The influence of salivary flow rate on diffusion of potassium chloride from artificial plaque at different sites in the mouth

Salivary elemental signature of dental caries: a systematic review and meta-analysis of ionomics studies

Trace- and macro-chemical elements are crucial for cellular physiological functioning, and their alterations in biological fluids might be associated with an underlying pathological state. Hence, this study aimed to examine and summarize the published literature concerning the application of salivary ionomics for caries diagnosis. An extensive search of studies was conducted using PubMed, EMBASE, Web of Science, and Scopus, without any language and year restriction for answering the following PECO question: "In subjects (i.e., children, adolescents, or adults) with good systematic health, are there any variations in the salivary concentrations of trace- or macro-elements between caries-free (CF) individuals and caries-active (CA) subjects?" A modified version of the QUADOMICS tool was used to assess the quality of the included studies. The Review Manager Version 5.4.1. was used for data analyses. The analysis of salivary chemical elements that significantly differed between CF and CA subjects was also performed. Thirty-four studies were included, involving 2299 CA and 1669 CF subjects, having an age range from 3 to 64 years in over 16 countries. The meta-analysis revealed a statistically significant difference (p < 0.05) in the salivary levels of calcium, phosphorus, chloride, magnesium, potassium, sodium, and zinc between CA and CF subjects, suggesting higher levels of calcium, phosphorus, potassium, and sodium in CF subjects while higher levels of chloride, magnesium, and zinc in CA patients. Half of the included studies (17/34) were considered high quality, while the remaining half were considered medium quality. Only zinc and chloride ions were found to be higher significantly and consistent in CF and CA subjects, respectively. Conflicting outcomes were observed for all other salivary chemical elements including aluminum, bromine, calcium, copper, fluoride, iron, potassium, magnesium, manganese, sodium, ammonia, nitrite, nitrate, phosphorus, lead, selenium, and sulfate ions.

Ratiometric imaging of extracellular pH in Streptococcus mutans biofilms exposed to different flow velocities and saliva film thicknesses

Introduction: Fluid flow has a prominent influence on the metabolism of surface-attached biofilms. Dental biofilms are covered by a thin saliva film that flows at different rates in different locations under stimulated and unstimulated conditions. Methods:The present study employed pH ratiometry to study the impact of different flow velocities, saliva film thicknesses and saliva concentrations on microscale pH developments in Streptococcus mutans biofilms of different age. Results:While saliva flow at a velocity of 0.8 mm/min (unstimulated flow) had little impact on biofilm pH, stimulated flow (8 mm/min; 80 mm/min) affected vertical pH gradients in the biofilms and raised the average pH in 48-h biofilms, but not in 72-h and 168-h biofilms. The saliva film thickness had a strong impact on biofilm pH under both static and dynamic conditions. pH drops were significantly higher in biofilms exposed to a thin saliva film (≤ 50 µm) than a thick saliva film (> 50 µm). pH drops in the biofilms were also strongly dependent on the saliva concentration and thus the buffer capacity of the salivary medium. For 48-h and 72-h biofilms, but not for 168-h biofilms, pH drops in distinct microenvironments were more pronounced when the local biofilm thickness was high.

The prevalence of non-carious cervical lesions (NCCLs) with or without erosive etiological factors among adults of different ages in Tokyo

OBJECTIVES

To evaluate the prevalence of non-carious cervical lesions (NCCLs) on teeth with or without erosive etiological factors across a broad range of ages of Japanese adults.

MATERIALS AND METHODS

The study sample consisted of a total of 1108 subjects aged 15 to 89 years in Tokyo, Japan. Two examiners evaluated NCCLs and dental erosion (DE) during a full-mouth examination. Subjects were asked to complete a self-administered daily diet, habits, and health condition questionnaire. Subjects who had frequent acid consumption or gastric reflux and at least one tooth with initial enamel wear were placed in the erosion present (EP) group, and the remainder of subjects were placed in the erosion not present (EN) group. Logistic regression analyses were carried out to identify etiological factors of NCCLs associated with DE.

RESULTS

Overall prevalence of NCCLs was 60.2%; the prevalence increased with age. There were no statistical differences in the prevalence of NCCLs between the EP and EN groups, except for the 60-69 years group. Multiple logistic regression analysis showed the frequency of consumption of carbonated soft drinks, citrus juice, and acidic fruits such as oranges; tooth brushing pressure; and bruxism were associated with the presence of NCCLs.

CONCLUSION

There were no statistical differences in the prevalence of NCCLs with or without erosive etiological factors except for the 60-69 years group.

CLINICAL RELEVANCE

NCCL distribution increased with age, and erosive risk factors caused by change in dietary habits might affect the incidence of NCCLs for elders.

TRIAL REGISTRATION

UMIN000041982.

Carbonic anhydrase VI activity in saliva and biofilm can predict early childhood caries: A preliminary study

AIM

This study aimed to investigate whether carbonic anhydrase VI activity (CA VI_ACT ), pH, and buffering capacity (BC) in saliva and biofilm could predict the number of lesion occurrence and early childhood caries (ECC).

DESIGN

A cross-sectional study was performed in a sample of 44 children aged 4 to 5 years who were examined regarding their caries status (dmfs + active white spot lesions-WSL) and allocated into two groups: ECC and caries-free (CF). Saliva and biofilm were collected to determine pH, BC, and CA VI_ACT . Data were analyzed using the Student t test, and multiple linear regression and logistic regression analyses followed by the ROC curve.

RESULTS

Children with ECC exhibited lower pH and BC in saliva and a higher CA VI_ACT in both saliva and biofilm. Only saliva pH could predict the dmfs + active WSL. In biofilm, if CA VI_ACT is increased by one pixel/µg, 0.85 ± 0.28 increase is expected in the number of active WSL. Salivary pH and CA VI_ACT in saliva and biofilm had the power to predict ECC occurrence.

CONCLUSION

Changes in saliva pH and CA VI_ACT in biofilm predicted the number of lesion occurrence. Furthermore, CA VI_ACT in both saliva and biofilm can predict propensity for ECC.

Combined effect of starch and sucrose on carbonic anhydrase VI activity in saliva and biofilm of children with early childhood caries. Exposure to starch and sucrose alters carbonic anhydrase VI activity in saliva and biofilm

OBJECTIVES

This study aimed to investigate whether combined exposure to starch and sucrose modifies the activity of carbonic anhydrase VI (CA VI) in saliva (Study 1) and biofilm (Study 2) of children with early childhood caries (ECC).

MATERIAL AND METHODS

For Study 1 and Study 2, respectively, 54 and 46 preschoolers aged 4 to 5 were allocated into two groups: caries-free (CF) and with ECC. Children were exposed to rinses with sucrose, starch, and sucrose plus starch solutions. CA VI activity, pH, and buffering capacity (BC) were evaluated in saliva and biofilm.

RESULTS

In Study 1, a significant reduction in saliva pH was observed after sucrose and sucrose plus starch rinses. CA VI activity was influenced by ECC independently of the type of carbohydrate to which children were exposed. CA VI activity was higher in children with ECC; however, after rinses, CA VI activity was reduced. In Study 2, biofilm pH and BC were reduced after rinses with sucrose and sucrose plus starch. CA VI activity was significantly high before rinse in ECC group when compared with CF group; however, no difference was observed between groups after rinses.

CONCLUSIONS

In saliva, exposure to starch and sucrose (isolated or combined) induced a reduction in CA VI activity in children with ECC. In biofilm, the combination of starch and sucrose did not modify CA VI activity in ECC children.

CLINICAL RELEVANCE

The responsivity of the CA VI reflects directly in important parameters related to the pH maintenance on the oral cavity.

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 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.

The human oral metaproteome reveals potential biomarkers for caries disease

Tooth decay is considered the most prevalent human disease worldwide. We present the first metaproteomic study of the oral biofilm, using different mass spectrometry approaches that have allowed us to quantify individual peptides in healthy and caries-bearing individuals. A total of 7771 bacterial and 853 human proteins were identified in 17 individuals, which provide the first available protein repertoire of human dental plaque. Actinomyces and Coryneybacterium represent a large proportion of the protein activity followed by Rothia and Streptococcus. Those four genera account for 60-90% of total diversity. Healthy individuals appeared to have significantly higher amounts of L-lactate dehydrogenase and the arginine deiminase system, both implicated in pH buffering. Other proteins found to be at significantly higher levels in healthy individuals were involved in exopolysaccharide synthesis, iron metabolism and immune response. We applied multivariate analysis in order to find the minimum set of proteins that better allows discrimination of healthy and caries-affected dental plaque samples, detecting seven bacterial and five human protein functions that allow determining the health status of the studied individuals with an estimated specificity and sensitivity over 96%. We propose that future validation of these potential biomarkers in larger sample size studies may serve to develop diagnostic tests of caries risk that could be used in tooth decay prevention.

Degradation of MUC7 and MUC5B in human saliva

Background

Two types of mucins, MUC7 and MUC5B constitute the major salivary glycoproteins, however their metabolic turnover has not been elucidated in detail to date. This study was conducted to examine turnover of MUC7 and MUC5B in saliva, by focusing on the relationship between their deglycosylation and proteolysis.

Methodology/Principal Findings

Whole saliva samples were collected from healthy individuals and incubated at 37°C in the presence of various protease inhibitors, sialidase, or a sialidase inhibitor. General degradation patterns of salivary proteins and glycoproteins were examined by SDS-polyacrylamide-gel-electrophoresis. Furthermore, changes of molecular sizes of MUC7 and MUC5B were examined by Western blot analysis. A protein band was identified as MUC7 by Western blot analysis using an antibody recognizing an N-terminal epitope. The MUC7 signal disappeared rapidly after 20-minutes of incubation. In contrast, the band of MUC7 stained for its carbohydrate components remained visible near its original position for a longer time indicating that the rapid loss of Western blot signal was due to the specific removal of the N-termimal epitope. Pretreatment of saliva with sialidase facilitated MUC7 protein degradation when compared with samples without treatment. Furthermore, addition of sialidase inhibitor to saliva prevented proteolysis of N-terminus of MUC7, suggesting that the desialylation is a prerequisite for the degradation of the N-terminal region of MUC7. The protein band corresponding to MUC5B detected in both Western blotting and glycoprotein staining showed little sign of significant degradation upon incubation in saliva up to 9 hours.

Conclusions/Significance

MUC7 was highly susceptible to specific proteolysis in saliva, though major part of MUC5B was more resistant to degradation. The N-terminal region of MUC7, particularly sensitive to proteolytic degradation, has also been proposed to have distinct biological function such as antibacterial activities. Quick removal of this region may have biologically important implication.

The biomechanics of abfraction

The role of occlusal loading in the development of non-carious cervical lesions is becoming increasingly prominent. It is suggested that high occlusal loads result in large stress concentrations in the cervical region of the teeth. These stresses may be high enough to cause disruption of the bonds between the hydroxyapatite crystals, eventually resulting in the loss of cervical enamel.

This article reviews the evidence to support the thesis that occlusal loading can contribute to the process of non-carious cervical tooth loss or abfraction. It also reviews the potential interactions between occlusal loading and erosion that may contribute to non-carious cervical tooth loss.

3D finite element model and cervical lesion formation in normal occlusion and in malocclusion

The aim of this study was to develop a three-dimensional (3D) finite element model (FEM) of the first maxillary premolar in order to compare the stress profiles in the buccal and palatal cervical regions. The 3D geometry of the tooth was reconstructed, the solid model was transferred into a finite element program where a 3D mesh was created, and the stress distribution analysis was performed. Two typical cases have been considered: the tooth under normal occlusion (case I) and the tooth under malocclusion (case II). In case I, larger compressive stresses were found in the cervical enamel and dentine. Tensile stresses were found in the fissure system, adjacent area, and at the vestibular surface of the buccal cusp. The peak values for the principal stress ranged from -259 to +2.25 MPa in the cervical areas. In the case II, larger compressive stresses were found in the palato-cervical enamel and dentine. Tensile stresses were found inside the enamel in the fissure system, adjacent area, at the vestibular surface of the buccal cusp, and in the bucco-cervical enamel. The peak values for the principal stress ranged from -501.947 MPa in palatal region to +82.4 MPa in the buccal region This study implies a role of occlusal forces in development of non-carious lesions. In the case of malocclusion, tensile stresses generated on the cervical areas were higher compared with the stresses generated in the case of normal occlusion and it is probably capable of producing non-carious cervical lesion.

Abfraction Lesions: Myth or Reality?

Loss of tooth substance in the cervical region is usually attributed to toothbrush abrasion, erosion, or a combination of both factors. Recently the role of occlusal loading has become increasingly prominent. It is suggested that high occlusal loads cause large cervical stress concentrations, resulting in a disruption of the bonds between the hydroxyapatite crystals and the eventual loss of cervical enamel. This process has been called noncarious cervical tooth loss or abfraction. This article reviews the available evidence to support the thesis that occlusal loading can contribute to the process of abfraction. It also reviews the potential interactions between occlusal loading and erosion that may contribute to abfraction lesion formation.

CLINICAL SIGNIFICANCE

It is important to recognize the potential role of occlusal loading in the loss of cervical tooth tissue so that management of the occlusion can be incorporated into a treatment plan for a patient with abfraction lesions.

Streptococcal diversity in oral biofilms with respect to salivary function

OBJECTIVE

In a previous study, we screened 149 subjects and established four groups high or low for salivary killing of oral bacteria, and for aggregation and live and dead adherence of oral bacteria (as a combined factor). Caries scores were significantly lower in both High Aggregation-Adherence groups. In this study we looked at the effects of those differences in salivary function on the quantity and diversity of oral biofilm streptococci.

DESIGN

Subjects from those four groups were recalled for collection of overnight oral biofilm from buccal upper central incisors, lingual lower central incisors, buccal upper and lower first molars, and lingual upper and lower first molars. At each site, groups were compared for total biofilm (by DNA concentration), total streptococci (by quantitative PCR), and streptococcal diversity (by Streptococcus-specific denaturing gradient gel electrophoresis).

RESULTS

Total biofilm DNA and total streptococci were correlated. Both were highest on buccal molar surfaces and lowest on lingual lower central incisors, and both were significantly lower in the High Aggregation-Adherence groups (particularly at the buccal molar site). Fifty distinct bands were observed in denaturing gradient gels. There was great diversity within and between sites. Three major bands were present in almost every person at every site. Densities for two of those bands were significantly lower in both High Aggregation-Adherence groups. Other less-prevalent bands also showed the same pattern.

CONCLUSION

These findings are consistent with our caries results in suggesting that differences in salivary function can influence the quantity and composition of streptococci in oral biofilms.

Abfraction lesion formation in maxillary incisors, canines and premolars: a finite element study

Abfraction lesions are angular, wedge-shaped defects found at the cervical region of teeth and are caused by mechanical overloading initiated by cuspal flexure. Clinically, these lesions are more prevalent on the labial aspect of maxillary incisors. The aim of this study was to provide a biomechanical explanation for this clinical variation. Two-dimensional plane strain finite element models of an maxillary incisor, canine and first premolar were developed and the cervical stress profiles were examined along a horizontal plane 1.1 mm above the amelo-cemental junction. The local X (horizontal) stress on the labial/buccal side was 176.4 MPa for the incisor, 57.8 MPa for the premolar, and 3.4 MPa for the canine. Similarly, the maximum labial/buccal principal stress was 181.4 MPa for the incisor, 25.2 MPa for the premolar, and 66.8 MPa for the canine. The labial/buccal stress profile in the cervical region of an maxillary incisor was always greater than that found in an maxillary canine or premolar tooth. These findings provide a biomechanical explanation for the clinical variation seen in the prevalence of cervical abfraction lesions.

Local delivery of chlorhexidine using a tooth-bonded delivery system

Films containing 20% w/w chlorhexidine base (particle size 63-125 microm) in poly(epsilon-caprolactone), MW 35,000-45,000, were prepared by solvent evaporation and sections attached to the mesio-lingual and mesio-buccal surfaces of the lower first molar in healthy volunteers. Saliva (<1.5 microl) was collected on Periopaper and chlorhexidine concentrations measured by HPLC were typically higher in the area immediately adjacent to the tooth-bonded film sections and lower at more distant sites. Analysis of variance of chlorhexidine concentrations, adjacent to the film sections, showed concentrations were significantly different on the buccal and lingual sides of the tooth and depended on the time of sampling (n=5, P<0.05).

Distribution of fluoride in the oral cavity after application of a bioadhesive fluoride-releasing tablet

Bioadhesive fluoride tablets are fluoride-releasing devices that can be applied to the oral mucosa by the patient and release fluoride for several hours. From earlier research, it is known that a single fluoride source in the mouth can lead to an uneven distribution of fluoride in the oral cavity. In this study, fluoride concentrations were determined at different sites of the oral cavities of 13 healthy human volunteers after the application of a bioadhesive fluoride tablet containing 0.5 mg fluoride. The sites were: (1) labial surfaces of the upper central incisors, (2) lingual surfaces of the lower central incisors, (3) labial surface of the first upper left molar, and (4) labial surface of the lower right first molar. The tablet was fixed either centrally on the palate or in the lower labial sulcus in two consecutive experiments. Saliva was sampled with polyethylene sponges 5, 10, 20, 30, 60, 120, 180, and 240 minutes after tablet insertion. Fluoride was determined electrochemically. It could be shown that the area under the curve (AUC) values were significantly (p < 0.05) higher after tablet insertion in the lower labial sulcus at sampling site 1, a trend (p = 0.06) could be calculated for sampling sites 2 and 3, and no difference was found at sampling site 4. Fluoride could be detected in concentrations above 0.01 mmol.L-1 at all sampling sites after tablet insertion in the lower labial sulcus. This location seems to be a more appropriate tablet location than the palate.

Fluoride in plaque fluid and saliva after NaF or MFP rinses

A micro-analytic method, capable of measuring the fluoride concentration in 5 nl of plaque fluid, was used to follow changes in fluoride concentration in saliva and plaque fluid at 6 single tooth-sites in 6 subjects for 180 min after a 0.048 M fluoride rinse as a NaF or MFP (sodium monofluorophosphate) solution. The maximum fluoride concentrations in saliva after NaF was 13x higher than with MFP. About 5% of the total amount of fluoride following the 20 ml NaF rinse was retained in the oral cavity. The corresponding figure followig MFP was <1%. The saliva/plaque fluid fluoride ratios for upper molars and lower incisors were significantly higher than for the upper incisors and lower molars. There was a tendency for a decline in the ratios with respect to time for all sites. To characterize the plaque fluid fluoride intra-oral single-site distribution and clearance, fluoride concentration versus time (AUC) was calculated from 10 to 60 min after a rinse. The NaF AUC followed the order: upper incisor, lower molar, upper molar and lower incisors reflecting a different exposure and clearance pattern due to the different access of the plaque to saliva. The MFP AUC values varied more, but were all significantly lower than the NaF AUC values. Analysis of plaque fluid fluoride curves at various sites revealed an exponential decline in most cases. With NaF, the baseline plaque fluid fluoride levels were not reached within 3 h. It is concluded that NaF solutions result in a significantly higher intra-oral fluoride exposure than MFP solutions. The fluoride distribution and clearance of fluoride from different sites in the oral cavity are linked to salivary access to these sites. These site-specific differences may have clinical consequences with regard to the dynamics of fluoride in the de- and remineralization processes.

The intra-oral distribution of unstimulated and chewing-gum-stimulated parotid saliva

The objective was to determine the percentage contribution of parotid saliva to whole saliva and to the saliva at 11 sites in the mouth, when flow rate was unstimulated or stimulated with chewing-gum. The marker substance used was alpha-amylase, as this is in much higher concentration in parotid saliva than in secretions from other salivary glands. Formulae were derived for calculation of the minimum, maximum, and mean percentage contributions of parotid saliva to saliva in different areas of the mouth. The results, from 10 individuals, showed that the contributions of parotid to unstimulated and stimulated whole saliva averaged 30.1% and 35.6%, respectively, whereas the corresponding values for samples from the region vestibular to the upper molars were 56.1% and 61.4%, but only 2.8% and 6.8% for samples from an area vestibular to the upper incisors. Thus parotid saliva was not evenly distributed throughout the mouth. Stimulated samples mostly contained significantly higher proportions of parotid saliva, but the distribution of the parotid saliva was still extremely variable. Because the different regions of the mouth are not exposed to the same fluid environment, this may influence the site-specificity of supragingival calculus deposition and of various diseases such as dental caries.

Mathematical modeling of biofilms

A set of mathematical equations constitutes a mathematical model if it aims to represent a real system and is based on some theory of that system's operation. On this definition, mathematical models, some very simple, are everywhere in science. A complex system like a biofilm requires modeling by numerical methods and, because of inevitable uncertainties in its theoretical basis, may not be able to make precise predictions. Nevertheless, such models almost always give new insight into the mechanisms involved, and stimulate further investigation. The way in which diffusion coefficients are measured for use in a model, particularly whether they include effects of reversible reaction, is a key element in the modeling. Reasons are given for separating diffusion from reversible reaction effects and dealing with them in a separate subroutine of the model.

Saliva protein binding to streptococcal layers placed at different oral sites in 48 persons

Preliminary studies of 10 subjects suggested that saliva protein binding to oral bacteria might vary among oral sites. This study investigated saliva protein binding to layers of oral streptococci in an expanded sample of 48 subjects. Those persons were at opposite extremes for unstimulated whole saliva amylase, sIgA, lactoferrin, and lysozyme in an initial screening of 128 individuals. Layers of Streptococcus gordonii Blackburn or Streptococcus oralis 10557 on enamel chips were placed on buccal left and right upper premolars and molars (UL, UR), labial upper central incisors (UC), and lingual lower central incisors (LL). After a 10-minute exposure to saliva, bacterial extracts were assayed for bound amylase, sIgA, lactoferrin, and lysozyme. Those proteins also were quantified in unstimulated whole saliva collected after chip exposure. Both strains bound significantly more amylase at UL and UR, and significantly less at UC. Blackburn bound more amylase than 10557 at all sites. Significantly less sIgA was bound at UC; strain differences for sIgA were inconsistent across sites. Significantly more lactoferrin and lysozyme were bound at LL. There were no strain differences for lactoferrin; 10557 bound significantly more lysozyme at UL and UR. Subjects at opposite extremes for saliva protein concentrations differed for bound amylase and lactoferrin; those differences were smaller than site and strain differences. Bound protein levels were correlated across sites and strains. Correlations between whole saliva and bound proteins were moderate and were most consistent at LL. These findings suggest that saliva protein effects on oral ecology may vary among oral sites.

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.

Does variability in salivary protein concentrations influence oral microbial ecology and oral health?

Salivary protein interactions with oral microbes in vitro include aggregation, adherence, cell-killing, inhibition of metabolism, and nutrition. Such interactions might be expected to influence oral ecology. However, inconsistent results have been obtained from in vivo tests of the hypothesis that quantitative variation in salivary protein concentrations will affect oral disease prevalence. Results may have been influenced by choices made during study design, including saliva source, stimulation status, control for flow rate, and assay methods. Salivary protein concentrations also may be subject to circadian variation. Values for saliva collected at the same time of day tend to remain consistent within subjects, but events such as stress, inflammation, infection, menstruation, or pregnancy may induce short-term changes. Long-term factors such as aging, systemic disease, or medication likewise may influence salivary protein concentrations. Such sources of variation may increase the sample size needed to find statistically significant differences. Clinical studies also must consider factors such as human population variation, strain and species differences in protein-microbe interactions, protein polymorphism, and synergistic or antagonistic interaction between proteins. Salivary proteins may form heterotypic complexes with unique effects, and different proteins may exert redundant effects. Patterns of protein-microbe interaction also may differ between oral sites. Future clinical studies must take those factors into account. Promising approaches might involve meta-analysis or multi-center studies, retrospective and prospective longitudinal designs, short-term measurement of salivary protein effects, and consideration of individual variation in multiple protein effects such as aggregation, adherence, and cell-killing.

Computer modeling of the effects of chewing sugar-free and sucrose-containing gums on the pH changes in dental plaque associated with a cariogenic challenge at different intra-oral sites

Variation in salivary access to different intra-oral sites is an important factor in the site-dependence of dental caries. This study explored, theoretically, how access is modified by chewing sugar-free and sugar-containing gums. A finite difference computer model, described elsewhere, was used. This allowed for diffusion and/or reaction of substrate, acid product, salivary buffers, and fixed-acid groups. Site-dependent saliva/plaque exchange was modeled in terms of a 100-microns-thick salivary film covering the plaque (a) flowing directly from the salivary ducts, (b) flowing from the intra-oral salivary pool, or (c) exchanging with the pool. Computed flow-velocities or rates of exchange were based on previous intra-oral measurements. The model was also tested against an in vitro study conducted by two of the authors. In addition, the three proposed models of saliva/plaque interaction were compared, and the effect of salivary film thickness investigate. Results suggested that: (1) although sugar-free gum chewed during a cariogenic challenge causes a rapid rise in plaque pH, sucrose-containing gums cause the pH, after a temporary rise resulting from increased salivary flow, to stay low for an extended period; (2) the computer model reproduced in vitro tests reasonably well; (3) although the three models of the plaque/saliva interaction start from different assumptions, two lead to closely related predictions; and (4) increasing the assumed salivary film thickness by a large amount (e.g., from 50 to 200 microns) caused no change in modeled Stephan curves, as long as these changes were accompanied by appropriate reductions in film velocity, in accord, theoretically, with the practical clearance data.

Saliva protein binding to layers of oral streptococci in vitro and in vivo

This paper reports a system for measuring saliva protein binding to oral streptococci. Enamel chips with layers of Streptococcus gordonii Blackburn or Streptococcus oralis 10557 were incubated in vitro with whole saliva from eight persons. Blackburn bound significantly more amylase than 10557; no strain differences were seen for lysozyme or lactoferrin. There were significant correlations between saliva and bound amylase and lactoferrin. Blackburn and 10557 chips were then placed in ten subjects. Sites included the buccal left and right upper premolars and molars (UL, UR), labial upper central incisors (UC), and lingual lower central incisors (LL). That study was repeated three months later; chips with Streptococcus sanguis 13379 were also placed then. Blackburn bound significantly more amylase than the other strains. Blackburn and 10557 both bound the most amylase at UL and UR, and the least amylase at UC. However, strain 13379 bound less amylase at UL. That strain also bound significantly less sIgA at UL. All three strains bound the least sIgA at UC. Lysozyme and lactoferrin binding showed few differences among sites or strains. Bound protein concentrations were significantly correlated across sites and strains within subjects, but not correlated with whole saliva. Strain differences may reflect species differences in amylase binding, or differences in species-specific sIgA titers. Site differences may indicate local variation in protein availability. Differences between chip correlations with whole saliva in vitro and in vivo suggest that the salivary film may be modified as it flows over tooth surfaces.

In situ models, physico-chemical aspects

In situ (intra-oral) caries models are used for two purposes. First, they provide information about oral physiological processes. Such information helps to detail our knowledge of the oral ecosystem and to verify conclusions from in vitro experiments. Second, in situ models are utilized to test preventive agents in the phase between laboratory testing and clinical trials. Most investigations involving enamel inserts have been aimed at testing new dentifrices. The experimental designs of such studies usually do not allow one to draw conclusions on physico-chemical processes, e.g., because of single point measurements. Studies of model parameters (lesion type, lesion severity, and de/remineralization in time) constitute only a minority of the research reports. The most striking observation obtained with in situ models has been the significant differences in de/remineralization observed among individuals and, more importantly, within one individual during different time periods and between different sites in the same mouth (for review, see ten Cate et al., 1992). Regardless of this, some general findings can be inferred: During in situ demineralization, up to 62 vol% microns/day may be removed from enamel. For dentin specimens, this value may be as high as 89 vol% microns/day. For remineralization, during fluoride dentifrice treatment, a median deposition rate of 0.7%/day (for lesions with integrated mineral loss values between 2000 and 4000 vol% microns) is found. The rate of deposition seems to be correlated with the extent of the pre-formed lesion. This suggests that the number of sites (crystallite surface) available for calcium phosphate precipitation is an important parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Human experimental caries models: intra-oral environmental variability

In situ caries models serve purposes other than just being a simpler way to obtain data than running a clinical trial. However, variation in information obtained not only among individuals but also, in particular, depending on different locations of the models within the oral cavity have so far been given little attention. In the present review, the aim has been to characterize the different designs of in situ caries models and to describe some important factors which may vary within the oral cavity and thus influence the outcome of the way the different in situ models are used. Advantages and disadvantages of in vivo models vs. in situ models are discussed. In the latter case, the distinction is made between dental appliance models and so-called "single tooth" models. The review concludes that in situ models differ distinctly with regard to their "biological potential". Because of regional differences in salivary film velocity, pH, and composition of the microflora, results obtained by the various models are not likely to be immediately comparable. Moreover, local factors in relation to specimen environment, such as degree of "protection" and plaque thickness, may further add to the differences. It is suggested that these observations are important in considerations of the relevance of substituting clinical trials with in situ studies. Because of the pronounced intra-oral variation in certain parameters thought to be important for caries lesion development, we conclude that no in situ model can, by itself, fulfill the role as the "model of choice". Finally, although in situ models are useful adjuncts in attempts to estimate the relative effects of new anticaries methods or compounds on caries initiation, the selection of in situ study model design will strongly depend on the aim and purpose of the study.

Oral retention of glucose at pharmacologically reduced salivary flow in man

The aim was to study the influence of mouthrinses with glucose, at concentrations ranging from 1 to 50%, on oral retention at two different locations in the oral cavity. Salivary secretion was reduced in 10 subjects by injection of methylscopolamine nitrate submucosally. The volunteers were randomly assigned to rinse with 10 ml of either 1%, 10%, or 50% glucose solution for 30 s, after which measurements of glucose concentration and parotid salivary secretion rate were performed during a 10-min period. The results showed higher salivary glucose levels vestibularly than sublingually. The difference in glucose retention between the two locations increased when the salivary flow rate recovered. The relationship between secretion rate and area under the curve for glucose measured sublingually, but not in the vestibule, was bilinear.

The pH response to urea and the effect of liquid flow in 'artificial mouth' microcosm plaques

This study examined in detailed the pH response of microcosm plaque biofilms to the application of 500 mmol/l urea, and the effect of modifying the flow rate of BMM (a basal medium containing 0.25% mucin). Microcosm plaques were cultured from the mixed salivary bacteria in a multi-plaque 'artificial mouth' supplied continuously with BMM at 3.6 ml/h per plaque, and periodically with sucrose (5 or 10%). Urea (500 mmol/l) induced a pH response that was the inverse of the Stephan pH curve induced by sucrose. In thicker plaques the ureolytic pH response was delayed and slower. With no BMM flow, the urea-induced pH curve reached a maximum and then slowly decreased indicating loss of ammonia. A flow of BMM reduced the magnitude of the pH response. Urea dilution explained (r2 = 0.97) the reduction in the maximum rate of pH rise caused by an increasing BMM flow. There were, however, additional flow-rate effects on the magnitude of the pH rise, the curve areas and the maximum rate of pH decrease back to the resting pH. These effects were greatest at low BMM flow rates, indicating that ammonia clearance may be limited at higher flow rates by the rate of intraplaque diffusion and metabolism. Application of 50 instead of 500 mmol/l urea reduced the rate of pH rise about 10-fold, and the area of the curve about seven fold. Metabolism of arginine (50 mmol/l) generated only about half the pH response of the same amount of urea.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of micro-organisms in caries etiology

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

The distribution of saliva and sucrose around the mouth during the use of chewing gum and the implications for the site-specificity of caries and calculus deposition

Over a 20-minute period, subjects expectorated 8 samples of whole saliva (EWS) while chewing gum. Flow rates were calculated, and sucrose was analyzed in these samples as well as in saliva collected on filter paper strips from different tooth surfaces. Salivary film velocity (SFV), based on a 0.1-mm-thick film, was estimated from the clearance half-times of KCl in agarose disks positioned in different regions of the mouth. Salivary flow rate peaked at 5.1 mL/min in the first min but fell to about 1.25 mL/min by the end of the 20 min of gum-chewing. In contrast, flow rate when subjects sucked sour lemon drops averaged about 5.3 mL/min throughout the 20-minute period. The mean salivary sucrose concentration during gum-chewing peaked in the second min at 384 mmol/L (13.1%) but had fallen to 14 mmol/L by the 15-20-minute time interval. The sucrose concentrations on the palatal surfaces of the upper incisors and the facial and lingual surfaces of the lower molars were not significantly different from that in EWS but were much lower on the facial surfaces of the upper incisors and molars, and on the lingual surfaces of the lower incisors. When flow was unstimulated, SFV was 0.8-1.0 mm/min on the facial surfaces of the upper incisors and lower molars but about 5-8 mm/min on the facial surfaces of the upper molars and on the lingual surfaces of the lower incisors and molars.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of fluoride in saliva and plaque fluid after a 0.048 mol/L NaF rinse

An ultramicro method has recently been described for measurement of plaque-fluid fluoride concentration (Vogel et al., 1990a). This method was used: (1) for exploration of the variation in fluoride concentration of plaque fluid collected from the same buccal tooth sites following a 0.048 mol/L NaF (0.2%) rinse, and (2) for examination of the distribution of fluoride in plaque fluid and saliva within one hour after this rinse. Results indicated an average coefficient of variation (CV) of 31% for plaque-fluid fluoride in triplicate samples recovered simultaneously from the buccal-proximal region of two teeth after the rinse. This was similar to the CV found for plaque-fluid fluoride from the same sites after separate administrations of the rinse. A strong linear correlation was found between salivary and plaque-fluid fluoride at 30 and 60 min after rinse administration, showing that plaque-fluid fluoride is influenced by the concentration of salivary fluoride after administration of this rinse. Plaque-fluid fluoride concentrations were higher than that in saliva at baseline, 30, and 60 min. Very large inter-site and intersubject variations in plaque-fluid distribution were observed, with the central incisors showing the slowest clearance. These variations suggest that an examination of plaque-fluid fluoride from specific tooth regions may be essential for understanding the effects of fluoride on the site-specificity of caries.

Effect of calcium in model plaque on the anticaries activity of fluoride in vitro

The uptake of calcium by a polysaccharide (agarose) gel used as a model for plaque from a two-step treatment (consisting of a calcium rinse followed by a fluoride treatment) and the effect of the deposited calcium in model plaque on caries lesion formation in enamel were determined. Calcium uptake was measured by treatment of the model plaques with [45Ca]-CaCl2 solutions with or without NaF. A two-step treatment consisting of calcium followed by fluoride produced a 100% increase in calcium content of model plaque, presumably due to the formation of CaF2, compared with a treatment with artificial saliva followed by calcium alone. The effects of these increased plaque minerals on caries lesion formation were studied by subjecting model-plaque-covered enamel blocks to a cyclic demineralization-remineralization treatment. Artificial-plaque-covered enamel blocks were treated daily with 180 ppm calcium for ten min, then 100 ppm fluoride for ten min, followed by demineralization for 16 h, and finally, remineralization for seven h and 40 min. After five days, the blocks were sectioned, and lesion formation was determined by microradiography-microdensitometry. Artificial plaque treated with a calcium rinse followed by a fluoride rinse reduced lesion size by 90%, compared with a 68% reduction by a fluoride rinse alone. When the experiment was repeated with a simulated pre-brush calcium rinse (180 ppm calcium) followed by a fluoride dentifrice suspension (110 ppm fluoride), lesion size was reduced by 46%, compared with a 32% reduction by the fluoride dentifrice suspension alone.

Delivery of antiplaque agents from dentifrices, gels, and mouthwashes

Antiplaque agents delivered from toothpastes, gels, or mouthrinses can augment mechanical oral hygiene procedures to control the formation of supragingival plaque and the development of early periodontal disease. Clinically effective antiplaque agents are characterized by a combination of intrinsic antibacterial activity and good oral retention properties. The overall oral retention of an antiplaque agent is determined by the strength and rate of association of the agent with its receptor sites and the accessibility of these sites. The substantivity of an antiplaque agent and its clearance from the oral cavity are determined by the rate of dissociation of the agent from the receptor sites and the salivary composition and flow rate. Positively charged and non-charged organic molecules, metal ions, enzymes, and surface-active agents have all been considered as antiplaque agents. To exert clinical antiplaque activity, an antimicrobial agent must be formulated in a chemically compatible delivery vehicle to give optimal release and uptake to the sites of action in a biologically active form during its time of application. In principle, antiplaque activity may be enhanced by combining antimicrobial agents with broadly similar, but complementary, modes of action. Alternatively, the activity of a single agent may be increased by use of a retention aid to enhance oral substantivity. Substantial evidence exists to demonstrate the validity of the first approach. However, there are few data, as yet, to support the effectiveness of the second. The oral mucosa is the bulk retention site for all clinically proven antiplaque agents. Plaque, the pellicle-coated tooth surface, and saliva are probably all sites of biological action. A detailed understanding of the interactions between agents and the various receptor sites, and of the importance of these receptor sites to biological activity, is generally lacking.

Relationship between calcium and inorganic phosphorus concentrations of both resting and stimulated saliva and dental plaque in children and young adults

Calcium and inorganic phosphorus concentrations of both resting and paraffin-wax stimulated whole saliva and dental plaque were estimated in 39 young adults and 98 children aged 12-14 yr. Plaque was collected from the adults after 48 h without tooth-brushing and consumption of a standardized diet. Plaque was collected from the children without any dietary or oral hygiene restrictions. The results from the study with children provided consistent evidence for a statistically significant relationship between salivary and plaque concentrations of both calcium and inorganic phosphorus. However, multiple regression indicated that only the concentrations in the stimulated secretion were directly associated with concentrations in plaque. The apparent relationship between concentrations in resting saliva and plaque was due to correlation between resting and stimulated saliva. These relationships were less apparent in the young adults, in whom the controlled conditions resulted in a narrower range of mineral concentrations in dental plaque.

Facts and artefacts in research on human dental plaque fluid

In 1966, Jenkins suggested that the plaque fluid environment was likely to have higher concentrations of extracellular solutes than was apparent from analyses of total plaque concentrations. Early work on plaque fluid confirmed this contention, but some artefact was also generated by the prolonged centrifugation used for separation. The solute concentrations in plaque fluid mostly exceed those in saliva or crevicular fluid. Thus, the environmental conditions are distinctly different from those based on the assumption that saliva readily permeates films of dental plaque. In contrast, the presence of serum proteins suggests a crevicular input to plaque fluid. These data suggest that exchange between dental plaque and its environment is apparently restricted. Diffusion rates measured in dental plaque by different methods do not agree on how restricted it is. However, measuring diffusion in plaque introduces artefacts in packing density, a major determinant of the diffusion rate. The conditions used for collection and analysis have been reported to produce artefactual changes in plaque fluid potassium, a predominantly intracellular ion. Measurements of predominantly extracellular ions, such as calcium, are no less prone to artefact, whether based on ion-selective electrodes or on total calcium. We have much to learn about the fluid environment of the teeth and about dynamic changes in plaque fluid composition and properties during perturbations. Such information can give insights into pathological processes such as tooth demineralization and dental caries, calculus formation, and gingival inflammation.

Plaque fluid and diffusion: study of the cariogenic challenge by computer modeling

Every cariogenic challenge involves a mixture of convective transport, diffusive transport, and biochemical reactions, plus physico-chemical reactions (including charge-coupling of diffusion), all of which together require numerical methods for their analysis. This presentation describes a one-dimensional finite-difference computer model of the cariogenic process, and some conclusions obtained from it. Sugar clearance from the mouth, together with site-dependent exchange between the bulk saliva and plaque surface via a salivary film, is combined with a finite-difference model of events occurring within the dental plaque. The latter includes: sugar diffusion and pH-dependent acid production; diffusion and dissociation equilibria for two acid end-products of fermentation and their anions (acetate and lactate); diffusion and dissociation equilibria of phosphate buffer; diffusion of potassium and chloride; diffusion of protons and simultaneous equilibration with fixed and mobile buffers. So that proper concentration distributions consistent with local charge neutrality can be ensured, an algorithm called Q-couple is used to impose charge-coupling between the fluxes of different ions including fixed charges. Mineral dissolution and precipitation are modeled as part of the same equilibrium calculations. The predictions of the model are compared with those of an earlier, much simpler one, in which fixed buffers were not included. It is shown that the known concentration of fixed buffer greatly extends the low pH of a Stephan curve. The isoelectric point of the plaque bacteria also appears to be of importance. The effects of various concentrations of mobile buffers, including acetate, are investigated. It is also shown that varying plaque/saliva contact over the known range derived from published studies has a profound effect on the modeled cariogenic challenge.

Kinetics of fluoride in the oral fluids

The normal concentration of fluoride in saliva is about 1 mumol/L, which is somewhat less than that in plasma, and the salivary concentration is relatively independent of flow rate. Even this low concentration appears to be significant in terms of maintaining the integrity of tooth mineral. After fluoride consumption, the level in plasma peaks within less than an hour, and this produces a corresponding increase in salivary levels, which achieve baseline values usually within a few hours. At low concentrations (less than 4 mmol/L) in oral fluids, fluoride undergoes only slight reaction with tooth mineral to form fluorohydroxyapatite. However, at higher concentrations calcium fluoride is formed on the tooth surface. Although this mineral is sparingly soluble in saliva, the process of dissolution is retarded for periods of up to a week or longer by surface deposition of salivary phosphate and pyrophosphate. The rate of clearance of exogenous fluoride from saliva is prolonged when initial concentrations are high, due to the deposition of CaF2 on the tooth surface and its gradual dissolution. The clearance rate is also not constant throughout the mouth, but shows considerable site-specificity. In general, clearance is much more rapid lingually than buccally. This appears to be due to the greater lingual exposure to secretions from the major salivary glands, principally the submandibular, whereas buccally, mainly minor mucous gland secretions are present, and these are very viscous and flow at a slow rate.

Implications of a model from olfactory research for the use of secretion rates in salivary studies

Secretion rates (amount protein per unit time) are often used as a means of adjusting saliva protein concentrations for the effects of variation in flow rate. However, findings in olfactory physiology may indicate a problem with that approach: olfactory neurones respond differently to a small amount of odorant over a short time than to twice that quantity over twice the time, although secretion rates remain the same. Whether a similar variation in amounts and times occurs in persons with similar secretion rates for lysozyme, lactoferrin, salivary peroxidase, sIgA, or total protein in stimulated parotid saliva was investigated. The data used were from 2 groups of 44 and 198 subjects previously found to differ in flow rate and concentrations of antimicrobial proteins. Multidimensional plots of secretion rates, amounts and times were generated for each protein. Wide ranges of amounts and times were seen among persons within the same percentile for secretion rate for every protein in both groups. These amounted to as much as a thirteen-fold difference in amounts and times. Experimental studies are needed to determine whether such differences affect the action of saliva proteins.

An analysis of factors influencing diffusion from dental plaque into a moving film of saliva and the implications for caries

Recent studies have indicated that saliva in the mouth is present as a film only about 0.1 mm thick, and that this film moves at different rates (about 0.8 to 7.6 mm/min) in different regions of the oral cavity. The clearance rates of KCl, as a model diffusant, from agarose gels at different sites in the mouth have also been found to vary markedly, and it has been proposed that these variations are related to differences in the velocity of the salivary film. A computer model has been developed for prediction of clearance half-times for substances diffusing from plaque of variable dimensions into a film of fluid 0.1 mm thick, moving at different velocities. The results show that over the range of velocities calculated to occur in the mouth, the clearance half-times are directly related to the length of plaque over which the fluid passes, and inversely related to the salivary film velocity. The predictions of the model are in good agreement with experimental results from a physical model. Tests were made of the predicted effect of salivary film velocity on the shape of the pH curve initiated by exposure of plaque to a saturated sucrose solution, followed by normal salivary clearance. With a low salivary film velocity, the fall in pH was greater and more prolonged.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of the velocity of the salivary film at some different locations in the mouth

Previously, we studied the clearance rates of KCl from agarose gels positioned at different locations in the mouth, and showed that the rates were much slower than when clearance was into a well-stirred solution. We designed the present in vitro study to test the effect on KCl clearance of the velocity of a 0.1-mm-thick film of water flowing over an agarose gel of the same diameter and composition as those used in vivo. The thickness of the salivary film overlying dental plaque has been estimated to be about 0.1 mm, and we assumed that when clearance rates in vitro matched those found in vivo, velocities of the fluid film (in vitro) and the salivary film (in vivo) must be equal. On this basis, it was calculated in the present experiments that when salivary flow was unstimulated, the velocity of the salivary film at the level of the teeth varied between about 0.8 mm/min (upper-anterior buccal region) and 8.0 mm/min (lower-anterior lingual region). When salivary flow was stimulated, this was estimated to increase the velocity of the salivary film from 2 to 40 times, depending on the location in the mouth. It is postulated that the slow movement of the salivary film when flow is unstimulated allows for accumulation of diffusants from dental plaque, which reduces the concentration gradient for diffusion from plaque and prolongs the clearance time of such metabolic products as acid.

Extracellular potassium concentrations in human dental plaque fluid recovered from single sites

Previous studies using potassium ion-selective microelectrodes have demonstrated that potassium concentrations in dental plaque fluid obtained by centrifugation are identical to whole plaque values determined immediately after collection. Such procedures were now used to examine the variations in potassium concentrations between single-site samples of overnight-fasted resting plaque fluid. The potassium concentrations (67.3 +/- 10.8 mmol/l, N = 50) were similar to those found before in whole plaque within 1 min of removal from the mouth and did not appear to be site-dependent. Possible mechanisms for the maintenance of potassium in plaque fluid at higher than salivary levels are described.