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

The Role of the Acquired Enamel Pellicle in Calculus Formation

This article reviews a new concept of pellicle formation based on recently published data, and some experiments concerning the role of the pellicle in relation to calculus formation. There are strong indications that the pellicle consists of a multilayer of globules with a diameter of from 20 to 300 nm. These globules have a raspberry-like surface with clusters of smaller globules which are bound together by calcium, probably by bridging. The globules have negatively charged surfaces and hydrophobic interiors and are very similar to the micelles present in milk. It was shown in the present experiments that the pellicle inhibited seeded precipitation of calcium phosphates on enamel in a saturated solution. It was further shown that several proteolytic enzymes were able to release peptides from both milk micelles and from salivary globules, and that this treatment eliminated or reduced the inhibiting effect of the pellicles with regard to precipitation of calcium phosphates on enamel. It is suggested that this may be related to calculus formation in vivo, and that the pellicle normally inhibits calculus formation, but that proteolytic enzymes from bacteria in the oral cavity degrade the pellicle and cause it to lose its inhibiting effect.

Salivary Anionic Changes after Radiotherapy for Nasopharyngeal Carcinoma: A 1-Year Prospective Study

Objectives

To investigate the salivary anionic changes of patients with nasopharyngeal carcinoma (NPC) treated by radiotherapy.

Material and Methods

Thirty-eight patients with T1-4, N0-2, M0 NPC received conventional radiotherapy. Stimulated whole saliva was collected at baseline and 2, 6 and 12 months after radiotherapy. Salivary anions levels were measured using ion chromatography.

Results

A reduction in stimulated saliva flow and salivary pH was accompanied by sustained changes in anionic composition. At 2 months following radiotherapy, there was a significant increase in chloride, sulphate, lactate and formate levels while significant reductions in nitrate and thiocyanate levels were found. No further changes in these anion levels were observed at 6 and 12 months. No significant changes were found in phosphate, acetate, or propionate levels throughout the study period.

Conclusions

Conventional radiotherapy has a significant and prolonged impact on certain anionic species, likely contributing to increased cariogenic properties and reduced antimicrobial capacities of saliva in NPC patients post-radiotherapy.

Related factors of dental caries and molar incisor hypomineralisation in a group of children with cystic fibrosis

AIM

To investigate dental caries and molar incisor hypomineralisation (MIH)-related factors such as treatment, diet, brushing and salivary factors in children with cystic fibrosis (CF) compared with healthy peers.

STUDY DESIGN

A cohort study was performed.

METHODS

This study was performed on 30 CF children comprising patients at the Faculty of Medicine and 30 control children recruited from the Dental School. Salivary factors, dental caries, MIH, daily diet, brushing habits were analysed. Statistical analysis was calculated by SPSS for Windows.

RESULTS

Decay missing filled teeth (DMF-T) score was 4.6 ± 4.0 in CF and 7.7 ± 2.7 in control (p = 0.001). 43% of CF children with MIH were found to use antibiotics, but no significant difference in the caries experience was found with antibiotic usage (p > 0.05). DMF-T of CF adolescents (23%) who use Tobramycin was 7 ± 3.5. DMF-T of CF children (20%) who take other antibiotics was 2.5 ± 3.5, but no statistical difference was found (p = 0.054). Saliva pH, salivary flow rate, and buffering capacity were not found statistically significant (p > 0.05).

STATISTICS

Percentage arithmetic mean value, standard deviation, independent sample t test, Fisher's exact test, Chi-square test and Mann-Whitney U test were used, while a p value of <0.05 was considered statistically significant.

CONCLUSIONS

Medication and diet could be considered as a risk factor for dental caries and factors such as salivary pH, good oral hygiene could play a protective role for oral health CF children. MIH frequency and lower caries experience seen in CF children could be due to salivary factors or pharmacological treatment they take. The multidisciplinary approach team would be advantageous in the management of children with CF and oral health should be under control during early years of life by paediatric dentists.

Elevated incidence of dental caries in a mouse model of cystic fibrosis

BACKGROUND

Dental caries is the single most prevalent and costly infectious disease worldwide, affecting more than 90% of the population in the U.S. The development of dental cavities requires the colonization of the tooth surface by acid-producing bacteria, such as Streptococcus mutans. Saliva bicarbonate constitutes the main buffering system which neutralizes the pH fall generated by the plaque bacteria during sugar metabolism. We found that the saliva pH is severely decreased in a mouse model of cystic fibrosis disease (CF). Given the close relationship between pH and caries development, we hypothesized that caries incidence might be elevated in the mouse CF model.

METHODOLOGY/PRINCIPAL FINDINGS

We induced carious lesions in CF and wildtype mice by infecting their oral cavity with S. mutans, a well-studied cariogenic bacterium. After infection, the mice were fed a high-sucrose diet for 5 weeks (diet 2000). The mice were then euthanized and their jaws removed for caries scoring and bacterial counting. A dramatic increase in caries and severity of lesions scores were apparent in CF mice compared to their wildtype littermates. The elevated incidence of carious lesions correlated with a striking increase in the S. mutans viable population in dental plaque (20-fold increase in CF vs. wildtype mice; p value < 0.003; t test). We also found that the pilocarpine-stimulated saliva bicarbonate concentration was significantly reduced in CF mice (16 ± 2 mM vs. 31 ± 2 mM, CF and wildtype mice, respectively; p value < 0.01; t test).

CONCLUSIONS/SIGNIFICANCE

Considering that bicarbonate is the most important pH buffering system in saliva, and the adherence and survival of aciduric bacteria such as S. mutans are enhanced at low pH values, we speculate that the decrease in the bicarbonate content and pH buffering of the saliva is at least partially responsible for the increased severity of lesions observed in the CF mouse.

Association of caries activity with the composition of dental plaque fluid

This study tests the hypothesis that caries activity is associated with lower degrees of saturation with respect to enamel mineral in dental plaque fluid following sucrose exposure. Plaque fluids were obtained from caries-free, caries-positive, and caries-active subjects. Samples were collected before and at 3 and 7 min after a sucrose rinse on consecutive weeks and analyzed for organic acids, inorganic ions, pH, calcium activity, and, in selected samples, total protein. After sucrose, pH values were significantly lower in the caries-active group in comparison with the caries-free and caries-positive groups. Total and free calcium concentrations increased with decreasing pH, with free calcium being about one-third of total calcium. The caries-active group exhibited significantly lower degrees of saturation with respect to enamel mineral, after sucrose, and had significantly higher mutans streptococci levels in plaque than did the caries-free samples. Thus, saturation levels in post-sucrose plaque fluids reflect the cariogenic potential of dental plaque.

Release of mineral ions in dental plaque following acid production

The release of appreciable amounts of calcium, phosphate and fluoride found in whole plaque into the plaque-fluid phase, following bacterial acid production, can potentially reduce the driving force for tooth demineralization. However, limited information is available on this topic, particularly on the release of fluoride. This study sought to determine the change in calcium, phosphate and fluoride concentrations in plaque fluid after sucrose exposure. 48 h overnight-fasted supragingival plaque samples were collected from all tooth surfaces (with the exception of the lower lingual anterior teeth) of one half of an individual mouth, following a 1 min water rinse. Plaque samples were then collected from the other half of the same mouth, following a 292 mM sucrose rinse. Plaque fluid was isolated by centrifugation and analysed for total calcium and phosphate (ion chromatography) and for free fluoride (ion-specific electrode). Samples were collected from seven individuals. Following sucrose exposure, plaque-fluid pH decreased significantly from 6.5+/- 0.3 to 5.4+/-0.2; calcium concentrations (mmol/l) also increased significantly (p < 0.01) from 1.9+/-0.5 to 5.0+/-2.1. Fluoride and phosphate concentrations in plaque fluid, however, did not increase significantly after sucrose exposure: mean concentrations (mmol/l) of fluoride after the water and sucrose rinses were 0.006+/-0.003 and 0.005+/-0.002, respectively, and mean phosphate concentrations (mmol/l) were 11.0+/-2.0 and 12.0+/-3.0, respectively. When results were expressed per wet plaque weight, phosphate concentrations were also found to increase significantly. The same trends were observed when additional plaque samples were treated in vitro with sucrose: fluoride-ion activity did not increase in plaque under in vivo-like conditions.

The effects of fluoride concentration and the level of cariogenic challenge on caries development in desalivated rats

Dental caries is an infectious and transmissible disease that continues to affect the majority of people. The presence of carbohydrate, mainly sucrose in the diet, is an important factor in its occurrence. The amount of fluoride required for optimal protective effect where there is a high caries challenge is unclear. Differences in the intensity of cariogenic challenge, for whatever reason, may play a part in determining fluctuations in the effectiveness of fluoride. The purpose of this study was to evaluate the effect of different concentrations of fluoride on the development of caries and explore the cariostatic effect of fluoride under various levels of cariogenic challenge. The study comprises two experiments. In experiment I, 60 desalivated Sprague Dawley rats infected with Streptococcus sobrinus were offered the following to drink for 21 days: group (1), sterile distilled water (SDW); (2) 10 parts/10(6) F SDW; (3) 20 parts/10(6) F SDW; (4) 30 parts/10(6) F SDW; (5) 40 parts/10(6) F SDW. In experiment II, eight groups of 9 rats were placed in a König Höfer programmed feeder and were exposed to different levels of cariogenic challenge through varying frequency of eating and offered water containing 10 parts/10(6) F. In experiment I, exposure to 20, 30 and 40 parts/10(6) F reduced caries development significantly: fluoride, at 10 parts/10(6), reduced the severity of the carious lesions. In this model of severe cariogenic challenge, the results suggest that elevated concentrations of fluoride might be effective in patients at high caries risk. In experiment II, fluoride reduced the incidence and severity of smooth-surface caries in all groups. The protective effect of fluoride decreased as the number of exposures to sugar increased. It is concluded that the effectiveness of fluoride is influenced by the level of cariogenic challenge and that consideration should be given to adjusting the level of fluoride exposure based on perceived caries risk, and that there is a maximum therapeutic effect of fluoride beyond which no additional protection can be expected.

Biochemical comparison of plaque fluid on tooth and acrylic surfaces during a sucrose challenge

Previous studies have investigated variations in dental plaque fluid composition within a single mouth after a sucrose exposure. The purpose of this study was to determine a potential source of calcium and phosphorus in plaque by comparing the pH, calcium and phosphorus concentrations in plaque fluid obtained from an acrylic appliance with samples taken from supragingival tooth surfaces within the same individual after a sucrose challenge. Separate plaque samples from 14 individuals were collected from an acrylic appliance or tooth surfaces within same individual before and 15 min after a 20% sucrose rinse. Each plaque sample was centrifuged and nanolitre samples of plaque fluid were analysed for pH with a pH microelectrode, for total calcium concentration by atomic absorption in a graphite furnace, and for phosphorus concentration by spectrophotometry. There was an increase in the calcium and phosphorus concentration in the plaque after the sucrose challenge and a significant increase in calcium and phosphorus concentrations in the plaque taken from the teeth compared to the acrylic surfaces. The results indicate that the increased total calcium and phosphorus in plaque during a sucrose challenge is probably derived from the demineralization of enamel or extracellular demineralized components.

Role of saliva in caries models

The crucial role played by the actions of saliva in controlling the equilibrium between de- and remineralization in a cariogenic environment is demonstrated by the effects on caries incidence of salivary dysfunction and by the distribution of sites of caries predilection to those were salivary effects are restricted. However, of the several properties of saliva which may confer protective effects, it is not certain which are most important. A distinction can be made between static protective effects, which act continuously, and dynamic effects, which act during the time-course of the Stephan curve. Evidence implicates salivary buffering and sugar clearance as important dynamic effects of saliva to prevent demineralization; of these, the buffering of plaque acids may predominate. Enhanced remineralization of white spot lesions may also be regarded as dynamic protective effects of saliva. Fluoride in saliva (from dentifrices, ingesta, etc.) may promote remineralization and (especially fluoride in plaque) inhibit demineralization. The design of experiments using caries models must take into account the static and dynamic effects of saliva. Some models admit a full expression of these effects, while others may exclude them, restricting the range of investigations possible. The possibility is raised that protective effects of saliva and therapeutic agents may act cooperatively.

Early dental loss in Sjögren's syndrome. Histologic correlates. European Community Study Group on Diagnostic Criteria for Sjögren's Syndrome (EEC COMAC)

Early dental loss is a well-known complication of Sjögren's syndrome. Forty percent (n = 16) of 39 consecutive patients with the syndrome had early dental loss. Dental loss correlated positively with histologic grading at lip biopsy. There was no significant correlation with any other feature of Sjögren's syndrome, including saliva flow. In 11 partially edentulous or completely edentulous patients, dental loss occurred 9 years on average before the first symptom of xerostomia. Early dental loss may reflect a silent involvement of the salivary glands and suggests that changes in saliva biochemistry occur long before xerostomia.

Saliva stimulation and caries prevention

The protective role of saliva is demonstrated by the rampant caries seen in human subjects with marked salivary hypofunction, and in desalivated animals. In normal cases, however, the relationship between saliva flow and coronal or root caries experience is doubtful, and to examine the concept that stimulation of saliva might have protective effects against caries, one must look beyond a simple correlation between caries and flow rate. Protective properties of saliva which increase on stimulation include salivary clearance, buffering power, and degree of saturation with respect to tooth mineral. These benefits are maximized when saliva is stimulated after the consumption of fermentable carbohydrates, by reducing the fall in plaque pH leading to demineralization and by increasing the potential for remineralization. Plaque acid production is neutralized, and experimental lesions in enamel are remineralized, when gum is chewed to stimulate saliva after a carbohydrate intake. The pH-raising effects are more easily explained by the buffering action of the stimulated saliva than by clearance of carbohydrates. The remineralization action depends upon the presence of fluoride. These findings suggest that the protective actions of saliva can be mobilized by appropriate salivary stimulation, and that in addition to established procedures such as tooth cleaning and fluoride regimens, eating patterns which lead to saliva stimulation to increase the potential for saliva protection might be included in recommendations for caries prevention. Confirmation of this concept in clinical tests is required.

Calculus formation and inhibition

The formation, development, and dissolution of hard deposits such as calculus are complex processes that involve numerous calcium phosphate phases as well as the interaction of these ions with organic molecules. Although formation is determined by thermodynamic driving forces, kinetic factors are also important determinants for the precipitation of specific calcium phosphate phases. The overall process, therefore, may involve the formation of metastable intermediates which may subsequently transform into the more stable hard deposits observed in vivo. A knowledge of the kinetics of growth of both individual calcium phosphate phases and their mixtures is important for elucidating the mechanism of calculus formation. Although salivary proteins are effective inhibitors of the mineralization reactions that take place in dental plaque, once adsorbed, their conformation may change to present surfaces that catalyze the nucleation of mineral phases. The variable pH conditions in plaque, expressed in terms of free ionic concentrations, will markedly alter the supersaturations with respect to typical calcium phosphate precursor phases such as dicalcium phosphate dihydrate (DCPD) and octacalcium phosphate (OCP). Physical-chemical studies have shown that the mineralization of all the calcium phosphate phases is controlled by reactions at the surface rather than by diffusion of lattice ions through the contacting liquid phase. This makes the rates of reaction very sensitive to ions and molecules in the solution that may absorb at the active growth sites and, while not significantly incorporating into the precipitated crystal phases, markedly influences the rates of mineralization and demineralization.(ABSTRACT TRUNCATED AT 250 WORDS)

Composition and cariogenic potential of dental plaque fluid

Our understanding of the chemical events that take place at the tooth-plaque interface has improved greatly through studies of the chemical composition and properties of dental plaque fluid. In the absence of fermentable carbohydrate, plaque fluid has been found to be supersaturated with respect to tooth mineral and other calcium phosphate phases, thus exhibiting the potential to support calculus formation and the remineralization of incipient carious lesions. Following the exposure to fermentable carbohydrate, the degree of saturation of plaque fluid decreases rapidly, primarily due to lactic acid production and the lowering of plaque fluid pH. The extent of these chemical changes has been shown to be associated with differences in caries history. Such studies have been facilitated by the recent development of microanalytical techniques. Unfortunately, little is known about the relationship between the observed chemical changes in plaque fluid and the microbial composition of plaque. Limited information is also available on the association of immune factors in plaque fluid with dental disease.

A quantitative study of calcium binding and aggregation in selected oral bacteria

By means of micro-equilibrium dialysis, calcium binding capacities and affinities were measured in three different oral bacteria, and the effects of extracellular polysaccharide, pH, and aggregation were investigated. Binding capacities of 31.0 +/- 2.1 (C. matruchotii), 34.7 +/- 3.7 (S. sanguis), and 41.5 +/- 5.4 (S. downei) mumol calcium/g wet weight of cells were found at pH 7.0, falling to 21.4 +/- 0.8 mumol calcium/g wet wt. cells at pH 5.0 for S. downei. Dissociation constants were found to vary between 0.78 +/- 0.24 and 1.77 +/- 0.30 mmol/L (at pH 7.0, depending on species), and between 0.62 +/- 0.04 and 1.77 +/- 0.30 (in the pH range 5.0 to 7.0, for S. downei only). Examination suggested that at pH 7.0 calcium-facilitated bacterial association occurs in the streptococci with calcium uptake curves analogous with those of positively cooperative systems. Desorption of calcium from aggregated S. downei suggested that the mechanism of desorption differed from that of uptake. This may be an important factor in plaque formation and in the binding of cells to the surface of formed plaque. Plaque calcium forms a reservoir, readily released by a pH drop, which may increase plaque fluid saturation and reduce demineralization.

Changes with time in the oral microflora and dental caries induction in hyposalivated rats fed on sucrose diet

The effects of hyposalivation on the induction of dental caries and the change in oral microflora were examined at weekly intervals in Sprague-Dawley rats fed on diet 2000 containing 56% sucrose. In hyposalivated rats, significant dental caries was induced within one week and its severity increased with the experimental period. Bacteriological examinations demonstrated that the number of total cultivable microorganisms, lactobacilli and Staphylococcus aureus increased significantly shortly after surgical induction of hyposalivation, while the number of streptococci and yeasts did not increase significantly until the 7th week, beyond which time remarkable gross caries developed. A positive correlation was found between the caries score and the recovery of lactobacilli from mandibles of hyposalivated rats, while there was no statistically significant correlation between the caries score and the recoveries of S. aureus. On the other hand, dental caries was not induced in control rats fed on sucrose diet with no surgically-induced hyposalivation. It was also found that the number of lactobacilli increased significantly shortly after diet 2000 was given to control rats, but S. aureus was rarely recovered from the mandibles of control rats throughout the experiments. The roles of lactobacilli and S. aureus in the induction of dental caries under the hyposalivated condition were discussed and it was suggested that lactobacilli may play some significant role in the induction of dental caries in hyposalivated rats.

Composition of pooled plaque fluid from caries-free and caries-positive individuals following sucrose exposure

The composition of pooled plaque fluid from five population samples was determined before and at selected times (7, 15, 30, and 60 min) after a 10% sucrose rinse. Subjects were grouped according to caries status (caries-free, CF, DMFS = 0; caries-positive, CP, DMFS > 10). Samples were also studied from white-spot surfaces and from sound surfaces of the same mouths of two additional CP groups. Plaque fluid was isolated by centrifugation and analyzed for organic acids, inorganic ions (ion chromatography), and pH (microelectrodes). Prior to sucrose exposure, plaque fluids from the CF subgroups and from sound surfaces of the CP subjects had higher pH values than samples from CP subgroups and from white-spot surfaces, respectively; the ionic compositions were otherwise similar. Starved plaque fluids were also found to be supersaturated with respect to enamel and to a significantly greater degree in the CF samples, suggesting that CF plaque fluid may have a greater remineralization potential than CP samples. Following sucrose exposure, a rapid decrease in plaque fluid pH was observed, which corresponded primarily to lactic acid production. For all times examined, mean pH and DS(En) values were lower and lactic acid concentrations were higher in the CP samples than in the CF samples; noted differences were statistically significant at 7 min for pH and DS(En), and at 7, 15, and 30 min for lactic acid. Lower values of DS(En) suggest that plaque fluid from CP subjects had a measurably greater cariogenic potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hyposalivatory medications on saliva flow rates and dental caries in adults aged 65 and older

Institutionalized adults aged 65 or older often receive medications that have been associated with decreased saliva flow. Flow rates depressed by hyposalivatory medications are thought to increase susceptibility to dental caries. In this study, a cross-sectional comparison was made of stimulated whole saliva rates and coronal and root caries prevalence in a group of older adults, in a long-term care facility, taking hyposalivatory medications vs. a control group. No significant differences were found between the two groups in masticatory or gustatory stimulated flow rates or in mean decayed coronal or root surfaces.

Enhancing the virulence of Streptococcus sobrinus in rats

The purpose of this study was to explore the virulence of strains of Streptococcus sobrinus that had been re-isolated from a desalivated rat. Furthermore, we wished to determine the influence of desalivation on the acidogenicity of fasting and sucrose-pulsed dental plaque in rats infected by strains of S. sorbrinus. Experimental groups were formed and infected as follows: Group 1, desalivated animals, S. sorbrinus ATCC27352; Group 2, intact animals, infected as in Group 1; Group 3, desalivated animals, S. sorbrinus re-isolated from a desalivated animal that had been infected with the ATCC 27352 strain for five weeks; Group 4, intact animals, infected as in Group 3; Group 5, desalivated animals, S. sobrinus re-isolated from a desalivated animal that had been infected with the ATCC27352 strain for ten weeks; Group 6, intact animals, infected as in Group 5; Group 7, intact animals, no infection. All animals were fed cariogenic diet 2000 and sucrose-sweetened drinking water ad libitum. After five weeks, desalivated and intact animals that had been infected with isolates obtained from desalivated animals had significantly higher (p less than 0.05) smooth-surface-caries scores than did intact and desalivated animals infected with cultures of the original stock ATCC strain. Moreover, fasting plaque pH values were statistically lower in desalivated animals (Groups 1 and 3) than in intact animals (Groups 2, 6, and 7) (Turkey analysis, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between total and ionized calcium concentrations in human whole saliva and dental plaque fluid

Ionized and total calcium were determined with an ion-selective electrode in unstimulated whole saliva and in simultaneously collected plaque fluid. The mean ionic and total concentrations in saliva from 20 subjects were 0.53 and 1.03 mmol/l respectively, and in plaque fluid 0.64 and 1.20 mmol/l. The total calcium concentration in saliva was closely related to the total calcium concentration in plaque fluid (r = 0.95, p less than 0.001) as was the ionized calcium concentration in saliva to that of plaque fluid (r = 0.84, p less than 0.001).

Relationship between calcium and inorganic phosphorus concentrations of both resting and stimulated saliva and dental plaque in children and young adults

Calcium and inorganic phosphorus concentrations of both resting and paraffin-wax stimulated whole saliva and dental plaque were estimated in 39 young adults and 98 children aged 12-14 yr. Plaque was collected from the adults after 48 h without tooth-brushing and consumption of a standardized diet. Plaque was collected from the children without any dietary or oral hygiene restrictions. The results from the study with children provided consistent evidence for a statistically significant relationship between salivary and plaque concentrations of both calcium and inorganic phosphorus. However, multiple regression indicated that only the concentrations in the stimulated secretion were directly associated with concentrations in plaque. The apparent relationship between concentrations in resting saliva and plaque was due to correlation between resting and stimulated saliva. These relationships were less apparent in the young adults, in whom the controlled conditions resulted in a narrower range of mineral concentrations in dental plaque.

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.

Facts and artefacts in research on human dental plaque fluid

In 1966, Jenkins suggested that the plaque fluid environment was likely to have higher concentrations of extracellular solutes than was apparent from analyses of total plaque concentrations. Early work on plaque fluid confirmed this contention, but some artefact was also generated by the prolonged centrifugation used for separation. The solute concentrations in plaque fluid mostly exceed those in saliva or crevicular fluid. Thus, the environmental conditions are distinctly different from those based on the assumption that saliva readily permeates films of dental plaque. In contrast, the presence of serum proteins suggests a crevicular input to plaque fluid. These data suggest that exchange between dental plaque and its environment is apparently restricted. Diffusion rates measured in dental plaque by different methods do not agree on how restricted it is. However, measuring diffusion in plaque introduces artefacts in packing density, a major determinant of the diffusion rate. The conditions used for collection and analysis have been reported to produce artefactual changes in plaque fluid potassium, a predominantly intracellular ion. Measurements of predominantly extracellular ions, such as calcium, are no less prone to artefact, whether based on ion-selective electrodes or on total calcium. We have much to learn about the fluid environment of the teeth and about dynamic changes in plaque fluid composition and properties during perturbations. Such information can give insights into pathological processes such as tooth demineralization and dental caries, calculus formation, and gingival inflammation.

Plaque fluid pH, calcium and phosphorus responses to calcium food additives in a chewable candy

Fourteen subjects between 7 and 17 years of age with an equal distribution of low and high caries activity were given: (1) a 10% sucrose rinse, (2) a reference candy, (3) a reference candy with 3% dicalcium phosphate dihydrate, and (4) a reference candy with 0.75% calcium lactate on four different occasions. Plaque samples were collected before and at 15-min intervals after the sucrose rinse or food challenge for a period of 1 h on each occasion. Plaque samples were centrifuged and the extracellular plaque fluid analysed by a microtechnique for pH, total calcium and inorganic phosphorus concentration. There was no significant increase in calcium and phosphorus in plaque fluid for the group using candy with added calcium compared to the reference candy or sucrose rinse. There was no significant difference between the measurements in subjects grouped as caries active or inactive. The results suggest no benefit can be expected from adding dicalcium phosphate dihydrate and calcium lactate to candy to decrease demineralization during a cariogenic challenge.

Composition of pooled resting plaque fluid from caries-free and caries-susceptible individuals

The composition of pooled resting plaque fluid from 10 population samples, grouped according to age (8-11, 14-17, 18-25 years) and caries status (caries-free, CF, DMFS = 0; caries-susceptible, CS, DMFS greater than 10), was determined by means of ion chromatography. Subjects received a dental prophylaxis one week prior to plaque collection, abstained from oral hygiene for 48 hours, and did not eat or drink for at least one hour prior to plaque collection. Plaque samples from each group were pooled under mineral oil and centrifuged (15,000 g) for 45 minutes at ambient temperature. Supernatants were analyzed for organic acids, inorganic anions, mono- and divalent cations, and pH value. The ions Na+, NH4+, K+, Ca2+, Mg2+, Cl-, and phosphate were present in all samples. Acetic and propionic acids were predominant, comprising over 75% of the acid (anions) present under resting conditions. Succinic, lactic, formic, and butyric acids were present in lower concentrations. Within each age group, the mean values for pH and NH4+ concentration were higher in the caries-free group; the differences between mean values (CF: pH, 6.35; NH4+, 52 mmol/L; CS: pH, 5.85; NH4+, 37 mmol/L) were found to be statistically significant (p less than 0.05) when all data for the CF and CS groups were combined. Significantly higher concentrations of Mg2+ and butyric acid were also found for the combined CF data. Concentrations of all other constituents were similar. Calculations indicate that plaque fluid is supersaturated with respect to enamel mineral and dicalcium phosphate dihydrate, with a significantly higher degree of saturation with respect to enamel mineral in the CF group.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of desalivation in rats on incidence of caries in intact cagemates

The evidence that dental caries is an infectious and transmitted disease in rodents is unequivocal. However, the factors controlling the transmission of micro-organisms from one animal to another have not been extensively explored. Results from previous studies in our laboratory showed that desalivated animals became infected by Streptococcus sobrinus in a shorter period of time than did intact animals. Furthermore, an additional study in our laboratory showed that animals with intact salivary function caged with desalivated animals harbored more S. sobrinus immediately following establishment of infection than did intact animals housed with other intact animals. Therefore, it seemed appropriate to determine the influence on caries development of caging a desalivated animal with an intact animal. In this study, intact Sprague-Dawley rats were caged with desalivated animals; additional groups of intact animals were housed with chlorhexidine-treated animals that were either intact or desalivated. Although chlorhexidine suppressed both caries development and the level of infection by S. sobrinus, nevertheless, intact animals caged with desalivated animals invariably developed more caries than did intact animals housed with other intact animals. Treating intact animals with chlorhexidine did not affect caries scores in untreated intact cagemates. Overall, the results suggest that a highly acidogenic flora with enhanced virulence (including S. sobrinus) is selected in the desalivated animals; this flora is apparently readily transmitted to intact cagemates, leading to enhanced levels of smooth-surface caries.

Composition of human plaque fluid

The composition of pooled resting plaque fluid was determined in four groups of college-age students (18-22 years), each composed of 50 individuals, who abstained from oral hygiene for 36 hours and did not eat or drink for at least one hour prior to plaque collection. Plaque samples from each group were pooled under mineral oil in small centrifuge tubes and centrifuged at 37,000 g for one hour at 4 degrees C. Supernatants were then combined under mineral oil and centrifuged at 5000 g (4 degrees C) for 15 minutes. In general, the inorganic composition of plaque fluid in the four groups was quite similar and in agreement with values reported by other investigators, but quite different from those of saliva or serum. The mean composition was: Ca, 7.07 +/- 0.51 mmol/L; P, 23.2 +/- 5.3 mmol/L; Na, 18.6 +/- 2 mmol/L; K, 85.1 +/- 5.3 mmol/L; Mg, 3.9 mmol/L; Cl, 42.8 +/- 9 mmol/L; F, approximately 0.004 mmol/L; pH, 5.69 (5.63-6.01). Acetate, propionate, succinate, butyrate, lactate, and formate were determined in two samples analyzed, with acetate and propionate being the predominant acids found. It was also demonstrated, through the titration of one of the plaque fluid samples, that the observed buffer capacity in plaque fluid was mostly related to its organic acid composition. It was noted, however, that when the initial pH in plaque fluid exceeded 6.5, phosphate contributed significantly to the buffer capacity. The contribution of other soluble species (proteins, peptides, amino acids) to the observed buffering in plaque fluid appeared to be small.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of desalivation on coronal and root surface caries in rats

Although the presence of coronal caries is declining in much of the Western Hemisphere, the prevalence of root surface caries is likely to increase as teeth are retained longer than heretofore. At the same time, an increasing number of the population suffer from dry mouth as a result of taking prescription drugs, with an apparent concomitant increased susceptibility to root surface caries. This study attempted to develop an animal model which would aid in the exploration of the effects of desalivation and the development of root surface caries. Animals were desalivated, infected with Actinomyces viscosus and Streptococcus mutans (sobrinus) 6715, and fed a cariogenic diet. Coronal caries developed rapidly in the animals; sufficient disease was present after two weeks to permit evaluation of potential therapeutic agents. Alveolar bone loss and root surface lesions developed in three to four weeks. S. mutans (sobrinus) and A. viscosus established readily in all animals; however, as the investigation progressed, populations of the latter declined, possibly because of the highly acidogenic environment. This model will facilitate investigation of the influence of hyposalivation and help in the exploration of agents to alleviate the adverse effects of salivary gland dysfunction.

Biochemical and microanalytical methods

Because of the small amounts of material available for study, investigations of plaque, caries lesions in enamel, and antibodies in saliva pose difficult challenges for investigators. Sophisticated biochemical and fluorescence techniques can now be used to investigate the microbial composition of plaque, thereby avoiding the need for tedious culturing techniques from single sites on tooth surfaces. A range of microchemical methodologies is available which greatly facilitates the analysis of plaque fluid, thereby enhancing our understanding of tooth-plaque interactions. The application of a range of novel physiochemical techniques should help to clarify our knowledge of the interactions involved in pellicle formation and elucidate the phenomena involved in the formation of the early caries lesion. A range of techniques is now available for the study of antibodies in saliva. These include ELISA, RIA, and solid-phase immunoassay. The application of these methodologies to the investigation of oral diseases should facilitate our understanding of the pathogenesis of dental maladies at the molecular level.

Prevention and treatment of the orofacial complications of radiotherapy

Radiotherapy of malignant head and neck tumors often causes extensive, permanent changes in salivary glands, peridental alveolar bone, and mucosal structures. Dental neglect and inappropriate dental management can cause complications. The potential orofacial side effects of radiotherapy are reviewed, as are preventive strategies for the dental treatment of patients scheduled to undergo radiotherapy.

Calcium and phosphate in human dental plaque and their concentrations after overnight fasting and after ingestion of a boiled sweet

The concentrations of ionized and total Ca inorganic and total phosphate were determined in the same pooled samples of fluid separated from 24 h plaque collected from volunteers at least 1 h after a mid-morning snack. About half the total concentration of Ca was ionized (1.53 mM, SD 0.73, n = 36). The mean total Ca concentration (2.88 mM, SD = 0.89, n = 34) was about half that reported previously. The inorganic phosphate was in the range reported previously and comprised about 80 per cent of the total pool of soluble phosphate. A small but significant pool of organic phosphate comprised about 20 per cent of the total phosphate. There were no differences in any of these measurements between plaque-fluid samples pooled from upper buccal posterior teeth and from other sites. The product ([Ca ion] X [inorganic phosphate]) in plaque fluid greatly exceeded saturation levels with respect to potential solid phases present at the enamel surface. Five adults provided overnight-fasted dental plaque for one year to examine the effects of ingesting a boiled sweet on the plaque Ca and phosphate when collected 15 min later. There were no significant differences between fasting control and post-sweet levels of plaque-fluid Ca (ionized and total) and phosphate (inorganic and total). In the post-sweet residue, there were lower total phosphate but not Ca concentrations; the variability in these measurements may explain the unexpected depletion of the organic pool of phosphate in the residue.

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.

Micro-analytical determination of pH, calcium, and phosphate in plaque fluid

Micro-analytical techniques for the determination of calcium, phosphate, and pH in a small volume (less than 0.25 microliter) of plaque fluid are described and evaluated. The accuracy and the precision of the techniques were compared with those for standard macrotechniques applied to a large pooled plaque fluid sample. The results obtained for the micro-analysis of pooled plaque fluid were in excellent agreement with those obtained by macromethods. The described techniques were also used to analyze plaque fluid obtained from single quadrants of the oral cavities of five individuals. In this fashion, it was determined that, although a significant variation in plaque fluid composition exists between the quadrants, a greater variation exists between subjects. Analyses of plaque fluid obtained from six individuals, following sucrose exposure, were also conducted. The pH value of the fluid changed with time, following a typical Stephan curve, with a minimum value occurring between 15 and 30 minutes; following this, the pH increased to a value near that for resting plaque. An inverse relationship between pH and calcium and phosphorus concentrations was observed. It is noted that the described techniques are sensitive enough to carry out the above analyses both accurately and precisely using plaque obtained from a single quadrant.

Carbohydrate composition of dental plaque from primates with irradiation caries

Carbohydrate analyses were performed on dental plaque collected from the teeth of irradiated monkeys, non-irradiated monkeys and a group of Streptococcus mutans free animals, all of which were fed the same standard cariogenic diet. Glucose was the predominant sugar constituent in plaque and was detected in highest concentration in the irradiated animals. Small amounts of pentoses and other hexoses were also present. Plaque from irradiated animals contained, by comparison with the other groups, higher levels of Strep. mutans and lower levels of Streptococcus sanguis and Actinomyces.

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.