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Biomedical subjects

P D Owens

Publications and source records attributed to P D Owens.

At least 19 recordsLinked to original sources
PubMed1991

Chick frontonasal process excision significantly affects mid-facial development.

The midfacial region in vertebrates may be considered as developing from five separate processes, namely the central frontonasal process (FNP) and the paired maxillary and lateral nasal processes. Relatively little is known about the mechanisms whereby these processes interact to produce structures of the neonatal/adult face. This study was undertaken to gain some insights into the events involved in this process, and involved observing the effects on facial development in the chick of surgical excision of the FNP, prior to its fusion with the other facial processes. In the absence of the FNP, outgrowth of the upper beak was dramatically reduced, agenesis of the primary palate occurred, and development of the maxillary processes and palatal shelves was impaired. Thus, in the chick, the frontonasal process plays a major role in midfacial morphogenesis. Not only does the FNP provide the primary palate and a contribution to the development of the nasal septum, it is also important in the ordered development of the maxillary processes and of the definitive secondary palate--contributions which have not emerged clearly from in vitro and teratogenic studies.

Animals↗
PubMed1991

The development and fate of the dental lamina of the mandibular first molar tooth in the rat.

The lamina of the first mandibular molar teeth of rats, age range 13 d intrauterine (i.u.) to 16 d postnatal (p.n.), was examined by light and transmission electron microscopy to establish histological baselines of its development and fate. All material was obtained from animals anaesthetised with ether, killed by cervical dislocation and prepared by routine methods for both types of examination. Contrary to earlier reports that the lamina remains intact throughout development, mesenchymal elements disrupt the lamina. These were seen first at 19 d i.u., as collagen-filled bays in the basal epithelial layers, associated with partial loss of related basal lamina. In the early stages, collagen deposition was limited and it was not obviously preceded by epithelial cell death or transformation, even though many bay-related cells showed lipid and glycogen accumulations. Later disruption of the lamina showed more mesenchymal cells as well as collagen in deeper spaces. After the onset of tooth eruption, mesenchymal cells external to and within the lamina contained lysosomal bodies and these plus evidence of related epithelial cell death and capillaries in the laminar spaces became more and more apparent. Similar collagen deposits were observed in a successional tooth primordium, which appeared at term but eventually aborted between days 5 and 10 p.n. Thus disruption of the lamina by connective tissue began earlier than has been reported previously and progressed as the tooth erupted towards the oral cavity. The evidence suggests that this disruption is initiated and sustained by mesenchymal cell activity rather than by programmed cell death or transformation of the epithelium.

Animals↗
PubMed1991

Reinnervation of developing rat molars.

The ability of regenerating inferior alveolar nerve (IAN) fibres to reinnervate dentine of developing rat first molar teeth was investigated. At intervals of 5, 15, 30 and 50 days after intramandibular transection of the IAN at the age of 20 days, the percentage of innervated dentinal tubules was estimated and compared with results from a series of control specimens. In addition, the myelinated axon populations of the root canal pulps were examined by light microscopy. Degeneration of almost all pulpal myelinated axons and dentinal unmyelinated axons occurred within 5 days of surgery. By 15 days after transection there was evidence of some pulpal reinnervation by myelinated axons but less than 2% of dentinal tubules showed reinnervation (control, 31.8%). At 30 days after surgery the figure for dentinal reinnervation was approximately 17.7% (control, 44.9%), and by 50 days after transection (70 days of age) mean innervation was about 70% of the level observed in control 70 days teeth, though the difference between control and experimental specimens was not significant at the 5% level of probability. The results indicate that reinnervation of dentine does occur in developing teeth after nerve transection. It is argued that the results suggest a faster and probably more complete reinnervation in young animals; and that reinnervation may be attributable more to an active than to a passive mechanism, and this may also apply to dentinal innervation during development.

Animals↗
PubMed1990

Dental histology in familial expansile osteolysis.

The dental histopathology is described of patients suffering from Familial Expansile Osteolysis (FEO), a rare and unique autosomal dominant disease which has severe bony as well as dental consequences. The predominant dental features are resorption of the cervical and apical regions of the roots, premature depositions both of irregular secondary dentin, which causes narrowing of the pulp cavities, and of cellular cementum, which causes patchy narrowing of the periodontal ligament. The dental pulp shows age-like changes, including multiple pulp stones and the ligament vasculature appears to be abnormal. Evidence for involvement of enamel is equivocal. This combination of dental effects together with the bony lesions distinguishes the disease from idiopathic external resorption of either the single or multiple kind, despite similarities in the histopathology of the resorptive lesions; and from other non-hereditary and hereditary osteolytic diseases.

Adolescent↗
PubMed1989

Intramembranous osteogenesis and angiogenesis in the chick embryo.

Membrane bone formation was examined in the developing chick frontal bone of Stage 32-36 embryos using alizarin red whole mounts, wax and resin histology, transmission electron microscopy and India ink injection techniques. Mineralised bone was seen at Stage 36, but was presaged by the appearance of twin mesenchymal condensations at Stage 35. The condensations appeared dorsolateral to the upper edge of the interorbital septum near its centre. The mesenchymal cells of the condensation were fusiform in shape and initially exhibited a close-packed, layered configuration which was avascular. Consequent differentiation of the central cells first into preosteoblasts and then into definitive osteoblasts, accompanied by secretion of bone matrix, coincided with blood vessel invasion of the frontal anlagen. It is suggested that these vascular changes associated with the onset of bone cell differentiation indicate that osteogenic cells may secrete an angiogenesis factor.

Animals↗
PubMed1988

Idiopathic external resorption of teeth.

An unerupted maxillary third molar tooth from a 57-year-old Caucasian male, which showed radiographic evidence of crown resorption, but was otherwise symptomless, was examined post-extraction by light and scanning electron microscopy. (SEM) Appearances of the residual dental tissues were consistent with a diagnosis of an invading external resorption with formation of pulpal granulation tissue, dentinal resorption and some dentinal metaplasia. SEM of crown fragments indicated a generally uniform pattern of enamel resorption, for which the ameloblasts rather than multinucleate cells were implicated. By extrapolation of the activity of the former cells during the late stages of amelogenesis and tooth eruption, it is suggested that resorptive activity of and by enamel epithelium may explain not only the coronal origin of this type of idiopathic resorption, (which is otherwise unexplained), but also its progress into the pulp and the pulp reactions.

Dental Enamel↗
PubMed1983

Microscopy of the dentine of enamel-free areas of rat molar teeth.

Dentine of the enamel-free areas (EFA) of first mandibular molar teeth of rats aged between 20-150 days was examined by scanning electron microscopy. Demineralized sections were stained with Gram-Twort's stain and examined for dental caries. In newly erupted teeth, a few dentinal tubules opened on the EFA surface. As teeth became worn down, extensive areas of EFA showed numerous patent tubules. In primary dentine, no occlusion or partial occlusion of tubules was apparent at any age except at the occlusal surface. It is postulated that this surface narrowing was caused either by dentine debris or salivary deposits. The only other covering of tubule openings appeared to be a thin salivary pellicle which in older animals was plaque-like. Patent tubules in primary dentine contained odontoblast processes which even in worn teeth extended to EFA surfaces. Processes in adjacent enamel-covered dentine also extended to the enamel-dentine junction. Only a few examples of bacterial invasion of EFA dentine were seen: in younger animals bacteria occupied cracks in the EFA surface, but in older animals they also occupied tubules. The EFA dentine does not appear to respond to attrition by infilling of the tubules; the persistence of vital odontoblast processes in worn teeth suggests that dead tract formation is not extensive. Continuous occlusal wear may restrict the progress of caries in EFA but odontoblasts in the rat may be also physiologically and immunologically involved in restricting the ingress of bacteria into otherwise poorly protected EFA.

Age Factors↗
PubMed1976

The root surface in human teeth: a microradiographic study.

In an attempt to clarify the nature of the human cemento-dentinal junction, ground sections of incompletely formed and fully formed extracted teeth were prepared and their histology compared with their microradiographic appearances. The results showed that incompletely formed teeth possess distinctive surface layers outside the granular layer of Tomes. The evidence indicates that these layers are of dentinal origin; their presence during development supports previous explanations by the author of the hyaline layer of Hopewell-Smith and of so-called intermediate cementum. The results also indicate that the granular layer of Tomes does not represent the outer limit of root dentine. The relationship of these surface layers to the definitive cementum which is present in fully formed teeth was studied in both young and older patients. From the results it was concluded that cementum formation begins in the more apical region of the teeth at a time when root formation is well advanced, and that it spreads towards the crown rather than in the generally accepted reverse direction.

Bicuspid↗