral bacteria increases their acid tolerance. The potential of urease activity in Streptococcus salivarius to fulfil a similar role was examined. In cell extracts between pH 5.0 and 8.0, urease activity was over 80% the maximal rate. The urease rate was zero at pH 4.3, and at pH 3.6 the enzyme was rapidly inactivated (t 1/2 of 0.6 min). The pH range of intact cells was broader. In Strep. salivarius cells acidified to pH 2.6 for 5 min, urease was completely retained and the ureolytic pH rise was rapid. There was no urease activity after acidification to pH 2. In cells acidified to maintain the pH between 3.3 and 4, viability was maintained for a short period (extrapolation indicated 20 min) and then decreased. This acidification induced alkali generation or acid removal that decreased in parallel to loss of viability. A small fraction (10%) of the urease was rapidly inactivated, after which both the remaining urease and pH response decreased at a similar rate to cell viability (t 1/2 of 15-20 min), but for at least 1 h following acidification, a rapid ureolysis induced rise in pH to above 7. In cells held at pH 3.6 and treated to compromise their membranes by freeze-thawing or transient acidification to pH 2.3, 70-80% of the urease was lost rapidly and the remainder inactivated at a rate similar to that in intact cells. Therefore, although at pH below 4, S. salivarius urease is outside its pH activity range and the free enzyme is rapidly inactivated, intact cells the urease is protected and ureolytic generation of ammonia is capable of substantially raising the pH for at least 1 h while the cell population is being progressively killed by acid.

Comparison of three different methods for measurement of plaque-pH in humans after consumption of soft bread and potato chips

Three different techniques for measurement of plaque-pH--the sampling, the microtouch, and the telemetric methods--were compared after subjects had consumed different starch products. Ten volunteers, equipped with partial lower prostheses, incorporating a miniature glass pH electrode, refrained from toothbrushing for 3 days. Four products were tested: (1) soft bread, (2) potato chips, (3) 5% starch, and (4) 5% sucrose. The pH of plaque was measured for 45 min by means of all three of the methods. The results showed that the mean pH at 10 min was 1.5 units lower with the telemetric than with the sampling method and 1.0 unit lower with the telemetric than with the microtouch method. Relatively small differences were found among the effects of the four test products for all three methods, with the clearest distinctions among the pH curves being with the microtouch and telemetric methods. The main conclusions from the present investigation are: (1) that there were large differences in pH levels measured with the sampling, the microtouch, and the telemetric methods, even though they ranked the test products in about the same order, and (2) that the two starchy foods, bread and potato chips, were both easily fermented by dental plaque.

Dental caries and its determinants among recent immigrants from rural Ethiopia

Adults (35-45 yr old) and children (5 and 12 yr old) recently arrived in Israel from rural areas in Ethiopia were examined. Caries levels were low: e.g. DMFT = 0.31 among 12-yr-olds, and 1.27 amongst adults. The 5-yr-olds were 86.8% caries-free, while 12-yr-olds were 81.8% and adults 54% caries-free respectively. According to interview data, the diet in Ethiopia had been based on local agricultural products and was almost sugar-free. The mean total count of salivary bacteria, as determined on blood agar, was 3.4 x 10(8); mean count of Streptococcus viridans, on mitis salivarius, was 6.7 x 10(7); and mean count of S. mutans, as determined on mitis salivarius with bacitracin, was 1.7 x 10(7). These levels were all high and were not significantly different from a control group of 20 Israelis. The mean number of lactobacilli, on Rogosa agar, was 2.75 x 10(4), which was significantly higher than among the controls (3.6 x 10(3). Salivary pH levels were generally similar between the Ethiopian group and the controls. Salivary flow was significantly higher for the Ethiopians (1.93 ml/min) than for controls (1.16 ml/min). Low levels of caries in this population can be attributed to an almost sugar-free diet and high salivary flow, but not to the composition of oral microflora.

pH responses to sucrose and the formation of pH gradients in thick 'artificial mouth' microcosm plaques

Artificial microcosm plaques were grown in a five-plaque culture system for up to 6 weeks, reaching a maximum depth of several mm. Procedures for long-term pH measurement with glass electrodes were established; they showed that the application of 5 or 10% sucrose for 6 min with a slow continuous flow of a basal medium containing mucin (BMM) generated the pH changes characteristic of in vivo Stephan curves. These pH responses were reproducible between plaques. Plaque mass and thickness were critical variables. Successive, sucrose-induced pH curves in plaques up to 4 mm thickness showed minor reductions only in the amplitude and rates of pH change. In plaques over 4 mm thick there was a pronounced reduction in pH response to successive sucrose applications, indicating increased diffusion limitations--a result of plaque growth to seal in the freshly-inserted pH electrode. In plaques of 6 mm maximum thickness, 10% sucrose induced a decrease to below pH 5.5 lasting 24 h, compared to the pH response in 2 mm thick plaque, which returned to the resting pH in 2 h. Differences in pH of up to 0.9 units were identified in thick plaques between inner and outer layers. The BMM flow rate was a critical determinant of the amplitude of the pH response to sucrose and subsequent return to resting pH. These results confirm, for microcosm plaque, the importance of clearance dynamics and diffusion-limited gradients in regulating plaque pH.

Assessment of the cariogenic potential of Streptococcus mutans strains and its relationship to in vivo caries experience

Strains of Streptococcus mutans isolated from the plaque of 6 subjects were studied using an in vitro model to determine whether differences in their cariogenic potential could be detected, and if so, whether the results correlated with the caries experience of the individuals. Each strain was incubated with a bovine enamel slab and 5% (w/v) sucrose for 24-h periods. The acidogenic potential was assessed by pH measurement and analysis of acid anion production. Microradiographic and microdensitometric assessment of the enamel, together with measurement of the change in calcium concentration of the reaction mixture were used to determine the demineralizing potential of each strain. Significant differences in cariogenic potential were found between some of the strains tested, and correlations were found between 3 of the test parameters and the decayed-missing-filled-surface score of the individuals. The results suggest that the caries experience of individuals may be related, to some extent, to the cariogenic potential of their S. mutans strains.

Chain formation and de-chaining in Streptococcus sobrinus SL-1

Regulation of chain length by chain-forming bacteria is believed to depend on wall-associated autolytic activity and environmental conditions. In this study, the chain length of Streptococcus sobrinus SL-1 was determined under various initial culture and pH conditions and NaF concentrations. Crude wall extracts were prepared by dilute alkali treatment of whole cells and were tested for de-chaining activity. The results indicate that S. sobrinus SL-1 grows primarily as short chains under alkaline growth conditions and at high (3.0 mM) medium fluoride levels, and growth as long chains occurs under acidic growth conditions. De-chaining activity was observed following incubation of the longer chain form of the organism with crude wall extracts. The evidence suggests that the chain length of S. sobrinus SL-1 depends on environmental conditions, including pH and fluoride, and that cell wall-associated factors may be active in regulating the chain length of the organism.

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

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

pH measurements with an ion sensitive field effect transistor in the mouth of patients with xerostomia

A transistor pH electrode (ion sensitive field effect transistor), placed in the upper dentures of eleven xerostomia patients and five healthy volunteers, was used to register pH changes in five-, six- and seven-day-old dental plaque. A mouth rinse with a 10% sucrose solution caused a pH fall of about three decades. A significant difference in duration of critical plaque pH was observed: in xerostomia patients, a 10% longer period of pH less than 5.7 was registered during 60 min following a sucrose rinse. Normal oral functions were not influenced by the denture with an integrated electrode. This method is usable for plaque pH registration in xerostomia patients.

pH-dependent fluoride inhibition of catalase activity

The inhibitory effects of fluoride on several catalases were examined over a range of pH conditions. Preparations of bovine-liver catalase were sensitive to fluoride under acidic conditions. Catalase activity associated with whole-cell preparations of Actinomyces viscosus NP 311A remained relatively constant between pH 3.0 and 8.0 and was inhibited by fluoride in a pH-dependent manner. Fluoride was also observed to enhance hydrogen peroxide killing of A. viscosus NP 311A under acidic pH conditions. Results suggest that some catalase enzymes, including those associated with common plaque bacteria, may be inhibited by fluoride in a pH-dependent manner.

Weekly variation in the acidogenic response of plaque

The fall in plaque pH after sucrose rinsing was monitored once a week for 9 (8) weeks in succession, to measure the weekly variation in the magnitude of pH drop in the same subject. The plaque pH was measured with a touch electrode placed interdentally between the first and second premolar. The subject rinsed his mouth with 10% (w/v) sucrose solution, and the plaque pH was thereafter monitored for 40 min. The minimum plaque pH (pHmin), the change between starting and minimum pH (delta pH), and the resting pH value were determined. The pH values of the maxilla and mandible differed. No difference was seen between the right and left sides. As a rule, intraindividual variation was lower in terms of pHmin values than in terms of delta pH values. It was concluded that pH assessment with the touch electrode appeared to show a small weekly variation intraindividually and to be sensitive enough to test the acidogenic potential of foods, but only in the maxilla.

Effect of pH on the growth and proteolytic activity of Porphyromonas gingivalis and Bacteroides intermedius

The effect of pH on the growth and proteolytic activity of the type strain and fresh isolates of Porphyromonas gingivalis and Bacteroides intermedius was investigated. B. intermedius strains grew with and without glucose at a pH as low as 5.0. These bacteria grew almost as well as Streptococcus mutans at pH 5.0 and better than Actinomyces viscosus at pH 5.5 and 5.0. Some B. intermedius strains raised the culture pH when grown at a low pH without glucose. In contrast, P. gingivalis strains grew only at pH 6.5 to 7.0. The P. gingivalis strains had proteolytic activities against azocoll, azocasein, and azoalbumin, while the B. intermedius strains degraded azocasein and azoalbumin, but not azocoll. B. intermedius showed maximum proteolytic activity at pH 7.0, and high activity over a wide pH range. In contrast, the optimum pH of proteolytic activity in P. gingivalis was pH 7.5 to 8.0. The P. gingivalis activities were more sensitive than those of B. intermedius to low pH. The capacity of B. intermedius to degrade proteins to more readily metabolizable substrates at low pH might explain the growth of this bacterium in an acidic environment. These differences between B. intermedius and P. gingivalis could explain their capacity to survive at different sites in the oral cavity and indicate how B. intermedius might positively influence the growth of P. gingivalis in subgingival plaque.

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.