Salivary clearance of sugar and its effects on pH changes by Streptococcus mitior in an artificial mouth

We recently developed a computer model of oral sugar clearance (Dawes, 1983), and an artificial mouth has now been constructed which will allow variation in the salivary parameters identified in the model and the study of their effects on bacterial acid production. Using a thin layer of S. mitior, strain 572, over a miniature Sb electrode to measure bacterial pH changes during sugar clearance from the "mouth", we found that three consecutive sets of "Stephan curves" could be obtained with the same bacteria during one day. In each of several experimental series, one salivary parameter was varied, while other parameters were held constant. The maximum pH decrease and the surface area of the registered Stephan curve (delta pH.min) were used as measures of acid production. The results indicate that the volume of "saliva" in the mouth before and after swallowing, the unstimulated salivary flow rate, and the buffer capacity had significant influences on the extent of the pH changes. Other factors, such as the maximum flow rate, the delay between start of stimulation and maximum flow, the volume of saliva in the mouth at time zero, and the taste threshold for sugar, were of lesser importance, confirming some predictions from the computer model.     

The effect of swallowing frequency on oral sugar clearance and pH changes by Streptococcus mitior in vivo after sucrose ingestion

A theoretical study of oral sugar clearance (Caries Res 17:321-334, 1983) suggested that the unstimulated salivary flow rate (UNSTFR) and the volume of saliva present in the mouth before swallowing (VMAX) can greatly affect the rate of sugar clearance. The object of this study was to determine whether variations in UNSTFR, by water infusion into the mouth, and in VMAX, which can be altered by varying the swallowing frequency, would influence sugar clearance and whether changes in VMAX would affect the extent of the pH fall produced by S. mitior in vivo after sucrose consumption. In three experiments on each of ten adult subjects, UNSTFR was measured initially (mean value = 0.55 ml/min), and a swallowing schedule was calculated so that the volumes swallowed were either 0.3 ml or 1.0 ml. After a 10-second rinse with 20 ml of a 10% sucrose solution, the subjects maintained a swallowing frequency such that the volumes swallowed were either 0.3 ml or 1.0 ml at normal UNSTFR or were 0.3 ml when UNSTFR was increased by infusing water at 0.5 ml/min. In all subjects, clearance of sugar was faster at the higher swallowing frequency and at the higher flow rate, as predicted by the theoretical model. Small acrylic splints were made to fit over the lower incisors of ten subjects and to hold in the floor of the mouth an antimony microelectrode covered by a 0.5-mm layer of S. mitior, which was held in place by a dialysis membrane.(ABSTRACT TRUNCATED AT 250 WORDS)     

In-vitro acid production by the oral bacterium Streptococcus mutans 10449 in various concentrations of glucose, fructose and sucrose

At intermediate and high concentrations, the results with the sugars were similar, with lactic acid as the main end product. Over 4 h, the pH fell from approx. 7 to 4. At low monosaccharide concentrations (2 mM glucose, 2 and 5 mM fructose), after an initial pH drop and period of lactic-acid production, evidence of pH rise and lactic-acid consumption were noted. This did not happen when sucrose was added to the bacteria. There was evidence of a heterolactic-acid fermentation pattern at low-sugar concentrations, lactic, acetic and formic acids being produced in similar amounts. The results suggest that, when low-sugar concentrations are present in dental plaque, Strep. mutans is capable of consuming previously-formed lactic acid.     

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.     

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

Chewing-gum stimulation of salivary flow (at the time of the pH minimum following exposure of plaque to carbohydrate) has been shown to cause a rapid increase in plaque pH. The objective of this study was to determine whether the rise in plaque pH is primarily due to the increased buffering capacity of stimulated saliva, or to the fact that an increased flow rate increases the concentration gradient for acid to diffuse from the plaque into the overlying salivary film, which will be moving at a higher velocity. This was investigated with an in vitro technique in which artificial plaque (0.5 or 1.5 mm deep) containing S. oralis cells was exposed to 10% sucrose for one min. The pH values at the proximal and distal undersurfaces of the plaque were then monitored during the passage of a 0.1-mm-thick film of a sucrose-free artificial saliva over the surface, at a range of film velocities (0.8-8 mm/min) that have been estimated to occur in vivo. When a minimum plaque pH had been achieved, the salivary film velocity was either (a) kept the same, with or without 15 mmol/L HCO3 (the concentration measured in chewing-gum-stimulated saliva), (b) increased to 86.2 mm/min, or (c) increased to 86.2 mm/min with 15 mmol/L HCO3 added to the artificial saliva. The findings suggest that after sucrose ingestion, the rapid rise from minimum plaque pH values, which can occur with gum-chewing stimulation of salivary flow, is due to the combined effects of the increase in salivary film velocity, and of a greater availability of bicarbonate.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 l 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.     

The demineralizing effects of EDTA at different concentrations and pH

The purpose of this study was to compare the effects of concentration and pH variations of EDTA on dentin demineralization. Twenty extracted, human permanent teeth with single canals were used in this study. Demineralizing effects of EDTA solutions at 10% and 17% concentrations at pH 7.5 and 9.0 were determined by measuring the amount of liberated phosphorus 1, 3, 5,10, and 15 min after exposure. The results showed that the amount of phosphorus liberated from dentin was greater with increased EDTA concentration and increased time of exposure, and it was more effective at neutral pH than pH 9.0. The pH of the EDTA solutions did not display any significant alterations during the demineralization process.     

Growth and viability of Streptococcus mutans in sucrose with different concentrations of Stevia rebaudiana Bertoni

Clinical Oral Investigations - To evaluate total absorbance, planktonic growth, biofilm formation, viability, metabolic activity, and pH of Streptococcus mutans UA159 cultures when different...     

Efficacy of chlorhexidine solution with fluoride varnishing in preventing enamel softening by Streptococcus mutans in an artificial mouth

For study of the enamel-protective effect of chlorhexidine-fluoride applications, the labial surfaces of pieces of bovine incisors were treated with 0.2% chlorhexidine gluconate solution, with Duraphat fluoride varnish, or with both of the above agents, while one group was treated with distilled water and one was left as an untreated control. Furthermore, a placebo varnish was used in the chlorhexidine- and distilled-water-treated groups; all the varnishes were removed after 24 h. The enamel slabs were mounted pairwise in an artificial mouth to form approximal contacts. The teeth were continuously rinsed with a common pool of artificial saliva to which was added 3% sucrose, and which was infected on the first day with Streptococcus mutans , "Ingbritt". The saliva was renewed daily and the incubation at 37°C lasted for 10 days. The appreciable softening found in the distilled-water- and placebo-varnish-treated group tended to be prevented by the chlorhexidine and even more by the fluoride treatment, while the chlorhexidine-fluoride treatment prevented enamel softening completely. The saliva, infected only on the first day, and renewed daily, tended to become more acidified toward the end of the experimental period, obviously because the fermenting organisms had infected the surfaces of the model and formed plaque-like coatings on the enamel.     

Enamel demineralization and the length of intra-oral exposure to different concentrations of glucose or sucrose

Six subjects wore intra-oral devices carrying eight bovine enamel blocks which were covered with a layer of S. mutans. They rinsed their mouths for five sec, one min, or multiples of one min with a 5 or 10% glucose (G) solution. Demineralization was measured after 45 min by determining the change in iodide permeability (delta Ip) of the enamel. In addition, saliva samples, taken at intervals during the test, were analyzed for G, and the time of clearance (tc) was calculated. Demineralization scores (delta Ip) were consistently greater from the 10% than from the 5% G solution. Both solutions produced an increase in delta Ip with an increase in the rinsing time (tr). The G remaining in saliva after the rinse did not significantly affect delta Ip. The delta Ip scores showed good correlation with the final pH of the S. mutants cell mass, r = -0.77. For each rinse solution, the scores also showed good correlations with tr (r = 0.87 and 0.79) and much weaker correlations with tr + tc (r = 0.44 and 0.53). Continuous in vitro exposure to 1, 5, or 10% solutions of sucrose (S) in saliva for 30 min or more caused a linear increase in delta Ip with time with no concentration effects. A linear increase was also observed in vivo when a one-minute mouth-rinse with 10% solution of S was administered every 30 min. The findings indicate that significant demineralization may occur while carbohydrate foods are consumed, and that brushing the teeth or rinsing the mouth after meals may not be as effective against caries as is generally believed.     

pH changes of mixed biofilms of Streptococcus mutans and Candida albicans after exposure to sucrose solutions in vitro

ObjectiveThis study aimed to standardize an in vitro experimental model able to reproduce the pH changes that occur in dental biofilm under in vivo conditions, using a mixed biofilm of Streptococcus mutans and Candida albicans.DesignBiofilms were developed for 96 h, and exposed to three different concentrations of sucrose (10, 20 or 30%) during 1, 3 or 5 min. The pH was measured before exposure to sucrose, immediately after its removal from the biofilms, and at 1, 3, 5 and 10 min after removal.ResultsSucrose solutions at 10 and 20% required 1 min to significantly reduce the biofilm pH, while for 30% sucrose a significant reduction was already seen immediately after its removal, even for the shortest exposure time. For an exposure of 3 min to 20% sucrose, the biofilm pH attained the critical value for hydroxyapatite dissolution when measured 1 min after sucrose removal, followed by a recovery phase.ConclusionsA mixed biofilm of S. mutans and C. albicans exposed to a 20% sucrose solution for 3 min exhibited a pattern of pH change similar to that observed in vivo, despite at a higher speed when compared to in vivo conditions.     

The role of H2O2 and the lactoperoxidase-SCN(-)-H2O2 system on the interaction between two bacteria originating from human dental plaque, Streptococcus rattus (mutans) BHT and Streptococcus mitior LPA-1, grown on human teeth in an artificial mouth

Teeth were inoculated with either the organisms separately or with a freshly-prepared mixture of both. The apparatus was swept with 5 per cent (v/v) CO2 in either air or N2, and incubated for 90 h. A nutrient supplement containing 1 per cent (w/v) glucose was supplied for 1 h in every 6 h. Both organisms achieved similar numbers when grown aerobically in pure culture, yet in mixed culture there was pronounced inhibition of BHT (p less than 0.001). When the synthetic saliva was supplemented with catalase the strain BHT count in mixed culture was much higher (p less than 0.001). It was concluded, therefore, that the strain LPA-1 produced inhibitory levels of hydrogen peroxide (H2O2) on the tooth surface under aerobic conditions. This was supported by finding that a lower viable count of LPA-1 in pure culture was attained when lactoperoxidase (LPO) was included in the saliva (p less than 0.005), as all components of the LPO-SCN-H2O2 system were presumably present. With the N2-CO2 mixture, conditions were not strictly anaerobic and both catalase and LPO increased all viable counts. Under these conditions, therefore, when H2O2 was limiting, LPO protected bacteria against its bactericidal effect.     

The diluting effect of saliva on the sucrose concentration in different parts of the human mouth after a mouth-rinse with sucrose

Saliva at four buccal sites [between the upper (UC) and lower (LC) central incisors, and between the upper (UM) and lower (LM) second premolar and first molar], and also whole saliva, was collected from 10 subjects at 0.5, 2.5, 5.5 and 10.5 min after a rinse with 10 ml of 0.3 mol/l sucrose solution. After 0.5 min, unstimulated salivary flow rate was inversely correlated with sucrose concentration in whole saliva (p less than 0.05). Sucrose concentration decreased faster at LC than at other sites. Sucrose dilution at UC and LC was inversely correlated (p less than 0.05) with salivary flow rate at times after 0.5 min. At 10.5 min, the sucrose concentration at all sites was significantly correlated (p less than 0.05) with the salivary flow rate.     

Turku sugar studies XI. Effects of sucrose, fructose and xylitol diets on glucose, lipid and urate metabolism.

The effect of chronic consumption of sucrose, xylitol and fructose on lipid, carbohydrate and urate metabolism was studied in conjunction with a clinical trial on the effects of these sugars on dental caries. No consistent differences were found in serum triglycerides, glucose, insulin, urate, lactate, or pyruvate concentrations or in the urinary excretion of urate between the groups using sucrose, fructose or xylitol as the dietary sweetener. Serum cholesterol tended to be lower in the fructose than in the xylitol group, but the difference disappeared when subjects with initial high serum cholesterol in the baseline examination were excluded from the calculations. The results suggest that the effects of peroral fructose and xylitol on the metabolic parameters studied in this investigation do not differ from that of sucrose.     

Monobacterial and mixed bacterial plaques of Streptococcus mutans and Veillonella alcalescens in an artificial mouth: development, metabolism, and effect on human dental enamel

To gain greater understanding of the role of Streptococcus mutans and Veillonella in the caries process, studies of both aerobically and anaerobically grown plaques of S. mutans C67-1 and V. alcalescens V-1 on human enamel slabs were carried out in an artificial mouth. Plaque development, acid production, and demineralization were measured. Early plaque development of monobacterial and mixed bacterial plaques started from randomly adhering cells on day 1 to confluent multilayered microcolonies on day 4. Differences were observed in viable cell counts, total cell mass, and in acid production. In most cases CFU, DNA and acid production were higher in the mixed bacterial plaque, especially in the anaerobic mixed plaque. Lactic acid was the predominant acid in all cases following the supply of sucrose to the plaque. No decisive role could be found for acetic, formic, and propionic acid. No inhibition of demineralization was observed in the enamel slabs inoculated with both aerobic and anaerobic mixed plaques. Demineralization ranged from the more classical picture of lesion development in the aerobic monobacterial plaque-treated samples to an aggressive etching of the enamel surface in the anaerobically mixed treated slabs.