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At least 163 records · Page 9Linked to original sources
PubMed1996

The localization of epithelial root sheath cells during cementum formation in rat molars.

The purpose of this study was to investigate the distribution of epithelial cells and the fate of the basement membrane along the root surface of rat molars during cementogenesis, and to test the hypothesis that the Hertwig's epithelial root sheath (HERS) cells remain on the root surface if mineralization is inhibited. To demonstrate the HERS cells and basement membrane, immunohistochemistry with antibodies against keratin and laminin were used. The dentin matrix mineralization was inhibited by a single injection of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP). A modified Gomori staining method was used to monitor the inhibition of mineral formation in dentin and cementum. Paraffin sections were stained with haematoxylin-eosin, and freeze-dried sections were used for Gomori and immunohistochemical stainings. We found that the formation of acellular cementum was suppressed above the dentin with inhibited mineralization. Instead, a hyperplastic matrix, different from acellular cementum, covered the dentin. This hyperplastic cementum had keratin- and laminin-positive cells incorporated; such cells were never incorporated in normal acellular cementum. The later formation of cellular cementum correlated, in controls, with the disappearance of HERS cells from the root surface. Treatment with HEBP resulted in a persistent presence of epithelial cells, interpreted as an inhibition of their disappearance. In conclusion, there is evidence that the cells of HERS are involved in the development of both acellular and cellular cementum. The developmental processes of these tissues appear in some way to be influenced by or associated with the initial mineralization of the dentin.

Animals↗
PubMed1996

Origins of cementum.

There are diverging opinions about the role of Hertwig's epithelial root sheath in the formation of cementum. In the present review this role is discussed. There is increasing evidence that Hertwig's epithelial root sheath is actively involved in the formation of both acellular and cellular cementum. The development of acellular cementum seems to be associated with secretion of enamel-related proteins by cells of the epithelial root sheath. Formation of the matrix for cellular cementum appears to be induced by exposure of the inner layer of the epithelial root sheath to the mesenchymal cells in the dental follicle. Experimental studies with 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) indicate that the formation of acellular cementum must be preceded by mineralization of the mantle dentin. If the mineralization is inhibited by means of HEBP, there is precocious separation of the two layers of the epithelial root sheath after which matrix for a cellular type of cementum is formed.

Animals↗
PubMed1981

Hard tissue repair in idiopathic external resorption of teeth.

A histopathological study has been made of 18 erupted and eight unerupted teeth which showed signs of idiopathic external resorption. The findings support the generally accepted theory that osteoclasts are actively involved in the resorptive process, there was no evidence that mononuclear cells were active in this process. The concept that metaplastic hard tissue was deposited on resorbed dentine surfaces, possibly as a means to shield the pulp from the external environment could not be supported from the evidence from this study. When measured, the length of resorption on which metaplastic hard tissues had been deposited, expressed as a percentage of the resorbed area ranged from zero to 69.3 per cent in the 18 erupted teeth. The percentage of metaplastic tissue replacing resorbed tissue in the eight unerupted teeth examined ranged from zero to 55.6 per cent. This study has provided some information on the type of cell responsible for idiopathic external resorption and these findings have been discussed in the light of the results of research of others in this field. The role of metaplastic hard tissue and its function have been evaluated.

Adolescent↗
PubMed1994

In vitro development of lower first molars from the osteopetrotic microphthalmic (mi) mouse.

While the precise mechanism of tooth eruption remains unknown it has been established that for tooth eruption to occur a functioning dental follicle is essential and normal bone resorption is required. In the osteopetrotic microphthalmic (mi) mouse, teeth fail to erupt and development is affected. In the present study, an organ culture technique was established to culture successfully lower first molars from normal and affected mi mice so as to determine if developmental defects were intrinsic to the dental tissue or whether such defects were a result of local environmental factors. Tissue was cultured for up to 13 days and development assessed morphologically at varying time intervals using standard light microscopy. Teeth developed similarly in both animal groups studied. The only variation in the appearance of cultured tissue occurred in the cervical loop region with more curling evident in dental tissue from the affected animals. The results of this study therefore showed that dental tissue from both normal and affected mi mice can be cultured for up to 13 days and that there is no difference in their development. It would appear that these teeth have the same ability to develop and consequently erupt, however the local environment influences tooth development and alters the eruption potential.

Ameloblasts↗
PubMed1975

Age detection by radiography in Hereford cross Friesian steers.

The mandibles of 78 Hereford cross Friesian steers all showing a full complement of temporary teeth were examined both visually and by radiography to determine whether it was possible to differentiate their various ages. All but one animal were slaughtered at the same weight (1020 lb-464 kg) and their ages at slaughter ranged from 1 year 3 months to 1 year 9 months. Differences were found between the mean ages for stages of resorption of the first temporary incisor roots, stages of first permanent incisor root formation and stages of second incisor crown formation, as determined by radiographic inspection. The results indicated that the age of a group of animals could be defined, but the age range within each development stage meant that it was not possible to define the age of individual cattle.

Age Determination by Teeth↗
PubMed1998

Phosphoprotein analysis of sequential extracts of human dentin and the determination of the subsequent remineralization potential of these dentin matrices.

Phosphoprotein appears to play an important role in the mineralization of dentin during tooth development and remineralization after demineralization by dental caries. To better understand this role, we describe the extraction and characterization of phosphoprotein from immature, human root apex dentin during and after EDTA demineralization. The extraction procedure included dissociation of the demineralized dentin matrix by guanidine hydrochloride (Gdn.HCl) followed by subsequent digestion with cyanogen bromide (CNBr) and collagenase. Characterization of these extracts included 'Stains-All' staining of SDS polyacrylamide gels (SDS-PAGE) and amino acid, protein and phosphorus analyses. The ability of these matrices to remineralize was determined by TEM and measuring calcium levels in the remineralized tissue by atomic absorption spectroscopy. The staining of SDS-PAGE gels and amino acid analysis showed that an intact phosphophoryn was extracted from the dentin of the immature apices during EDTA demineralization and that it had an apparent Mr approximately 140,000. In the subsequent extracts and digests, the phosphoprotein has a range of molecular weights, some of which may have been degraded products of the intact phosphoprotein. A greater quantity of phosphoprotein was found in the EDTA-demineralized dentin matrices than in dentin after Gdn.HCl, CNBr and collagenase digests. These EDTA-demineralized matrices also remineralized to a greater extent than those dissociated with Gdn.HCl. The differences in both the quantity and the quality, as defined by the amino acid residue profile, of the phosphoprotein in the sequential extracts of the root apex dentin may be important in affecting the ability of this tissue to remineralize.

Adolescent↗
PubMed1999

A polarized light and scanning electron microscopic study of human fissure and lingual enamel of unerupted mandibular third molars.

Using histological and ultrastructural techniques the aims of this study were to investigate whether the mineralization pattern and surface microanatomy of the caries-susceptible fissure enamel were different from those on the caries-inactive lingual surface. The material consisted of 31 unerupted third mandibular molars. The specimens were initially grouped into four categories: (1) without, (2) with initial, (3) with almost completed and (4) with completed root formation. One ground section with fissure-like morphology was selected from each tooth. Using water as a medium the observed birefringence was negative along the lingual and fissure transverses in specimens with almost completed and with completed root formation, while the observed birefringence was positive at different distances in the enamel in sections representing less maturation stages. Qualitative imbibition studies revealed hypomineralized enamel in the lower part of the fissures in specimens representing almost and completed root formation. Imbibed in quinoline, parts of the hypomineralized enamel behaved like a molecular sieve due to the presence of micropores, indicating that the structural arrangement is different from that in the enamel adjacent to this areas. After division of the sections into a lingual and a buccal part, SEM features were described from lower and upper parts of the buccal fissure wall and on lingual enamel in the area corresponding to the bottom part of the fissure. The surface microanatomy varied greatly. Negative developmental irregularities such as fissures and holes were associated with the immature enamel, while matured enamel - particularly fissures - housed many positive developmental irregularities such as enamel caps and protrusions. The crystal size in the mature specimens appeared smaller and more uniform than the crystals from the immature specimens. Apart from the occurrence of hypomineralized enamel in fissures and numerous positive developmental irregularities on the fissure surface, no major differences between fissure and lingual enamel were noticed, neither with respect to mineralization pattern during final stages of tooth development nor to the degree of surface porosity prior to tooth emergence.

Crystallography↗
PubMed1975

Dental eruption patterns in Parapithecidae (Primates, Anthropoidea).

Radiographic analysis of mandibular fragments of the Oligocene primates Apidium phiomense and Parapithecus grangeri provides sequences of postincisor development and eruption. Although retaining the premolar eruption sequence (P2 leads to P4 leads to P3), the parapithecids possessed the derived feature of delayed canine appearance which, with other characters of cranial and postcranial morphology, aligns them with Anthropoidea and not Prosimii or platyrrhines.

Animals↗