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Biomedical subjects

C Dawes

Publications and source records attributed to C Dawes.

At least 55 records · Page 3Linked to original sources
PubMed1989

Studies on fluoride excretion in human whole saliva and its relation to flow rate and plasma fluoride levels.

Five volunteers participated in two separate experiments where whole saliva was collected without stimulation or with stimulation by chewing on paraffin wax. The saliva was collected continuously for 120 min after ingestion of 1 mg fluoride as NaF. Blood was collected at intervals throughout the experiments. The results showed that the concentration of fluoride in whole saliva mirrored the fluoride concentration in plasma, but at a lower level. Variations in salivary flow rate (0.34 +/- 0.15 ml/min for unstimulated and 1.06 +/- 0.28 ml/min for stimulated) did not affect the salivary fluoride concentration. The amount of fluoride excreted into stimulated whole saliva was significantly correlated with the salivary flow rate, with a correlation coefficient of 0.98. The fraction of the ingested fluoride dose recovered in whole saliva within 2 h was 0.05 +/- 0.02 and 0.18 +/- 0.09% for the unstimulated and the stimulated whole saliva, respectively.

Administration, Oral↗
PubMed1989

Studies on fluoride concentrations in human submandibular/sublingual saliva and their relation to flow rate and plasma fluoride levels.

Submandibular/sublingual saliva and blood were collected from five subjects after ingestion of 1 mg fluoride as NaF. An individual collection device, made from a silicone impression material, was used to collect the saliva in 10-minute samples, before and during 2 hr after the fluoride intake. In two separate experiments on each individual, submandibular/sublingual saliva was collected continuously at different flow rates: without stimulation and with gustatory stimulation. Blood was also collected at intervals throughout the experiments. The concentration of fluoride in the submandibular/sublingual saliva was less than that in the plasma but independent of salivary flow rate. The ratio between the saliva and plasma fluoride concentrations at the peak of the mean plasma fluoride concentrations was 0.55 +/- 0.13 and 0.69 +/- 0.11 in the experiments on unstimulated and stimulated salivary, flow rate, respectively. The total amount of the ingested fluoride dose that was excreted through the submandibular/sublingual glands during 130 min was highly correlated with the salivary flow rate. The fraction of the ingested fluoride dose excreted in 2 hr was 0.04 +/- 0.02% in the unstimulated saliva and 0.15 +/- 0.09% in the stimulated saliva.

Fluorides↗
PubMed1989

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

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

Chemical Phenomena↗
PubMed1989

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

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

Dental Caries↗
PubMed1988

A comparison of the effects of tasting and chewing foods on the flow rate of whole saliva in man.

The objective was to determine the relative contributions from gustatory and mechanical stimulation of salivary flow in response to consumption of three foods. In a preliminary study on 6 males and 6 females the weights of normal bite-size portions and their chewing times for rhubarb pie, boiled rice, and raw carrot were established for each subject. In the main study the foods were either (a) divided into the calculated bite-size normal portions or (b) the portions were mashed (rhubarb pie), untreated (rice) or finely ground (raw carrot). The subjects chewed the foods of type (a) in the normal way but, with type (b), simply held the food between the palate and the dorsum of the tongue, with no masticatory movements (tasting). After the normal chewing time the food was not swallowed but spat into a weighed container; the volume of saliva secreted was determined from the increase in weight of the food portions. Rhubarb pie elicited a significantly higher flow rate than did the rice and carrot; the flow rates in response to tasting, as a percentage of those in response to chewing were 86.7 +/- 12.2, 79.3 +/- 17.9 and 73.4 +/- 15.4, respectively. It is concluded that in humans the effect of the gustatory stimulation of foods is much more important than the mechanical stimulation from chewing in producing the flow of saliva.

Adult↗
PubMed1988

The effects of different foods and concentrations of citric acid on the flow rate of whole saliva in man.

The effects of seven different foods and three concentrations of citric acid in 16 adult subjects of each sex were evaluated. The foods were steamed rice, french fries, cheeseburger, cookie, milk chocolate, apple, and rhubarb pie. The volume of saliva was determined by subtracting the initial weight of food from that of the food bolus after subjects had chewed it normally and then spat it into a weighed container, without swallowing. The flow rates were compared with those produced in response to infusion into the mouth of 52, 156 and 260 mmol/l citric acid through a plastic tube at a constant rate of 5.0 ml/min, controlled by a peristaltic pump. Mean salivary flow rates were highest with rhubarb pie and lowest with rice; these were 70.5 +/- 11.3 and 43.2 +/- 14.4 per cent, respectively, of the maximum flow rate (7.07 +/- 2.16 ml/min) elicited by 260 mmol/l (5 per cent) citric acid. The chewing times per 10 g of food were inversely related to the water content (r = -0.82). The water content of the food bolus varied over a wide range (28-87 per cent). Thus normal foods elicit a salivary flow rate which is a high fraction of the maximum secretory rate achieved in response to acid.

Adult↗
PubMed1987

The effect of taste adaptation on salivary flow rate and salivary sugar clearance.

To provide an objective measure of the rate of taste adaptation, we measured changes in the flow rate of parotid saliva from 12 subjects while a tastant was infused continuously into their mouths. The tastants employed were sucrose, sodium chloride, and citric acid, each at two different concentrations. With all stimuli, the higher concentration elicited significantly higher initial flow rates, which declined exponentially with time. The half-time for adaptation of flow rate was independent of the nature or concentration of the stimulus and averaged 11.3 sec, which suggests that adaptation follows a single exponential curve. The model of salivary sugar clearance developed by Dawes (1983) predicted that the rate of clearance would be independent of the initial sucrose concentration. However, this model did not take into account the effect of taste adaptation on salivary flow. This process was thus incorporated into the model, which then predicted that the time for clearance would be dependent on the initial sucrose concentration, as found experimentally by Goulet and Brudevold (1984). Hence the process of taste adaptation progressively reduces the stimulated salivary flow rate, which retards the rate of salivary clearance of sugar from the oral cavity.

Adaptation, Physiological↗
PubMed1987

The surface area of the adult human mouth and thickness of the salivary film covering the teeth and oral mucosa.

The surface area of the mouth was measured to calculate the average thickness of the salivary film which separates the opposing layers of the oral mucosa and which also overlies the dental plaque. The subjects were 10 adults of each sex, all of whom had essentially a full complement of teeth. Impressions were taken of the upper and lower jaws, the buccal and labial vestibular mucosa, and the ventral surface of the tongue, and stone models were cast. The dorsum of the tongue was assumed to have the same area as the palate plus that of the palatal surfaces of the upper teeth. The six separate areas considered were the teeth, the palate, the buccal and lingual gingival and alveolar mucosa, the buccal and labial vestibular mucosa, the ventral surface of the tongue, including the floor of the mouth, and the dorsum of the tongue. Aluminum foil, of known weight per unit area, was adapted to the models of the different regions of the mouth, and the surface areas were calculated from the weights of the foil. The mean total surface area of the mouth was 214.7 +/- 12.9 cm2, and there was no significant difference due to gender. The teeth, keratinized epithelium, and non-keratinized epithelium occupied about 20%, 50%, and 30% of the total surface area, respectively. Given that the average volumes of saliva present in the mouth before and after swallowing have been estimated to be 0.77 and 1.07 mL, respectively, it can be calculated that the average thickness of the salivary film in the mouth varies between 0.07 and 0.10 mm.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

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

The rate at which substances diffuse from dental plaque influences the rate of clearance of acid and bacterial toxins from plaque into saliva. The aim of this study was to compare the rates of clearance of potassium chloride, as a model substance, from artificial plaque of 3-, 4-, and 6-mm-diameter, positioned bilaterally at different locations in the mouth. The diffusant was KCl (1 mol/L) in a 1.0% agarose matrix, placed in wells 1.5 mm deep, in small acrylic devices 3 mm thick, which could be fastened to the teeth with dental floss and removed after different time periods. The half-time for clearance was determined from the best-fitting least-squares line of the potassium concentration remaining in the gel plotted against the square root of time. For 14 subjects, half-times for the lower anterior lingual and upper posterior lingual regions averaged about 2.5 times greater than those for clearance into a large, stirred volume in vitro, whereas those for the upper and lower anterior buccal regions averaged about 12.8 times greater. This difference may be due to the fact that anterior buccal sites are exposed only to minor rather than to major salivary gland secretions. When salivary flow was stimulated by the sucking of sour lemon drops, all in vivo half-times were reduced by about one-half. The half-times were also directly related to the surface areas of the chambers, which implies that rates of diffusion from plaque of substances such as acid or bacterial toxins are inversely related to the surface area of the plaque at a particular site.

Acrylic Resins↗
PubMed1987

Physiological factors affecting salivary flow rate, oral sugar clearance, and the sensation of dry mouth in man.

This paper discusses methods for collection of both whole saliva and individual gland secretions, the normal ranges of salivary flow rate, the effects of physiological variables which influence flow rate, and the role of saliva in oral sugar clearance. The physiological basis for the sensation of dry mouth is discussed, and a new concept is advanced which states that the sensation of dry mouth will occur when the salivary flow rate is less than the sum of the rates of water absorption and evaporation from the mouth. In a study of the effects of anticholinergic agents on salivary flow, the subjects experienced the sensation of dry mouth when the normal flow rate of unstimulated saliva was reduced by from 40 to 50%.

Absorption↗
PubMed1986

A theoretical analysis of the effects of plaque thickness and initial salivary sucrose concentration on diffusion of sucrose into dental plaque and its conversion to acid during salivary clearance.

A mathematical model, written in FORTRAN, has been developed to simulate the interrelated processes of salivary sucrose clearance from the mouth, diffusion of sucrose into dental plaque, and conversion of sucrose to acid and glucan. Reaction of acid with enamel is not included in the model. A total of 28 parameters can be varied by the user, and the relative importance of the different factors affecting acid formation can be assessed. The output of the program gives sucrose and acid concentrations and pH at different depths within the plaque. The initial variables studied were plaque thickness, the salivary sucrose concentration, and the duration of exposure of the plaque to sucrose. Stephan curves typical of those recorded in vivo were generated by the model. With any particular salivary sucrose concentration, there was an optimum plaque thickness at which a minimum pH was achieved at the enamel surface, with very thin or thick plaque samples producing a smaller pH fall. With thick plaque, the minimum pH was often not achieved at the inner surface but at some intermediate depth, which may explain the location of early caries lesions in fissures. The extent of the pH fall at the inner surface and the duration of the pH-minimum region of the Stephan curve were directly related to the initial salivary sucrose concentration and to the duration of exposure to sucrose prior to normal salivary clearance. Simulation of a water rinse at as short a time as two min after the beginning of normal salivary sugar clearance showed that this procedure had only a very small effect on the shape of the Stephan curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed1986

A comparison of the potassium content and osmolality of plaque fluid and saliva, and the effects of plaque storage.

Previous determinations of osmolality and potassium concentrations in plaque fluid, much higher than those in saliva, suggest a restricted exchange between the two, which must be reconciled with recent findings of quite rapid diffusion in plaque. Possible reasons for the high values were considered, and of these the effect of solute leakage from bacteria to the plaque fluid during typical periods of storage was investigated. It was also shown that the osmotic pressure of plaque fluid could be measured quite accurately by vapor pressure osmometry on whole plaque samples without the need for centrifugation. Samples of plaque, or plaque fluid prepared by centrifugation at 12,000 g, were compared for osmolality or potassium content with matched samples prepared from plaque stored chilled or in liquid nitrogen. Saliva samples obtained just prior to plaque collection were also analyzed. Freshly collected plaque from overnight-fasted subjects had a plaque fluid osmolality of 156 +/- 35 as compared with 98 +/- 23 mOs/kg for saliva. Potassium in plaque fluid from freshly collected "mature" plaque was 40.6 +/- 5.1 as compared with 20.3 +/- 5.3 mmol/L for saliva, but for 1-2-day-old plaque from fasted subjects it was significantly lower (30.4 +/- 5.6 mmol/L). These values for plaque fluid are all much less than those previously found, and storage was found to cause a marked increase (range, 35-100%). Centrifugation at 12,000 g caused little change in plaque fluid osmolality but seemed to accelerate the rate of increase during subsequent storage.

Adult↗
PubMed1985

The effects of different concentrations of sucrose, fructose, and glucose on pH changes by Streptococcus mitior in an artificial mouth.

The aim of this study was to determine the effects of the initial sucrose (S) concentration, as well as those of fructose (F), glucose (G), and invert sugar (F/G), on the pH developed by a layer of S. mitior, to represent dental plaque, in an artificial mouth which simulates the process of oral sugar clearance. At S, F. G, and F/G concentrations of 2% and with normal oral sugar clearance rates, the bacteria produced a smaller pH fall from S than from the other sugars; at initial concentrations of 20%, however, the differences were not significant. With constant S concentrations of 0.5-35%, the minimum pH reached was 4.03 +/- 0.14 (S.D.); with S concentrations of 50% and above, slightly but significantly higher values (4.41 +/- 0.34) occurred. However, with normal sugar clearance, the pH fall was much less than with a constant concentration and was dependent on the S concentration over the range of 0-10%, but was independent at higher concentrations. Exposure of the bacteria to S for as short a period as two min during normal sugar clearance gave a nearly maximum pH fall. This suggests that rinsing the mouth with water more than two min after consumption of sucrose in liquid form will have very little effect in reducing the pH fall in dental plaque. A more appropriate method for reducing acid formation by dental plaque would be consumption of a salivary stimulant which would increase the flow rate and buffer capacity of the saliva.

Acids↗
PubMed1985

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)

Adolescent↗