Shahid H. Ashrafi

The Canalicular Structure of Compact Bone in the Rat at Different Ages

Osteocytes communicate through a canalicular system that maintains the vitality and mineral metabolism of bone. Casting the vascular canals and canaliculi of compact bone with methacrylate and viewing them with scanning electron microscopy shows their extent and relationships. Confocal laser scanning microscopy of the same specimen before corrosion establishes the degree of calcification of the different tissue components. These methods were used to compare basal with alveolar compact bone in the rat mandible at different ages. Sections of the mandibular molar region were placed in a methacrylate resin. After polymerization and study with confocal microscopy, the organic matrix was removed. Juvenile rats had large irregular central vascular canals and lacunae that were more concentric in the basal than the alveolar bone. Cast lacunae were round, and the canaliculi from these lacunae were short and thick in both bones. Adult rats had regular concentrically arranged lacunae in the basal bone. Cast lacunae were ellipsoid and flatter in the basal bone than in the alveolar bone. The intercommunicating canaliculi were increased and canaliculi had more branching than the juvenile rats. The aged rats had fewer vascular canals, lacunae, and canaliculi and had osteoporotic changes. The cast lacunae were slender and flat especially in the basal bone. The porosity of the mandible became more pronounced in the alveolar than in the basal bone with aging. The canaliculi of mandibular compact bone thinned and developed extensive branching with adulthood but decreased in size and number with advanced age. Lacunae proceed from the large circular structures of youth to the flat forms of the aged. These studies show that the internal structure of compact bone changes with age and mirrors its functional state.

Morphological variations and population density of membrane-coating granules in human gingival sulcular epithelium

Surgically excised specimens of sulcular wall with minimal inflammatory response as judged by clinical then histological criteria were processed for electron microscopy. The specimens were divided into crestal, middle and cervical areas of the sulcular epithelium. The highest concentration of membrane-coating granules was found in the upper spinous cell layers of sulcular epithelium. The profiles of these granules showed examples of both classical keratinized (lamellated) and non-keratinized (non-lamellated) forms but also other appearances that were not derived from them through differences in the plane of section. The population of granules decreased between the crestal and cervical zones, and the decrease in number was marked for the lamellated granules. This decrease in numbers of membrane-coating granules, together with the wider intercellular spaces, may be the reason why the sulcular epithelium is most permeable in the cervical region.

Microradiographic and electron microscopic observations of the enamel-covered dentine in rat molars

The enamel-covered primary and secondary coronal dentine in the molars of 90-day-old and 360-day-old rats was examined using microradiography. Some preparations were subsequently examined by transmission and scanning electron microscopy (SEM). Fractured dentine surfaces and methacrylate casts of the tubular system in the primary dentine were also examined with SEM. No microradiographic evidence of a hypermineralized peritubular matrix, such as that seen in man and other species, was seen in either young or old rats. Transmission and SEM confirmed the microradiographic findings. The tubule obliteration and extensive intra-luminal mineral deposits which have been reported in the enamel-free coronal dentine of the rat molar were not seen in the enamel-covered coronal dentine but some evidence of tubule obliteration was seen in the secondary dentine.

Midinfrared ablation of dentin with the Vanderbilt FEL

Absorption spectra of 0.1 - 0.2 mm thick, dehydrated sections of human teeth were measured in the transmission mode with a Bruker FT-IR spectrometer from 2.5 - 20 micrometers . Absorption peaks for amide I, II and III, carbonate and phosphate were identified. Craters were ablated in dentin and enamel using a tunable FEL at 6.45 micrometers at various fluences. Pulse duration: 3 microsecond(s) ; spot size (Gaussian, FWHM): 300 micrometers ; repetition rate: 10 Hz. Crater depth and width were measured from digitized optical images. Ablation rates were computed from crater depth and volume data. Selected specimens were examined with scanning electron microscopy to determine ablation surface characteristics. Depth of thermal damage and dentinal tubule morphology were estimated from SEM examination of fractures through ablation sites. Functions describing crater depth vs. number of pulses (quadratic function) were not the same as crater volume vs. number of pulses (linear function). Crater depth decreases with successive pulses, concurrently, the crater width increases. Thus, each pulse removes approximately a constant volume. Material was observed to flow through the dentinal tubules during and after ablation. Patent tubules on crater walls and floor were observed with SEM. Ablation rates in dentin were approximately 3X those in enamel at 6.45 micrometers . Ablation rates and surface characteristics varied across wavelengths from 5.8 to 8.0 micrometers .

Time-related changes induced by zinc-deficient diet in the concentration of rat cheek epithelial membrane-coating granules

Weanling male Sprague-Dawley rats were fed a diet containing 0.4 parts/10(6) zinc and controls were fed an identical diet supplemented with 40 parts/10(6) zinc. After 9, 18 and 27 days of zinc deficiency, specimens were excised from cheek epithelium and processed for transmission electron microscopy to study the concentration of membrane-coating granules (MCG). Their concentration was increased in the granular-cell layers of the zinc-deficient epithelium and became significantly greater after 18 and 27 days than 9 days of deficiency. MCGs appeared in the parakeratinized layers of zinc-deficient epithelium and their concentration became significantly greater after 27 days in comparison with 9 and 18 days of deficiency. Thus the intracellular retention of MCGs was increased in the granular and parakeratinized layers with the increase in time of zinc deficiency.

Elemental and cytochemical localization of calcium in rat cheek epithelium

Energy-dispersive X-ray microanalysis, combined with scanning electron microscopy, was applied to 18 microns thick freeze-dried cryosections to determine the level of calcium in successive layers of the epithelium. This indicated low levels of calcium in basal cells, high in spinous cells, moderate in granular cells, lowest in the inner keratin and highest in the outer keratin layers. The potassium pyroantimonate technique was used to study the cytochemical distribution of Ca2+. The reaction product, calcium pyroantimonate (Ca-PA), was generated from cellular and intercellular calcium by perfusion of the anaesthetized rat with a solution of potassium pyroantimonate in glutaraldehyde. Ca-PA was localized in nuclei, mitochondria, lysosomal-type bodies and membrane-coating granules. A denser Ca-PA distribution was found between upper spinous and lower granular cells. The proposed identification of Ca2+ as a major component in Ca-PA was confirmed by EDTA decalcification and X-ray microprobe analysis of the reaction product. Thus X-ray microanalysis in combination with cytochemistry can localize Ca2+ in a growing and differentiating tissue such as stratified squamous epithelium.