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Biomedical subjects

B Nyvad

Publications and source records attributed to B Nyvad.

At least 37 records · Page 2Linked to original sources
PubMed1990

Comparison of the initial streptococcal microflora on dental enamel in caries-active and in caries-inactive individuals.

This study compared the initial (4 h) microflora on enamel in 7 caries-active and in 7 caries-inactive adolescents. In both groups the microflora was dominated by streptococci which comprised 61 and 78% (median values) of the total viable counts in caries-active and caries-inactive individuals, respectively (p less than 0.01). Identification of a total of 700 streptococcal isolates according to a recently revised classification showed that the predominant streptococci belonged to the species Streptococcus oralis, Streptococcus mitis biovar 1, and Streptococcus sanguis. Early plaque from caries-inactive individuals differed from that of caries-active individuals by significantly higher proportions of S. sanguis (p less than 0.05) and IgA1 protease producing streptococci (p less than 0.05). In caries-active individuals, there was a tendency to elevated levels of S. mitis biovar 1 (p less than 0.10). In addition, caries-active individuals were colonized by significantly higher numbers of mutans streptococci on the enamel surfaces (p less than 0.01). However, in both groups Streptococcus mutans (serotype c) comprised less than or equal to 2% of the early streptococcal flora. Streptococcus gordonii, S. mitis biovar 2, and Streptococcus salivarius were present in low proportions and did not show differences in distribution that could be related to caries activity. The observed differences in the composition of the early streptococcal microflora may be a factor that governs the eventual cariogenic potential of dental plaque.

Adolescent↗
PubMed1990

An ultrastructural study of bacterial invasion and tissue breakdown in human experimental root-surface caries.

This study describes the structural features of the interface between microbial deposits and root cementum in actively progressing root-surface caries lesions developed experimentally in six elderly individuals. A total of 18 specimens was examined by microradiography, and a further 18 by light and transmission electron microscopy after intra-oral periods of one, two, and three months. All specimens showed various degrees of subsurface dissolution of mineral and bacterial invasion of the cementum. Although the microradiographic pattern of mineral loss was subsurface in nature, transmission electron microscopy showed dissolution of crystals in the outermost layers of the cementum, with a distinct gradient inward. Bacterial invasion occurred along the borders between bundles of relatively well-mineralized extrinsic collagen fibers in which the characteristic cross-banding remained intact. The pattern of bacterial invasion was influenced by the incremental lines and the cemento-dentinal junction. The invading bacteria were almost exclusively Gram-positive, of various shapes, and possessed thick, moderately electron-dense cell walls and electron-lucent "vacuoles" in the cytoplasm. It is concluded that because of pronounced mineral loss of the outermost cementum, accompanied by bacterial invasion, the surface of an active cementum caries lesion, as observed by transmission electron microscopy, is not identical to that seen in microradiograms.

Aged↗
PubMed1989

Structure of dental plaque and the plaque-enamel interface in human experimental caries.

This study describes the ultrastructure of dental plaque and the plaque-enamel interface after 2 and 3 weeks' exposure to a cariogenic challenge. Five dental students carried a total of 25 specimens of smooth surface enamel in intraoral acrylic appliances. During the initial 3 days the volunteers refrained from oral hygiene and performed nine daily mouthrinses with 10% (w/v) solutions of sucrose. After the 3rd day the volunteers cleaned their natural teeth, whereas the experimental sites were left undisturbed except for nine daily extraoral 5-min immersions in 5% (w/v) solutions of sucrose. Clinically, three patterns of colonization were observed after 3 days. At the histological level the experimental bacterial deposits also exhibited three distinctly different structural patterns after 2 and 3 weeks. Individual patterns consistently differed with regard to the microbial composition, the structural organization of the deposits, and the presence or absence of crystal-like material. However, in all individuals a layer of densely packed gram-positive bacteria resembling Actinomyces was consistently present close to the enamel surface. In 1 individual the microbial deposits were dominated by large bacteria, the ultrastructure of which conformed to the description of Stomatococcus mucilaginosus. These findings may partly explain pronounced individual variations in the rate of caries lesion development and progression in vivo.

Bacteria↗
PubMed1989

Microradiography of experimental root surface caries in man.

The aim of this study was to describe the pattern and rate of mineral loss during experimental root surface caries in situ without giving frequent sucrose rinses as a supplementary cariogenic challenge. Six elderly persons carried at total of 18 specimens of unerupted human root surface in recessions of lower partial dentures for 1, 2 and 3 months. Another six root surfaces served as controls. No cleaning of the specimens was allowed during the experimental period whereas the natural dentition was cleaned with a nonfluoride toothpaste. All the specimens, as observed by quantitative microradiography, exhibited subsurface caries lesions. Despite variation between individuals the depth of subsurface demineralization increased linearly with time, the average depth of the lesions being 240 microns after 1 month and 630 microns after 3 months. Delta MC, calculated as the difference in total mineral content between control and test specimens throughout the lesions, increased linearly with time from 2,000 to 8,400 vol% microns after 1 and 3 months, respectively. Preparation for microradiography induced a certain shrinkage of the lesions which resulted in an underestimation of the actual loss of mineral. It is concluded that this experimental model is suitable for studying the etiology and prevention of root surface caries provided the interindividual variation is taken into account.

Aged↗
PubMed1988

Organic structures of developmental origin in human surface enamel.

The aim of this study was to examine the distribution of organic material in mature enamel surfaces immediately prior to eruption. Thirty-six samples of buccal or lingual enamel from unerupted third molars were prepared for transmission electron microscopy by a method involving demineralization of the enamel after embedding in Epon. The results showed that at time of eruption human surface enamel is a highly porous structure containing large amounts of developmental protein which appear as a variety of triangular, funnel-shaped, or invaginated configurations extending into the enamel. The implications of this finding may be of importance to the understanding of early caries lesion formation in the enamel since organic structures may modify the diffusion of ions in and out of the tissue.

Crystallography↗
PubMed1987

Microbiology of the early colonization of human enamel and root surfaces in vivo.

This study describes the predominant early microflora on human teeth on the basis of microbiologic identification of 1742 fresh isolates. The isolates were obtained from four dental students who carried test pieces of enamel and root surface in the oral cavity for 4, 8, 12, and 24 h. During the experimental periods oral hygiene was discontinued. Under equal conditions root surfaces were more heavily colonized than were enamel surfaces. However, the composition of the microbiota was the same. Within the first 24 h the microflora was dominated by streptococci and Gram-positive pleomorphic rods. S. sanguis contributed only 6-18% of the early colonizers whereas S. mitis and S. oralis varied between 24-42% and 1-27% (mean values), respectively. The relative proportion of S. oralis increased significantly within the observation period while the proportion of S. salivarius and arginine-positive S. mitis showed a declining tendency. Actinomyces species adsorbed to the tooth surfaces within the first 4 h but did not increase their relative proportions until after 8-12 h, possibly due to a long doubling time. In one individual, encapsulated bacteria resembling Stomatococcus mucilaginosus were observed among the early colonizers. The time-dependent shifts in the bacterial populations within 24 h corroborate parallel ultrastructural findings.

Bacteria↗
PubMed1987

Scanning electron microscopy of early microbial colonization of human enamel and root surfaces in vivo.

This study describes the pattern of microbial colonization in six dental students, who carried test pieces of enamel and root surface in intraoral acrylic appliances for 4, 8, 12, 24, and 48 h, respectively. Oral hygiene was discontinued during the experimental periods. The results showed that oral microorganisms colonized enamel and root surfaces individually. The pattern of colonization mimicked the surface structure of the tooth; on enamel surfaces the first bacteria appeared in pits and surface irregularities followed by proliferation along the perikymata, while on root surfaces bacterial colonization was characterized by a haphazard distribution. Within the initial 24-h period root surfaces were more heavily colonized than were enamel surfaces. This pattern was characteristic irrespective of differences in the intra- and interindividual rates of bacterial coverage. It is concluded that early microbial colonization in vivo is determined by the surface structure of the tooth. Consequently, natural tooth surfaces should not be replaced by artificial surfaces in structural studies of microbial deposits in the oral cavity.

Adult↗
PubMed1987

Transmission electron microscopy of early microbial colonization of human enamel and root surfaces in vivo.

This study describes the early microbial colonization of teeth by the use of light- and transmission electron microscopy. Six dental students carried a total of 60 test pieces of unerupted enamel and root surface in intraoral acrylic appliances for 4, 8, 12, 24 and 48 h, during which periods oral hygiene was abandoned. Pronounced variations were recorded in structure and thickness of the pellicle across the individual surfaces of both dental tissues. Bacterial single-cell colonization increased the electron density of the adjoining pellicle. Micro-colonies of bacteria were observed in relation to enamel surface irregularities such as perikymata, while the distribution on root surfaces appeared incidental. Root surfaces were generally colonized by thicker deposits than homologous enamel surfaces although the structural composition of the microbiota was similar. Gram-positive bacteria with thick cell walls appeared in coccoid or rod-shaped configurations depending on the age of the bacterial deposit. These bacteria were further characterized by selective invasion between collagen fibers. After 48 h the complexity of the microbiota was increased by the establishment of new bacterial species in the superficial layer. It is concluded that the pattern and composition of the early microbiota on teeth is more complex and variable than hitherto assumed.

Bacteria↗
PubMed1986

Active root surface caries converted into inactive caries as a response to oral hygiene.

The clinical characteristics of 24 active root surface lesions on buccal surfaces were recorded through 18 months after implementation of meticulous toothbrushing with a fluoride toothpaste (F congruent to 0.1%). Within a period of 2-6 months all lesions had changed from soft, greasy and yellowish to leathery or hard, darkly discoloured tissue, indicating a gradual transition from active into inactive stages of caries. The observations stress the dynamic nature of the root caries process. It is concluded that when dealing with root surface caries it is essential to distinguish between active and inactive lesions and that classical operative treatment to a great extent can be avoided.

Adult↗
PubMed1973

[Dental practice].

Explore the source record for details and available documents.

Education, Dental↗
PubMedDate not supplied

Reliability of a new caries diagnostic system differentiating between active and inactive caries lesions.

Current scoring systems for dental caries do not consider the dynamic nature of the disease. The aims of the present study were to describe a new set of clinical caries diagnostic criteria which differentiate between active and inactive caries lesions at both the cavitated and non-cavitated levels and to evaluate the reliability of this criteria system in a population with high caries experience. Ten diagnostic codes were defined: 0 = sound; 1 = active (intact); 2 = active (surface discontinuity); 3 = active (cavity); 4 = inactive (intact); 5 = inactive (surface discontinuity); 6 = inactive (cavity); 7 = filling; 8 = filling with active caries; 9 = filling with inactive caries. Distinction between active and inactive caries lesions was made on the basis of a combination of visual and tactile criteria. The inter- and intra-examiner reliability was assessed through repeated examinations of 50 children by 2 recorders over a period of 3 years. The percentage agreement of caries diagnoses varied between 94.2 and 96.2%. The kappa values ranged between 0.74 and 0.85 for intra-examiner examinations and between 0.78 and 0.80 for inter-examiner examinations; 81.6% of all misclassifications involved non-cavitated caries lesions. Disagreement between sound surfaces and non-cavitated active or non-cavitated inactive lesions (31.3 and 31.2%, respectively) was more common than disagreement between non-cavitated active and non-cavitated inactive lesions (10. 6%). The probability of reconfirming a sound, non-cavitated active or non-cavitated inactive caries lesion - given that the surface was diagnosed as either sound, non-cavitated active or non-cavitated inactive at the first examination - was 98.0, 68.7 and 72.5%, respectively. The results show that the use of a new set of clinical caries diagnostic criteria based on activity assessment can be performed with a high reliability, even when non-cavitated diagnoses are included in the criteria system.

Adolescent↗
PubMedDate not supplied

A comparison of clinical and radiographic caries diagnoses in posterior teeth of 12-year-old Lithuanian children.

Bite-wing radiography has been recommended for use in adolescents as clinical examinations alone may lead to underestimation of carious lesions in approximal and occlusal surfaces. The aim of this study was to describe the relationship between clinical and radiographic caries diagnoses among 12-year-old Lithuanians using a new clinical scoring system which differentiates between cavitated and non-cavitated caries lesions. Eight hundred and seventy-two children were examined clinically and two standardized posterior bite-wing radiographs were taken of each participant. Bite-wing radiography contributed significantly to the total number of lesions diagnosed only at the dentin level in approximal surfaces. Clinical examination performed better than radiographic examination at the non-cavitated/enamel level, particularly on occlusal surfaces. Less than 2% of the clinically sound surfaces were diagnosed with dentin lesions/fillings radiographically. When using the cavitated level of clinical diagnosis, the frequency of 'hidden' caries lesions increased from 1.9 to 2.9% in approximal surfaces, and from 1.7 to 5. 2% in occlusal surfaces. The intra-examiner reliability data for the clinical and radiographic recordings supported the conclusion of an additional diagnostic value of bite-wings only for approximal surfaces. The findings demonstrate that the diagnostic yield of bite-wing radiography is higher for approximal than for occlusal surfaces. The efficacy of bite-wings depends on the refinement of the clinical caries diagnostic criteria. 'Hidden' caries does not seem to be a major problem when the clinical caries diagnostic criteria include non-cavitated diagnoses.

Bicuspid↗
PubMedDate not supplied

Strain-related acid production by oral streptococci.

Acid production, in particular at low pH, is thought to be an important ecological determinant in dental caries. The aim of the present study was to determine the acid producing capability at different pH levels of 47 streptococcal strains, representing 9 species, isolated from human dental plaque. The bacteria were grown until mid log-phase under anaerobic conditions and acid production was measured in a pH-stat system at pH 7.0, 6.0, 5.5 and 5.0. At all pH values, the mean velocity of acid production (V(ap)) by Streptococcus mutans and S. sobrinus was significantly higher (p<0.01; ANOVA) than that of the other oral streptococci, including S. mitis, S. oralis, S. gordonii, S. sanguis, S. intermedius, S. anginosus, S. constellatus, and S. vestibularis. However, the V(ap) of some strains of S. mitis biovar 1 and S. oralis, particularly at pH values of 7.0 and 6.0, exceeded that of some strains of S. mutans. The V(ap) decreased with pH for all strains, but some strains of S. mitis biovar 1 and strains of the mutans streptococci maintained a relatively high rate of acid production. The results suggest that some strains of S. mitis biovar 1 and S. oralis may play an important role in caries development by modifying the environment in dental plaque to become favourable for the succession of aciduric species. The study furthermore emphasises the need for detailed species and biovar identification of oral streptococci and for recognition of the significant physiological differences that occur within single species.

Acids↗