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.     

Sugar alcohols: what is the evidence for caries-preventive and caries-therapeutic effects?

The most widely used sugar alcohols are: xylitol, sorbitol, mannitol, maltitol, lactitol and the products Lycasin and Palatinit. It is often claimed that xylitol is superior to the other sugar alcohols for caries control. This paper examines clinical studies on the caries-preventive and therapeutic effects of sugar alcohols with emphasis on sorbitol and xylitol. It is concluded that chewing sugar-free gum 3 or more times daily for prolonged periods of time may reduce caries incidence irrespective of the type of sugar alcohol used. It may be sufficient to do this only on school days. Sucking xylitol-containing candies or tablets may have a similar effect as chewing xylitol chewing gum. Clinical trials suggest greater caries reductions from chewing gums sweetened with xylitol than from gums sweetened with sorbitol. However, the superiority of xylitol was not confirmed in 2 out of 4 clinical trials comparing the caries-preventive effect of xylitol- with sorbitol-sweetened gums. The caries-preventive effects of polyol-containing gums and candies seem to be based on stimulation of the salivary flow, although an antimicrobial effect cannot be excluded. There is no evidence for a caries-therapeutic effect of xylitol. These conclusions are in line with those of recent reviews and with the conclusions of the Scientific Committee on Medicinal Products and Medical Devices of the EU Commission.     

Xylitol binding in human dental plaque.

Human dental plaque and whole saliva sediment were tested for their ability to bind 14C-labeled sucrose, fructose, glucose, sorbitol, and xylitol. Sucrose, glucose, sorbitol, and fructose were bound to all materials tested, in this decreasing order. The binding was strongest with plaque given a five-second ultrasonic shock, and lowest with salivary sediment. Xylitol was only insignificantly bound, indicating that plaque microorganisms possess specific recognition sites for xylitol to a very restricted extent.     

Effect of long-term, peroral administration of sugar alcohols on man

Certain sugar alcohols (polyols), notably mannitol, sorbitol and xylitol have gained use in food manufacturing for sweetening and technical purposes. These compounds are natural polyols that occur in small amounts in animals and plants. Some sugar alcohols, like xylitol, appear as normal intermediates in the carbohydrate metabolism. Exogenous mannitol, sorbitol and xylitol are metabolized in the human body along pre-existing, physiological pathways. Moderate doses of least xylitol and sorbitol are almost totally absorbed and metabolized, chiefly in the liver cells, thereby eventually contributing to the formation of glucose and liver glycogen. Various slowly absorbed carbohydrates, including sugar alcohols, when taken in orally in large quantities, can give rise to osmotic diarrhea. The available data indicate that the severity of such gastro-intestinal disturbances, induced by large doses of polyols, decrease in the following order: mannitol, sorbitol, xylitol. This osmotic diarrhea resembles that caused by lactose in subjects with restricted or frank lactose intolerance. The quantities of xylitol, for example, required to elicit diarrhea are so high that the consumption of xylitol for dental purposes does not cause any problems in children or adults. Long-term feeding trials and peroral loading experiments on human subjects have been unable to show any clinically significant differences between chronic users of xylitol and comparative human material in factors related to various metabolic functions of the body. These subjects have not shown any delayed or acute reactions which could be distinguished from those caused by the consumption of a sucrose diet. The available clinical data generally suggest that moderate consumption of the above polyols is not harmful to human metabolism.     

Fermentation of sugars and sugar alcohols by plaque Lactobacillus strains

Objective

The objective was to analyse the ability of Lactobacillus strains isolated from supragingival plaque of subjects with hyposalivation and from healthy controls to ferment sugars and sugar alcohols.

Material and methods

Fifty strains isolated from interproximal plaque from subjects with radiation-induced hyposalivation (25 strains), subjects with primary Sjögren’s syndrome (16 strains) and from subjects with normal salivary secretion rate (9 strains) were tested. Growth and pH were determined after 24 and 48 h of anaerobic incubation in vials containing basal media with 1 % of glucose, fructose, sucrose, mannitol, sorbitol or xylitol.

Results

No differences between strains isolated from hyposalivated subjects and controls were detected. All strains lowered the pH to <5.0 from fructose and the majority of the strains from glucose and sucrose. A pH of <5.5 was seen for 52 % of the strains using mannitol, 50 % using sorbitol and 36 % using xylitol. The ability to produce acids from sugars and sugar alcohols was highest among strains of Lactobacillus rhamnosus, Lactobacillus casei and Lactobacillus paracasei and lowest among Lactobacillus fermentum strains.

Conclusion

A large number of Lactobacillus strains are able to ferment not only sugars but also the sugar substitutes mannitol, sorbitol and xylitol to pH levels critical for enamel demineralisation.

Clinical relevance

Our findings suggest that products containing mannitol, sorbitol and/or xylitol may contribute to the acidogenic potential of the dental plaque and especially in hyposalivated subjects with high numbers of lactobacilli.     

Dental effects of xylitol compared with other carbohydrates and polyols in the diet of laboratory rats

Xylitol at 10 and 20 per cent disturbed gastro-intestinal function but was tolerated better than sorbitol or mannitol. Toleration improved when dietary polyol levels were increased gradually to a maximum of 20 per cent. Twenty per cent of xylitol in the diet replacing that amount of sucrose reduced the level of caries, but 20 per cent of wheat starch was equally effective. Ten per cent of xylitol in place of sucrose produced as much caries as the basic cariogenic diet, but xylitol at a level of 2 per cent was associated with an increase in caries. There was no confirmation of an active caries-reversing effect of xylitol when xylitol-containing diets were alternated with the basic high-sucrose cariogenic ration.     

Comparative effects of the substance-sweeteners glucose, sorbitol, sucrose, xylitol and trichlorosucrose on lowering of pH by two oral Streptococcus mutans strains in vitro

Streptococcus mutans suspensions were incubated with each of the sweeteners in suspending media of increasing complexity. The lower pH levels were generally attained by sucrose and glucose; higher pH values were obtained with sorbitol, trichlorosucrose, and xylitol, respectively. The acidogenicity of sucrose was more often decreased by the presence of trichlorosucrose than by the presence of xylitol.     

Interaction between xylitol and sorbitol in plaque metabolism

Xylitol and sorbitol, when metabolized by microorganisms, are transported through the cell membrane and phosphorylated by membrane-bound phosphoenolpyruvate-dependent phosphotransferase systems. Sorbitol-6-phosphate may be oxidized by a sorbitol-6-phosphate dehydrogenase to fructose-6-phosphate and further decomposed in the Embden-Meyerhof pathway. Xylitol-5-phosphate - if not metabolized - may be toxic to the cell. There are few specific pathways known for xylitol metabolism in microorganisms. Due to structural resemblance between the xylitol and the sorbitol molecules interaction between xylitol and sorbitol metabolism is likely to occur. Xylitol - although only slowly taken up by plaque and oral microorganisms - may reduce plaque formation and cause an increase in plaque pH. Evidence for a phosphotransferase system for xylitol has recently been demonstrated in Strep. mutans, which may cause accumulation of xylitol-5-phosphate in the cell. Some studies carried out by the author and associates on acid production in the oral cavity from cell. Some studies carried out by the author and associates on acid production in the oral cavity from sorbitol in the presence of xylitol in chewing gum containing sorbitol reduces acid production from sorbitol. This may be explained by the following effects of xylitol: Reduction of plaque and the number of microorganisms on the teeth. This is thought to be a consequence of the toxic effect of xylitol-5-phosphate. Inhibition of acid production from sorbitol. This is believed to be a consequence of competitive blocking of the phosphotransferase system due to structural similarities between xylitol and sorbitol.     

Acid production from sugars and sugar alcohols by probiotic lactobacilli and bifidobacteria in vitro

Some probiotic bacterial strains have been suggested to improve oral health. However, lactobacilli and bifidobacteria are associated with the progression of dental caries. The pH fall caused by 14 probiotic and dairy bacterial strains from glucose, lactose, sucrose, sorbitol and xylitol was followed. All strains used glucose, nine lactose and seven sucrose. Six of the lactobacilli caused a small decrease in pH with sorbitol and two with xylitol. None of the bifidobacteria fermented sugar alcohols. As all the strains could be considered acidogenic, more long-term clinical trials are needed before recommendations for oral health purposes can be made.     

The breakdown of glucose, xylitol and other sugar alcohols by human dental plaque bacteria.

The aerobic and anaerobic incubation of plaque bacteria in media consisting of saliva supernatant containing ribitol, arabinitol, sorbitol and mannitol produced a fall in pH whereas incubations and serial transfer in saliva-xylitol media did not lead to any significant change. Addition of 100 mM xylitol did not affect pH fall during incubation with 100 mM sucrose, nor did 5–100 mM xylitol alter the rate of plaque glycolysis in 25 mM glucose solutions when measured as the release of ³H₂O from [5-³H]-glucose at pH 5.0 and 7.5. Plaque carbohydrate catabolism, when measured as the evolution of ¹⁴CO₂ from [U-¹⁴C]-glucose and -xylitol in 25 and 250 mM sugar solutions, respectively, at pH 7.5, showed that carbon dioxide release from xylitol was 7–27 per cent of that released from glucose. However, the anaerobic oxidation of glucose to carbon dioxide only represented 4 per cent of the total glucose utilised by glycolysis in 250 mM glucose solutions and demonstrates the minor role of oxidation in plaque sugar breakdown. Xylitol had no inhibitory effect on plaque sugar metabolism but was itself oxidised, although at a slower rate than was glucose; this metabolic inertness probably contributes to its relative non-cariogenicity.     

In vivo measurements of sulcal plaque pH in rats after topical applications of xylitol, sorbitol, glucose, sucrose, and sucrose plus 53 mM sodium fluoride

In two series of experiments, Sprague-Dawley-derived rats were infected orally with cariogenic micro-organisms and fed caries-promoting diets. By means of an antimony electrode, resting pH values were measured in the mesial sulcus of the maxillary left first molar. 100 or 200 microL of the test solutions were applied, and the change in pH (delta pH) was recorded for three min. Test solutions were: (a) 10% sucrose, 10% glucose, 10% sorbitol, or 10% xylitol; (b) 0%, 10%, 20%, or 40% sucrose; (c) 0%, 3%, 7%, or 10% sucrose; and (d) 10% sucrose, 10% sucrose + 53 mmol/L NaF (1000 ppmF-), or 10% sucrose + 53 mmol/L NaCl. Experimental design was a 4 X 4 Latin square (a, b, c) or a cross-over design (d). Solutions of sucrose and glucose gave significantly greater decreases in pH than did sorbitol or xylitol. pH fall was maximal for 10% sucrose and significantly less for 40% sucrose during the three-minute experimental period. For sucrose solutions ranging in concentration from 3 to 10%, pH fall was highest after application of 10% sucrose when plaque was previously rinsed with water, but this pH fall did not differ significantly from that obtained using a 7% sucrose solution. Adding 1000 ppmF- to a 10% sucrose solution caused an increase in pH. Rinsing the teeth to remove saliva resulted in significantly lower resting pH values. The results of these experiments are in agreement with the results of human plaque pH measurements.     

Effect of xylitol and other carbon sources on the cell wall of Streptococcus mutans

Abstract – Transferring actively growing bacteria or Streptococcus mutans ATCC 27351 into a xylitol-containing reaction mixture caused distinct alterations in bacterial ultrastructure without notable effect on the total viability of the strain. Incubations in media containing 50 mg/ml of glucose, fructose, sucrose, lactose, sorbitol or mannitol as the primary carbon source did not affect bacterial ultrastructure. These fermentations were reflected biochemically in the amounts of insoluble glucans, as expected. A negative correlation was found between the cell mass and the lipoteichoic acid formation. But these aspects could not be visualized in the electron microscope. In the xylitol series, however, degrading cells and autolysis, intracellular vacuoles and lamellated formations in the cytoplasmic membrane were frequently seen independent of the concentration of xylitol in the reaction mixtures. In freeze-fracturing replicas, however, the membrane intercalated particles of the cytoplasmic membranes seemed to be unaffected and like those in the controls. Minor ultrastructural changes in the fracture-faces were detected. Despite the alterations in ultrastructure of the xylitol-incubated bacteria, there was no difference in their viability when compared to the controls.     

Aggregation of human salivary Ca-proteinates in the presence of simple carbohydrates in vitro

Abstract — The effect of 8 polyols and 14 aldoses or ketoses on the spontaneous aggregation of Ca-proteinates was followed spectrophotometrically in supernatants and filtrates of human mixed saliva. Each carbohydrate was added to the saliva samples at 37°C and the precipitated material was analyzed for protein, total carbohydrate and Ca. Based on their effect on aggregation, the carbohydrates could be divided into three groups: 1) those that showed no effect on aggregation: D-xylose, D-ribose and i-erythritol, 2) those that inhibited aggregation strongly: xylitol, Dsorbitol and D-mannitoi, and 3) those that inhibited aggregation moderately: glucose, fructose and sucrose. The inhibitory effect of the above polyols on the aggregation of Ca-proteinates varied greatly among the saliva donors, and correlated positively with the turbidity of the saliva and its protein content more than with the Ca-concentration or the pH of the saliva sample. It is suggested that inhibition of aggregation shown the most clearly for xylitol, sorbitol and mannitol manifests itself as a retardation of the final, irreversible aggregation of those glycoproteins that already exist in a precipitated form and which are responsible for the turbidity of saliva.     

Prevention of sucrose-induced demineralization of tooth enamel by chewing sorbitol gum

Measurements were made of the effect of chewing sorbitol gum on the intra-oral demineralization induced by rinsing with 10% sucrose solutions. Blocks of bovine enamel were covered with a layer of Streptococcus mutans IB1600, and mounted on palatal appliances that were worn by five subjects for defined periods of time. Enamel demineralization was determined by following changes in iodide penetrability (delta Ip) of the enamel surfaces. Delta Ip increased to a maximum of about 15 units between 30 and 45 min, while the pH of the S. mutans plaque dropped to below 4 by 15 min. Plaque pH returned to 4.9 by 60 min. Chewing sorbitol gum after the sucrose rinse minimized further increases in delta Ip and brought about a more rapid return of the S. mutans plaque pH toward neutrality. The effect of chewing gum was greater when chewing was initiated earlier so that, when gum was given at five min after the sucrose rinse, demineralization was only 37% of that obtained without gum. The findings confirm earlier reports on the effect of gum on plaque pH, and directly demonstrate the profound protective effects that chewing sorbitol gum can have on tooth enamel.     

The effect of sugar alcohols on plaque and saliva level of Streptococcus mutans

The usage of sucrose substitutes such as polyols in snack-type foods is a logical and practical means of reducing caries incidence without perturbing normal dietary eating patterns. S. mutans and L. casei can ferment mannitol and sorbitol, but are inactive towards xylitol. This ability of these cariogenic organisms to ferment the hexitols does not seem to be of concern when gums containing them are used at the normal rate. However, when hexitol gum usage is excessive, the S. mutans levels may increase. In contrast to the hexitols, excessive usage of gums sweetened with xylitol caused a significant decrease in the levels and proportions of S. mutans in saliva and plaque. While this effect on S. mutans may be an indirect one, this finding provides added evidence for the superiority of xylitol as a sucrose substitute in dentistry.     

Effects of 3 months frequent consumption of hydrogenated starch hydrolysate (Lycasin), maltitol, sorbitol and xylitol on human dental plaque.

Lozenges containing hydrogenated starch hydrolysate (Lycasin), maltitol, sorbitol or xylitol were consumed 4 times daily during 3 months by 4 groups of persons (in all 85 subjects). In the maltitol-, sorbitol- and xylitol-group the plque wet weights were of the same magnitude before and after the test period. In the Lycasin-group, a higher value was found after than before the 3-month period (p less than 0.01). The acid production in suspensions of dental plaque material from Lycasin, maltitol and sorbitol expressed as per cent of that from glucose was approximately the same before and after the test period. From xylitol no acid production could be demonstrated either before or after the 3-month period. There were no statistically significant differences between the plaque pH-changes induced by rinsing with 50% solutions of Lycasin, maltitol, sorbitol or xylitol before and after the test period. However, there was a tendency (p less than 0.05) towards lower pH-values induced by the maltitrol and sorbitol rinse after the 3-month period compared with before. No difference in the relative numbers of facultative anaerobic streptococci. Streptococcus mutans or facultative anaerobic lactobacilli before and after the test period was found.     

Effect of xylitol-containing carbohydrate mixtures on acid and ammonia production in suspensions of salivary sediment

pH changes and the production of lactic acid, acetic acid and ammonia were studied in suspensions of salivary sediment supplemented with mixtures of xylitol and other carbohydrate sweeteners. The only mixtures which increased the pH values of the suspensions were those containing xylitol alone or mixtures of xylitol and sorbitol. Mixtures of xylitol and Lycasin 80/55 caused a relatively small pH reduction. Xylitol was not able to inhibit the acid production from the easily fermented glucose, fructose and Lycasin 05/60. The levels of lactic acid, determined in the incubation mixtures, directly reflected these pH changes. The levels of acetic acid and ammonia were, however, relatively similar in all incubation mixtures. The results suggest that the inhibitory effects of xylitol on acid production of oral flora should be retained, provided that xylitol is used either alone or in mixtures with slowly fermentable carbohydrates, such as sorbitol and Lycasin 80/55.     

Turku sugar studies XXI: Xylitol-, sorbitol-, fructose- and sucrose-induced physico-chemical changes in saliva

The aim was to study eventual physico-chemical changes occurring in whole saliva due to sweetened and unsweetened stimulators. The assay was carried out in 10 female subjects with regard to changes of pH, buffering capacity and electrolytes in saliva as influenced by chewing of fructose, sucrose, sorbitol and xylitol gum, gum base and paraffin. The flow rate of saliva was measured in relation to use of xylitol and sucrose chewing gum and unsweetened gum base. These sweeteners increased significantly the salivary flow rate in comparison to the unsweetened gum base. Generally, xylitol and sorbitol on one hand, and sucrose and fructose on the other, behaved in an almost similar way. Increased buffering capacity and elevation of pH in saliva was found in the presence of the polyols tested.     

Turku sugar studies XXI. Xylitol, sorbitol-, fructose- and sucrose-induced physico-chemical changes in saliva.

The aim was to study eventual physico-chemical changes occurring in whole saliva due to sweetened and unsweetened stimulators. The assay was carried out in 10 female subjects with regard to changes of pH, buffering capacity and electrolytes in saliva as influenced by chewing of fructose, sucrose, sorbitol and xylitol gum, gum base and paraffin. The flow rate of saliva was measured in relation to use of xylitol and sucrose chewing gum and unsweetened gum base. These sweeteners increased significantly the salivary flow rate in comparison to the unsweetened gum base. Generally, xylitol and sorbitol on one hand, and sucrose and fructose on the other, behaved in an almost similar way. Increased buffering capacity and elevation of pH saliva was found in the presence of the polyols tested.     

Adaptation of dental plaque to metabolise maltitol compared with other sweeteners

There is some evidence that plaque can adapt to regular exposure to some bulk sweeteners, leading to increased metabolism and acidogenic potential of the sweetener. This potential for adaptation varies between non-sugar sweeteners and has important implications for manufacturers of food, confectionery and medicines used long-term. Maltitol (99% purity crystalline D-maltitol) is a relatively newly approved non-sugar sweetener and appears to have potentially good dental properties. OBJECTIVES: To compare plaque adaptation to pure sucrose, sorbitol, xylitol or maltitol and the effect of their prolonged use on acid production by plaque from sucrose, in vivo. METHODS: Two series of plaque pH experiments were carried out. Each experiment involved a 14 day adaptive period when four 5 g lozenges of the sweetener were taken between meals each day. Each experiment was separated by a 14 day wash-out period. Acid production was quantified as: (a) minimum pH; and (b) cH area (difference between plaque pH curve and resting value, expressed as cH units). RESULTS: Thirteen adults, of mean age 41 years completed the study. When adaptation of dental plaque to the metabolism of sweeteners was compared, there was a statistically significant difference (p = 0.033) between xylitol and sorbitol, and between xylitol and sucrose but not between xylitol and maltitol. When the effect of prolonged use of sweeteners on acid production after sucrose rinsing was compared, there were no statistically significant differences between the sweeteners. CONCLUSION: Dental plaque does not adapt to metabolise xylitol or maltitol following prolonged exposure over 14 days.