Comparative cariogenicity and dental plaque-forming ability in gnotobiotic rats of four species of mutans streptococci

The four species, each represented by two strains, all produced high levels of fissure caries in the upper and lower jaws of gnotobiotic Fisher rats. Streptococcus rattus strains and Streptococcus mutans NCTC 10832 gave low levels of approximal caries, whereas Streptococcus cricetus, Streptococcus sobrinus and Strep. mutans NCTC 10449 gave high levels. The only strains to produce buccal surface lesions were Strep. sobrinus and Strep. cricetus. All strains were able to form dense plaque in the central fissure of the second molar. Strep. cricetus, Strep. rattus and Strep. sobrinus strains were capable of producing smooth-surface plaque. This difference in plaque-forming ability did not correlate precisely with differences in cariogenicity, and such differences occurred between strains of the same species.     

In vivo dental plaque-forming ability and cariogenicity of the bacterium Streptococcus bovis in gnotobiotic rats

Germ-free Fisher rats, fed on a high sucrose diet, were monoinfected with Streptococcus bovis strains. High levels of fissure caries were formed by three strains; one strain produced moderate levels; another produced only very low levels. No strain could produce approximal or buccal/lingual lesions. All strains could colonize the fissures of teeth in the lower jaw, as shown by scanning electron microscopy. The most cariogenic strains were associated with caries scores similar to those of Strep. salivarius and members of the mutants streptococci.     

Relative cariogenicity and in-vivo plaque-forming ability of the bacterium Streptococcus oralis in gnotobiotic WAG/RIJ rats

The rats, fed a high sucrose diet, were mono-infected with seven strains of Streptococcus oralis. Moderate levels of caries were induced by four strains, and three others induced low levels. Approximal lesions were induced by two strains; no buccal/lingual lesions were produced. Scanning electron microscopy showed that all strains colonized the tooth fissures, some strains producing a moderately abundant and dense plaque. The most cariogenic strains (PB178, PB180 and PB186) induced similar levels of caries to Streptococcus milleri.     

In-vivo dental plaque-forming ability and relative cariogenicity of the bacteria Streptococcus mitis and Streptococcus sanguis I and II in mono-infected gnotobiotic rats

Sixteen strains of Streptococcus mitis, Streptococcus sanguis I and Strep. sanguis II were tested for cariogenic potential and in-vivo plaque-forming ability in a gnotobiotic WAG/RIJ rat test system. All strains produced far less fissure plaque in vivo than strains of Streptococcus milleri or Streptococcus mutans. There was less extracellular matrix around cells of Strep. mitis or Strep. sanguis than around Strep. mutans, in the fissures. Dense sheets of cells were observed only with Strep. mutans. Some localized colonization of exposed smooth surfaces occurred with most strains. Strep, mitis produced no caries in three tests, low-caries scores in two tests and high-caries scores in one test. A single strain of Strep. mitis produced a highly-cariogenic variant able to ferment raffinose. Strep. sanguis I induced low-levels of caries in 12 tests; one test of NCTC 7865 produced moderate levels of caries, and another test of 311 produced no caries. Strep. sanguis 311 was dextran-negative. Strep. sanguis II strains induced no caries in three tests, low caries scores in six tests and moderate levels of caries with Strep. sanguis 402. No strain of Strep. mitis or Strep. sanguis was able to induce smooth-surface lesions.     

An examination of strains of the bacterium Streptococcus vestibularis for relative cariogenicity in gnotobiotic rats and adhesion in vitro.

The cariogenicity and adhesion of six strains of Streptococcus vestibularis were compared with those of strains of Strep. salivarius. All strains of Strep. vestibularis produced low levels of caries, confined to the fissures, whereas the two strains of Strep. salivarius produced high levels of caries, with one strain producing approximal as well as fissure caries. The values for adhesion to saliva-coated hydroxyapatite of Strep. vestibularis in the absence (median 4.74%) and the presence (median 4.67%) of sucrose were not statistically different, nor did they differ significantly from those of Strep. salivarius. Strains of Strep. vestibularis were able to adhere to buccal epithelial cells (median 1.19%) as well as could Strep. salivarius strain HB (1.65%). Neither sucrose nor saliva greatly aggregated the strains of either species. Strep. vestibularis did not adhere to hexadecane (median 18.5%) to the same extent as did Strep. salivarius strains (median 69%). There was a significant correlation between the adhesion in the presence and absence of sucrose (p less than 0.01). Strep. vestibularis strains could not coaggregate with either actinomycetes or Veillonella spp. whereas Strep. salivarius strains were able to coaggregate with Veillonella spp.     

Comparative cariogenicity of oral streptococci in different strains of gnotobiotic rats

Testing the cariogenicity of specific streptococci in gnotobiotic Sprague-Dawley rats in the U.S.A. and in gnotobiotic Liverpool-hooded and WAG rats in Britain produced very similar results. This suggests that the use of gnotobiotic rats is advantageous for inter-laboratory tests of the cariogenicity of streptococci.     

Pulp response to and cariogenicity of Lactobacillus casei in monoinfected gnotobiotic rats

The maxillary molar pulps of germ-free rats were mechanically exposed and suspensions of a strain of freshly grown Lactobacillus casei were applied to the pulp wounds. The pulps were left open to the oral environment, and the animals were maintained within the isolator until death. In the majority of teeth, pulp necrosis was evident and apical inflammation was present in 40% of the specimens. The remaining monoinfected animals were bred and the litters were placed on a 46% sucrose diet to determine the cariogenicity of the test strain of L. casei in the mandibular molars. The organism proved to be noncariogenic. The effects of mechanical exposure of the maxillary molars in these animals were similar to those observed in the direct-inoculation study, with the exception of a reduced incidence of apical inflammation.     

A comparison between osteoclasts in vitro and in vivo in the periodontal ligament of the adult mouse

Twelve expiants of the first mandibular molar and surrounding periodontium of young adult mice were cultured for 7 days in vitro. The number and size of osteoclasts, the number of nuclei per osteoclast and the distribution of the osteoclasts in the periodontal ligament were compared with osteoclasts in periodontal ligament in vivo in mice of the same age as the mice from which the expiants were taken. Light microscope comparison of the two groups indicated that resorption of bone had occurred in vitro. There was a significant increase in the number and size of osteoclasts in the cultured expiants compared with the in vivo material. The numbers of nuclei per osteoclast and the distribution of osteoclasts in the periodontal ligament was similar in the two groups, but the greatest increase in osteoclast numbers occurred on the distal aspect of the distal root where there were most osteoclasts in vivo. It was concluded that there was active bone resorption and that osteoclasts formed de novo during culture of these expiants.     

The relative cariogenicity of different streptococci in the gnotobiotic WAG/RIJ rat

The relative carogenicity of 19 strains of streptococci in the gnotobiotic WAG/RIJ rat was studied and the results from 6 of these strains compared with data from gnotobiotic Liverpool-hooded rats. The high level of caries produced by Streptococcus salivarius and Streptococcus milleri was similar for both strains of rat. These findings, considered with the results from longer-term experiments, question the exclusive cariogenic status sometimes accorded to Streptococcus mutans.     

The cariogenicity of sucrose, glucose and maize starch in gnotobiotic rats mono-infected with strains of the bacteria Streptococcus mutans, Streptococcus salivarius and Streptococcus milleri

Twenty-one-day-old weanling gnotobiotic WAG/RIJ rats were mono-infected with Streptococcus mutans NCTC 10832, Streptococcus salivarius JMB or Streptococcus milleri NCTC 11169, and maintained on a high carbohydrate diet containing sucrose, glucose or maize starch for 21-days. Fissure caries developed with all combinations of streptococcal strain and carbohydrate except maize starch/Streptococcus salivarius JMB. Caries incidence was highest with Streptococcus mutans NCTC 10832. For all species, the ranking of carbohydrates by cariogenic potential was sucrose greater than glucose greater than maize starch.     

In vivo and in vitro study of the effects of chlorpromazine on tooth mineralization in rats and mice

The effects of chlorpromazine (CPZ) on tooth mineralization were examined using incisor dentine in adult rats and cultured tooth germs of mandibular first molars dissected from mouse embryos. CPZ (10, 50 and 250 mg/kg, s.c.) substantially inhibited dentine mineralization as evaluated by contact microradiographs. Plasma calcium and phosphorus concentrations were not decreased by CPZ (10 and 50 mg/kg). Physicochemical effects were not involved in the action of CPZ on the mineralization. In vitro experiments showed that CPZ (1 and 10 μM) inhibited mineralization and alkaline phosphatase (ALP) activity in the tooth germs. As CPZ has the properties of a calmodulin antagonist, the calmodulin antagonists W-7 and W-5 were also examined. Both inhibited mineralization and ALP activity in tooth germs; W-5 had less effect than W-7. These in vivo and in vitro findings suggest that CPZ inhibited cell-mediated mineralization in dentine without affecting the calciumdashregulating system and physicochemical mineral deposition. In addition, calmodulin could be involved in cell-mediated mineralization.     

Cariogenic potential in vitro in man and in vivo in the rat of lactate dehydrogenase mutants of Streptococcus mutans

Human tooth fragments transferred daily in sucrose containing cultures of Streptococcus mutans strain BHT-2 developed visible white spots, the characteristic lesion of early dental caries, within 10 days. By contrast, tooth fragments exposed to an L(+)-lactate dehydrogenase (LDH)-deficient derivative of BHT-2 showed no visible lesions, even after 21 days of transfer. More direct evidence for the non-cariogenic nature of LDH-deficient mutants was provided by gnotobiotic and conventional rat models, in which the mutants could colonize the mouth to approximately the same extent as their parent, but produced a significantly lower incidence and severity of dental caries. Reversion studies suggested that single gene mutations are responsible for the deficiency in lactate dehydrogenase catalytic activity, which in turn is responsible for the observed decreases in acid production and cariogenic potential of the mutants. These results lend strong support to the acidogenic theory of caries aetiology.     

2种镁基材料的体内外生物相容性研究

目的 探讨高纯镁和镁-1钙合金2种镁基材料的体内外生物相容性,为其临床应用提供安全性数据.方法 选择高纯镁和镁-1钙合金2种镁基材料,参照ISO 10993系列标准,开展细胞毒性、遗传毒性、皮内反应、致敏性、急性全身毒性和26w肌肉植入后组织反应的研究,探讨细胞活力的影响因素,评价其生物相容性.结果 高纯镁和镁-1钙合...     

A histochemical and radiobiological study of in vitro and in vivo human epithelial cell rest proliferation

Epithelial cell rests from periodontal ligament in vitro and epithelial trabeculae in apical granulomata were studied. The epithelial lining of dental cysts was also examined because of its probable origin from proliferated cell rest epithelium. Proliferated cell rests were obtained by culturing periodontal ligament explants in a closed culture system with McCoy's medium. DNA synthesis in this epithelium was confirmed by labelling explants with tritiated thymidine. A characteristic feature of the proliferated cells was their greatly increased amount of cytoplasm. Proliferated cell rest epithelium in vitro and in vivo exhibited little succinic dehydrogenase activity and contained no glycogen. However, lactic dehydrogenase and glucose-6-phosphate dehydrogenase activity was readily demonstrable. Lipid accumulation was a characteristic feature of proliferated epithelium. These findings are interpreted to formulate the thesis that in response to local environmental change, probably to change in oxygen/carbon dioxide tension, epithelial cells proliferate and are able to do so by virtue of their ability to undertake anaerobic glycolysis. It is suggested that endogenous protein synthesis required for cell multiplication is brought about partly by pentose shunt activity which is, in turn, linked with lipid synthesis.     

A comparison of the ability of strains of streptococci to form dental plaque-like deposits in vitro with their cariogenicity in gnotobiotic rats

Representative strains of Streptoccocus mutans, Streptococcus milleri, Streptococcus sanguis. Streptococcus mitis, Streptococcus salivarius and Streptococcus faecium were tested in vitro for their ability to form an adherent mass resembling plaque on nichrome steel wires. The potential of these streptococci for forming plaque in vitro was then compared to their cariogenicity in a known reproducible gnotobiotic rat system. The consistency and morphology of the plaque varies considerably between strains. However, no clear relationship was found between cariogenicity and the four plaque parameters of grade, weight, total extra-cellular polysaccharide and number of colony-forming units.     

An in vivo evaluation in children of the HPL bitewing device

The HPL bitewing device, a new beam-aiming collimating bitewing film holder, has recently been developed. The aims of this study were to assess the practicability of using the new device clinically and to compare the diagnostic yield obtained with the new technique with those obtained using a conventional freehand method and the Rinn XCP instrument. For each of the three techniques a pair of bitewings was taken of 30 randomly selected patients aged 6–15 years. These bitewings were evaluated for technical errors using seven different criteria, including the number and severity of overlapping contacts. The results show that the HPL method produced the greatest number of unoverlapped surfaces and the smallest proportion of moderate and severe overlaps. For five of the seven criteria, the HPL method produced fewer technical errors than the other two methods. Assessment of the acceptability of the procedures to the children revealed few differences between the three radiographic techniques. Further studies of the new technique, involving larger numbers of patients and sequential radiographs, are indicated.     

Fluoride uptake in human dentine from glass-ionomer cement in vivo

The purpose was to examine F uptake and distribution in dentine from a F-containing glass-ionomer cement in vivo. Nine volunteers were selected from dental students who were scheduled for extraction of their third molars. Two cavities were prepared on the same occlusal surface of the third molars for each subject; one was restored with glass-ionomer cement (Virtabond), the other with zinc phosphate cement as a control. After 3 months the teeth were extracted. F profiles in the dentine from the cavity floor to the pulpal surface were determined in tissue immediately adjacent to the restorations. An abrasive micro-sampling technique was used. The F concentration of the dentine was highest immediately beneath glass-ionomer cement filling, decreasing towards the pulpal surface. Overall F concentrations were greater in the dentine beneath the glass-ionomer cement than in that beneath the zinc phosphate cement. It was concluded that the glass-ionomer cement markedly enhanced fluoride uptake by underlying dentine in vivo.     

The production of dental plaque and caries by the bacterium Streptococcus salivarius in gnotobiotic WAG/RIJ rats

The abilities of ten strains of Streptococcus salivarius to colonize rat molars and to induce caries were determined using mono-infected germ-free rats. Scanning electron microscopy revealed the production of micro-colonies and spheroids by Strep. salivarius on exposed surfaces of molar teeth, and abundant dense plaque formation in fissures. Most strains colonized fissures and smooth surfaces as effectively as Streptococcus mutans NCTC 10832, yet produced no buccal or lingual lesions. The four K^? strains of Strep. salivarius produced more approximal lesions than the K⁺ strains but fewer lesions than Strep. mutans. All but one Strep. salivarius strain fell into the high-caries category, together with Strep. mutans. They were all more cariogenic than either Streptococcus milleri NCTC 11169 or Streptococcus faecalis 47.     

新型高氮无镍不锈钢骨植入材料的体内外生物相容性研究

目的 探讨新型高氮无镍不锈钢(-HNS)骨植入材料的体内外生物相容性,为其临床应用提供安全性方面的科学依据.方法 对HNS开展了细胞毒性、溶血性、遗传毒性(Ames和MLA试验)和致癌性方面的体外实验研究;进一步选择不同的动物评价了其皮内反应、致敏性和急性/亚慢性全身毒性;并以316L医用不锈钢材料为对照,研究兔胫骨内植入4w、12w和26w后HNS材料与骨组织之间的生物相容性.结果 HNS无明显的细胞毒性:无溶血;未诱发鼠伤寒沙门氏菌的体外基因回复突变;未引起体外哺乳动物细胞L5178Y/TK+/-的TK基因突变和染色体诱变;体外细胞转化试验结果为阴性;未引起动物皮肤过敏和皮内反应、不引起小鼠的急性全身毒性反应;亚慢性全身毒性试验中SD大鼠均未见临床全身毒性症状、试验组和对照组之间的体重及主要脏器体重比的差异均无统计学意义(P＞0.05)、血液学和临床生化主要检测指标与对照组之间的差异均无统计学意义(P＞0.05),动物的心、肺、肝、脾、肾、脑等主要脏器均未见异常改变.HNS植入后各期的组织学分析表明:相比316L医用不锈钢,HNS能更明显促进骨种植体周围的新骨形成.结论 新型HNS骨植入材料对生物体全身组织器官无潜在的危害性,生物相容性好,具有临床应用前景.     

Expression, localisation and synthesis of versican by the enamel organ of developing mouse molar tooth germ: An in vivo and in vitro study

Objective

Versican is a large, aggregating chondroitin sulphate proteoglycan. In dental tissue, versican expression occurs primarily in mesenchymal tissue but rarely in epithelial tissue. We investigated the expression, localisation and synthesis of versican in the enamel organ of the developing tooth germ.

Design

To elucidate versican localisation in vivo, in situ hybridisation and immunohistochemistry were conducted in foetal ICR mice at E11.5–E18.5. Epithelium and mesenchyme from the lower first molars at E16.0 were enzymatically separated and versican mRNA expression was investigated by semi-quantitative RT-PCR. Organ culture of the separated samples combined with metabolic labelling with [³⁵S], followed by gel filtration, was performed to analyse secreted proteoglycans.

Results

Versican mRNA was first expressed in the thickened dental epithelium at E12.0 and continued to be expressed in the enamel organ until the bell stage. Versican immunostaining was detected in the stellate reticulum areas from the bud stage to the apposition stage. The enamel organ at E16.0 expressed versican mRNA at a level comparable to that in dental mesenchyme. Furthermore, when compared to dental mesenchyme, about 1/2–3/4 of the [³⁵S]-labelled versican-like large proteoglycan was synthesised and released into tissue explants by the enamel organ.

Conclusions

The dental epithelium of developing tooth germ is able to synthesise significant amounts of versican.