An in vitro study of the coronal leakage of two root canal sealers using an obligate anaerobe microbial marker.

The aim of this in vitro study was to investigate the coronal leakage of obligate anaerobes into root canals obturated with lateral condensation of cold gutta-percha with two root canal sealers. Sixty extracted human teeth with straight, single root canals were prepared using the modified double-flared technique with balanced force under copious irrigation until the master apical file was size 40. The teeth were divided randomly into experimental groups (40 teeth) and control groups (20 teeth). In the experimental groups, 20 teeth were obturated with lateral condensation of cold gutta-percha and AH26 sealer and 20 teeth were obturated with the same technique using TubliSeal EWT sealer. In the control groups, 10 teeth were obturated with the same technique either with AH26 or TubliSeal EWT sealer. These teeth were completely sealed to serve as negative controls. The remaining 10 teeth were not obturated and served as positive controls. The root surface of each tooth was sealed with nail varnish except the apical 2 mm. The coronal part of each root canal was sealed with the cut end of polypropylene tube and placed in a glass bottle containing sterile Fastidious Anaerobe Broth (FAB). Aliquots of 0.5 mL of FAB were injected into the polypropylene tube and the model system was centrifuged at 168 g. An inoculum of Fusobacterium nucleatum in FAB was placed in each coronal chamber at 7-day intervals and daily observations were made for bacterial growth in the apical reservoir for 12 weeks. All positive control teeth showed bacterial leakage within a week, while the negative control teeth remained uncontaminated throughout the test period. All the experimental teeth exhibited leakage of bacterial metabolites within 12 weeks, ranging from 1 to 12 weeks. The mean time for complete leakage in the AH26 and the TubliSeal EWT groups was 8.4 and 8.2 weeks respectively. There was no statistically significant difference (P > 0.05) in leakage between the AH26 and the TubliSeal EWT groups.

Intra- and inter-individual differences in salivary sucrose clearance over time.

Salivary clearance of sugars influences acid production of dental plaque. The aim of the present study was to follow the clearance of sucrose over time. Ten subjects participated in five or six experiments each during a period of 20 months. The subjects rinsed with a 20% sucrose solution. Before the rinse and after 2, 5, 10 and 30 min a saliva sample was collected. The salivary sucrose concentration was determined by an enzymatic technique. As a measure of the clearance of sucrose in saliva, the area under the concentration versus time curve (AUC) was used. Analysis of variance revealed no differences with time in the intra-individual AUC. However, the differences in AUC among individuals were highly significant (p < 0.001). The results show that the clearance pattern of sucrose may be an individual property which is constant over long time periods.

Comparison of the plaque microflora from natural and appliance-borne enamel surfaces.

Human enamel sections and slabs, mounted on a mandibular removable appliance, were worn by 5 adult subjects for a 1-week period. Plaque was allowed to accumulate on the in situ test sites and on the adjacent natural dentition. At the end of the experimental period, the plaque microflora associated with (1) the enamel sections, (2) the enamel slabs, and (3) the acrylic base of the appliance test site was compared with that obtained from lingual and interproximal areas of the lower molar teeth. In addition, the acid anion and pH profiles of plaque obtained from both the exogenous and natural tooth surfaces were also determined. Although some quantitative differences were found between the proportions of isolates obtained from the different enamel surfaces, qualitatively the microflora was very similar, and no significant differences were found in the plaque lactate/acetate ratios or pH measurements following a sucrose mouthrinse. Thus, human tooth specimens mounted on the intra-oral device produced a plaque ecosystem similar to that present on the adjacent natural dentition, suggesting that the model is suitable for studies on early plaque development and the microbiology of enamel demineralization.

The effect of salivary clearance of sucrose and fluoride on human dental plaque acidogenicity.

Ten subjects rinsed with a 20% (0.58 M) sucrose solution with or without 0.2% NaF (905 parts/10(6) F-) added in two separate experiments. Saliva and plaque were collected before rinsing and after 2, 5, 10 and 30 min. Sucrose and fluoride concentrations in saliva and acid anion and fluoride concentrations in plaque were analysed. There was a statistically significant and positive correlation between the concentration of sucrose in the saliva 2 min after the rinse and the subsequent concentrations of lactate in plaque at 10 and 30 min after the rinse with sucrose alone but not in the presence of fluoride. Salivary fluoride concentrations during 2-30 min after the sucrose rinse were significantly correlated with plaque fluoride concentrations during the same time. The addition of fluoride to the sucrose rinse significantly inhibited lactate production.

Growth and acid production of Candida species in human saliva supplemented with glucose.

Growth characteristic and acid production of oral isolates of Candida albicans and Candida glabrata in glucose supplemented and glucose-free, pooled, human whole saliva were examined. Both Candida species exhibited sigmoidal growth curves in batch cultures of mixed saliva, supplemented with glucose. The growth of Candida in saliva was accompanied by a rapid decline in pH from 7.5 to 3.2 over 48 h and the major acidic components initiating and sustaining this pH drop were pyruvates and acetates. These acidic metabolites may play an important role in the pathogenesis of oral Candida infections.

Instrumentation for measurement of dental plaque thickness in situ.

A commercial digital micrometer has been modified mechanically and electronically to allow the measurement, in situ, of the thickness of dental plaque. The device detects initial contact between a moving probe and the plaque, and measures subsequent probe displacement through to the tooth surface. Instrument accuracy is +/- 5 micron over a displacement range of 0-5 mm, with 1 micron resolution. In practice, after a short 'learning' phase, reliable clinical results can be obtained.

Growth and acid production of Candida albicans in carbohydrate supplemented media.

Aerobic and anaerobic growth characteristics and acid production of a clinical and a reference laboratory strain of Candida albicans in 0.1 M, glucose or sucrose-supplemented batch cultures were examined for 72 h, at 37 degrees C. Both strains gave sigmoid growth curves, aerobically, and the pH dropped from 7.0 to 3.5 in 48 h. Candidal growth or acid production was not observed in submerged, anaerobic cultures. The specific growth rate (mu) of the clinical strain of Candida was significantly greater than the reference strain, in both sugar media. The major acidic component initiating and sustaining the pH drop appeared to be acetate, although formate, pyruvate and propionate were detected in varying proportions in glucose or sucrose cultures. These anionic, acidic metabolites of C. albicans, may play a role in the pathogenesis of mucosal candidoses such as chronic atrophic candidosis.

Diffusion of sugars and acids in human dental plaque in vitro.

Using a clearance technique, diffusion coefficients, D, were measured in plaque samples in which metabolic activity was eliminated by fixation with glutaraldehyde. Diffusion coefficients for sucrose, sodium acetate and sodium lactate at 37 degrees C were 3.0, 5.0 and 4.8 x 10(-6) cm2 s-1, respectively. Diffusion rate in plaque was between 2- and 5-fold slower than in water with uncharged species retarded less than charged species. However, diffusion in thin layers of plaque (100 microns) was rapid with clearance-halving times. T1/2, of about 6 s for acetate and lactate and 9 s for sucrose. Acetic and lactic acids diffuse faster than sucrose in plaque. Thus, the prolonged lowering of plaque pH following exposure to dietary carbohydrate is due to continued acid production in the plaque rather than to a restriction of diffusion of acid.

Isotachophoretic analysis of short-chain carboxylic acids produced by Candida albicans.

Short-chain carboxylic acids produced by Candida albicans in glucose supplemented batch cultures and in human denture plaque has been qualitatively and quantitatively analysed using isotachophoresis. This rapid, simple and relatively new technique which has advantages over other conventional methods, such as gas liquid chromatography, could be a valuable tool in the analysis of carboxylic acids produced by other yeasts of clinical and industrial importance.

Effect of extracellular polysaccharides on diffusion of NaF and [14C]-sucrose in human dental plaque and in sediments of the bacterium Streptococcus sanguis 804 (NCTC 10904).

It has been postulated that extracellular polysaccharides form a barrier to diffusion in dental plaque. Diffusion coefficients, D, were measured for NaF and [14C]-sucrose in glucan-free and glucan-containing sediments of Strep. sanguis 804 at 37 degrees C. There was a tendency for NaF and [14C]-sucrose to diffuse faster as the carbohydrate concentration in the sediments increased. NaF diffused only 38 per cent more slowly in cell-free glucan sediment than in water, suggesting that glucan per se does not form a barrier to diffusion. The diffusion coefficient for NaF was positively correlated with carbohydrate concentration in individual plaque samples from 15 subjects and incubation of 3 plaque samples with sucrose resulted in both an increase in carbohydrate concentration in the plaque and an increase in D for NaF. Thus the presence of extracellular polysaccharides in plaque leads to slightly faster rates of diffusion. Nevertheless, the total time for diffusion through plaque may be increased if the presence of extracellular polysaccharides results in thicker layers of plaque.