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

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)

Biochemical change exhibited by oral streptococci resulting from laboratory subculturing

The intent of this study was to assess the effects of continued laboratory subculturing on selected biochemical properties of oral streptococci freshly isolated from dental plaque. Six fresh isolates (3 Streptococcus mutans and 3 non-mutans) and 2 laboratory strains were subcultured daily for a total of 225 transfers, and cells were harvested every 75 transfers from duplicate batch cultures grown with glucose at a constant pH. Eleven biochemical properties were assayed with cells, membranes and cell-free extracts and the results subjected to statistical analysis for differences between the duplicate cultures and the various subcultures. In addition, the activity of 19 hydrolytic enzymes was assayed with the semiquantitative apiZYM system (Analytab products). The activity of zero-time samples varied by as much as 241-fold for a single property with particularly low activity for EIIglc of the phosphoenolpyruvate phosphotransferase system and cell-associated extracellular polysaccharide synthesis. The 3 S. mutans fresh isolates had higher activity in 8 of the 11 assays compared with the 3 non-mutans strains, with extracellular polysaccharide synthesis the most significant trait. Statistical analysis of the 2816 assays of the 11 traits for the 8 test strains at the 4 selected time intervals revealed considerable change in the activity of the test parameters. The most notable changes in the S. mutans strains over the 225 subcultures were significant increases in glycolytic activity and decreases in hydrophobicity and extracellular polysaccharide synthesis activity. Of the measured properties, lactate dehydrogenase and cell-associated extracellular polysaccharide synthesis activity were the most stable and H+/ATPase activity was the most variable.(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.

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.

Measurement of tooth hypersensitivity and oral factors involved in its development

The various methods of measurement of dentinal hypersensitivity are based upon the types of stimuli used to elicit a pain response in teeth, which include thermal, tactile, evaporative, electrical and osmotic. Pulpal inflammation in its early stages reduce the threshold of pain response to these stimuli but electrical stimulation may make it possible to assess the possible contribution of such inflammation to sensitivity determinations. Although the magnitude of each stimulus is quantifiable, patient response is subjective, which necessarily makes measurements of dentinal sensitivity semisubjective. Various methods of testing dentinal sensitivity are discussed, along with their advantages and disadvantages. The teeth most suited for measurement in clinical studies are the canines and premolars. This is because approx. 80% of the sensitivity lesions are associated with these teeth, which have similar thicknesses of root dentine. Data from several studies involving the same subjects indicate that individual measurements readily return to baseline and that the commonly seen placebo effect is probably due to some as yet unidentified factor in desensitizing formulations. Possible roles of salivary and plaque environmental factors in the development of dentinal sensitivity are discussed, as well as methods for their measurement.

Plaque pH and oral retention after consumption of starchy snack products at normal and low salivary secretion rate

The effect of plain potato chips, sugar-free cheese doodles, and sweetened crackers on plaque pH and oral retention was tested in 10 volunteers and compared with 5% starch and 5% sucrose, during both normal and low salivary secretion rate. The first 30 min 5% sucrose gave the most and 5% starch the least attenuated pH drop, but the three snack products reached or even passed the level seen by sucrose during the second 30-min phase. All products resulted in greater pH falls and remained at a low level for a longer period during low secretion rate. There were no differences in concentration of carbohydrates in saliva after consumption of potato chips, cheese doodles, and a cracker. However, low secretion rate increased the oral retention for all three products. To conclude, this study showed that low salivary secretion rate accentuated the pH decrease in dental plaque and prolonged the oral retention of carbohydrates.

Urease activity in Streptococcus salivarius at low pH

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

Glucose clearance from different surfaces of human central incisors and first molars

The study examined the glucose clearance (retention) in saliva at different surfaces of these teeth in 23 subjects. The mouth was thoroughly rinsed for 15 s with 20 ml of a 0.5 M glucose solution. The concentrations of glucose absorbed by small pieces of paper, placed on the mesial, distal, labial (buccal), lingual and occlusal surfaces 3 min after rinsing, were measured using an immobilized enzyme system and an electrochemical sensor. On the maxillary and mandibular central incisors, the glucose concentrations on the labial surfaces were significantly higher than on all other surfaces and lowest on the lingual surfaces. In the mandibular molars, glucose concentrations were significantly higher on the buccal surfaces than on the lingual surfaces. Clear site-specific differences in glucose clearance were thus observed at the different tooth surfaces. It is considered that the differences in the glucose retention rate might be indicative of factors important for the site specificity of dental caries.

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)

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

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

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

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

Comparison of the effects of galactose and glucose on the pH responses of human dental plaque, salivary sediment and pure cultures of oral bacteria

Comparisons made in dental plaque in vivo demonstrated that galactose produces a significantly smaller decrease in pH than does glucose. In vitro studies with plaque, salivary sediment and pure cultures of oral bacteria done in the absence of intraoral factors such as flowing saliva confirmed this lesser acidogenicity of galactose. Pure culture showed that most of the bacteria tested produce a moderate to large decrease with glucose but only a few do so with galactose; most produced a moderate to little or no pH response with this sugar. This suggested that the smaller decreases in pH seen in plaque in vivo with galactose were largely due to bacterial differences, basically that resident micro-organisms individually have less galactolytic than glucolytic capability. Variance in capability was attributed to differences in membrane transport processes and metabolic pathways normally available to bacteria for galactose and glucose catabolism. In the in vitro experiments, because plaque and sediment can produce base as readily as they can produce acid, the nitrogenous substrates identified earlier as major stimulants of base formation, urea and arginine, were concurrently examined for their attenuating effects on the galactose and glucose pH responses. These showed, consistent with its lesser acidogenicity, that galactose could be countered more readily in its ability to reduce the pH by either of these two base-forming substrates than could glucose. The effects were different with urea and with arginine, urea attenuation occurred sooner and arginine attenuation later in both plaque and sediment. The corresponding acid-base pH profiles for pure cultures were different.(ABSTRACT TRUNCATED AT 250 WORDS)

Salivary and metabolic factors involved in oral malodor formation

Saliva plays a central role in the formation of oral malodor. Such formation has as its basis bacterial putrefaction, the degradation of proteins, and the resulting amino acids by microorganisms. Saliva provides substrates that are readily oxidized and in the process facilitates oxygen depletion. This favors the reduced conditions conducive to production of odoriferous volatiles. At the same time, saliva is a major source of oxygen for the oral bacteria which generally is inhibitory of their formation. The pH is also critical to malodor development; acidity inhibits, whereas neutrality and alkalinity favor malodor production. Since the pH on oral mucosal surfaces where odor formation occurs is largely determined by the fermentative and putrefactive activities of the adhering bacteria, these acid-base processes are necessarily of major regulatory importance. Because oral malodor and periodontitis both involve excessive oral putrefaction, a better understanding of putrefaction could lead to more substantive methods of oral malodor treatment than exists today, as well as identifying new approaches to amelioration of the bacterial attack on the soft tissues leading to the destruction associated with periodontal disease.

The effect of sucrose on plaque pH in the primary and permanent dentition of caries-inactive and -active Kenyan children

The hypothesis that the Stephan pH responses of dental plaque would be different in caries-active and -inactive individuals was tested in 20 seven-year-old and 19 14-year-old Kenyan children. In each age group, half the children had greater than or equal to 2 dentin cavities; the other half had no such lesions. With a palladium-touch microelectrode, interdental plaque pH was monitored between m1/m2 in each quadrant in the primary dentition and in the four molar/premolar regions in the permanent dentition. pH was also monitored in caries cavities in the occlusal surfaces of lower first molars and on the tongue. pH was measured before and up to 60 min after the children rinsed with 10 mL of 10% sucrose. Caries status of the individual was unrelated to plaque pH in comparable non-carious sites in both of the age groups. The pH minimum in the maxilla was about 0.5 pH units lower than that in the mandible. Active occlusal caries lesions had a resting pH value of about 5.5, about 1 pH unit lower than that of sound surfaces. The pH dropped to about 4.5 in caries lesions and recovered slowly. In sound occlusal sites, a pH drop to about 6.0 was followed by a relatively rapid return to the resting value. Thus, when the mean values were considered, the classic Stephan curve response was evident. However, when the pH changes at single sites were considered at various time intervals, a substantial, erratic fluctuation was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

A random effects model for some epidemiological features of dental caries

We describe a random effects model for caries lesion development and progression based on considering the effects of the pH fluctuations over time in microbial dental plaque as a Wiener process with a single absorptive barrier. The model predicts that the period of greatest risk to developing caries occurs shortly after eruption, but thereafter the longer a surface survives without developing a lesion, the less likely will it be that a lesion will subsequently develop. The model is able to anticipate why the effect of water fluoridation on caries prevalence is most pronounced when caries is diagnosed at cavity level. This model offers one way in which the variability which characterizes the complex ecosystem associated with dental caries may be considered a subject of interest for enhancing our understanding of its pathogenesis and epidemiology.

Mutans streptococci and non-mutans streptococci acidogenic at low pH, and in vitro acidogenic potential of dental plaque in two different areas of the human dentition

Samples of human dental plaque were obtained from sound tooth surfaces in the lower anterior and upper posterior areas of each of 11 subjects with various degrees of caries experience. Both types of plaque were compared for: (1) their pH-lowering potential [pH at 10 and 60 min after sugar addition and the pH drop between 0 and 10 min (delta pH)] with an in vitro method involving dispersed plaque suspensions and excess glucose supply; (2) the proportions of mutans streptococci; and (3) the distribution of the predominant non-mutans streptococci according to their final pH in glucose broth. Compared with plaque from the lower anterior area, plaque from the upper posterior area exhibited a significantly higher pH-lowering potential, i.e., a lower pH at 10 and 60 min and a greater delta pH and significantly higher levels of mutans streptococci. The final pH values for the non-mutans streptococci exhibited a wide range from about 4.4 to over 5.0. The proportions of such organisms designated as capable of acidogenesis at low pH (final pH less than 4.6), whether expressed as a percentage of the total non-mutans streptococci or of the total plaque flora, were significantly increased in plaque from the upper posterior area. The proportions of non-mutans streptococci capable of acidogenesis at low pH in plaque from the upper posterior area were also significantly increased, with decreasing pH values at 10 and 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Urea concentration in minor mucous gland secretions and the effect of salivary film velocity on urea metabolism by Streptococcus vestibularis in an artificial plaque

Our purpose was to determine the urea concentration in minor mucous gland (MMG) secretions and the pH at proximal and distal aspects of the lower surface of artificial plaque in vitro during infusion of urea solutions over the surface, at different film velocities. Saliva is present in the mouth as a slowly moving film (ca. 0.1 mm thick) with an estimated velocity in the range of 0.8-8.0 mm/min. At low velocities, due to the accumulation of bacterial products, a progressive increase in their concentration may occur in both the plaque and the overlying salivary film at the distal edge (where the film leaves the plaque). S. vestibularis, an oral micro-organism possessing ureolytic activity, was combined with 1% agarose, to give a urease Vmax similar to that of natural plaque. The artificial plaque was in the chamber (6.0 x 6.0 square and 0.5 or 1.5 mm deep) of a diffusion apparatus, and a urea-containing artificial saliva (3.3 or 13.2 mmol/l) was infused over the surface, as a film 0.1 mm deep, at velocities of 0.8, 8.2 and 86.2 mm/min. At the lower (physiologically normal) urea concentration and the two lower film velocities, most urea appeared to be metabolized at the proximal end of the plaque, which developed a higher pH. At the higher urea concentration, and a film velocity of 8 mm/min, a higher pH was found at the distal end. This was probably due to the combination of greater urea availability and a reduced rate of ammonia loss distally. At a film velocity of 86.2 mm/min, proximal/distal pH gradients did not develop.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of salivary film velocity on pH changes in an artificial plaque containing Streptococcus oralis, after exposure to sucrose

Results from a computer model suggest that following exposure of dental plaque to sucrose, the rate of clearance of acids from plaque into the overlying salivary film will be greatly retarded at low film velocities. This was investigated with an in vitro technique in which artificial plaque containing S. oralis cells was exposed to 10% sucrose for one min. The pH at the proximal (P) and distal (D) undersurfaces of the plaque (0.5 or 1.5 mm thick) was then monitored during the passage of a 0.1-mm-thick film of a sucrose-free solution over the surface. Over the range of salivary film velocities that have been estimated to occur in vivo (0.8-8 mm/min), lower minimum pH values and increased times for the pH to recover toward neutrality occurred at the lower salivary film velocity. Lower pH values were also reached with the 0.5- than with the 1.5-mm-thick plaque. P/D pH gradients, with a lower pH distally, developed at film velocities of 0.8 and 8 mm/min, and the gradients were much more pronounced at the lower velocity. No P/D pH gradients developed when the film velocity was 86.2 mm/min. Incorporation of dead S. oralis cells into the plaque at percentages up to 57% reduced the extent of the pH fall and prolonged the recovery of the pH toward neutrality. The results support the prediction that, other factors being equal, plaque located in regions of the mouth with low salivary film velocity will achieve pH values lower than those of plaque of identical dimensions and microbial composition located in areas where salivary film velocity is high.

Comparative study on mineralization-related intraoral parameters in periodontitis-affected and periodontitis-free adults

The parameters related to an intraoral mineralization tendency in periodontitis-affected (P+) and periodontitis-free (P-) study subjects (16 adults, 46-74 yr, matched for sex and age) were compared. For this purpose the calcium (Ca) and phosphate (P) concentration of both plaque and saliva, resting pH and the acidogenic response of interdental plaque, plaque wet weight, salivary flow rate, buffering capacity and sucrase activity, interdental plaque, plaque S. mutans levels as well as salivary lactobacilli and yeast levels were estimated. Plaque Ca (micrograms/mg protein, P less than 0.025) and P (micrograms/mg protein, P less than 0.05), saliva Ca (micrograms/ml, P less than 0.005) and the saliva Ca:P ratio (P less than 0.005) were higher in the P+ than in the P- group. The resting pH values were higher (P less than 0.025) and the acidogenic response of the interdental plaque was lower (P less than 0.025) in the P+ group than in the P- group. The P+ group had lower S. mutans levels in saliva and interdental plaque. No differences were found in the wet weight of plaque and in the flow rate, buffering capacity or sucrase activity of saliva between the groups. The findings of the mineralization-related parameters in the two "extreme" groups of periodontal status suggest a higher intraoral mineralization tendency in periodontitis-affected persons than in periodontitis-free subjects. Ca and P accumulation of supragingival plaque seem to be connected with low acidogenicity of plaque and high salivary Ca concentration.

Incidence of selected ureolytic bacteria in human dental plaque from sites with differing salivary access

Saliva is the main source of urea in the human mouth and may be responsible for the predilection of ureolytic bacteria for certain tooth sites. As a test of this hypothesis, the ureolytic bacteria, Haemophilus parainfluenzae, Actinomyces naeslundii, Actinomyces viscosus and coagulase-negative oral staphylococci, were enumerated in supragingival plaque from various sites in each of 10 subjects. The sites sampled included the maxillary and mandibular incisors (chosen because the lower incisors are more exposed to the submandibular-sublingual secretion than the upper) and the maxillary and mandibular molars (the upper molars being closer to the source of parotid saliva). After dispersion of the plaque samples in saline, subsamples of each suspension were plated on appropriate selective media and other subsamples were taken for nitrogen analysis to measure the amount of plaque sampled. H. parainfluenzae that used urea was present in the largest numbers, A. viscosus was next and A. naeslundii and coagulase-negative staphylococci were least. The staphylococci and H. parainfluenzae were more numerous from mandibular than from maxillary incisors and from maxillary than mandibular molars, a pattern which suggests that salivary access favours their selection. The numbers of A. viscosus and A. naeslundii were not related to salivary access: A. viscosus was most numerous from the maxillary incisors, possibly because this site is normally the most acidic of the four studied and A. viscosus is strongly acidogenic and aciduric; the incidence of A. naeslundii had no relationship with site.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-base pH curves in vitro with mixtures of pure cultures of human oral microorganisms

Pure cultures of microorganisms commonly found in supragingival plaque were incubated alone and in combinations to determine the bacterial contribution to the pH-fall-pH-rise that is the central characteristic of the Stephan-curve pH change seen in plaque in vivo after brief exposure to a sugar solution. To avoid the complicating conditions of saliva flow and plaque diffusion, experiments were done with bacterial suspensions in incubations in vitro. In an initial experimental series where each microorganism was incubated only with glucose, all but a few produced the initial pH fall. Some also showed a subsequent small, sharp rise in the pH which then quickly levelled off; this was due to metabolism of endogenous substrate accumulated by most microorganisms during their growth in culture. When arginolytic and non-arginolytic bacteria were each then incubated with both glucose and arginine present (the glucose substrate to stimulate a pH fall and the arginine to stimulate a pH rise), the non-arginolytic gave a progressively more acidic pH response with progressive increase in the cell concentration, whereas the arginolytic bacteria produced a much smaller and variable pH decrease with similar cell concentration increase. Mixing pure cultures of either arginolytic or non-arginolytic bacteria gave acid-base pH responses similar to those of their respective pure cultures, whereas mixing arginolytic with non-arginolytic bacteria resulted in an approximate averaging of their different curves. The organisms present in highest proportion in a mixture had the greatest effects. The outcome of mixing the most numerous streptococcal and actinomyces species found normally in supragingival plaque indicated that the well-established difference in the acidity level of the Stephan pH response of caries-active and caries-inactive plaques could be due to differences in the proportions of their arginolytic and non-arginolytic members.

Arginolytic and ureolytic activities of pure cultures of human oral bacteria and their effects on the pH response of salivary sediment and dental plaque in vitro

Thirty-nine different microorganisms commonly found in supragingival plaque and salivary sediment were screened for their ability to raise the pH by producing base from arginine, lysylarginine and urea. Only Actinomyces naeslundii and Staphylococcus epidermidis showed significant pH-rise activity with all three compounds. Eleven bacteria demonstrated such activity with arginine and lysylarginine but not with urea. Only one, Actinomyces viscosus, produced a pH-rise with urea but not with the two arginine compounds. The remaining 26 bacteria showed little or no base-forming activity with any of the three test substrates. The ability of the different oral bacteria to produce base (especially from urea) was a less universal function than their ability to produce acid from fermentable carbohydrate. Substituting pure cultures of arginolytic or non-arginolytic bacteria for portions of the mixed bacterial populations of plaque or sediment in test incubations containing glucose and arginine altered their ability to produce pH-fall-pH-rise responses shaped like those of the Stephen curve in vivo. In general, addition of arginolytic bacteria made these in vitro pH responses less acidic, whereas addition of non-arginolytic bacteria made the responses more acidic. Because of the relatively high arginolytic activity of the plaque harvested in this study, the effect of adding non-arginolytic bacteria was more readily seen than the converse. Similar changes in levels of ureolytic microorganisms and incubation with glucose and urea had little effect on sediment or plaque being able to produce a pH-fall-pH-rise type of response. When increasing proportions of the mixed bacteria in salivary sediment were replaced with the highly cariogenic Lactobacillus casei or Streptococcus mutans, the pH minimum became slightly more acidic and then slightly more alkaline, whereas the pH-rise became progressively and significantly less. Thus arginolytic bacteria have a different and greater effect on shaping the pH response of plaque or sediment than ureolytic bacteria. A large change in the proportions of arginolytic or non-arginolytic microorganisms may be needed to make a plaque microflora potentially non-cariogenic or cariogenic, respectively.

Analysis of the buffering systems in dental plaque

A semi-micro method was used for investigation of the buffering properties of whole plaque, plaque fluid, and washed plaque bacteria. Artifacts associated with titration of samples containing live bacteria were noted and their effects estimated. All three sample types showed minimal buffering in the region of neutrality, with much stronger buffering in the regions pH 4-5.5 and pH 8-9. For the range pH 4-7, almost 90% of the total buffer capacity of plaque appeared to be accounted for by macromolecules of bacterial cell walls and plaque matrix. Extracellular buffers in plaque fluid removable by centrifugation contributed up to 11%. These buffers (probably soluble proteins, peptides, organic acids, and phosphate) are, potentially at least, capable of exchange with saliva. In vitro, bicarbonate (dissolved in the extracellular fluid) contributed only 2-5% of total buffering; there was no evidence of formation of carbamino compounds. However, in vivo, salivary bicarbonate may be important as a continually replenished source of additional buffering.

pH changes during simultaneous metabolism of urea and carbohydrate by human salivary bacteria in vitro

The effect of the wide natural variation in oral ureolysis rates on the pH changes resulting from simultaneous metabolism of 25 mM urea and 2.8 mM glucose in salivary-sediment bacteria were investigated. The pH curves were complex, and included distinctive plateaux indicative of balanced acid and base production. These neutralization plateaux occurred at different pHs, which were a function (r2 = 0.98) of the ureolytic rate as measured by the log of the initial pH-change rate in the urea-only reaction. In the simplest case, the pH curve was characterized by a rise or fall to the neutralization plateau, a variable period of time at the plateau (up to 1 h), then a pH rise. The pattern of pH changes induced by glucose alone varied between different sediments: in some cases, the pH decreased smoothly to an end-point; in others, the curve was more complex, and these features became superimposed on the urea/glucose curve. The rate of ureolytic ammonia release was almost constant and unaffected by simultaneous carbohydrate metabolism. Concomitant metabolism of endogenous carbohydrate present in sediments prepared 1-2 h following a meal was of sufficient magnitude to affect ureolytic pH curves. If the ureolytic activity was high, this effect was negligible; if it was low, metabolism of the endogenous carbohydrates could completely suppress the ureolytic pH rise. Soluble salivary components had little effect on ureolysis but pH changes were modified by buffering, and the presence of urea, ammonia, N-catabolic and acidogenic substrates in the saliva.

Salivary glucose clearance, dry mouth and pH changes in dental plaque in man

The aim was to study the effect of different salivary secretion rates on glucose clearance in saliva and on pH changes in dental plaque in man. Eighteen dental students, 21-33 yr old, participated. Dry mouth was induced by injecting methylscopolamine-nitrate submucosally in the labial sulcus. When dry mouth was established, two variables were measured at 1 h intervals, while the salivary flow was recovering: (1) secretion rate of resting and paraffin wax-stimulated whole saliva, and (2) glucose clearance in saliva after ingestion of a glucose tablet. pH changes in dental plaque were studied in 9 of the 18 subjects after a mouth rinse with 10% glucose at two separate occasions, once before and once after an injection of methylscopolamine-nitrate. Higher glucose concentration levels in saliva were found at low than at normal salivary secretion rate. After logarithmic transformation of the salivary glucose concentration values, a biphasic elimination pattern could be seen, with a steeper initial phase followed by a slower one. A critical value for the secretion rate with respect to the salivary glucose clearance time was found to be 0.14 ml/min for resting and 0.62 ml/min for stimulated whole saliva (mean values). The pH changes in dental plaque after the mouth rinse with glucose at extremely low secretion rate were significantly more pronounced than at normal flow rate. Thus, salivary secretion rate affects both the glucose clearance in saliva and the pH changes in dental plaque in man.

Site-specific differences in human dental plaque pH after sucrose rinsing

The object was to find out whether site-specific variations of pH might correlate with those of oral clearance as indicated by past studies using fluoride, sucrose and glucose as markers. Eleven subjects with 24 h growth of dental plaque rinsed the mouth with a 10% solution of sucrose. The pH of plaque, harvested from the labial or buccal cervical and approximal regions of certain teeth or groups of teeth, was then measured. The results confirmed previous reports that plaque pH varies from site to site in the mouth; the pattern observed was similar in each of the subjects. In the anterior part of the mouth, concentrations of hydrogen ion were invariably higher in plaque from the upper than from the lower surfaces of the teeth. The reverse pattern was found in the posterior part. This site-specific pattern was similar to that of oral clearance, as indicated by comparison with known values for glucose concentrations, a finding consistent with the view that site-specific pattern of plaque pH may reflect or at least be influenced by such differential clearance patterns.

Malnutrition and the role of nutritional support for radiation therapy patients

The nutritional status of a tumor patient can be negatively influenced by the local and systemic effects of the malignant tumor (tumor cachexia, anorexia, difficult oral food intake), by the effects of the various antitumoral therapy modalities (surgery, radiotherapy, chemotherapy), and by the complications associated with such modalities (anorexia, nausea, vomiting, mucositis, xerostomia, alterations of the smell and taste sensations, odynophagia, dysphagia, maldigestion, malabsorption, diarrhea, steatorrhea, conditioned aversions, radiogenic late effects), as well as by the psychological reactions of the patient to the real or feared existence of his tumor. The radiation-induced nutritional disorders depend on the tumor localization, the region irradiated, the dose and length of radiotherapy, the fractionation, the volume irradiated, and the combination with other therapeutic modalities ("combined modality therapy"). The acute radiation-induced reactions are usually of limited duration and for this reason tend to interfere with the nutritional status to a lesser extent than the permanent chronic consequences of irradiation. Weight loss and malnutrition tend to develop particularly in patients in whom segments of the gastrointestinal tract are subjected to irradiation. The incidence and severity of deficient nutrition depend not only on the region irradiated (head-neck region, thorax, abdomen, pelvis) but also, and most particularly, on the volume of the digestive tract irradiated. Chemotherapy and radiotherapy combined act very strongly on rapidly proliferating cell populations (skin, mucosa, epithelium of the gastrointestinal tract). In this context, actinomycin D and adriamycin act like real sensitizers, whereas the majority of the other drugs are likely to produce only an additive effect. The first named cytostatics give rise to the so-called recall phenomenon, i.e., the reactivation of latent radiation effects in response to the subsequent administration of the drug. Malnutrition impairs organ function and ultimately results in increased morbidity and mortality. For this reason it has proven mandatory and reasonable that the organism of all tumor patients suffering from malnutrition is provided with the missing essential nutrients (especially amino acids for protein synthesis). This tends to clearly improve the Karnofsky performance status, with a positive effect on response rates, toxicity, and survival rates in retrospective studies.(ABSTRACT TRUNCATED AT 400 WORDS)

In-vitro urea-dependent pH-changes by human salivary bacteria and dispersed, artificial-mouth, bacterial plaques

The pH effects of urea metabolism were studied in washed salivary-sediment bacteria from subjects that had up to 10-fold variation in oral ureolytic activity, and in dispersed artificial-mouth plaques. Adequate evaluation required analysis of the [OH-] as well as the pH curve. An initial constant rate of pH-change, lasting until pH 7.8, was derived from the pH curve; this gave the best correlation (r = 0.95) with the ureolysis rate. From the [OH-]-curve, between pH 7.8 and 8.3 (approx.), a constant and maximal rate of change in [OH-] was determined. Although theoretically this was directly related to the rate of ammonia release, it was 10(-2) to 10(-3) times its value and correlated less well (r = 0.83) with ureolysis. Together with the initial and final pH, these two rates largely described urea-induced pH changes. After 12.5-fold dilution of the cells, changes in the pH curve were minor. Although the rate of ureolytic ammonia release was proportional to cell-protein concentration, the reduction in ureolytic activity was compensated by a corresponding reduction in cell pH-buffering. Consequently, in order to relate pH and [OH-] changes to ureolysis, it was necessary to control, or correct for, variations in the cell mass present. Buffering capacity in plaques was greater than in sediments. The 10-fold range in oral ureolytic activity by salivary bacteria gave a 10-20-fold range in base changes.

The vulnerability of unexposed human dental roots to demineralization

Crowns and roots of human molars, the roots from which had not been exposed to the oral environment, were exposed for 0, 3.5, 7, and 14 days to buffer solutions which were undersaturated or supersaturated with respect to hydroxyapatite. Densitometric measurements on contact-microradiograms of transverse sections of the crowns and of the cervical parts of the roots yielded plots of the mineral content as a function of the distance to the outer surface. From these plots, the rate of demineralization was calculated. It was found that the mineral of the roots dissolved even in buffer solutions which were supersaturated with respect to hydroxyapatite. Comparison of the results obtained from the crowns with those from the roots showed that the root hard tissues were more vulnerable to demineralization than was the dental enamel.

A technique for assessment of the cariogenic potential of foods by plaque pH changes on enamel surfaces of rat molars

Plaque pH changes on rat molars subjected to cariogenic challenge were measured with an antimony microelectrode. Measurements were made after feeding one of seven different reference or snack foods. Resting plaque pH was measured after fasting and minimum plaque pH after feeding the various foods. This reproducible technique may be of use in determining the cariogenic potential of foods.

Kinetics and product stoichiometry of ureolysis by human salivary bacteria and artificial mouth plaques

Ureolysis was investigated in salivary bacteria from persons with widely-differing oral ureolytic activities. Rate curves and product stoichiometry were established for urea disappearance, ammonia appearance and conversion of [14C]-urea to 14CO2. Ammonia, released stoichiometrically from urea, was best measured by a direct phenate-hypochlorite reaction. About 80 per cent of the urea-C was liberated as free CO2. Slight deviations from ammonia stoichiometry and most of the CO2 loss occurred in the first 5-10 min of reaction, when the rate of urea disappearance was constant and up to 2-fold higher than subsequently. This rate-change suggests that flux in the ureolysis pathway may be under feedback control. Ureolysis by salivary-sediment bacteria followed Michaelis-Menten kinetics with a Km of 2.5 mM; rates of end-product formation were independent of urea concentration between 25 and 500 mM. Ureolysis was inhibited 98 per cent by 5 mM acetohydroxamic acid, a urease inhibitor, and could be partly solubilized by sonication to give an enzyme preparation which, without cofactor supplementation, quantitatively hydrolysed urea. Thus urea metabolism by oral bacteria may principally involve urease-catalysed hydrolysis, rather than non-urease pathways.

The impact of antitumor therapy on nutrition

The treatment of the cancer patient by surgery, chemotherapy or radiation therapy can impose significant nutritional disabilities on the host. The nutritional disabilities seen in the tumor-bearing host from antitumor therapy are produced by factors which either limit oral intake or cause malabsorption of nutrients. The host malnutrition caused as a consequence of surgery, chemotherapy or radiation therapy assumes even more importance when one realizes that many cancer patients are already debilitated from their disease.

Nutritional support as an adjunct to radiation therapy

Patients with malignancies which are treated with therapeutic radiation are at risk for nutritional problems, both from their underlying malignancy as well as from their treatment. These effects may be acute or chronic and relate to the site of the tumor and regions irradiated. There is a large experience with nutritional intervention in irradiated patients, including oral feedings and enteral and parenteral nutritional support. The indications for the specific administration of nutritional support during radiotherapy depend on the nutritional status of the patient and the area irradiated, as well as the individual prognosis. Patients who are malnourished at the time of treatment are most likely to profit from nutritional intervention. To date, prospective randomized trials of nutritional support in patients undergoing radiotherapy fail to show a benefit of routine adjuvant nutritional intervention in terms of improved response and tolerance to treatment, improved local control or survival rates, or reduction of complications from therapy.

A comparison of the acid-base metabolisms of pooled human dental plaque and salivary sediment

The acid-base metabolisms of the mixed bacteria in pooled dental plaque and salivary sediment sampled from the same subjects were compared in vitro. Plaque at a suspension concentration of 8.3 per cent (v/v) was found to produce pH responses like those of sediment at 16.7 per cent (v/v) with all substrates and under all incubation conditions tested. The substrates examined included several carbohydrates (glucose, sucrose and starch) and several nitrogenous substrates (urea, arginine and the arginine peptide glycyl-glycyl-lysyl-arginine also called sialin). Also examined were the effects of endogenous substrates and of salivary supernatant and fluoride. A difference in suspension concentration was necessary to achieve similarity in pH response which was attributed to the presence of more non-viable epithelial cells in sediment than in plaque. Under these conditions, salivary sediment showed a slightly greater buffering capacity than plaque, a difference that was not evident if salivary supernatant was present. It was clear from this study that salivary sediment and pooled dental plaque from the same subjects have similar acid-base metabolisms and that the more abundant and readily available sediment could be used to study such metabolism in dental plaque.

The free amino acids in human dental plaque

Analysis of plaques from maxillary and mandibular incisors for free amino acids showed that the dicarboxylic amino acids, glutamic and aspartic, were present in largest amounts, with glutamic acid comprising at least 50 per cent of the total pool. Other amino acids in decreasing order of prominence included proline, ornithine, alanine, lysine, glycine, threonine and serine. This pattern was basically the same in the plaques from the different incisor sites but was clearly different from those of hydrolysates of either the plaque bacteria or the plaque matrix. The results were consistent with the most prominent plaque-free amino acids being associated mainly with the intermediary metabolism of the plaque bacteria. Urea and glucose were then applied to plaque in vivo in the form of rinses to determine if during their metabolism any of the plaque amino acids are affected. Glutamic- and aspartic-acid concentrations both rose after plaque exposure to urea accompanied by a small rise in alanine. After glucose exposure, aspartic- and glutamic-acid concentrations both showed large decreases and alanine showed a small increase. With glucose plus urea, glutamic acid rose and fell, aspartic acid decreased slightly and alanine increased several fold. In each case, the other free amino acids showed little or no change. Thus glutamic and aspartic acids are major components of the intra-cellular pool of amino acids and probably play an important role in alanine synthesis, presumably by facilitating transamination of pyruvate.

Quantitative assessment of urea, glucose and ammonia changes in human dental plaque and saliva following rinsing with urea and glucose

The rates of three processes associated with the rise and fall in plaque pH, that normally occur following a urea rinse, were determined: (i) disappearance of urea from plaque, (ii) disappearance of urea from saliva and (iii) formation and disappearance from plaque of the ammonia produced by the plaque bacteria from the urea. Also examined were two processes associated with the fall and rise in pH following a glucose rinse: the disappearance of glucose from plaque and from saliva. Entry into plaque of either urea or glucose during rinsing was immediate; the subsequent disappearance of both from the plaque was slow and followed first-order kinetics. The ammonia formation and urea-disappearance results suggested that clearance of urea from the plaque occurred mainly by bacterial degradation and not by diffusion out of the plaque. The rate constants for ammonia formation and for its subsequent disappearance from the plaque made it clear why a rapid rise and a slow subsequent fall in the pH occurs after urea rinsing. The rate constants enabled calculation of the ammonia produced as a percentage of the urea utilized. Only 16-26 per cent of the urea was recovered as ammonia and the remainder of the urea-N was stored probably as NH2 moieties of certain amino acids. Such storage may enable the plaque bacteria to maintain the pH at an elevated level for an extended period of time by bacterial production of ammonia from these stored compounds after the urea ceases to be available as a source of substrate.

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

Changes in human dental plaque pH can be used to obtain estimates of the acidogenic potential of ingested foods. The presence of acid in plaque is influenced by a large number of host, microbial, and substrate factors. Several useful methods have been developed for monitoring changes in plaque pH. Plaque sampling involves repeated removal of small samples of plaque from a number of teeth at intervals after food ingestion, dispersion of the sample, and in vitro measurement of pH. Touch electrode methods utilize glass or antimony microelectrodes, which are placed onto plaque in situ where direct readings can be obtained. Telemetry methods involve placement of glass microelectrodes or ion-sensitive field effect transistors within the dentition. Plaque is allowed to accumulate, and pH changes can subsequently be transmitted with radio or wire. Each of the methods has clear advantages and limitations. The methods have been simultaneously compared in human volunteers using solutions of fermentable carbohydrate. Inter-method differences in response were observed depending upon the site of measurement. Data obtained from caries-prone surfaces via telemetry showed lower pH minima and retarded returns to resting pH levels. The technology is available for controlled comparative plaque pH studies, with the method of choice depending upon the goals of the investigation. It is essential that the results be compared to data obtained with other models designed to evaluate the cariogenic potential of foods.

Duration of response and stimulus sequence in the interpretation of plaque pH data

Evaluation of cariogenicity from evidence provided by plaque pH data may be assisted if the duration as well as the extent of the pH fall is examined. Consumption of foods in sequence may alter the pH response to individual items.

Calcium, phosphorus, fluoride, and pH levels of human dental plaque from areas of varying fluoride levels

Plaque calcium, phosphorus, fluoride, and pH in samples obtained from 149 life-long resident children, aged from six to seven and 12 to 13 yr, from one of three naturally fluoridated communities were determined. In general, smaller amounts of phosphorus and fluoride, and larger amounts of calcium and hydrogen ions (lower pH values) are associated with smaller amounts of fluoride in the drinking water supply. Significant differences among the mean pH, fluoride, and Ca/P concentrations both in the six-to-seven- and 12- to 13-year age group were found when comparing the results of the three areas with different levels of fluoride in their drinking water supply.

The effect of saliva on plaque pH in vivo

The effect of saliva on plaque acidogenesis was studied in ten caries-resistant and ten caries-susceptible subjects. Plaque pH was measured in vivo following exposure to a sucrose substrate under varying conditions of salivary access. Our findings demonstrate that when there is no salivary access, plaque pH levels are similar in the CR and CS groups. As the access to saliva is increased, the observed pH minima increased to a greater degree in the CR subjects than was noted in the CS subjects. This indicates that saliva (notably stimulated saliva) plays a major role in modifying plaque pH and quantitatively reflects caries status.

The in vivo effect of glucose solutions containing Cu++ and Zn++ on the acidogenicity of dental plaque

A series of experiments were performed to evaluate the lowest concentration of copper or zinc effective in reducing the acidogenicity of dental plaque in vivo when applied simultaneously with a carbohydrate challenge. The effect of a combination of sub-effective concentrations of these metals was also determined. The results showed a significant reduction in acid production in plaque challenged with glucose solutions containing 0.25 mM CuSO4 or 5.0 mM Zn (C2H3O2).2 as compared to glucose solutions alone. Neither 0.1 mM copper sulphate nor 2.5 mM zinc acetate reduced the acidogenicity of plaque significantly, whereas a combination of these subeffective concentrations was effective. The low metal concentrations causing reduction in acid formation in this study may be explained by the inhibiting substances reaching the bacteria at the same time as the substrate. The synergistic effect of the combination of low concentrations of copper and zinc is consistent with the view that these metals effect dental plaque by the same mechanisms.