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At least 343 records · Page 19Linked to original sources
PubMed1985

[Structure of the periodontal ligament during tooth eruption in the dog: descriptive aspects].

Serially stained uncalcified sections of young dog mandibles were examined to study the structure of the periodontal ligament of the erupting first right molar. The periodontal ligament around tooth crown presents three zones. The first, near the dental follicle, is a tick layer of parallel collagen bundles with numerous flattened fibroblasts. The second, intermediate, contains a blood vessels network, particularly veins and capillaries. The third, outer, is occupied by a continuous layer of osteoclasts and osteoblasts. Also the periodontal ligament around the tooth presents three layers, the outer and the intermediate rich of cells more than the inner. Particularly, the outer layer shows numerous osteoblasts surrounding the developing trabeculae of the alveolar bone and the collagen fiber bundles of the periodontal ligament. These penetrate into the trabeculae and appear similar to the osteoid layer. These results indicate that the alveolar bone increases by ossification of the connective tissue of the periodontal ligament.

Alveolar Process↗
PubMed1994

The relationship between preparation convergence and retention of extracoronal retainers.

PURPOSE: Although traditional ideal convergence (the sum of taper of the opposite sides) for crown preparation has been arbitrarily set at 4 degrees to 10 degrees, some believe absolute parallelism yields the highest retention. This study examined the relationship between the degree of convergence of a machined metal die and the retention of its casting. MATERIALS AND METHODS: The method used was that of cementing cast metal crowns onto full crown preparations on brass dies with varying convergence angles, and then recording the force required to remove the crowns from the dies in a vertical direction using a Tate-Emery Testing Machine and Load Indicator. RESULTS: It was found that retention (i.e., the force needed to remove the cemented castings from the die in their common long axis) increases from 0 degree convergence to peak between 6 degrees to 12 degrees convergence. It also seems that a critical film thickness does exist for optimum retention, and that film thicknesses smaller than the critical thickness may be responsible for the phenomenon that we have observed and directly related to the convergence angle itself. CONCLUSIONS: There seems to be experimental data supporting the use of traditionally taught convergence. Our study found that convergence angles between 6 degrees and 12 degrees seem to be optimum for tooth crown preparation when one plans to use zinc phosphate cement. Convergence angles of less than 6 degrees may not be desirable even if they can be clinically achieved. The results of our study indicate that a relationship exists between the convergence angle and the critical cement thickness that is necessary to realize the maximum strength properties of zinc phosphate cement.

Analysis of Variance↗
PubMed2003

Delayed tooth eruption in membrane type-1 matrix metalloproteinase deficient mice.

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is expressed highly in mineralizing tissues including bones and teeth. Mice deficient in MT1-MMP (-/-) display severe defects in skeletal development including dwarfism, osteopenia, and craniofacial abnormalities. Death occurs in these mice by about 3 weeks of age. Since MT1-MMP is expressed by the ameloblasts of the enamel organ and by the odontoblasts of the dental papilla, we asked if the developing teeth were adversely affected in the knockout animals. Molars from MT1-MMP -/- mice and controls were examined by histological, X-ray, and SEM analysis at 4, 18-20, and 25 days of postnatal development. At 4 days of development the molars from the -/- mice appeared histologically normal. At 18-20 days of development, the first molars of the -/- mice had apparently normal tooth crowns with normal dentin and enamel; however, the roots were truncated and the teeth had not yet erupted. In contrast to the -/- mice, the first molars of the 18-20-day control animals had erupted. SEM analysis of a -/- first molar and incisor revealed a normal enamel prism pattern. However, X-ray analysis demonstrated that tooth eruption was delayed by approximately 5 days and that the tooth roots were abnormally short in the knockout animals. Since MT1-MMP-deficient mice have been demonstrated to display a generalized increase in bone resorption, these data suggest that inefficient growth of bone surrounding the tooth root complex causes a delay in tooth eruption.

Animals↗
PubMed1987

Biological relationships derived from morphology of permanent teeth: recent evidence from prehistoric India.

Morphological variation in permanent teeth of prehistoric populations yields clues to their relationships with other prehistoric and living people. This paper documents variation in fourteen variants of the permanent tooth crown for the late Chalcolithic skeletal series from Inamgaon (1600-700 BC), an early farming settlement in western India. In comparison of the dental morphology profile at Inamgaon with American Indians and American Whites, the people of Inamgaon were found to more closely resemble American Whites. However, specific traits deviated in the direction of Amerindian dental trait frequencies, suggesting gene flow from north and east Asian populations. The dental morphology of the Inamgaon sample is similar to dental patterns characteristic of prehistoric Pakistani samples from Sarai Khola and Timargarha. However, Inamgaon and Timargarha exhibit somewhat more complex crown morphology than the Sarai Khola sample, suggesting a closer relationship between them and greater antiquity of residence in the subcontinent, in contrast to Sarai Khola sample.

Genetic Variation↗
PubMed2003

A prospective clinical trial comparing preformed metal crowns and cast restorations for defective first permanent molars.

AIM: This study investigated two methods for the restoration of permanent molars affected by amelogenesis imperfecta (AI) or severe enamel defects. METHODS: A prospective clinical trial was carried out on 17 subjects affected by AI or severe enamel defects of first permanent molars. A split mouth design was used so that each right or left permanent molar in both jaws was restored using either a preformed metal crown (SSC) or a cast adhesive coping (CAC). Subjects were followed for up to 24 months and assessed for longevity and quality of the restorations. Sequential analysis was used to compare longevity. RESULTS: Records for 42 restorations (19 SSC; 23 CAC) were kept. The split mouth design was possible on 24 occasions (right versus left=14; maxilla versus mandible=10). Three restorations, one SSC (at 6 months) and two CAC (at 2 and 19 months) failed and required replacement. There was no significant statistical difference between the two types of restorations. CONCLUSION: While there was no difference between the two restorations for quality and longevity, the SSC was considerably cheaper to use and needed only one visit, but more tooth tissue was lost in preparation and fitting. The CAC was significantly more expensive but left nearly all of the tooth crown intact. The choice of which restoration to use is indicated by the immediate and long-term needs of each individual patient.

Adolescent↗
PubMed1996

Immunolocalization of vitamin D receptor and calbindin-D28k in human tooth germ.

The role of vitamin D in ameloblasts and odontoblasts has been studied experimentally in rodents. Dental dysplasias have also been reported in clinical studies of children with rickets. Vitamin D acts via a nuclear receptor which binds the major metabolite, 1,25-dihydroxyvitamin D3, and positively or negatively controls the expression of specific genes. The most extensively studied markers of 1,25-dihydroxyvitamin D3 action are calbindin-D9k, calbindin-D28k, and osteocalcin. Therefore, to study in more detail the potential role of 1,25-dihydroxyvitamin D3 in human dental development, 1,25-dihydroxyvitamin D3 receptor (VDR) was localized by immunofluorescence in forming teeth (8-26 wk of gestation). Calbindin-D28k was also mapped by immunoperoxidase in antenatal and postnatal forming and formed teeth. VDR were detected in both dental epithelium and mesenchyme of bud, cap, and bell stages of tooth germs. Nuclei of overtly differentiated ameloblasts and odontoblasts were also immunostained. Calbindin-D28k was present in differentiated ameloblasts and odontoblasts. The presence of VDR and calbindin-D28k in ameloblasts and odontoblasts suggests that 1,25-dihydroxyvitamin D3 may contribute to the regulation of enamel and dentin formation, as classically reported for bone formation. Finally, the early appearance of VDR supports the concept that 1,25-dihydroxyvitamin D3 may also control forward stages of tooth crown development in humans.

Ameloblasts↗
PubMed1996

Marginal leakage of cast gold crowns luted with zinc phosphate cement: an in vivo study.

Marginal gaps of cast restorations are filled with luting agents that are soluble in intraoral fluids. This study investigated the marginal openings in eight extracted teeth with cast crowns that had been intraoral for 20 years or more. These teeth were extracted either because of periodontal disease or to facilitate insertion of a removable partial denture. Initially, the roots of the teeth were sealed with two coats of fingernail polish within 2 mm of the crown-tooth interface. Next, the teeth were immersed in a 0.05% aqueous solution of basic fuchsin die for 24 hours. Finally, each tooth was sectioned at four locations 1 mm apart. At each of these four sections, cement film thickness between tooth and casting, and microleakage were determined. The results of this study showed a mean cement film thickness of 74 microns on the mesial surface and 57 microns on the distal surface. Mean microleakage values were 432 microns on the mesial surface and 274 microns on the distal surface.

Adult↗
PubMed1996

Three-dimensional arrangement of enamel prisms and their relation to the formation of Hunter-Schreger bands in dog tooth.

The three-dimensional architecture of enamel prisms and their relationship to Hunter-Schreger bands were examined in the developing enamel of several dog teeth by light and electron microscopy, and computer-assisted reconstruction. Sections were prepared from a single demineralized tooth germ. Longitudinal semithin sections parallel to the meridian of the tooth showed parazones and diazones of the Hunter-Schreger bands in alternate rows at equal intervals. On sections vertical to the tooth crown through the middle region of parazone or diazone, a row of parallel prisms were angulated with the largest tilting angle being 55 degrees to the enamel-dentin junction, running in opposite directions in the respective zones. Tangential sections parallel to the enamel-dentin junction showed numerous belt-like zones arranged perpendicular to the meridian of the tooth. Each belt-like zone consisted of a group of enamel prisms oriented in the same direction, those in the neighboring zones being oriented in an opposite direction. The densely stained boundaries between the adjacent belt-like zones corresponded to the interface between parazone and diazone. Computer-reconstructed enamel prisms in the adjacent two zones were oriented in the opposite sidewards direction with occasional confluence and divergence. Scanning electron-microscopic observation of the developing enamel surface exposed by dissolution of the enamel organ revealed band-like arrangements of groups of pits encasing the Tomes' processes of secretory ameloblasts. The secretory faces of the pits inclined uniformly in the same sidewards direction, with those in the neighboring groups, in the opposite direction.

Animals↗
PubMed2000

[The influence of different root length on stress distribution in the bone around abutment root of telescopic overdenture].

OBJECTIVE: To investigate the influence of bone height around the roots on stress distribution in a mandible with two canines remained and covered with an telescopic overdenture. METHODS: Three-dimensional finite element method. RESULTS: As the height of the bone around the roots decreased, the stress increased. But the maximum stress in the bone in this study is lower than that in the bone around the canine under normal condition. CONCLUSION: In the mandible, when the alveolar bone resorption reaches the apical 1/3 of canine (root length 4, 5 mm), if part of the tooth crown was removed, to make an acceptable crown/root ratio, so the canine can be used as the abutment of an overdenture.

Compressive Strength↗
PubMed1996

Mandibular postcanine dentition from the Shungura Formation, Ethiopia: crown morphology, taxonomic allocations, and Plio-Pleistocene hominid evolution.

Over 200 hominid specimens were recovered by the International Omo Expedition of 1967-1976. Despite the fragmentary nature of this primarily dental collection, these hominid remains represent a major body of evidence about hominid evolution in eastern Africa during the 2-3 myr time period. Our analysis of the Omo dental collection is based on a large comparative sample of 375 quantifiable mandibular postcanine teeth of A. afarensis, A. africanus, A. aethiopicus, A. boisei, A. robustus, and early Homo. A total of 48 isolated mandibular premolars and molars of the Omo collection spanning the 2-3 myr time period is sufficiently preserved to allow reliable serial allocations and intertaxon comparisons and is the object of study in this paper. We present taxonomic identifications of these teeth and seven other mandibular specimens preserving tooth crowns. Metric analyses of this study include cusp area and crown shape variables taken on occlusal view diagrams. Nonmetric analyses were based on simultaneous observations of all relevant material to ensure accuracy of categorical evaluations. First, a combined metric and morphological evaluation was conducted to allocate each Omo tooth to either robust or nonrobust categories. Further taxonomic affinities were then examined. Our results indicate that nonrobust and robust lineages cooccur by circa 2.7 myr. We consider the Shungura robust specimens from Members C through F to represent A. aethiopicus. A significant phenetic transformation occurs at circa 2.3 myr, with the mosaic emergence of the derived A. boisei morphology across Member G times. Characterization of the East African nonrobust lineage is more difficult because of the comparatively subtle morphological differences seen among the dentitions of A. afarensis, A. africanus, and early Homo. The earlier Members B and C nonrobust specimens are difficult to evaluate and are considered indeterminate to genus or species. Both molars and premolars from Members E through G exhibit phenetic similarities to the early Homo condition and are considered as aff. Homo sp. indet. At present, there is no indication of multiple species in the Omo nonrobust sample at any time horizon. The 2-2.4 myr Omo nonrobust specimens exhibit some similarities to the stated Homo "rudolfensis" condition in size and morphology and are likely to represent the ancestral condition of the genus Homo. The bearing of these results on interpretations of early hominid evolution and diversification is considered.

Animals↗
PubMed1998

A new classification and techniques for simple restorative dentistry.

It is nearly one hundred years since G. V. Black proposed a simple, five-stage classification for carious lesions based upon the site of the lesion and the type of restorative material likely to be used for restoration. In the absence of both effective preventive measures and a knowledge of remineralization his approach was essentially surgical: having identified a lesion remove it surgically, as well as all surrounding susceptible tooth structure, to prevent recurrence. Surgery is no longer regarded as the primary choice for treatment of a disease and there are many factors which suggest that this system is out of date. Preservation of natural tooth structure should be the principal aim and this is best achieved through remineralization. Remaining cavitated areas can then be restored more conservatively, thus assisting in maintaining aesthetics as well as strength in the tooth crown. If the profession is to adopt a new approach to operative dentistry it is suggested that the psychology of introducing a new classification for carious lesions is a desirable move.

Dental Cavity Preparation↗
PubMed1998

Association of developmental regulatory genes with the development of different molar tooth shapes in two species of rodents.

While the evolutionary history of mammalian tooth shapes is well documented in the fossil record, the developmental basis of their tooth shape evolution is unknown. We investigated the expression patterns of eight developmental regulatory genes in two species of rodents with different molar morphologies (mouse, Mus musculus and sibling vole, Microtus rossiaemeridionalis). The genes Bmp-2, Bmp-4, Fgf-4 and Shh encode signal molecules, Lef-1, Msx-1 and Msx-2, are transcription factors and p21CIP1/WAF1 participates in the regulation of cell cycle. These genes are all known to be associated with developmental regulation in mouse molars. In this paper we show that the antisense mRNA probes made from mouse cDNA cross-hybridized with vole tissue. The comparisons of gene expression patterns and morphologies suggest that similar molecular cascades are used in the early budding of tooth germs, in the initiation of tooth crown base formation, and in the initiation of each cusp's development. Furthermore, the co-localization of several genes indicate that epithelial signalling centres function at the three stages of morphogenesis. The earliest signalling centre in the early budding epithelium has not been reported before, but the latter signalling centres, the primary and the secondary enamel knots, have been studied in mouse. The appearance of species-specific tooth shapes was manifested by the regulatory molecules expressed in the secondary enamel knots at the areas of future cusp tips, whilst the mesenchymal gene expression patterns had a buccal bias without similar species-specific associations.

Animals↗
PubMed1991

Prolonged effects of hypofunction on the mechanical strength of the periodontal ligament in rat mandibular molars.

The ultimate loads required to extract three mandibular molars in the dissected jaw were examined after elimination of the antagonistic teeth for up to 64 days. The ultimate loads in the experimental first and second molars decreased rapidly in the first few days, while those in the third molar remained low during the same period in both experimental and control groups. The ultimate loads in all three molars of the experimental animals then increased gradually towards the end of the experiment at rates similar to those in controls. Maximum relative reductions of the ultimate load were observed within the first 8 days in all three molars. An increase in the length of roots was also found in all hypofunctional molars. Daily rates of root elongation ranged from 13 to 19 microns/day in the control and from 18 to 26 microns/day in the experimental molars during the whole experiment. The greatest value (80 microns/day) was obtained during the first 8 days in the third molars of both control and experimental animals. Thus the mechanical strength of the periodontal ligament estimated in vitro may be increased by the development of teeth and by non-functional occlusal contacts with the opposing gingiva-covered alveolar ridge deprived of its tooth crowns. The ligament of the third molar was apparently immature at the beginning of the experiment.

Animals↗
PubMed1997

Different racemization ratios in dentin from different locations within a tooth.

It has been reported that the amount of D-aspartic acid in dentin is highly correlated with age. However, further studies are necessary to determine the details of this correlation. We quantitatively determined L- and D-aspartic acids in dentin, and from the data calculated the D/L ratio. We did not find any statistically significant difference in the D/L ratio between the same type of left and right teeth from the same jaw, and between the vestibular and lingual sides of the root dentin. However, the D/L ratio was significantly higher on the lingual side than on the labial side of the dentin. Although the D/L ratio in young subjects was comparatively high in the tooth crown and decreased toward the apex of the root, we did not always observe such a tendency in middle- to advanced-age individuals. These results indicate that the ratio of D/L aspartic acid in dentin varies between the lingual side and vestibular side of the crown dentin. Therefore, it appears that the racemization rate of aspartic acid is not uniform but differs with the region of the dentin, and may be affected by differences in factors such as temperature.

Adolescent↗
PubMed2001

Enamel hypoplasia in the deciduous teeth of great apes: variation in prevalence and timing of defects.

The prevalence of enamel hypoplasia in the deciduous teeth of great apes has the potential to reveal episodes of physiological stress in early stages of ontogenetic development. However, little is known about enamel defects of deciduous teeth in great apes. Unresolved questions addressed in this study are: Do hypoplastic enamel defects occur with equal frequency in different groups of great apes? Are enamel hypoplasias more prevalent in the deciduous teeth of male or female apes? During what phase of dental development do enamel defects tend to form? And, what part of the dental crown is most commonly affected? To answer these questions, infant and juvenile skulls of two sympatric genera of great apes (Gorilla and Pan) were examined for dental enamel hypoplasias. Specimens from the Powell-Cotton Museum (Quex Park, UK; n = 107) are reported here, and compared with prior findings based on my examination of juvenile apes at the Cleveland Museum of Natural History (Hamman-Todd Collection; n = 100) and Smithsonian Institution (National Museum of Natural History; n = 36). All deciduous teeth were examined by the author with a x10 hand lens, in oblique incandescent light. Defects were classified using Fédération Dentaire International (FDI)/Defects of Dental Enamel (DDE) standards; defect size and location on the tooth crown were measured and marked on dental outline charts. Enamel defects of ape deciduous teeth are most common on the labial surface of canine teeth. While deciduous incisor and molar teeth consistently exhibit similar defects with prevalences of approximately 10%, canines average between 70-75%. Position of enamel defects on the canine crown was analyzed by dividing it into three zones (apical, middle, and cervical) and calculating defect prevalence by zone. Among gorillas, enamel hypoplasia prevalence increases progressively from the apical zone (low) to the middle zone to the cervical zone (highest), in both maxillary and mandibular canine teeth. Results from all three study collections reveal that among the great apes, gorillas (87-92%) and orangutans (91%) have a significantly higher prevalence of canine enamel defects than chimpanzees (22-48%). Sex differences in canine enamel hypoplasia are small and not statistically significant in any great ape. Factors influencing intergroup variation in prevalence of enamel defects and their distribution on the canine crown, including physiological stress and interspecific dento-gnathic morphological variation, are evaluated.

Age Factors↗
PubMed1994

A possible explanation for the response characteristics of multi-tooth periodontal ligament mechanoreceptors in the cat.

During the course of a study on the morphology of periodontal ligament mechanoreceptors it was observed that a direct relation, without intervening bone, existed between the mandibular canine and first premolar tooth roots in the cat. An area, representing a window in the alveolar septal bone, extended 2-3 mm from the apex towards the tooth crown. Ruffini nerve terminals were observed amongst the collagen bundles in the ligament between the roots of the two teeth. Light and electron microscopy were used to identify the receptors. It is proposed that a periodontal ligament mechanoreceptor can respond to forces applied to adjacent teeth; movement of both teeth need not occur. This may explain the observation made in the past that single periodontal ligament mechanoreceptors respond to forces applied to more than one tooth.

Alveolar Process↗
PubMed2006

Buccal and palatal talon cusps with pulp extensions on a supernumerary primary tooth.

This paper reports an unusual occurrence of talon cusp on a supernumerary primary incisor, presenting on both labial and palatal sides. The tooth was scheduled for extraction due to its interference with the occlusion. Morphometric analysis of the taloned cusps was performed on digitized replicas of the tooth crown using open-source image analysis toolkit (ImageJ). Further non-destructive investigation of the taloned crown under cone-beam X-ray computed tomography revealed pulpal extensions in both talon cusps.

Child, Preschool↗
PubMed1989

Hertwig's epithelial root sheath differentiation and initial cementum and bone formation during long-term organ culture of mouse mandibular first molars using serumless, chemically-defined medium.

Studies were designed to test the hypothesis that Hertwig's epithelial root sheath (HERS) synthesizes and secretes enamel-related proteins that participate in the process of acellular cementum formation. Our experimental strategy was to examine sequential root development of the mouse mandibular first molar in vivo and in long-term organ culture in vitro using serumless, chemically-defined medium. Using anti-amelogenin, anti-enamelin and anti-peptide antibodies, enamel-related antigens were localized within intermediate cementum during HERS differentiation and root formation in vivo. Cap stage molars maintained for periods of up to 31 days in organ culture expressed morphogenesis and cytodifferentiation as identified by tooth crown and initial root, cementum and bone formation. Metabolically-labeled HERS products were analyzed by immunodetection using enamel-related antibodies and one- and two-dimensional SDS gel electrophoresis. A 72 kDa and 26 kDa polypeptide were identified in forming mouse cementum. Both of these root putative cementum proteins yield similar (identical) amino acid compositions; however, both proteins differed from the compositions of either mouse crown enamelin or amelogenin proteins. This approach provides a new and novel in vitro model towards understanding HERS differentiation and functions related to root and bone formation. The data support the hypothesis that HERS cells synthesize polypeptides related to but also different from canonical crown enamel proteins.

Animals↗