The pH of dental plaques in the different areas of the mouth before and after meals and their relationship to the pH and rate of flow of resting saliva

The oral microbiome analysis reveals the similarities and differences between periodontitis and Crohn's disease-associated periodontitis

Patients with Crohn's disease (CD) have higher incidences of oral diseases such as dental caries and periodontitis than healthy people. Studies indicate that the interaction between gut and oral microbiota is an important factor. To compare the composition and diversity of the oral microbiome in periodontitis and CD-associated periodontitis, subgingival plaque and saliva samples from patients with these diseases were collected for 16S rRNA gene sequencing analyses. In CD-associated periodontitis, the subgingival plaque had greater microbial diversity than saliva. Subgingival plaque had decreased abundances of Firmicutes, Streptococcus, and Haemophilus and increased abundances of Bacteroidetes, Actinomyces, Treponema_2, Capnocytophaga, and Porphyromonas relative to saliva. The microbial composition in subgingival plaque was similar between the two diseases. Both red complex (Porphyromonas, Tannerella, and Treponema) and orange complex (Fusobacteria) bacteria were abundant in periodontitis subgingival plaque, while orange complex bacteria (Prevotella_2 and Prevotella) were abundant in CD-associated periodontitis subgingival plaque. Pocket depth was significantly positively correlated with multiple periodontal pathogens, including Porphyromonas, Tannerella, and Treponema. This study reveals the similarities and differences in the oral microbiome between periodontitis and CD-associated periodontitis, which provides a foundation to further explore the associations between CD and periodontitis.

Diversity of site-specific microbes of occlusal and proximal lesions in severe- early childhood caries (S-ECC)

Background

Severe-early childhood caries (S-ECC) a global problem of significant concern, commonly manifest on the occlusal, and proximal surfaces of affected teeth. Despite the major ecological differences between these two niches the compositional differences, if any, in the microbiota of such lesions is unknown.

Methods

Deep-dentine caries samples from asymptomatic primary molars of children with S-ECC (n 19) belonging to caries-code 5/6, (ICDAS classification) were evaluated. Employing two primer pools, we amplified and compared the bacterial 16S rRNA gene sequences of the seven hypervariable regions (V2—V4 and V6—V9) using NGS-based assay.

Results

Bray-Curtisevaluation indicated that occlusal lesions (OL) had a more homogeneous community than the proximal lesions (PL) with significant compositional differences at the species level (p = 0.01; R- 0.513). Together, the occlusal and proximal niches harbored 263 species, of which 202 (76.8%) species were common to both , while 49 (18.6%) and 12 (4.6%) disparate species were exclusively isolated from the proximal and occlusal niches, respectively. The most commonl genera at both niches included Streptococcus, Prevotella, and Lactobacillus. S. mutans was predominant in PL (p ≤ 0.05), and Atopobium parvulum (p = 0.01) was predominant in OL.

Conclusions

Distinct differences exist between the caries microbiota of occlusal and proximal caries in S-ECC.

Duration of dentin tubule occlusion by the calcium phosphate precipitation method: An in vivo study in beagle dogs

The aim of the present study was to assess the duration of dentin tubule occlusion by the calcium phosphate precipitation (CPP) method in the vital teeth of beagle dogs. Vital teeth were treated using the CPP method, potassium oxalate, or a bonding agent (Liner bond II) after cavity preparation and acid etching. The dentin tubules of all groups, except for the bonding agent, opened more widely with time in the absence of plaque control. Dentin tubules treated with the CPP method were open and no precipitate remained in the absence of plaque control. Differences were observed in dentin tubule occlusion when plaque control was achieved by daily tooth brushing. The majority of dentin tubules were occluded with an apatitic precipitate seven days after the CPP method with plaque control. The present results demonstrated that the CPP method is useful with proper plaque control.

Spatial Ecology of the Human Tongue Dorsum Microbiome

A fundamental question in microbial ecology is how microbes are spatially organized with respect to each other and their host. A test bed for examining this question is the tongue dorsum, which harbors a complex and important microbial community. Here, we use multiplexed fluorescence spectral imaging to investigate the organization of the tongue microbiome at micron to hundred-micron scales. We design oligonucleotide probes for taxa both abundant and prevalent, as determined by sequence analysis. Imaging reveals a highly structured spatial organization of microbial consortia, ranging in linear dimension from tens to hundreds of microns. The consortia appear to develop from a core of epithelial cells, with taxa clustering in domains suggestive of clonal expansion. Quantitative proximity analysis provides the basis for a model of tongue dorsum microbiome organization and dynamics. Our work illustrates how high-resolution analysis of micron-scale organization provides insights into physiological functions and microbiome-host interactions.

How microbes are spatially organized is a fundamental question in microbial ecology about which little is known. Using fluorescence spectral imaging, Wilbert et al. discover dense, highly structured microbial consortia on the human tongue. Analysis of the organization of these consortia permits inferences about community dynamics and oral microbial ecology.

A standardised semi-dynamic in vitro digestion method suitable for food – an international consensus

Standardised recommendations for a physiologically relevant, semi-dynamic in vitro simulation of upper GI tract digestion.

High-throughput DNA sequencing of microbiota at interproximal sites

Objective: The oral microbiota has been deeply studied by high-throughput sequencing techniques. However, although the interproximal regions have one of the highest caries rates in the oral cavity, information about the bacterial composition at those sites is scarce.

Methods: In this study, we used 16S rRNA Illumina sequencing to describe the microbiota associated to interproximal regions at two time points. In addition, dental plaque samples at the vestibular and lingual surfaces from the same teeth were also analysed at the two time points.

Results: Interproximal-associated microbiota was found to be similar to already described bacterial communities in other mouth niches. Streptoccocus, Veillonella, Rothia, Actinomyces, Neisseria, Haemophilus and Fusobacterium were the most abundant genera in this oral region. Statistical analyses showed that the microbiota from interproximal sites was more similar to that sampled from the vestibular surfaces than to the lingual surfaces. Interestingly, many potentially cariogenic bacteria such as Scardovia, Atopobium or Selenomonas were over-represented in the interproximal regions in comparison with vestibular and lingual sites.

Conclusion: The microbiota at interproximal regions appears to be specific and stable through time. Potentially pathogenic bacteria may increase caries development risk and gingival inflammation at those sites.

Biogeography of the Oral Microbiome: The Site-Specialist Hypothesis

Microbial communities are complex and dynamic, composed of hundreds of taxa interacting across multiple spatial scales. Advances in sequencing and imaging technology have led to great strides in understanding both the composition and the spatial organization of these complex communities. In the human mouth, sequencing results indicate that distinct sites host microbial communities that not only are distinguishable but to a meaningful degree are composed of entirely different microbes. Imaging suggests that the spatial organization of these communities is also distinct. Together, the literature supports the idea that most oral microbes are site specialists. A clear understanding of microbiota structure at different sites in the mouth enables mechanistic studies, informs the generation of hypotheses, and strengthens the position of oral microbiology as a model system for microbial ecology in general.

A Review of Selected Studies That Determine the Physical and Chemical Properties of Saliva in the Field of Dental Treatment

Physiological whole saliva is a unique body fluid constantly washing the mucous membranes of the mouth, throat, and larynx. Saliva is a clear, slightly acidic mucinous-serous secretion, composed of various electrolytes, small organic substances, proteins, peptides, and polynucleotides. There are many ways to use saliva as a biological fluid (biofluid). The significant advantages of saliva as a unique diagnostic material are its availability and the noninvasive method of collection. The aim of this review is to emphasize the diagnostic value of saliva as a research material in the configuration of its structure and secretion disorders. The data were obtained using the MEDLINE (PubMed) search engine, as well as an additional manual search. The analysis covered 77 articles selected from a group of 1986 publications and initially qualified for devising. The results were evaluated and checked for the correctness of qualifying in accordance with inclusion and exclusion criteria. The diagnostic use of saliva has attracted the attention of many researchers due to its noninvasive nature and relative simplicity of collection. In addition, it should be noted that the determination of chemical and physical saliva parameters can be effectively performed in the patient's presence in the dental office.

A spatial gradient of bacterial diversity in the human oral cavity shaped by salivary flow

Spatial and temporal patterns in microbial communities provide insights into the forces that shape them, their functions and roles in health and disease. Here, we used spatial and ecological statistics to analyze the role that saliva plays in structuring bacterial communities of the human mouth using >9000 dental and mucosal samples. We show that regardless of tissue type (teeth, alveolar mucosa, keratinized gingiva, or buccal mucosa), surface-associated bacterial communities vary along an ecological gradient from the front to the back of the mouth, and that on exposed tooth surfaces, the gradient is pronounced on lingual compared to buccal surfaces. Furthermore, our data suggest that this gradient is attenuated in individuals with low salivary flow due to Sjögren's syndrome. Taken together, our findings imply that salivary flow influences the spatial organization of microbial communities and that biogeographical patterns may be useful for understanding host physiological processes and for predicting disease.

Calibration of a lactic-acid model for simulating biofilm-induced degradation of the dentin-composite interface

OBJECTIVE

To verify and calibrate a chemical model for simulating the degradation of the dentin-composite interface induced by multi-species oral biofilms in vitro.

METHODS

Dentin-composite disks (5-mm dia.×2-mm thick) were made from bovine incisor roots and filled with either Z100™ (Z100) or Filtek™ LS (LS) composite. The disks, which were covered with nail varnish, but with one of the dentin-composite margins exposed, were immersed in lactic acid solution at pH 4.5 for up to 48h. Diametral compression was performed to measure the reduction in bond strength of the dentin-composite disks following acid challenge. Scanning electron microscopy (SEM) was used to examine decalcification of dentin and fracture modes of the disks. To better understand the degradation process, micro-computed tomography, in combination with a radiopaque dye (AgNO3), was used to assess interfacial leakage in 3D longitudinally, while SEM was used to determine the path of leakage. One-way analysis of variance (ANOVA) was used to analyze the results, with the level of statistical significance set at p<0.05. The results were compared with those obtained previously using multi-species biofilms for verification and calibration purposes.

RESULTS

After 48h of acid challenge, the debonding load of both the LS- and Z100-filled disks reduced significantly (p<0.05). In the Z100-filled disks, debonding mostly occurred at the adhesive-dentin interface, while in the LS-filled disks, this happened at the adhesive-composite interface, instead. The degree of dentin demineralization, the reduction in debonding load and the modes of failure observed were very similar to those induced by multi-species oral biofilms found in the previous work. Leakage of AgNO3 occurred mainly along the hybrid layer. The specimens filled with Z100 had a thicker hybrid layer (∼6.5μm), which exhibited more interfacial leakage than those filled with LS.

SIGNIFICANCE

The chemical model with lactic acid used in this study can induce degradation to the dentin-composite interface similar to those produced by multi-species biofilms. With appropriate calibration, this could provide an effective in vitro method for ageing composite restorations in assessing their potential clinical performance.

A pilot study on the feasibility of training nurses to formulate multicomponent oral health interventions in a residential aged care facility

OBJECTIVES

This 10 weeks feasibility study investigated whether residential care nurses with 12 hours advanced oral health training in assessments and saliva testing could formulate, implement and monitor individualised oral care plans of early dementia residents.

METHOD

Four trained lead advocate nurses using SXI-D, OHIP14, oral health assessment tool (OHAT) assessments and a modified saliva test formulated nurse scheduled comprehensive oral care plans (NSCOCPs) by selecting and scheduling preventive products and procedures multiple times throughout the day to alkalise the mouth of 8 residents as an adjunct to assisted brushing and high-fluoride toothpaste.

RESULTS

Nurse assessments, saliva tests and care plans were validated against oral health therapist (OHT) findings. Care plan agreement between Nurse and OHT intervention selection and scheduling was high (75%-88%). Untrained nurse compliance was very high, 86%-99% for the 4930 scheduled interventions. Untrained nurses delivered multiple scheduled interventions by following NSCOCPs despite initially not understanding the reason for each of 9 interventions categories. NSCOCPs could track and monitor whether a recommended intervention had been completed by general nursing staff over 3 nursing shifts.

CONCLUSION

The role of nurses may have to be expanded beyond traditional roles to meet the growth and changes in oral health needs in residential facilities. Intensive training of a few lead advocate nurses to assess risk and formulate individualised NSCOCPs provides a method to transfer knowledge to untrained staff and deliver multicomponent preventive interventions soon after entry into residential care where timely visits by dental professionals to examine residents and prescribe preventive interventions are infrequent or unlikely.

The Landscape Ecology and Microbiota of the Human Nose, Mouth, and Throat

Landscape ecology examines the relationships between the spatial arrangement of different landforms and the processes that give rise to spatial and temporal patterns in local community structure. The spatial ecology of the microbial communities that inhabit the human body-in particular, those of the nose, mouth, and throat-deserves greater attention. Important questions include what defines the size of a population (i.e., "patch") in a given body site, what defines the boundaries of distinct patches within a single body site, and where and over what spatial scales within a body site are gradients detected. This Review looks at the landscape ecology of the upper respiratory tract and mouth and seeks greater clarity about the physiological factors-whether immunological, chemical, or physical-that govern microbial community composition and function and the ecological traits that underlie health and disease.

Normal Oral Flora and the Oral Ecosystem

The oral ecosystem comprises the oral flora, so-called oral microbiome, the different anatomic microniches of the oral cavity, and its bathing fluid, saliva. The oral microbiome comprises a group of organisms and includes bacteria, archaea, fungi, protozoa, and viruses. The oral microbiome exists suspended in saliva as planktonic phase organisms or attached to oral surfaces as a plaque biofilm. Homeostasis of the plaque biofilm and its symbiotic relationship with the host is critical for oral health. Disequilibrium or dysbiosis within the plaque biofilms is the initiating event that leads to major oral diseases, such as caries and periodontal disease.

Monitoring of extracellular pH in young dental biofilms grown in vivo in the presence and absence of sucrose

Background and objective

pH in dental biofilms is of central importance for the development of caries. We used the ratiometric pH-sensitive dye C-SNARF-4 in combination with digital image analysis to monitor extracellular pH in dental biofilms grown in situ with and without sucrose supply.

Design

Dental biofilms (48 h) from 10 individuals were collected on glass slabs mounted on intra-oral appliances. During growth, appliances were immersed extra-orally in either physiological saline or 4% sucrose for 2 min, eight times per day. Fluorescence emissions of C-SNARF-4 in deep layers of the biofilms were recorded ex vivo with confocal microscopy for 15 min or for 1 h after exposure to 0.4% glucose. Extracellular pH was determined ratiometrically using digital image analysis.

Results

Extracellular pH dropped rapidly in most examined sites after addition of glucose. Distinct pH microenvironments were observed within single biofilms. The variation in pH was similar between sites within the same biofilm and sites from different individuals. pH drop patterns did not differ between biofilms exposed to sucrose-free and sucrose-rich environments.

Conclusion

The present study is the first of its kind to apply the combination of pH ratiometry and digital image analysis to systematically record extracellular pH in intact dental biofilms from several individuals for up to 1 h. We observed highly heterogeneous pH landscapes and the presence of acidogenic microenvironments – ‘acidogenic hotspots’ – within the biofilms. The data suggest that pH drops in young (48 h) dental biofilms are independent of the sucrose supply during growth.

Polymicrobial Biofilm Studies: From Basic Science to Biofilm Control

Microbes rarely exist as single species planktonic forms as they have been commonly studied in the laboratory. Instead, the vast majority exists as part of complex polymicrobial biofilm communities attached to host and environmental surfaces. The oral cavity represents one of the most diverse and well-studied polymicrobial consortia. Despite a burgeoning field of mechanistic biofilm research within the past decades, our understanding of interactions that occur between microbial members within oral biofilms is still limited. Thus, the primary objective of this review is to focus on polymicrobial biofilm formation, microbial interactions and signaling events that mediate oral biofilm development, consequences of oral hygiene on both local and systemic disease, and potential therapeutic strategies to limit oral dysbiosis.

Characterization of the arginolytic microflora provides insights into pH homeostasis in human oral biofilms

A selected group of oral bacteria commonly associated with dental health is capable of producing alkali via the arginine deiminase system (ADS), which has a profound impact on the pH of human oral biofilms. An increased risk for dental caries has been associated with reduced ADS activity of the bacteria in oral biofilms. Arginolytic bacterial strains from dental plaque samples of caries-free and caries-active adults were isolated and characterized to investigate the basis for differences in plaque ADS activity between individuals. Fifty-six ADS-positive bacterial strains were identified by 16S rRNA gene sequencing, and their ADS activity levels were compared under standard growth conditions. The spectrum of bacterial ADS activity ranged from 45.2 to 688.0 units (mg protein)(-1). Although Streptococcus sanguinis was the most prevalent species, other Streptococcus sp. were also represented. Biochemical assays carried out using 27 ADS-positive strains under conditions known to induce or repress ADS gene expression showed substantial variation in arginolytic activity in response to pH, oxygen and the availability of carbohydrate or arginine. This study reveals that the basis for the wide spectrum of arginolytic expression observed among clinical strains is, at least in part, attributable to differences in the regulation of the ADS within and between species. The results provide insights into the microbiological basis for intersubject differences in ADS activity in oral biofilms and enhance our understanding of dental caries as an ecologically driven disease in which arginine metabolism moderates plaque pH and promotes dental health.

Caries Distribution, Prevalence, and Treatment Needs among 12–15-Year-Old Secondary School Students in Port Harcourt, Rivers State, Nigeria

Objective. There is a change in the trends and distribution of dental caries in established and nonestablished market economies. The aim of this study was to describe caries distribution, prevalence, and treatment needs among school children in Port Harcourt, Nigeria. Materials and Methods. The study was a cross-sectional survey of students between the ages of 12 and 15 years. Data was collected using a structured questionnaire and clinical oral examination. Analysis of data was done using statistical package for social science version 20.0. Association between variables was tested using chi-square, independent t-test, and one-way analysis of variance. Results. The study population consisted of 195 school children of mean age 13.21±1.09 years. The prevalence of dental caries was 15.4% (n=30). The mean DMFT score for the entire group was 0.25±0.66. Dental caries occurred more significantly (P<0.005) on the mandible (66.7%) than on the maxilla (33.3%) and was significantly (P<0.005) more prevalent on the first molars (66.7%) than on the second molars (26.6%). Conclusion. The number of untreated dental caries was high and the restorative index was low among the students. The overall caries prevalence and mean DMFT were low even when compared to other studies in similar populations in Nigeria.

Microbial geography of the oral cavity

We aimed to determine the bacterial diversity of different oral micro-niches and to assess whether saliva and plaque samples are representative of oral microbial composition. We took minute samples from each surface of the individual teeth and gingival crevices of two healthy volunteers (112 samples per donor), as well as samples from the tongue dorsum and non-stimulated and stimulated saliva. DNA was extracted from 67 selected samples of each donor, and the 16S rRNA gene was amplified by PCR and pyrosequenced to obtain, on average, over 2,700 reads per sample, which were taxonomically assigned to obtain a geographic map of bacterial diversity at each tooth and sulcus location. Analysis of the data shows considerable differences in bacterial composition between teeth at different intra-oral locations and between surfaces of the same tooth. The most pronounced differences were observed in incisors and canines, where genera like Streptococcus were found at 40% to 70% on the vestibular surfaces but were almost absent on the lingual sides. Saliva samples, especially non-stimulated saliva, were not representative of supra-and subgingival plaque in the two individuals tested. We suggest that more precise sampling is required for the proper determination of oral microbial composition and to relate that diversity to epidemiological, clinical, and etiological parameters.

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.

The Role of Bacteria in the Caries Process

Dental biofilms produce acids from carbohydrates that result in caries. According to the extended caries ecological hypothesis, the caries process consists of 3 reversible stages. The microflora on clinically sound enamel surfaces contains mainly non-mutans streptococci and Actinomyces, in which acidification is mild and infrequent. This is compatible with equilibrium of the demineralization/remineralization balance or shifts the mineral balance toward net mineral gain (dynamic stability stage). When sugar is supplied frequently, acidification becomes moderate and frequent. This may enhance the acidogenicity and acidurance of the non-mutans bacteria adaptively. In addition, more aciduric strains, such as ‘low-pH’ non-mutans streptococci, may increase selectively. These microbial acid-induced adaptation and selection processes may, over time, shift the demineralization/remineralization balance toward net mineral loss, leading to initiation/progression of dental caries (acidogenic stage). Under severe and prolonged acidic conditions, more aciduric bacteria become dominant through acid-induced selection by temporary acid-impairment and acid-inhibition of growth (aciduric stage). At this stage, mutans streptococci and lactobacilli as well as aciduric strains of non-mutans streptococci, Actinomyces, bifidobacteria, and yeasts may become dominant. Many acidogenic and aciduric bacteria are involved in caries. Environmental acidification is the main determinant of the phenotypic and genotypic changes that occur in the microflora during caries.

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.

The Effect of Miswak Extract on Plaque pH

The aim of this study was to document changes in plaque pH when an acidic challenge was followed by rinsing with miswak extract (Salvadora persica), and to evaluate the effect of miswak rinse on parotid gland secretion rate. Plaque pH was measured in 3-day-old plaque using the microtouch electrode. Rinsing with miswak extract, compared with water rinsing, resulted in protracted elevation of plaque pH (>6.0). The difference in plaque pH between miswak extract and water rinse was statistically significant at 30 min (p < 0.001). Rinsing with miswak extract stimulated parotid gland secretion (p < 0.01). In conclusion, miswak extract raised the plaque pH, suggesting a potential role in caries prevention.

Susceptibility of Streptococcus mutans biofilms to photodynamic therapy: an in vitro study

OBJECTIVES

The purpose of this study was to evaluate the antimicrobial effect of toluidine blue O (TBO), in combination with either a helium/neon (HeNe) laser or a light-emitting diode (LED), on the viability and architecture of Streptococcus mutans biofilms.

METHODS

Biofilms were grown on hydroxyapatite discs in a constant depth film fermentor fed with artificial saliva that was supplemented with 2% sucrose four times a day, thus producing a typical 'Stephan pH curve'. Photodynamic therapy was subsequently carried out on biofilms of various ages with light from either the HeNe laser or LED using energy densities of between 49 and 294 J/cm(2).

RESULTS

Significant decreases in the viability of S. mutans biofilms were only observed when biofilms were exposed to both TBO and light, when reductions in viability of up to 99.99% were observed with both light sources. Overall, the results showed that the bactericidal effect was light dose-dependent and that older biofilms were less susceptible to photodynamic therapy. Confocal laser scanning microscopy images suggested that lethal photosensitization occurred predominantly in the outermost layers of the biofilms.

CONCLUSIONS

Photodynamic therapy may be a useful approach in the treatment of dental plaque-related diseases.

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.

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.

Genetics of acid adaptation in oral streptococci

A growing body of information has provided insights into the mechanisms by which the oral streptococci maintain their niches in the human mouth. In at least one case, Streptococcus mutans, the organism apparently uses a panel of proteins to survive in acidic conditions while it promotes the formation of dental caries. Oral streptococci, which are not as inherently resistant to acidification, use protective schemes to ameliorate acidic plaque pH values. Existing information clearly shows that while the streptococci are highly related, very different strategies have evolved for them to take advantage of their particular location in the oral cavity. The picture that emerges is that the acid-adaptive regulatory mechanisms of the oral streptococci differ markedly from those used by Gram-negative bacteria. What future research must determine is the extent and complexity of the acid-adaptive systems in these organisms and how they permit the organisms to maintain themselves in the face of a low-pH environment and the microbial competition present in their respective niches.

Adaptation of oral streptococci to low pH

The strategies employed by oral streptococci to resist the inimical influences of acidification reflect the diverse and dynamic niches of the human mouth. All of the oral streptococci are capable of rapid degradation of sugar to acidic end-products. As a result, the pH value of their immediate environment can plummet to levels where glycolysis and growth cease. At this point, the approaches for survival in acid separate the organisms. Streptococcus mutans, for example, relies on its F-ATPase, to protect itself from acidification by pumping protons out of the cells. S. salivarius responds by degrading urea to ammonia and S. sanguis produces ammonia by arginolysis. The mechanisms by which these organisms regulate their particular escape route are now being explored experimentally. The picture that emerges is that the acid-adaptive regulatory mechanisms of the oral streptococci differ markedly from those employed by Gram-negative bacteria. What remains to be elucidated are the breadth of the acid-response systems in these organisms and how they permit the microbes to sustain themselves in the face of low pH and the bacterial competition present in their respective niches. In this article, we summarize reports concerning the means by which oral streptococci either utilize acidification to subdue their competitors or protect themselves until pH values return to a more favorable level.

Oral glucose retention, saliva viscosity and flow rate in 5-year-old children

There are significant differences of glucose retention in site-specificity and individuals. Sixty-two 5-year-old nursery schoolchildren participated in this study on the relation between the viscosity of saliva and flow rate and glucose retention. Each child was instructed to rinse his/her mouth with a glucose solution (0.5 M, 5 ml) and then to spit out. Three minutes after rinsing, glucose retention was determined. Resting saliva was collected by a natural outflow method, then the flow rate was determined. A rotational viscometer was used to determine the viscosity. Glucose retention and flow rate were correlated at the left maxillary primary molars, and glucose retention and viscosity were correlated at the maxillary central primary incisors. It was concluded that glucose retention after glucose mouth rinsing was site-specific, and that glucose retention and the index of decayed, missing and filled primary teeth (dmft) were slightly correlated with the salivary viscosity and flow rate.

The pH of dental plaque in its relation to early enamel caries and dental plaque flora in humans

Dental caries appears to result from the action of multiple, interrelated factors. A companion study dealt with the plaque-flora/caries relationship (van Ruyven et al., 2000). The plaque-pH/caries relationship is the subject of this study. Since both studies involve the same subjects, plaques, and tooth surfaces, data on the examined factors have also been integrated. In vivo plaque pH determinations (microelectrode) were done on buccal sound (s) and "white-spot" (ws) caries surfaces in a selected dentition area in a low-caries (no ws) and higher-caries subject group. The pH response to sugar was evaluated before and after a sugar rinse, a local sugar application, or sucking on a sugary lozenge. pH profiles with sugar rinsing and normal or limited salivary flow conditions, showed progressively decreasing plaque pH values at various time points in the order of: low-caries subjects (s sites), higher-caries subjects (s sites), higher-caries subjects (s + ws sites), and higher-caries subjects (ws sites). The minimum pH values showed the same trend. Analyses of all data indicated only a statistical difference for minimum values for s sites in low-caries subjects vs. ws sites in higher-caries subjects, and for s and ws sites in the latter. Local sugar application and sucking on a sugary lozenge induced smaller pH drops than sugar rinsing; such suboptimal sugar exposure caused a disappearance of the difference between the minimum pH values for s and ws sites observed with sugar rinsing in the higher-caries subjects. Initial plaque pH values were similar regardless of subject or tooth caries status. The values were also not correlated with the plaque levels of strongly iodophilic polysaccharide-storing bacteria. Collectively, both studies indicate that increasing subject caries status is characterized by increasing plaque levels of highly-acid-tolerant, acidogenic bacteria and an increasing plaque-pH-lowering potential and support the dynamic relationship between these parameters.

Subgingival calculus: where are we now? A comparative review

OBJECTIVE

To critically analyse the formation, composition, ethnic variations and pathogenic potential of subgingival calculus in comparison with supragingival calculus.

DATA SOURCES

Using CD-ROM and index medicus, scientific papers relating to subgingival calculus or subgingival and supragingival calculus written in the English language since 1960 were considered, with the emphasis on more recent articles.

STUDY SELECTION

Studies were selected for their relevance and contemporary nature re:composition and formation of dental calculus and comparisons of ethnic groups with regard to dental calculus, especially subgingival calculus. Some similar studies were not included.

DATA EXTRACTION

Abstracts of studies were kept brief unless particularly important to the review. Population, methodology, statistics and accurate conclusions were used as important guides to the quality and validity of studies.

DATA SYNTHESIS

Similarities and differences between supragingival and subgingival calculus in composition and formation were shown. Different morphological types of subgingival calculus were demonstrated. There was evidence for an association between calculus formation and ethnicity with regard to supragingival and subgingival calculus, and an association between subgingival calculus composition and ethnicity was indicated.

CONCLUSIONS

An association between ethnicity and subgingival calculus formation and composition was found. Further research into the reasons for these ethnic differences in dental calculus and the role of the mineral constituents especially of subgingival calculus would be valuable.

Antimicrobial susceptibility and composition of microcosm dental plaques supplemented with sucrose

The aims of this study were to evaluate the effects of repeated chlorhexidine gluconate (CHG) pulsing on the viability and bacterial composition of microcosm dental plaques derived from human saliva. The biofilms were grown on bovine enamel discs in a constant-depth film fermentor fed with an artificial saliva which was supplemented thrice daily with sucrose. The microcosm plaques had total viable anaerobic counts of 5 x 10(8) CFU per mm2 and consisted of 12% Actinomyces spp., 85% streptococci, and 0.2% Veillonella spp. When pulsed twice daily with 0.2% CHG, there was an immediate 1.3-log10 reduction in the total viable (anaerobic) count. However, as pulsing continued, the viable counts recovered, and after 4 days, the anaerobic count reached its pre-CHG-pulsing level, although the bacterial composition of the biofilms had changed. The results of this study show that twice-daily pulsing with 0.2% CHG over a 4-day period was ineffective at reducing the total anaerobic viable count of the biofilms but did alter their bacterial composition.

Oral mucosal wetness in hypo- and normosalivators

After a person swallows, a film of residual saliva covers the oral hard- and soft-tissue surfaces. Here, the thickness of this film was measured at 11 selected mucosal surfaces on each side of the mouth (22 sites total) in two groups of dry-mouth and one group of normal individuals. Each group contained 25 individuals; one of the dry-mouth groups had resting flow rates < or = 0.1 ml/min while the other and the normal had flow rates above that. Residual saliva thickness was determined by placing frying-pan-shaped filter-paper strips (Sialopaper) against the mucosa at each site for 5 s and measuring the saliva volume collected with a modified Periotron 6000 micro-moisture meter; the thickness was then calculated by dividing the collected saliva volume by the strip area. The two groups with dry-mouth symptoms had mean resting (unstimulated) saliva flow rates of 0.04 and 0.19 ml/min and mean mucosal saliva thicknesses of 22.4 and 27.8 microns, respectively. The control group had a higher mean saliva flow rate of 0.39 ml/min and mucosal saliva thickness of 41.8 microns. As was observed in a previous study on normosalivators, the various sites had a characteristic pattern of wetness, with the hard palate and lips the least moist regions. In this study, these observations, were also true in the two dry-mouth groups. Lower resting saliva flow rates were associated with lower mucosal thickness of saliva and with dryness symptoms becoming evident when hyposalivation was below about 0.1-0.2 ml/min. The characteristic pattern of mucosal wetness was not affected by saliva flow rate. As saliva readily collects in the floor of the mouth and is then spread over other mucosal surfaces upon swallowing, it was suggested that hyposalivation could also lead to the dryness symptoms because there was not enough saliva to cover the various oral surfaces, especially the palate and the lips. In this regard, a critical level of moisture was proposed as necessary to protect vulnerable mucosal surfaces from becoming dry. Lower resting saliva flow rates and correspondingly lower mucosal wetness were also associated with a more acidic salivary pH, which was shown earlier to be associated with lower dental plaque pH.

Inactivation of tumor necrosis factor-alpha by proteinases (gingipains) from the periodontal pathogen, Porphyromonas gingivalis. Implications of immune evasion

Porphyromonas gingivalis is one of the major pathogens associated with adult periodontitis, a major chronic inflammatory disease. Potent proteinases elaborated by these bacteria aid directly and indirectly in both the development of the pathophysiology of the disease and in host defense evasion. For these reasons they are considered key virulence factors. To investigate whether possible immune evasion mechanisms involve the dysregulation of the host cytokine network, we examined the ability of P. gingivalis cysteine proteinases, including Arg-specific gingipains HRGP and RGP2 and Lys-specific KGP, to degrade the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). All three gingipains rapidly degraded TNF-alpha as exhibited by immunoblot analysis. Moreover, all biological activity was significantly reduced over extended incubation periods with the proteinases tested, whereas the host neutrophil proteinases were ineffective. These results indicate that the gingipain proteinases elaborated by P. gingivalis are capable of disrupting the cytokine network at the site of infection through the degradation of the proinflammatory cytokine TNF-alpha, suggesting the removal of one of several mediators important to the function of polymorphonuclear leukocytes. Such a mechanism is likely to be utilized by other infective organisms not only for survival but also for growth and proliferation.

Factors affecting the resting pH of in vitro human microcosm dental plaque and Streptococcus mutans biofilms

The aim was to examine factors that potentially control the resting pH, defined as the pH unaffected by meals, of microcosm dental plaques and Streptococcus mutans biofilms under standard conditions, and to examine the effect of supplying urea at concentrations found intraorally. Microcosm plaques were cultured from plaque bacteria-enriched saliva in an 'artificial mouth' with a continuous supply of a medium including 0.25% mucin [Basal Medium Mucin, (BMM), 3.6 ml/hr per plaque] and a periodic supply of sucrose. The steady-state resting pH was 6.4 (range +/- 0.1) in BMM containing no urea and supplied at the standard flowrate. This is a robust property of the ecosystem. In one experiment with a replicated (n = 9) set of measurements, the resting pH was approx. pH 6.3, 6.4, 6.7 and 7.3 with 0, 1, 5 and 20 mmol/l urea in the BMM. The magnitude of sucrose- and urea-induced pH responses was unaffected by elevating the resting pH to produce parallel pH curves. The sucrose-induced pH curves were analogous to those classically reported by Stephan that showed an association between caries activity and increasingly acidic plaque pH responses to glucose. Stopping the BMM flow caused a pH rise, indicating continuing net alkali generation from BMM components in the absence of a fluid flow. Step. mutans monoculture biofilms had an acidic resting pH of 5.0 to 5.3, which increased to 6.8 following an adventitious superinfection by Bacillus cereus. It was concluded that the resting pH in plaque results from a delicate balance between alkali and acid generation, which is in turn dependent both on the bacterial composition of the plaque and on the supply of substrates and buffers from, and metabolite clearance into, flowing oral fluid. In vivo the resting pH will vary with site-specific changing saliva flows. Urea continuously supplied at concentrations normal for saliva and gingival crevicular fluid can raise the resting pH of microcosm plaque by an amount tat in vivo would probably be significant in reducing dental caries.

Construction and characterization of a recombinant ureolytic Streptococcus mutans and its use to demonstrate the relationship of urease activity to pH modulating capacity

To begin to understand the contribution of oral microbial ureolysis to the inhibition of dental caries, we sought to construct a recombinant, ureolytic mutans streptococcus and correlate the ureolytic capacity of plaque bacteria with pH moderating ability. Streptococcus mutans GS-5 was transformed with a plasmid containing the urease genes from Streptococcus salivarius 57.I. The recombinant strain, S. mutans AC04, stably maintained the urease genes. High levels of urease activity were detected, with a maximum specific activity of 0.9 mumol of urea hydrolyzed/min/mg cell dry weight when the growth medium was supplemented with 50 microM exogenous NiCl2. Harboring the recombinant plasmid, or growth in NiCl2, did not markedly affect the glycolytic capacity of S. mutans. In vitro pH drop analysis of S. mutans AC04, metabolizing glucose and physiologically relevant concentrations of urea simultaneously, demonstrated that increasing the urease activity of plaque bacteria resulted in a corresponding reduction in the depth and the duration of the glycolytic pH fall. The results demonstrate the feasibility of engineering urease producing S. mutans and suggest that enhancing the ureolytic capacity of dental plaque, particularly cariogenic plaque, may help to offset the progression of the caries process.

Use of a paper-strip absorption method to measure the depth and volume of saliva retained in embrasures and occlusal fussae of the human dentition

Embrasures and occlusal fossae are regions of the human dentition that readily retain saliva, as well as dental plaque and dietary substrates. In this study, a wax filling and weighing technique was used to determine the volumes of these irregularly shaped spaces, and a paper-strip absorption method was developed for measuring the thickness and amounts of saliva therein. The volumes were measured on dental stone models prepared from alginate impressions of the maxillary arches of each of eight individuals and on an acrylic maxillary denture representative of the shape and alignment of normal-sized adult teeth. Embrasure volumes in the two cases were similar and ranged between 4.0 and 16.4 microliters for the individual participants, and between 4.8 and 14.9 microliters for the denture. Occlusal fossae volumes of posterior teeth determined on the denture ranged between 6.0 and 9.8 microliters. The paper-strip absorption method for the thickness or amount of saliva in embrasures or fossae consisted of the absorption of the saliva in these sites on to filter-paper strips and the measurement of the collected volumes electronically with a Periotron 6000 micro-moisture meter. Residual saliva for the embrasures between the two central incisors and the second premolar and first molar ranged between 0.12 and 0.56 with means of 0.28 and 0.37 microliter, respectively, for the same eight participants. Corresponding saliva Vmax volumes were 0.48 and 0.63 microliter, respectively. Further paper strip absorption measurements of saliva in embrasures and fossae showed a linear relation between Periopaper dipstick values and embrasure saliva volumes when these were less than 1 microliter. This range includes most residual saliva volumes normally found in these sites in vivo. For volumes of saliva greater than 1 microliter, small increments in dipstick values in embrasures corresponded to very large changes in total embrasure volumes, which reflects their exponential widening beyond about that point. For saliva thickness measurements, a blue food dye was used to construct a standard curve relating depth of saliva in embrasures and fossae (measured with an electronic micrometer) to Periopaper dipstick scores (measured with the Periotron). The relation was linear for both sites, with r values of 0.98 and 0.99, respectively (p < 0.001 for each), and was used to convert extensive in vivo depth measurements of embrasures and fossae determined in microlitres by the dipstick method in an earlier study to thicknesses in millimetres here. In the earlier study, residual saliva on oral mucosal and smooth dentition surfaces was quantified by the blotting method. Together with the method developed here, it should now be possible to measure the saliva, residual or otherwise, on all oral surfaces whether uniform or irregular in shape.

Measurement and comparison of the residual saliva on various oral mucosal and dentition surfaces in humans

Using a paper-strip absorption method, the amounts of residual saliva on 20 soft-tissue sites in different regions of the mouths of 20 individuals were surveyed once in the morning after a 12-h fast and again approx. 1-2 h after lunch. After swallowing, saliva at each site was immediately collected on filter-paper strips in a dipstick fashion for 5 s and the volumes were measured electronically with a Periotron micro-moisture meter. A clear pattern of wetness was evident and was almost identical for fasting and postprandial determinations. The hard palate and labial mucosa were covered with the least residual saliva; the floor of the mouth and back of the tongue were the wettest. In the same 20 participants, the amounts of residual saliva on various dentition sites were next measured and, as expected, much higher residual amounts were found in approximal embrasures and occlusal fossae than on adjacent facial or lingual smooth areas. Molars gave higher values than premolar and incisor embrasures. To relate residual saliva dipstick volumes to saliva thickness values, filter-paper strips were applied flat against the same mucosal or dentition surfaces in 10 of the participants, and the volume of the saliva absorbed was measured electronically as before. As the areas of the strips used were known, saliva thicknesses could be calculated. These ranged from 0.01 mm on the hard palate to 0.07 mm on the posterior of the dorsum of the tongue. For the incisor teeth, the calculated residual saliva thickness determined in the same way was about 0.01-0.02 mm. Blotting values plotted against dipstick values for oral sites where blotting could be readily performed showed a linear relation, which could be used as a standard curve to enable the easily done dipstick measurements in microlitres to be converted to saliva thicknesses in millimeters. As blotting could not be done in embrasures and occlusal fossae, this paper-strip absorption method was unsuitable for similar quantification of residual saliva in these sites but was done in another way described elsewhere. Overall, the results indicated that variations in dental morphology, and in the saliva secreted and available to the different oral regions, are the basic factors responsible for the wide variations in residual amounts of saliva seen on the diverse hard- and soft-tissue surfaces of human mouths. Also, finding that the hard palate and inner lips are covered by very thin films of residual saliva suggested that only a small reduction in their quantity would be needed to trigger the dry mouth sensation in hyposalivators.

Bacteria in human mouths involved in the production and utilization of hydrogen peroxide

Earlier studies have demonstrated that pure cultures of oral streptococci produce hydrogen peroxide but none has found any free peroxide in dental plaque or salivary sediment despite streptococci being major components of their mixed bacterial populations. The absence of peroxide in plaque and sediment could be due to the dominance of its destruction over its formation by bacterial constituents. To identify which of the oral bacteria might be involved in such a possibility, pure cultures of 27 different oral bacteria were surveyed (as well as dental plaque and sediment) for their peroxide-forming and peroxide-removing capabilities. Peroxide production was measured for each of the pure cultures by incubation with glucose at low and high substrate concentrations (2.8 and 28.0 mM) for 4 h and with the pH kept at 7.0 by a pH-stat. Removal of hydrogen peroxide was assessed in similar experiments where peroxide at 0, 29.4, 147.2 or 294.4 mM [0, 0.1, 0.5 and 1% (w/v)] replaced the glucose. Hydrogen peroxide formation was seen with only three of the bacteria tested, Streptococcus sanguis I and II (sanguis and oralis), and Strep. mitior (mitis biotype I); levels of hydrogen peroxide between 2.2 and 9.8 mM were produced when these micro-organisms were grown aerobically and 1.1 and 3.9 mM when grown anaerobically. Earlier reports indicate that such levels were usually sufficient to inhibit the growth of many plaque bacteria. The amounts formed were similar at the two glucose levels tested, suggesting that maximum peroxide production is reached at low glucose concentration. None of the three peroxide-producing organisms was able to utilize hydrogen peroxide but five of the other 24 tested, Neisseria sicca, Haemophilus segnis, H. parainfluenzae, Actinomyces viscosus and Staphylococcus epidermidis, could readily do so, as could the mixed bacteria in salivary sediment and dental plaque, both of which contain relatively high numbers of these peroxide-utilizing micro-organisms. The ability of the bacteria in plaque and sediment to degrade hydrogen peroxide was considerable and extremely rapid; peroxide removal and usually complete within the first 15 min of the incubation even when its initial level was as high as 294.4 mM. This almost overwhelming ability to remove peroxide was confirmed when peroxide-producing and -using cultures were mixed and when each of eight salivary sediments was incubated with glucose and with peroxide at concentrations up to 294.4 mM. In the glucose incubations, no hydrogen peroxide was observed, indicating dominance of microbial peroxide removers over hydrogen peroxide producers.(ABSTRACT TRUNCATED AT 400 WORDS)

Association of free arginine and lysine concentrations in human parotid saliva with caries experience

We determined the free-amino acid content of stimulated parotid (ductal) saliva from two groups of adult subjects whose caries experiences were markedly different. The levels of free arginine and free lysine in the parotid saliva of caries-free adults were significantly higher than those found in the parotid saliva of individuals with a history of dental decay. There was no correlation, however, between the levels of these amino acids and the DMFS score within the caries-susceptible groups. Microbial catabolism of dibasic amino acids contributes to the neutralization of plaque acids and may partially account for the higher resting plaque pH observed in caries-free subjects. Alternatively, the elevations observed in free levels of arginine and lysine may reflect a systemic alteration in amino acid metabolism which is common to the caries-free group of subjects.

Effect of buccal administration of a lactose-containing nitroglycerin tablet (Suscard) on plaque pH

The aim of this study was to monitor pH in 2-day-old dental plaque after administration of a long-acting, lactose-containing nitroglycerin tablet (Suscard). The tablet was placed under the lip of the maxilla. This was done both in two older subjects suffering from heart problems and in 10 younger, healthy subjects. In the latter group, a sucrose-containing lozenge was used as a control. The influence of a 5-wk period of daily use of Suscard (in the two elderly subjects) and the effect of normal oral hygiene procedures (in the 10 younger subjects) on the pH response was also studied. Plaque pH was measured in situ up to 1 h, at five different approximal sites in the front region of the maxilla by the micro-touch method. The Suscard tablet resulted in a fall in plaque pH in both groups when teeth had not been brushed for 2 days. The lowest pH was recorded at the sites close to where the tablet had been placed. The most attenuated pH drop was found in the two older subjects, who showed a mean minimum pH of 5.7, as compared with 6.2 for the younger subjects. No further increase in the pH fall from Suscard was seen after the 5-wk period in the two patients with heart problems. In the 10 younger healthy subjects, the most pronounced pH decrease was registered after administration of the sucrose-containing lozenge. The pH drop for Suscard was not significant when normal oral hygiene procedures preceded the test.(ABSTRACT TRUNCATED AT 250 WORDS)