Low temperature scanning electron microscopy: advantages and applications

Cryo-preparation of specimens for scanning electron microscopy can be completed within a few minutes. Chemical fixation and contact with solvents is avoided, levels of specimen hydration are maintained, low melting-point materials are stabilized, volume changes are minimized and internal structure can be revealed by freeze-fracture. Elements are not lost or substantially relocated prior to X-ray microanalysis and specimen luminescence is enhanced. The displacement of internal structure and material subject to X-ray microanalysis by the growth of ice crystals in hydrated samples can be minimized by adopting fast freezing methods designed to limit ice crystal growth. The technique enables a wide range of industrial and biological materials to be examined rapidly and free from artifacts commonly associated with more conventional preparation methods.

White sponge nevus. Diagnosis by light microscopic and ultrastructural cytology

The lesions of white sponge nevus, an autosomal dominant abnormality of squamous epithelial differentiation that primarily affects the oral cavity, may be grossly similar to those of other hereditary mucosal syndromes, infections or preneoplastic/neoplastic processes. This differential diagnosis is best resolved in many cases by exfoliative cytology, interpreted in the context of clinical history and physical findings. The following report describes a case of white sponge nevus with typical clinical and cytologic findings, in which the diagnosis was confirmed by ultrastructural cytology. Light microscopic cytology revealed parakeratotic cells and many cells containing dense eosinophilic intracytoplasmic inclusions. Electron micrographs of exfoliated cells demonstrated that these inclusions are composed of disordered aggregates of tonofilaments.

Scanning electron microscopy of oral mucosa in vivo and in vitro: a review

The oral mucosa is classified by function into lining, masticatory and specialized oral mucosa, with regional structural adaptation. In this review, the surface structures of the human oral mucosa have been studied in the scanning electron microscope (SEM). Regional variations in regard to keratinization, cell arrangements and microplications with related specific structures observed in SEM are described and correlated with the appearance of similar areas observed in the light microscope. Furthermore, human oral tissue and cell cultures have also been studied. These systems offer usable and complementary models for performing similar studies in vitro under controlled experimental conditions. We now show that explant cultures of human oral mucosa can propagate both normal epithelial cells and fibroblasts. The surface morphology of both cell types has been investigated in SEM.

Microridges of oral mucosal epithelium in carp, Cyprinus carpio

The surface of carp oral mucosa is characterized by various patterns of microridges about 0.3 micron wide, 0.1 micron high, and of various lengths. To elucidate the derivation and function of these microridges, the oral epithelium was examined by light- and electron microscopy. Microridges were present only on the surfaces of the superficial cells. Therefore, microridges on renewed superficial cells have been discarded, and the various patterns of microridges found on the cell surface appear to indicate the progress of their development. In thin sections, the outer leaflet of the plasma membranes of microridges stained strongly with ruthenium red, and the underlying cytoplasm was packed with many fine filaments. The superficial cells contained many secretory vesicles that were PAS-positive but Alcian blue-negative at pH 2.5 and pH 1.0. However, after sulfation the vesicles gave a positive reaction with toluidine blue. These vesicles are secreted by exocytosis at the free surface of the cells. After release, the membranes of the vesicles are thought to be utilized for formation of microridges. On the basis of these observations, the possible function of microridges is discussed.

Myofibroblasts in healing laser wounds of rat tongue mucosa

The distribution of myofibroblasts was studied in healing laser incisions compared with scalpel-incision and excision wounds in dorsal tongue mucosa and excision wounds in back skin. Myofibroblasts (m-f-b) were visualized by staining with NBD-phallacidin, a fluorescent probe specific for F-actin, and by electron microscopy. Few, randomly-orientated m-f-b were found in laser wounds over 28 days. Neither m-f-b nor contraction were seen in the scalpel-incisions. No contraction was observed in the laser wounds whereas an organized network of m-f-b with substantial contraction occurred in excision wounds. It is suggested that lack of contraction in laser wounds is partially due to the fewness of m-f-b. The residual connective tissue matrix resisting the laser treatment also seems to play a role in preventing the wound contraction.

Ultrastructural investigation of hard palate mucosa under complete dentures

An ultrastructural investigation was made to study the tissue changes occurring under complete dentures. Biopsy from 45 patient specimens were obtained from lesions of hard palate mucosa. Narrow intercellular space with less distinct bridges, loosely knit arrangement of tonofilaments, prominent endoplasmic reticulum, and vacuolar conformation of mitochondria were observed in the cells of epithelium. The underlying connective tissue was characterized by a preponderance of newly formed collagen fibers and numerous fibroblasts. Macrophages were located in the lamina propria and perivascular regions. Lymphocytes, neutrophils, and plasma cells were seen in moderate numbers. These cells, when present in clusters, should be considered as a component of the defense system.

A histometric/scanning electron microscope study of normal and loaded oral epithelium of the vervet monkey

To investigate the functional significance of the epithelial cell surface features found in oral mucosa, a histometric analysis of the pits, microvilli and microplications was carried out in normal and mechanically loaded attached gingiva and alveolar mucosa of the vervet monkey throughout the full thickness of the epithelium. An electronic image analysing system and point counting methods were used to obtain the necessary data from micrographs of tissue specimens viewed in the scanning electron microscope. The results indicate that the cell area increases and the density of microvilli and microplications decreases from the deepest to the superficial cell layers. There was no statistically significant difference between the diameter of the pits and microvilli in the attached gingiva. Similarly there was no statistically significant difference between the widths of the grooves on the oral cell surface and the microplications on the under-surfaces of the alveolar mucosa cells. This indicates that the cell surfaces are complementary within each tissue type. Furthermore mechanical loading caused a significant decrease in the density of microvilli and microplications in the two tissues, confirming that these structures serve as reserve areas for cell stretching.

Nuclear DNA analysis of oral hyperplasia and dysplasia using image cytometry

We investigated the value of image analysis in discriminating among oral white lesions with hyperplasia without dysplasia and oral white or white-and-red lesions with moderate or severe dysplasia. Normal oral epithelial tissue was used as a control. Image analysis was applied to 5-micron formalin-fixed sections stained with the azure A-Feulgen reaction for nuclear DNA. For 150-200 cells from each section, 5 nuclear variables were assessed: area, form factor, total stain, average stain and ellipticity. For each variable, 2 measurements were obtained, the mean and the interquartile range, and were used for stepwise discriminant analysis. Using this test, a model of 3 measurements with the most discriminating power was developed. When the jackknife classification test was applied to this model, we could discriminate with 81% accuracy between the 4 groups of tissue studied.

Tobacco-specific nitrosamines in the saliva of Inuit snuff dippers in the Northwest Territories of Canada

Levels of tobacco-specific nitrosamines (TSNA), nicotine and cotinine were estimated in the saliva of 20 snuff dippers (Inuit, Northwest Territories, Canada). Levels of N'-nitrosonornicotine (NNN), 4-(methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and N-nitrosoanatabine (NAT) plus N-nitrosoanabiasine (NAB) found in the saliva following a 15-min period of keeping 0.5-1.5 g of moist snuff in the gingival groove are considerable: 115-2610 ppb NNN, 123-4560 ppb NAT + NAB, and up to 201 ppb NNK. The amount of TSNA in the saliva increases with the length of time that the snuff is kept in the mouth. The estimated total amount of 444 micrograms TSNA, the largest part of which will be swallowed, exceeds by far the amounts of nitrosamines ingested through drinking beer (0.34 micrograms/day), eating cured meat products (0.17 micrograms/day), or using cosmetics (0.41 micrograms/day). The relatively high levels of potentially carcinogenic TSNA in the saliva, together with the current popularity of snuff usage by teenagers, is of particular concern.

Scanning electron microscopy in oral mucosal research: a review

This review paper highlights some aspects of the contribution of SEM in the field of oral mucosa research. These include 1) different preparative techniques, 2) structure of the oral mucosa and its role in normal function, 3) advances in oral microbiology, 4) development of the oral mucosal epithelium, 5) pathological diagnosis and 6) morphometry. There are four main ways to study the oral mucosa with SEM; biopsy (autopsy) samples, smears, replica technique, and cell culture techniques. The structural studies can be divided as studies of the surface structure of the superficial cells of the oral mucosa and studies of the interactions between epithelium and connective tissue. Colonization and the morphology of micro-organisms are easy to see with SEM. Morphometric techniques have been used to determine the density of connective tissue papillae and to analyse surface structures of epithelial cells. In this paper, computerized image analysis systems for use in SEM research are presented.

Fixation of vervet monkey oral mucosa for ultrastructural investigation--TEM

This study was undertaken to determine optimal fixation procedure for vervet monkey (Cercopithecus pygerythrus) oral mucosa. Perfusion and immersion fixation were investigated using glutaraldehyde and glutaraldehyde-paraformaldehyde fixatives with either a phosphate or sodium cacodylate buffer as vehicle and with osmolarities varying from 2010 to 320 mosm. Good fixation could not be obtained uniformly or consistently by perfusion. Vervet monkey oral mucosa is best fixed by first perfusing the head and neck of the animal with 250-500 ml 0.9% saline containing Procaine-HCl and heparin, followed by decapitation and immersion of the head in a 2.5% glutaraldehyde: 2% paraformaldehyde: 0.02 M sodium cacodylate buffered fixative (900 mosm) at 4 C for 24 hr.

Ultrastructural findings in oral Kaposi's sarcoma (AIDS)

Ten biopsies of oral Kaposi's sarcoma were examined histologically and ultrastructurally. Histologically, early and late tumor stages could be differentiated. On the ultrastructural level, endothelial-like and spindle-shaped tumor cells were revealed. Tumor cells associated with vessel-like spaces showed partly interrupted basal membranes, Weibel-Palade bodies, desmosomes and tight-junctions, while spindle-shaped cells lacked these ultrastructural features of endothelial cells. Within the cytoplasm of endothelial-like cells, aggregates of tubular structures were observed. Histological and ultrastructural findings in oral Kaposi sarcoma are comparable to those of such other organs as skin and intestines. The ultrastructural findings indicate an endothelial origin, at least of endothelial-like tumor cells.

Effects of fixative composition on the ultrastructure of oral epithelium in guinea pigs

Keratinizing epithelium from the hard palate of guinea pigs was used to investigate effects of variations in composition of fixative solutions on tissue preservation. With 2.5% glutaraldehyde as fixative, the volume of the basal intercellular spaces increased significantly when the buffer osmolality was increased by intervals of about 100 mOsm (0.05 M, 0.10 M and 0.15 M). The intercellular space volume appeared to be insensitive to differences in concentration of the fixative within the range of 2.5-5% glutaraldehyde. The preservation of mitochondria was improved by increasing the concentration of glutaraldehyde to 5% or by adding formaldehyde as a second fixative.

Ultrastructure of oral leukoplakia and lichen planus. II. A correlated scanning and transmission electron microscopic study of epithelial surface cells

Nine cases of homogenous leukoplakia and 21 cases of lichen planus (11 reticular and 10 erosive) were studied under the scanning and transmission electron microscopes. Characteristic differences between leukoplakia and lichen planus in surface patterns of the epithelial surface cells were noted. Microridges in leukoplakia form parallel and anastomosing rows whereas the picture in lichen planus is irregular with microridges varying in width. The transmission electron microscopic findings confirm and correlate with these findings, the microridges representing invaginations of the plasma membrane. The keratin patterns exhibited by the surface cells were also characteristic regarding type and site of lesion. Scanning electron microscopy can be used as an additional diagnostic aid in differentiating these lesions.

Microplication patterns on human buccal epithelia following radiotherapy: a scanning electron microscopic analysis

Surface topographical detail in human buccal smears of normal and irradiated tissue have been studied with scanning electron microscopy. Cells collected by buccal smearing show patterns of microplicae and microvilli, although such detail is occasionally masked by mucus and to a lesser extent by debris and bacteria. Buccal smearing permits collection of numerous specimens with little discomfort to the patient, but requires caution in identification of superficial and deep cell layers and of upper and lower surfaces. The analysis of specimens derived in this way shows that variations in the pattern of surface microplicae reflect the radiotherapeutic regimes of the patients from which they were obtained. Straight parallel microplicae characteristic of normal control and pre-irradiated specimens were absent in specimens collected during early irradiation treatments (between 24-48 Gy), but instead were present as short discontinuous ridges and microvillous projections. At the highest levels of radiation treatment (54-60 Gy) cells exhibited small areas devoid of any surface projections in addition to a range of normal and early irradiated microplicae patterns. From these results it is suggested that the patterns of microplications and microvilli on cell surfaces can be used to obtain information on the state of the stratified squamous epithelium from which they come.

The morphology of keratohyalin granules in orthokeratotic and parakeratotic skin and oral mucosa

We compared morphologic features of keratohyalin granules (KHG) that were directly related to keratinization in oral mucosa (tongue, cheek, gums, palate; n = 4) with those in parakeratotic epidermis (psoriasis, n = 2; pityriasis rubra pilaris, n = 1; acute dermatitis, n = 1) and normal orthokeratotic epidermis. Among others, the ultrastructural features of globular KHG were observed in the cheek, nonspecialized tongue mucosa, and parakeratotic epidermis occurring in psoriasis, pityriasis rubra pilaris, and acute dermatitis, whereas gums and palate showed a mixture of characteristics, also resembling stellate KHG as seen in normal skin. From literature as well as from our studies, the impression was gained that globular KHG were found especially in quickly dividing epithelia and could easily be distinguished from the irregular or stellate KHG that were found in slowly dividing normal epidermis. Therefore, we studied keratinization features on days 3, 7, and 14 after autografting normal human skin (n = 4), thus inducing high cell turnover. Stellate KHG, present in granular cells of normal skin, were almost absent on the third day. Active cell division on the seventh day resulted in sparse keratohyalin formation inside globular granules of low electron density, whereas numerous, rather electron-translucent lipid droplets occurred in upper spinous and horny cells. These two phenomena seemed to be interrelated. After 14 days, round and increasingly electron-dense KHG were noted.(ABSTRACT TRUNCATED AT 250 WORDS)