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A D Beynon

Publications and source records attributed to A D Beynon.

At least 19 recordsLinked to original sources
PubMed1998

The mixed dentition and associated skull fragments of a juvenile fossil hominid from Sterkfontein, South Africa.

In April-May 1983, the late A.R. Hughes and his field team recovered more than 40 bone fragments and teeth from a single solution pocket of the Sterkfontein Formation. After preparation and reconstruction by JMC, it was recognised that these fragments represent a single juvenile individual (Stw 151), consisting of more than 40 cranial and dental parts, with mixed dentition. It constitutes the most complete set of jaws and teeth of an early hominid child since the Taung child was recovered in 1924. In this paper, the morphological and metrical features of the individual teeth are described. The other associated skull fragments (right ramus of the mandible, left petrous bone, right glenoid region) are also described. Comparisons are made with other South (and East) African fossil hominids. The beautiful preservation simultaneously of most of the deciduous teeth and of the permanent teeth exposed in their crypts allows an accurate analysis of the developmental sequence. A report on the dental developmental status of this juvenile is presented. On the basis of the microanatomical study of the developing permanent teeth, the estimated age at death is 5.2-5.3 years. Reconstructions of the maxillary and mandibular arcades are also offered. The morphological and metrical features of Stw 151 raise the possibility that it may represent a hominid more derived towards an early Homo condition than the rest of the A. africanus sample from Member 4.

Animals↗
PubMed1998

Comparative dental development and microstructure of Proconsul teeth from Rusinga Island, Kenya.

Eighteen histological sections were prepared from eleven teeth attributed to Proconsul heseloni and two molar teeth attributed to Proconsul nyanzae. Measurements of spacings and counts of daily incremental markings in both enamel and dentine were possible in the majority of these tooth sections. Measurements of the spacings and angles to the enamel dentine junction (EDJ) of regular striae of Retzius and of equivalent markings in dentine were also made. In addition to these measurements, counts of perikymata were made on replicas of all other Proconsul teeth housed in the National Museum of Kenya, Nairobi, that preserved good perikymata on any aspect of their tooth surface. The sequence of crown formation in Proconsul and the crown formation times of the enamel and dentine were estimated from these data. In addition, the rates of root extension were estimated using the formula derived for this purpose by Shellis (Archs. oral Biol. 29, 697-705, 1984) and estimates of the total period of root formation subsequently made for premolar and molar teeth based on measurements of root length. A composite chart of dental development for P. heseloni is presented which suggests M3 root completion was between six and seven years of age. In general Proconsul molar teeth have high stria angles to the EDJ, a high ratio of enamel formed with respect of dentine formed at the same time, median values of rates of enamel formation close to the EDJ in excess of 4 microns per day and the occasional presence of "S-shaped" striae in the lateral enamel. There is no evidence to suggest that Proconsul from Rusinga Island, Kenya, had relatively thin enamel on molar or premolar teeth. When all of these data are considered in a comparative context, Proconsul emerges overall as hominoid-like in its enamel and dentine microstructure and as most similar to Pongo but with some features shared with Pan and Homo. Similar data for other Miocene primates will have considerable bearing on how these data are interpreted. These new data on dental microanatomy and on dental development in Proconsul make a further contribution to our understanding of the total morphological picture of this early Miocene primate.

Animals↗
PubMed1997

Preliminary quantitative microradiography study into the distribution of bone mineralization within the basal bone of the human edentulous mandible.

Six edentulous human hemimandibles (three male, three female) of similar ages were sectioned transversely at the midline, mental foramen, midway between mental foramen and angle (body), and angle of the mandible. Planoparallel sections were prepared of the cortical plate on buccal and lingual surfaces and microradiographed alongside an aluminium step-wedge for computerized quantitative microradiography. Mean mineralization values and mineralization frequency distribution curves were calculated. Gender had no effect on the mean mineralization values, but did show a significant difference in the mineralization frequency distribution. There was no difference in mean mineralization between lingual and buccal cortical plates, but the distribution curves differed, with the lingual cortex distributions being more uniform. Each sample site was significantly different from all others, with the mental foramen and body sites showing the greatest variation in distribution of mineralization level.

Aged↗
PubMed1994

A comparative study on tissue processing procedures for the immunohistochemical investigation of oral mucosal Langerhans cells.

An immunoperoxidase technique was used to compare wax-embedded tissue with frozen tissue for quantitative immunohistochemistry of oral mucosal Langerhans cells. Initial experiments using anti-CD1a, -HLADR and -S100 antisera showed that phenotype, fixative, antibody dilution and trypsinisation of the tissue section significantly affected Langerhans cell counts. Only the anti-HLADR antibody detected Langerhans cells in both frozen and wax-embedded sections. Some 38% of S100-positive dendritic cells were situated in the stratum basale, and 41-84% of these contained melanin as determined by double-labelling. Sections from 39 volunteers were then reacted with the anti-CD1a and -HLADR antibodies. The morphology of Langerhans cells was more dendritic in frozen sections, and the mean HLADR-positive Langerhans cells count in frozen sections was significantly higher than that in wax-embedded sections from the same individual. The intra-individual ratio of counts between frozen and wax-embedded sections was variable; hence, the apparent loss of HLADR antigenicity as a result of tissue processing was unpredictable. Counts of CD1a-positive Langerhans cells were consistently higher. We conclude that the use of anti-CD1a antibody on frozen tissue is the optimum method for quantitative studies of oral mucosal Langerhans cells, and that such studies performed on wax-embedded tissue may be unreliable.

Adolescent↗
PubMed1994

Adhesion of composite resin to bone--a pilot study.

This pilot study investigated the adhesion of composite resin to pig calvarium using All-bond 2 dentine bonding agent in an in vitro model. The bone was subjected to different methods of preparation. Acid-etching decreased the bond strength between bone and composite. Roughening the bone with a surgical bur prior to application of the adhesive produced bond strengths in the range 11.1-16.1 MPa.

Animals↗
PubMed1993

Histological reconstruction of dental development and age at death of a juvenile Paranthropus robustus specimen, SK 63, from Swartkrans, South Africa.

There has been disagreement about whether the earliest hominids grew in a similar manner to great apes or modern humans. This has important biological implications, since it may have been inappropriate to apply modern human developmental standards to early hominids. The aim of the present study was to combine data from replicas of tooth surfaces, computed tomographic (CT) scans, and radiographs with data from a histological section of the canine crown, in order to provide a complete description of tooth crown and tooth root development in a single early hominid specimen (SK 63). Although partially destructive in nature, we have been able to determine the most reliable data yet for aspects of dental development in an important juvenile early hominid specimen. Appositional enamel formation time in the permanent right canine was estimated at between 305 and 418 days, imbricational enamel formation time at 819 days, and total crown formation time at between 3.18 and 3.48 years. The most likely age at death was estimated at around 4 years with a range of ages calculated between 3.18 and 4.23 years based on differences in timing of initial mineralization of the canine and differences in appositional enamel formation times. Crown formation times of the lower central and lateral incisors were estimated between 2.35-2.68 years and 2.57-2.91 years, respectively. Crown formation time of the first permanent molar was estimated at 2.4 years. Wear facets on the first permanent molars indicate that gingival emergence had occurred sometime prior to death, between 3 and 4 years of age. Estimates of root extension rates in the first permanent molars and in the permanent incisors are fast, and either within or above ranges of rates estimated for modern great apes. While we recognize that data for one individual may not be representative of data for a whole population of early hominids, the data for age at death, for age of M1 emergence, and for root extension rates presented here accord with those known for modern great apes and fall beyond the known ranges for modern humans.

Age Determination by Teeth↗
PubMed1993

Unmasking and abolition of Sudanophilia of the mineralizing front.

The effect of various treatments on the Sudanophilia of the mineralizing fronts of hard tissues has been examined. We have shown that a variety of organic solvents, but not all lipid unmasking protocols, expose Sudanophilic lipids at the mineralizing fronts of dentine, enamel matrix, bone and cartilage by the extraction of a substance which is not Sudanophilic. A variety of organic solvents, but not all extraction protocols, abolish Sudanophilia at the mineralizing fronts of bone and cartilage. The present study indicates that only solvent mixtures containing methanol abolished Sudanophilia at the mineralizing fronts of dentine and enamel matrix.

Animals↗
PubMed1991

A histochemical study on the distribution of melanin in human oral epithelium at six regional sites.

Oral mucosa from six sites in 95 autopsies was tested for melanin using the Masson-Fontana silver reduction method. Melanin was detected in 51.6% of labial, 46.3% of palatal, 45.3% of buccal, 28.4% of mandibular gingival, 25.3% of lingual and 21.1% of maxillary gingival samples. 93.7% of epidermal samples from the same population were positive. In 24.2% of the subjects there was no detectable melanin at any intraoral site and 4.2% showed activity in all six sites. The mean number of positive oral sites per individual was 2.2. There are thus regional differences in oral epithelial melanocyte activity, but no parallel with the known regional incidence of primary oral melanoma.

Adolescent↗
PubMed1991

Tooth crown heights, tooth wear, sexual dimorphism and jaw growth in hominoids.

The aim of this review is to bring together data that link tooth morphology with tooth function and tooth growth: We aim to show how the microanatomy of hominoid teeth is providing evidence about rates of tooth growth that are likely to be a consequence of both masticatory strategy and social behaviour. First, we present data about incisor and molar tooth wear in wild short chimpanzees that demonstrate how crown heights are likely to be related to relative tooth use in a broad sense. Following this we review recent studies that describe the microanatomy of hominoid tooth enamel and show how these studies are providing evidence about tooth crown formation times in hominoids, as well as improving estimates for the age at death of certain juvenile fossil hominids. Next, we outline what is known about the mechanisms of tooth growth in the sexually dimorphic canine teeth of chimpanzees and compare these patterns of growth with tooth growth patterns in the canines of three fossil hominids from Laetoli, Tanzania. Finally, we discuss how selection pressures that operate to increase or reduce the size of anterior teeth interact with jaw size. We argue that the space available to grow developing teeth in the mandibles of juvenile hominoids is determined by the growth patterns of the mandibles, which in turn reflect masticatory strategy. The consequences of selection pressure to grow large or small anterior teeth are likely to be reflected in the times at which these teeth are able to emerge into occlusion.

Animals↗
PubMed1989

Evidence against the existence of acetylated Sudan Black B.

The nature of acetylated Sudan Black B (aSBB) has been investigated, and it has been found, by thin layer chromatography, that each fraction of aSBB has an Rf which is the same as that of a similar fraction of Sudan Black B (SBB). However, aSBB has been found to have fewer fractions, 9-12 than SBB, 14-16. The two major fractions from aSBB and SBB were examined, and a great similarity was found between the absorption spectra of the respective fractions of aSBB and SBB. The major fraction of aSBB was investigated by mass spectroscopy and found to have a similar molecular weight to that expected of SBB. This demonstrates that aSBB is not in fact acetylated, and that the components of aSBB are chemically no different from the corresponding components of SBB.

Acetylation↗
PubMed1989

Mineralization differences between human deciduous and permanent enamel measured by quantitative microradiography.

The mineralization levels of erupted buccal enamel from 24 deciduous teeth were compared to those of 28 permanent teeth. Sections were prepared in a defined plane using a lapping machine which gave plano-parallel sections. Mineralization levels were recorded by quantitative microradiography at 25 equivalent anatomical sites in each section. Deciduous incisors and canines were compared with their homologous successors: overall mineralization levels were lower in the deciduous dentition, with no significant differences being found close to the amelo-dentinal junction, but highly significant differences being found in the outermost sites. Deciduous molars were compared with premolars, and were also relatively less mineralized. However, deciduous molars did not show the consistent diminishing occlusocervical gradient observed in all other tooth types tested; on the contrary, they showed a cervical reversal with higher values than permanent premolar enamel. These results confirm the generally lower mineral levels in deciduous enamel, and provide quantitative information on site-specific mineralization levels.

Cuspid↗
PubMed1988

Distinct dental development patterns in early fossil hominids.

New studies on the jaws of hominids, based on incremental growth markings in teeth, can now provide an absolute timescale with which to calibrate dental developmental events such as tooth emergence. These new estimates of crown-formation times and the observed sequences of dental development are different in the hominids Australopithecus and Paranthropus. Early hominids evidently had shorter periods of dental development than modern humans and therefore a less prolonged infancy.

Animals↗
PubMed1987

Crown-formation time of a fossil hominid premolar tooth.

Studies using surface or internal enamel growth indicators in hominids have suggested that crown-formation times were shorter than those in modern man. The crown-formation time in a robust australopithecine premolar tooth was calculated by counting enamel cross-striations, which correspond to daily increments of formation, on a replica of the fractured internal enamel surface of cuspal enamel using scanning electron microscopy. Cervical enamel completion time was estimated using other growth indicators including striae, and using measured and calculated cross-striation repeat intervals, giving a completion time of approx. 2.4 yr. This is much shorter than reported premolar crown formation times in modern man. These findings support the concept of an abbreviated period of dental development, with implications on the duration of the growth period in early hominids.

Animals↗
PubMed1987

Clinical considerations from axon-myelin relationship in human inferior alveolar nerve.

A histological study analysed the axon-myelin relationships in human inferior alveolar nerve fibres in both transverse and longitudinal sections. Observations on fibres cut in transverse section showed variation in myelin thickness upon axons having approximately the same diameter. Large diameter axons had relatively thinner myelin sheaths than small-diameter axons. A longitudinal reconstruction of a 470 micron length of fibre demonstrated the presence of 13 Schmidt-Lantermann clefts. The surgical and clinical implications of these finding are discussed.

Axons↗
PubMed1987

Replication technique for studying microstructure in fossil enamel.

The present paper describes a two stage impression technique using a silicone elastomer suitable for field replication studies; which requires high dimensional stability, defined resolution, and being capable of reproducing inaccessible details. A test object consisting of etched pearlite possessed fine detail [greater than 1 micron to less than 0.1 micron] which was suitable for testing negative/positive replica combinations. Coltene President light-body impression material was capable of resolving parallel side depressions of widths greater than or equal to 0.2 micron, and it possesses very good dimensional stability with time, allowing the production of positive casts to be deferred for several months. Low viscosity Spurr resin reproduced this detail, and flowed into inaccessible sites. Although there was evidence of bulk contraction on curing, there was no significant shrinkage on flat [linear] surfaces or in vertical relief dimensions. Replicas of fractured hominid teeth showed good surface detail, and reproduction of inaccessible three-dimensional features on enamel surfaces. Enamel prism shape was pattern 3.

Animals↗
PubMed1987

Quantitative and spectrum analysis of human mylohyoid nerves.

Histological analysis of 30 postmortem specimens of human mylohyoid nerve showed a mean fibre count of 1251 and, in each case, a bimodal fibre diameter distribution curve. No relationship was found between the fibre counts and the age, weight or sex of subjects. Counts in nerves from edentulous subjects were significantly lower (P less than 0.001) than those in nerves from dentate subjects. This apparent loss of fibres was not restricted to small diameter axons.

Female↗
PubMed1987

Myelinated axon counts of human inferior alveolar nerves.

A quantitative, postmortem study of 36 human inferior alveolar nerves is described. The total myelinated fibre count (TMFC) of nerves was not related to sex or age of the subjects but significant positive correlations were found between TMFC and subject body weight in both dentate (r = 0.616) and edentulous (r = 0.676) groups. The TMFC was significantly lower in nerves from edentulous subjects than in nerves from dentate subjects.

Adolescent↗