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At least 433 records · Page 24Linked to original sources
PubMed1989

[Fine structural observations of age changes in cementocytes of human permanent teeth].

Human cementum formation is a continuous process which occurs throughout life. Young cementocytes are situated near the periodontal membrane and old cementocytes towards the cementodentinal junction. Electron microscopic observations on 110 cementocytes of human permanent teeth were carried out to analyze the morphological and morphometric changes due to ageing. Cementocytes with ageing showed a rapid decrease in the number of the cell and a gradual decrease in the size of the cell, nucleus and cytoplasm. The location of the nucleus was changed from the periodontal side to the dentinal side and was hyperchromatic. Organelles showed a decrease in the size of the mitochondria, the rough-surfaced endoplasmic reticulum and the Golgi apparatus, meanwhile showing a gradual increase in the number of vacuoles and lysosomes. The cell death with ageing showed a rapid increase in number and their lacunae contained nuclear remnants, mitochondrial-like structures and fine fibrillar materials. Two distinct types of age changes were recognized: cytoplasmic swelling with scanty organelles and pronounced vacuoles, and cytoplasmic atrophy preserving the rough-surfaced endoplasmic reticulum in the narrowing cementum lacuna.

Aging↗
PubMed1995

Evaluation of acidogenicity of commercial isomaltooligosaccharides mixture and its hydrogenated derivative by measurement of pH response under human dental plaque.

The acidogenicity of commercially available isomaltooligosaccharides mixture (IMO) and its hydrogenated derivative (IMO-H) were evaluated by the in vivo pH response under dental plaque of six subjects (aged 25-28) using intraoral apparatus. The apparatus, an indwelling pH sensor of a hydrogen ion-sensitive field effect transducer (ISFET), was placed on the buccal site of the mandibular first molar, and the plaque was accumulated for four days. The test sugars were applied with three methods-dropping the solution directly on the plaque, rinsing the oral cavity with the solution, and sucking a candy made of the test sugar (weight 3-4 g). IMO could not be evaluated as a type of sugar with low acidogenicity, especially by the candy method, but IMO-H could be evaluated as a type of sugar with very low acidogenicity in a similar manner as maltitol or sorbitol in all type of applications. The acidogenic response of dental plaque should be assumed to be closely related to salivary parameters such as the secretion rate or to mutans streptococci level of subjects and types of application.

Adult↗
PubMed1989

Ultrastructure of a new generation of odontoblasts in grafted coronal tissues of mouse molar tooth germs.

Third molar tooth germs were removed from 14-day-old mice and freed from the enamel organ and follicle. After section of the apical tissues, including Hertwig's sheath, they were transplanted in 1-day-old newborn mice of the same lineage. Electron microscopy of grafts removed 7, 14 and 21 days later showed that, following the disappearance of the initial layer of odontoblasts and a period of adaptation, 14 days after transplantation newly differentiated odontoblasts deposited tubular dentine. The dentine matrix production was increased over that of controls, demonstrating that synthesis was accelerated, possibly because of lack of nerves in the grafts. Numerous characteristic structures that might be involved in the transit of proteoglycans from the Golgi apparatus were seen, as far as the extremity of the odontoblast processes. The particular experimental conditions allowed the observation in the neck region of the odontoblast of a concentration of coated vesicles which might be involved in cellular lengthening. Thus, in the presence of a fine and regular vascular network, a new generation of odontoblasts may differentiate, even in the absence of epithelial and nervous elements, and so predentine may contain inductive factors that allow the odontoblastic differentiation of pulp cells in contact with it.

Animals↗
PubMed1989

Ultrastructural changes in rat-molar cementoblasts after administration of puromycin.

Ultrastructural changes in rat-molar cementoblasts after administration of puromycin were observed. Young Wistar male rats were injected with 200 mg/kg of puromycin dihydrochloride. At 10, 30, 60, and 180 minutes after the injection, the animals were fixed by perfusion with 2.5% glutaraldehyde-2.0% paraformaldehyde. After perfusion, the lower first molars were dissected out of the mandibles, and their cementoblast were observed in an electron microscope. Striking changes were seen in the Golgi apparatus and the rough endoplasmic reticulum after puromycin administration. The Golgi saccules were dilated and devoid of content. Golgi vacuoles and secretion granules were reduced in number. Numerous small, smooth-walled vesicles, 45-70 nm in diameter and a large number of coated vesicles were present in the Golgi area. The rough endoplasmic reticulum showed unusual shapes and arrangement. Ribosomes attached to the reticulum lost polysomal arrangement. These changes progressed following the time elapsed after experiment, and a great number of large vacuoles which contain fine flocculent material came to predominate the supranuclear areas of the cementoblasts.

Animals↗
PubMed1990

Shear bond strength of light-cured glass ionomer to enamel and dentin.

The shear bond strengths of a light-cured glass-ionomer cement to enamel and dentin were determined with use of extracted human maxillary permanent canines and molars. Bonding sites on the ground, etched enamel and ground dentin surfaces were demarcated by the punching of a hole, 3 mm in diameter, in an adhesive tape. The mixed glass-ionomer cement was transferred to the demarcated site, cured by exposure to visible light for 30 s, and the cement surface treated with Scotchprep Dentin Primer followed by Scotchbond 2 Light Cure Dental Adhesive. The embedded teeth were positioned in an assembly apparatus, and Silux composite was bonded to the glass-ionomer-cement surfaces. The specimens were disassembled after 15 min and subjected to a shear load (in an Instron machine) immediately after disassembly; after storage in water at 37 degrees C for 24 h, without and with temperature cycling; and after storage in water for four weeks, without and with temperature cycling. The shear bond strength of the glass-ionomer cement to etched enamel was in the order of 12 MN.m-2, and to dentin it was 9 MN.m-2. Temperature cycling and duration of storage had no adverse effect on the shear bond strength. The enamel and dentin aspects of fractured test specimens were examined, and the percentage of the bonding area that failed in the cement was estimated. Most of the test specimens failed partly at the enamel and dentin interfaces and within the glass-ionomer cement.

Analysis of Variance↗