Extracellular administration of lactate dehydrogenase and its effects on human plaque pH and acid anion concentrations

The effect of lactate dehydrogenase (LDH) on human plaque pH and acid anion concentrations in vivo was investigated. Rinsing with sucrose solutions supplemented with LDH (1 or 2 U/ml) gave rise to reduced pH fall, decreased cH area and an increase in the mean minimum pH when compared with rinsing with sucrose only (p less than 0.05). Mean acid anion estimations showed that plaque fluid concentrations of lactate, acetate and proprionate significantly decrease (p less than 0.05) following rinsing with sucrose containing LDH at both levels and decreases in succinate when 1 U/ml LDH was present, whereas formate concentrations were only significantly lower when 2 U/ml LDH was added to sucrose rinses. It is thought that the ability of LDH to produce an alteration in the acid end-products of plaque metabolism may provide some protection against dental caries.

Plaque fluid as a bacterial milieu

Studies of the extracellular, free concentrations of substrates, growth factors, inhibitors, and end-products of metabolism to which the intact plaque microflora is exposed in situ can assist in the understanding of factors controlling plaque pathogenicity. Information is becoming increasingly available from analysis of fluid separated by centrifugation of plaques collected at various intervals after an intra-oral pulse of dietary or experimental substrate, or different procedures or treatments having cariostatic potential. Such analytical results give more information than those obtained by analysis of aqueous or other extracts, because they yield values of substrate concentration representing those occurring at the bacterial cell surface. The largest body of information concerns extracellular levels of acid end-products of sugar catabolism in relation to food quality or sequence, and of amino acids and other products of nitrogen metabolism, in relation to studies of the detailed metabolic events of the Stephan curve, and of the demineralizing effect of the plaque environment. Areas where little information is available and which merit further study include plaque clearance of salivary and other components with anti-caries activity (e.g., antibodies, enzymes, fluorides, cations, other antimicrobials, etc.), and substrate concentrations to determine gradients for diffusion into and out of plaque.

Chewing gum and dental health--a review

Recent evidence of the actions of chewing gum on plaque pH needs to be assessed against the background of other evidence, including clinical data. 'Sugar-free' gums are non-cariogenic and potentially beneficial in reversing early caries, while the potential cariogenicity of sucrose-sweetened gums can be modified by additives or selected patterns of use.

Effects of lactate dehydrogenase on fissure caries in rats

The effect of supplementing the diet or drinking water with lactate dehydrogenase (LDH) on the formation of caries lesions in rats was investigated. Addition of LDH [20 and 5 mg/kg in the high-sucrose (65%) diet, 2 and 1 U/ml in the drinking water (LDH-specific activity 735 U/mg solid)] resulted in significant reductions (p less than 0.01) in the number and severity of caries lesions when the enzyme was administered to rats for 4 or 7 days, although no significant differences were found after 14 or 21 days. No differences were observed between effects of addition to water or diet. Fissure caries failed to develop when rats were fed a low sucrose diet (5%) containing LDH (20 mg/kg diet), whereas 50% of the animals in the control group developed lesions. The findings indicate that LDH may play an important role in delaying the onset of caries lesion formation in rats, and that the protection observed may be inversely related to the intensity of the cariogenic challenge.

Remineralization of artificial caries-like lesions in human enamel in situ by chewing sorbitol gum

The objective of the study was to determine quantitatively the effect on the potential for in situ remineralization of artificial caries-like lesions in human enamel when sugar-free gum containing mainly sorbitol as sweetener was chewed after meals and snacks. Artificial white-spot lesions were created in extracted human premolars and divided into three parts. One part was used as reference and the other two worn consecutively for two 21-day periods by 10 volunteers in a cast silver band cemented on lower molar teeth and covered with gauze to promote plaque formation. During the experimental periods, the subjects used fluoridated toothpaste twice daily, and consumed three meals (breakfast, lunch, and dinner) and two snacks (selected from chocolate bar, raisins, chocolate wafer, and iced cupcake). Sorbitol gum was chewed for 20 min immediately after each meal or snack during one of the experimental periods. The three parts of the enamel lesions were then sectioned (congruent to 80 microns) and examined together by means of quantitative microradiography and by polarized light microscopy. All estimates of mineral content indicated that significant remineralization occurred and was approximately doubled with gum-chewing. It is suggested that sorbitol gum stimulates salivation, which is responsible for the significantly enhanced remineralization, thus contributing to a therapeutic, caries-preventive effect. Because the gum was chewed immediately after meals and snacks, inhibition of demineralization may also have occurred.

The effect of daily gum-chewing on salivary flow rates in man

Following reports of increased salivary gland size and increased function, induced by increased mastication in animals, the effects of long-term, frequent gum-chewing on resting and stimulated flow rates were studied in human volunteers in separate experiments in Newcastle upon Tyne and in Toronto. In both experiments, unstimulated and stimulated saliva flow rates were measured in student volunteers at intervals of one or two weeks over a baseline period. Approximately half of the subjects were then given sugarless gum to be chewed (four pieces per day) over the experimental period; controls refrained from vigorous mastication. During (and, in Newcastle, after) the experimental period, salivary flow rates were measured at intervals, as before. In Newcastle unstimulated, but not stimulated, flow rates increased in the gum-chewing group and were still elevated (compared with controls) eight weeks following the experiment. In Toronto, the mean results showed no effect of gum-chewing, but the seven gum-chewers among the 11 subjects with low baseline flow rates (less than 0.3 mL/min) showed a 43% rise in unstimulated flow rate (p approximately 0.05). The results suggest that increased mastication, in the form of gum-chewing, can increase unstimulated flow rates, especially in those with low salivary function. In addition to short-term beneficial effects of sugarless gum, these long-term effects indicate the possibility of a beneficial effect in caries prevention.

Human dental plaque pH, and the organic acid and free amino acid profiles in plaque fluid, after sucrose rinsing

The relationship between these factors was studied in plaque and plaque fluid samples taken at intervals during the Stephan pH curve following a sucrose mouth rinse. Levels of lactate rose after the rinse, then fell during the pH recovery phase. Levels of acetate, propionate and phosphate fell after rinsing, then rose again. Amino acid concentrations also changed, with many showing a fall followed by a rise; others rising then falling; and some showing a more variable or complex pattern. In resting plaque fluid, only alanine, proline, glutamic acid, glycine and ammonia were present at concentrations above 1 mmol/l. Delta-aminovaleric acid was detected at levels below those that have been found in monkeys. Hydroxyproline and hydroxylysine were consistently detected, levels of arginine were generally low, and those of cystine consistently very low. The results may provide a basis for understanding the complex metabolic interrelations that occur in the course of the Stephan curve and which may reflect or produce the observed pH changes. They suggest that besides the amount of acid produced, the type of acid, buffering power and base production should be considered as determinants of plaque pH.

Effects of Parafilm and cheese chewing on human dental plaque pH and metabolism

The effects of chewing Parafilm and cheese following sucrose rinsing on human dental plaque pH and plaque fluid organic and amino acid concentrations were investigated. Immediate increases in plaque pH were observed following chewing with concomitant decreases in lactate and acetate concentrations and increases in the concentration of formate and many amino acids. Chewing with cheese when compared with Parafilm resulted in significantly higher (p less than 0.05) plaque fluid concentrations of most amino acids, although significant decreases (p less than 0.05) in phosphate, succinate, and acetate concentrations were observed. However, no significant difference in the levels of formate, lactate, and propionate were found between the two chewing treatments.

The relationship between plaque pH, plaque acid anion profiles, and oral carbohydrate retention after ingestion of several 'reference foods' by human subjects

The primary aim of this study was to rank several reference foods (apple drink, caramel, chocolate, cookie, skimmed milk powder, snack cracker, and wheat flake) according to their plaque pH response as monitored in a panel of 12 volunteers by the plaque-sampling method for comparison with data previously reported with other methods used to assess cariogenicity potential. Secondary experiments (using subsets of the panel of subjects) were undertaken in an attempt to elucidate some of the reasons for the observed plaque pH changes. Oral carbohydrate retention was measured at a single time period after food use as total anthrone-positive carbohydrate material, and as specific acidogenic sugars by gas-liquid chromatography after gel-exclusion chromatography. The concentrations of acid anions in the plaque fluid after food consumption were measured by isotachophoresis eight min after food use. According to the plaque pH response, apple-flavored fruit drink and chocolate were the most acidogenic foods and skimmed milk powder the least acidogenic. There were significant correlations (p less than 0.05) between the plaque pH data and lactate-plus-acetate concentrations in plaque fluid, but the correlations between the pH data and any of the carbohydrate retention parameters were not significant.

Effects of dietary sucrose levels on pH fall and acid-anion profile in human dental plaque after a starch mouth-rinse

The effects on the metabolism of starch by plaques formed in human subjects during periods of dietary sucrose limitation or supplementation were studied. High sucrose (HS) plaques showed lower resting pH and pH minima, and higher concentrations of lactate ion after the starch mouth-rinse than low sucrose (LS) plaques. Plaque samples incubated with starch solutions in vitro showed no differences in final pH or acid-anion concentrations between HS and LS diets. Plaque-amylase activity was higher on HS than LS diets. Thus starch was more acidogenic when consumed as part of a diet already rich in sucrose, but it is unclear whether this was a specific or non-specific effect of starch on plaque metabolism.

Prediction of the cariogenicity of various foods

Because of the complex nature of the interactions between dietary constituents and the teeth in the development of dental caries it is inappropriate to try to arrive at an absolute determination of whether or not consumption of a food will always give rise to the formation of cavities. Prediction of a food's cariogenicity can be most usefully regarded as a relative assessment of the food's potential, among other foods, to give rise to caries, with other modifying factors held constant. Cariogenic potential cannot be assessed in human studies for a wide range of foods. However, the most productive experimental approaches have employed animal feeding studies, where eating patterns can be strictly controlled and human biochemical tests on pH responses to food consumption by dental plaque in vivo. Such studies have now produced data on dietary items normally consumed in western countries as snacks, sweets, soft drinks as well as mealtime items. Data on the relative cariogenic potential of foods are of value not only to the dental profession in advising patients on food selection, but also to the food industry in relation to product development and marketing and to government agencies with the responsibility for health education and marketing regulation.

The effect of sweeteners on acid production in plaque

In studies of the pH response of dental plaque in situ to rinses with conventional sugars, glucose and maltose give similar falls in pH, and fructose only slightly smaller effects compared with sucrose. Lactose and galactose are less acidogenic, while the pH response to glucose syrups varies according to their composition. Of the sugar alcohols, sorbitol, mannitol, maltitol and lactitol are all slowly fermented to acid by oral bacterial, and xylitol is virtually non-fermentable. Acid formation in plaque by fermentable sugar alcohols can be too slow to overcome the buffering power of plaque and saliva and plaque pH can rise following exposure to these compounds. Lycasin, a synthetic sweetener containing sorbitol, maltitol and some higher sugar alcohols gives effects similar to its major constituents. Palatinit, L-sorbose and trichlorogalactosucrose are of low acidogenicity, but coupling sugar is more fermentable and can give rise to a substantial pH response, albeit less than sucrose. Non-nutritive intense sweeteners may affect plaque pH by their sialogogue effects.

Effects of cigarette smoking on the rate of plaque formation

In 2 separate studies, plaque was harvested (i) from 15 smokers and 15 non-smokers after a 48-h period without oral hygiene, and (ii) from 15 smokers and 12 non-smokers after a 48 h hygiene-free period following complete plaque removal by toothbrushing. No significant association emerged between wet weight of accumulated plaque and cigarette smoking, in either study. In the second study, the mean plaque calcium concentration was raised in smokers compared with non-smokers, and significantly raised in 7 heavy smokers relative to non-smokers. In both instances, calcium concentration was significantly raised relative to (total) phosphorus concentration, which may indicate that the additional calcium was not in mineral deposits. These results may reflect an association between calcium concentration of plaque and tobacco consumption.

Nosocomial infection with hepatitis A

Nosocomial spread of hepatitis A is very uncommon but may occur under unusual circumstances, as shown by the incident described here and by the few other published reports. In this incident it is concluded that the patient, who was the index case, was excreting hepatitis A virus in the faeces 16 days before jaundice developed and 17 days before alanine aminotransferase (ALT) values reached a peak.

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.

Protein components in saliva and plaque fluid from irradiated primates

Irradiation of the major salivary glands of monkeys (Macaca mulatta) fed cariogenic diets leads to caries clinically indistinguishable from radiation caries in man. This study compares the organic composition of individual samples of plaque fluid and saliva from irradiated and control monkeys receiving the same cariogenic diet. Plaque and saliva were collected from fasting, tranquillised animals. Four irradiated animals were sampled repeatedly as were non-irradiated controls. Total protein, albumin, immunoglobulins A, G, and M, and the third component of complement (C'3) were quantitated in plaque fluid and whole saliva. Salivary amylase and peroxidase activities were also determined. Plaque fluid and saliva samples were also subjected to polyacrylamide gel electrophoresis. The total viable anaerobic count and numbers of Streptococcus mutans were determined in samples of plaque. The results suggest that the major effect of irradiation leading to increased numbers of S. mutans and caries susceptibility is in the amount, and not the composition, of the saliva produced by the residual gland tissue. The scanty flow of saliva may reduce the effectiveness of cleansing, buffering and lubrication mechanisms as well as resulting in a marked reduction in the total amount of specific and non-specific immune factors entering the mouth.

Development of rampant dental caries, and composition of plaque fluid and saliva in irradiated primates

Co-60 gamma irradiation of the salivary glands of Macaca mulata monkeys fed a cariogenic diet led to the rapid onset of dental caries resembling that in irradiated human patients. Plaque fluid and saliva were sampled from irradiated monkeys, nonirradiated controls and a group of animals fed a noncariogenic diet in order to look for changes which might occur in inorganic composition related to the caries development and to dietary differences. Salivary calcium and phosphate levels were not markedly changed after irradiation: iodide levels were raised, while thiocyanate levels fell. In plaque fluid, calcium concentrations were not affected by irradiation, but were higher in animals fed a noncariogenic diet. Phosphate levels were higher with a cariogenic diet and further increased in irradiated animals. Magnesium levels were occasionally higher than those of calcium. Other differences in plaque fluid composition may be related to secondary effects of the concomitant gingival disease. The results do not point clearly at a specific change in the quality of the saliva produced by the residual gland tissue after irradiation which precipitates the rampant caries. It is more likely that the great reduction in the quantity of saliva with its protective constituents is responsible.