Tsutomu Takei

The Caries Inhibitory Effects of GOS‐Sugar in vitro and in Rat Experiments

The caries inhibitory activity of GOS‐sugar (panose‐ and maltose‐rich sugar mixture) was examined and compared with that of sucrose, maltose, or glucose in in vitro and in vivo experiments. Streptococcus mutans MT8148R (serotype c) and Streptococcus sobrinus 6715 (g) did ferment GOS‐sugar and produce acid in a similar way as with maltose and glucose. However, GOS‐sugar could not be a substrate for the glucosyltransferases (GTases) of these mutans streptococci to synthesize the water‐insoluble glucan. Also, it significantly inhibited not only the synthesis of water‐insoluble glucan from sucrose by the crude GTases but also the sucrose‐dependent adherence of these cells to a glass surface. In particular, adherence of growing cells of 6715 was markedly inhibited by the presence of GOS‐sugar. GOS‐sugar was found to induce significant but minimal dental caries in SPF rats infected with either MT8148R or 6715. Furthermore, the replacement of half of the dietary sucrose content with GOS‐sugar resulted in a significant reduction of caries development in rats infected with strain 6715.

MUTACIN ACTIVITY OF STRAINS ISOLATED FROM CHILDREN WITH VARYING LEVELS OF MUTANS STREPTOCOCCI AND CARIES

A total of 157 isolates of mutants streptococci from plaque and saliva of 94 children were studied for their serotypes, mutacin production, frequency and spectrum of activity. Of these isolates 71% were identified as serotype c and 22% as serotype e. Serotypes f, d and g, and one untypable strain made up about 7% of the isolates. More than one serotype was found in 13% of the children. Mutacin was produced by 83% of the isolates against one or more of the 14 indicator strains representing mutants streptococci. Streptococcus sanguis, Strep. oralis, Strep. gordonii, Strep. salivarius and Strep. pyogenes. Isolates that had a broad inhibitory spectrum also produced larger inhibition zones than isolates that inhibited fewer strains. When evaluating the effect of mutacin in vivo on plaque ecology, it was found that the counts of mutans streptococci or the proportion of mutans streptococci in the total streptococcal count of plaque did not differ between plaques containing strains that produced much mutacin and those with little production. The findings also failed to reveal an association between caries experience and mutacin activity.

Plaque formation of dietary isomaltulose in humans.

The plaque formation of isomaltulose, a sucrose isomer, was examined in 15 human volunteers with both diet and oral hygiene under supervision. The subjects were requested to refrain from all oral hygiene procedures for 3 days and were provided between-meal snacks containing 157 g of 4 test sugars (100% isomaltulose, 70% isomaltulose + 30% sucrose, 50% isomaltulose + 50% sucrose, and 100% sucrose). The study was repeated 4 times over 4 weeks. The isomaltulose diet resulted in the lowest plaque index, while sucrose induced a significantly greater deposition. In the absence of sucrose-containing snacks, mutans streptococci in saliva decreased below the baseline level. These results suggest that isomaltulose may be a suitable substitute for sucrose in between meal snacks.

Change of Salivary IgA Secretion and Caries Development in Irradiated Rats

Xerostomia is a serious side-effect of radiotherapy for head and neck cancer and often enhances caries activity. However, the relationship between caries induction and the IgA level in saliva in rats subjected to irradiation of the salivary glands is unclear. The effect of salivary gland irradiation on salivary function was examined in specific pathogen-free Sprague-Dawley rats infected with or without Streptococcus mutans MT8148R (serotype c). The flow rate of saliva and the protein concentration in saliva were significantly reduced in irradiated rats, regardless of infection of S. mutans. The caries activity was enhanced in these rats, and an irradiation level of 50 Gy significantly increased the caries score. However, longitudinal study indicated that the salivary concentration of IgA reactive with S. mutans whole cells maintained similar or significantly higher levels in irradiated rats, when compared with those of nonirradiated rats. In addition, there was no negative correlation between the caries score and the salivary concentration of IgA reactive with S. mutans. These findings suggest that the secreted IgA against S. mutans may not play a significant role in the caries induction of hyposalivated rats.

Latex agglutination test for detection of mutans streptococci in relation to dental caries in children.

A simple and rapid system based on a latex agglutination (LA) reaction was devised for the detection of mutans streptococci in dental plaque. Latex particles were sensitized with antibodies against whole cells of Streptococcus mutans strains MT8148 (serotype c), MT703R (e) and OMZ175 (f) and Strep. sobrinus strains B13 (d) and 6715 (g). These sensitized particles were agglutinated within a few minutes after addition of 1.0-10 ng serotype-specific antigen from the homologous organisms or the nitrous acid extract of whole cells at 10(5)-10(6) c.f.u. The LA test specifically differentiated not only mutans streptococci from the other oral streptococci but also Strep. sobrinus from Strep. mutans. The LA test was also applicable to extracts of plaque from 206 human subjects who harboured mutans streptococci. In clinical trials, the outcome of the LA test correlated significantly with the number of mutans streptococci found in plaque (p less than 0.0001), which was quantified by the selective cultivation of mutans streptococci. Furthermore, the LA test discriminated between Strep. mutans and Strep. sobrinus from human dental plaque. The sensitivity and the specificity of the LA test for detection of mutans streptococci were 78.9 and 100%. The degree of reactivity in the LA test correlated significantly with the number of decayed tooth surfaces (p less than 0.0001) and decayed and filled tooth surfaces (p less than 0.0001). These results suggest that the LA test could be useful clinically for the detection of mutans streptococci in dental plaque as well as serving as a caries-activity test.

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.

The effect of X-ray irradiation-induced hyposalivation on caries induction in SPF rats infected withStreptococcus mutans

The effects of X-ray irradiation to the salivary glands on the induction of dental caries and on the oral microflora were examined in specific pathogen-free Sprague-Dawley rats fed a sucrose diet and inoculated with a strain ofStreptococcus mutans. Hyposalivation was induced by irradiation of 35 Gy and dental caries was significantly enhanced in irradiated rats infected withS. mutans. Bacteriological examinations at the end of the experiment demonstrated that the recoveries of lactobacilli and staphylococci significantly increased in hyposalivated rats with 50 Gy of irradiation. However, the recovery of the strain ofS. mutans from hyposalivated rats were not significantly higher than that of non-irradiated rats. These findings suggest that some acidogenic microorganisms such as lactobacilli and staphylococci may have played some role in promoting dental caries.