Quantitative diameter analysis of lingual nerve axons in man.

Previous studies on axon counts and fiber-diameter spectra in lingual nerves have been carried out only on animal models. This study reports an histological investigation on a series of 20 lingual nerves removed post mortem from human subjects. The results show wide variation in the myelinated fiber counts--a variation which does not appear to be related to the ages of the subjects. When the results are compared with those of a previous study (Heasman and Beynon, 1983), it is seen that the lingual nerve:inferior dental nerve ratio of axon counts is not a consistent index. The fiber-diameter spectrum for the human lingual nerve is characterized by a bimodal curve with the more pronounced peak in the small-diameter fiber range.

Myelinated fibre diameters of human inferior alveolar nerves.

These were examined in a series of 36 human post-mortem specimens. One unimodal, 32 bimodal and 1 trimodal diameter curves were demonstrated; group analysis of all samples gave a bimodal curve with 2-4 and 8-9 microns peaks.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Variations in enamel thickness and structure in East African hominids.

Tooth fragments are an appreciable but neglected proportion of fossil hominid specimens. The present study on 47 naturally fractured enamel surfaces of premolar and molar teeth of Plio-Pleistocene East African hominids measured enamel thickness, slope of incremental lines (striae of Retzius), and the morphology of Hunter Schreger bands (HSBs). Specimens allocated to three categories--"robust" australopithecines (EAFROB), "early Homo" (EAFHOM), and "unknown"--were photographed in ethanol with polarised light. Enamel thickness was measured on the occlusal (OT), cuspal (CT), and lateral (LT) aspects. The angle of intersection of striae of Retzius (D) with the enamel-dentine junction (EDJ) was recorded, together with the degree of curvature and width of Hunter-Schreger bands (HSB). Absolute measurements of enamel thickness were scaled by using two allometry correction factors. Absolute thicknesses of all enamel measurements were significantly greater in the EAFROB (OT 3.1 mm; CT 3.3 mm; LT 2.4 mm) compared with EAFHOM (OT 1.4 mm; CT 1.6 mm; LT 1.6 mm) categories. Correction for size reduces the mean difference between the two taxa, but CT and OT thickness remain significantly different (P less than 0.05). HSBs in EAFROB were relatively straight and narrower (means = 52.8 micron) than in EAFHOM, which are more curved and wider (means = 62.0 micron), suggesting greater enamel prism decussation in early Homo. The slope of striae was less in EAFROB permanent molars (means = 23 degrees) compared with EAFHOM (means = 31 degrees), indicating faster rates of coverage during crown formation in "robust" australopithecines. We conclude that the study of fractured enamel surfaces can contribute to our understanding of the systematic relationships and patterns of enamel growth of early hominids.