Scanning electron microscopic study of giant tubule content in bovine dentin

Abstract — Incisal segments of unerupted permanent incisors from l/Z-l l/2-yr-old calves were fractnred along an axiomesiodistal plane exposing the organic components within the giant tubule lumina situated in this plane. Along the lining wall of the pulpal vasclurized giant tub & portion, large flattened cells and a few odontoblasts were situated in shallow depressions. Just incisal to the vascular loop numerous cells were seen, both along the giant tubule wall and enclosed within a loosely textured collagsnous matrix. Further incisally, the number and size of the cells decreased, and they were embedded in a compact nnmineraPized collagenous matrix that completely filled out the giant tubule lumina. This matrix consisted of fibrils regularly arranged in separate bundles whose orientation was mainly longitudinal. The initial origins of the giant tubes were filled with coarse Fmhrils being about three times thicker than those of the luminal matrix and those of the circumpulpal dentin proper.     

Transmission electron microscopic study of giant tubules in bovine dentin

Abstract – Giant tubules in the axiomesiodistally extended incisal dentin of unerupted permanent bovine incisors from 1/2-11/2-yr-old calves were studied by TEM. The pulpal portion of each giant tubule contained two capillaries forming a loop incisally. The capillaries consisted of a delicate, continuous, or fenestrated endothelium and often had a pericyte coating. Cells with a rich RER, mitochondria, and Golgi apparatus dominated along and just incisal to the vessels. Extravasated erythrocytes and occasional macrophages were also seen in the latter location. It was suggested that the pulpal retraction of the giant tubule vessels during primary dentinogenesis might be the result of an intermittent sequestration of the most incisal portion of the loop, concomitant with endothelial proliferation in the pulpal portion of the capillaries. The major portion of the giant tubules, incisal to the vessels, contained a dense matrix of more or less axially oriented unmineralized 0.07–0.1-um-thick collagen fibrils and single cells showing gradually increasing degenerative and necrotic changes in an incisal direction. Longitudinal sections of the mineralized tubular walls revealed transversely cut collagen fibrils. The incisally located giant tubule origins were circumvented by dentinal tubules and contained 0.10–0.22-um-thick, densely packed collagen fibrils with an electron dense perifibrillar zone.     

Light microscopic study of giant tubules in bovine dentin

Abstract – Demineralized, H-E stained longitudinal and transversal sections of unerupted permanent incisors from 1/2–3-yr-old calves were studied by light microscopy. The most incisal dentin in all teeth was. characterized by a regular pattern of straight axially oriented giant tubules situated in the axiomesiodistal plane with interglobular dentin between them. In younger teeth, the pulpal part of every giant tubule contained an afferent and an efferent blood vessel, forming a hairpin loop and being surrounded by basophil cells. Incisal to the blood vessel loops, cells enbedded in an eosinophil matrix were present in the giant tubule lumina, showing increasing degenerative changes incisally. In older teeth there was a mesiodistally extended eosinophil dentin band near the pulp, with few, irregularly arranged, tortuous dentinai and gianl tubules, the latter containing single blood vessels accompanied by pulpal cells. Isolated degenerating odontoblasts in lacunar cavities were seen in the transition area of the normal circumpulpal dentin and the eosinophil dentin band. A hypothesis on the initiation and subsequent development of giant tubules is presented.     

Light microscopic and transmission electron microscopic study of initial phases of giant tubule formation in bovine dentin

Abstract – Bovine tooth germs dissected from the mandible immediately after bleeding of the less than 1-yr-old calves (Bos taureus) were used to study the initial phases of giant tubule (GT) formation. Three stages could be discerned. Firstly, the initial manifestations were represented by loci about 150 μm apart in the axiomesiodistal plane along the pulpal border of the I00–200-μm-thick incisal dentin. Some of these loci showed only a blunt capillary loop and associated cells, whereas in most others there was a 50–100-μm-wide dense matrix consisting of coarse collagen fibrils and showing a metachromatic staining reaction to toluidine blue. Fibroblasts lined this matrix, and a capillary loop was always present underneath. Both kinds of GT origins were eventually circumvented by the odontoblasts situated incisal to them. The matrices became enclosed in the dentin. In the second stage, the GT grew in length as new dentin was formed. In this stage the vascular loops and the adjoining fibroblasts remained stationary within the GT lumina relative to the origins. In the third stage the GT vessels started to migrate pulpally relative to the origins. This seemed to be the result of a sequestration of the most incisal portions of the vascular loops. In this last stage the formation of collagen fibrils in the GT lumen incisal to the vessel loops started.     

Scanning electron and incident light microscopy of giant tubules in red deer dentin

Abstract – Incisal and cuspal teeth from red deers 2½–6½ yr of age were used in this study. Incident light microscopy was used for screening of the specimens with respect to presence of orifices and exposures of giant tubules. Scanning electron microscopy (SEM) was used for study of structural details. For SEM the specimens were pretreated with a 1% solution of NaCIO for 2 or 20 h. One specimen was in addition exposed to a 35% solution of phosphoric acid for 30 s. Two teeth received no pretreatment. Many incisal/occlusal exposures of giant tubules were more or less blocked by a dense, probably mineralized, substance, whereas others were filled with spherical bodies, probably microorganisms. The walls of the pulpal chambers and root canals revealed an abundance of orifices of giant tubules. They were funnel-shaped with circular or oblong pulpal outlines, the diameters of which in untreated specimens ranged from 15 to 100 μm.     

Scanning electron microscopic, light microscopic and microradiographic study of giant tubules in bovine dentin

Giant tubules (GT) in the axiomesiodistal plane of the incisal dentin of 21 unerupted permanent incisors of 1/2-2-yr-old calves were studied by scanning electron microscopy, light microscopy and contact microradiography. A technique is described by which the incisal dentin was split along the axiomesiodistal plane exposing the GT lumina longitudinally for SEM study. The luminal organic content was carefully removed mechanically or chemically. The GT originated 50-250 microns underneath the incisal dentino-enamel junction and converged pulpally, terminating in the incisal edge of the pulp. A confluence of adjacent tubules towards the pulp was seen. Each GT had a relatively constant diameter along its length, in the range of 10-50 micron. The dentinal tubules circumvented the GT origins and pursued a straight course pulpally, parallel to the characteristic wall zone surrounding each GT. Very few dentinal tubules entered the GT lumen at any level. The luminal lining along the larger part of the GT consisted of collagen fibrils forming a criss-cross pattern, while the most pulpal part was lined by a smooth organic sheath. The GT walls at any transversal level within one tooth had a lower mineral content than the circumpulpal dentin between them. It was concluded that the GT formation is not caused by crowding of the odontoblasts.     

A light microscopical and microradiographic study of coronal dentin in red deer with special reference to the occurrence of giant tubules

Abstract – The coronal dentin of red deer (Cervus elaphus L.) was studied by light microscopy and microradiography. The material consisted of incisors from 10 animals, 2½–6½ years of age. Sections in the long axes of the crowns in the buccolingual and mesiodistal planes were prepared, as well as transverse sections. A few crowns were also examined in toto. A system of giant tubules of the same type as in human dentin is described. It was, however, characterized by more regularity in the number and the morphology of the tubules. As in human dentin, the giant tubules extended from the border of the pulpal cavity and could be followed, though not continuously, through secondary and primary dentin almost to the incisal dentinoenamel junction. Up to 60 giant tubules could be counted in the mesiodistal axis of the dentin. Contrary to the situation in man, areas of interglobular dentin were abundant in the crowns.     

Observations on giant tubules in human coronal dentin by light microscopy and microradiography

Abstract – Human coronal dentin was studied by light microscopy and microradiography. The material comprised 50 permanent and 10 primary anterior teeth and microradiographs of 63 primary anterior teeth from a previous study. Both intact and worn teeth were examined. Ground sections in the long axes of the crowns in the buccolingual and mesiodistal planes were prepared, as well as transverse sections. A few crowns were also examined in toto. A system of giant tubules extending from the border of the pulpal cavity could be followed, though not continuously, through the secondary and primary dentin almost to the incisal dentinoenamel junction was observed. The lumina of the tubules were 5–40 μm wide and bordered by an approximately 10-μm-wide, usually hypermineralized rim of dentin in which only a few dentinal tubules were clearly discernible. The giant tubules were located along the mesiodistal axes of the teeth. The number of such tubules varied between 0 and 30.     

Microradiographic and polarized light study of red deer root dentin with special reference to occurrence of giant tubules

Abstract – Radiolucent bands following the course of the dentinal tubules were observed in sections of undemineralized roots of permanent red deer incisors. Some of these bands, previously unreported in mammalian root dentin, contained giant tubules similar to those described earlier by the author in the coronal dentin of this animal. The root giant tubules initiated with funnelshaped orifices at the border of the pulpal cavity and, generally, terminated in the peripheral dentin, whereas a few penetrated into the cementum. Whether the giant tubules should be considered to be anomalous dentinal tubules or a different type of structure could not be determined. The distinction between root giant tubules and accessory canals being part of the apical ramification did not represent any problem.     

Column-like structures following the course of tubules in human dentin

Abstract – Sections, 60–180μm thick, of permanent teeth, intact or with minor fillings, were cut parallel or transversal to the course of the dentinal tubules. Some teeth were dermineralized, embedded in paraffin wax, cut in series, and stained with toluidine blue pH 5.6, hematoxylineosin, or PAS. Altogether, sections of 90 teeth were examined by ordinary and polarized light microscopy and contact microradiography. Alternating light and dark bands, usually 8–30μm wide, extended from the pulpal border along the course of the tubules, gradually increasing in width, fading in the mantle dentin. Cross-sectioned bands appeared as dark and light "discs". This was the background for the term "columns". In the dark columns, usually exhibiting crowding of tubules, the intertubular dentin was dark and radiolucent; in the light columns, light and radiopaque. Dark columns contained a high amount of GAGs, assumed to have exerted an inhibitory effect on their mineralization. The columns probably represent structural elements in the architecture of dentin, possibly offering resistance against mechanical stress. It was suggested that the columns might depict functional differences in the matrix secretion and mineralization capacities of odontoblasts.     

Amelogenesis imperfecta: a scanning electron microscopic and microradiographic study

The aim of the present study was to use scanning electron microscopy (SEM) to visualize the morphology of the enamel surface in 12 primary teeth from children with amelogenesis imperfecta (AI). The observations were correlated to genetic, clinical and microradiographic data from the same teeth and to non-affected control teeth. SEM showed similar disturbances in teeth with a clinical predominance of hypoplasias and in teeth with a predominance of hypomineralization. In the microradiographs the enamel of most teeth showed both hypoplasias and areas of hypomineralization, independently of the predominant clinical manifestation. In the one boy with an X-linked inheritance pattern, both SEM and microradiography showed the morphology of the enamel to be unique in the present study. In the other teeth, similar manifestations were found in cases with AI as an AD trait and in the sporadic cases.     

Polarized light study of giant tubules in human and red deer coronal dentin

Abstract – Previously described giant tubules in human and red deer coronal dentin have been subjected to a study by polarized light microscopy. Structure of the giant tubules was similar in both species. The lumen of each tubule was bordered by a 5–15-μm-thick collagenous mantle in which the fibers were orientated parallel to its long axis. In a circular dentin area encompassing the mantle, the course of the collagen fibers might be characterized as a winding of fibers around the cylindrical mantle. This structure of the giant tubules conforms with that described earlier in the rudimentary maxillary canine of a red deer. Thus, such tubules do not represent a rare anomaly, but occur regularly in both human and red deer coronal dentin.     

Column-like structures following the course of dentinal tubules In bovine, red deer, and rat teeth

Abstract – A material of bovine, red deer, and rat incisors was investigated, with emphasis on the bovine teeth. Both ground sections and paraffin wax sections of demineralized material were used. The sections were investigated by ordinary and polarized light microscopy and contact microradiography. In the bulk of the dentin irregular column-like light structures, alternating with largely similar, but dark, columns, followed the course of the dentinal tubules from the pulpal border to just below the mantle dentin. Each column, 10–100 μm in diameter, contained a highly varying number of tubules. The difference between light and dark columns was mainly related to the intertubular dentin of the globules of which they were composed. Light columns were slightly more mineralized than the dark ones and seemed to contain fewer GAGs, but more glycoproteins. A difference in fiber direction between light and dark columns was also evident. To the authors' knowledge these structures have not attracted the attention of previous workers.     

Scanning electron microscopy of attrited dentinal surfaces and subjacent dentin in human teeth

abstract – Attrited dentinal surfaces and subjacent dentin were examined in the scanning electron microscope. In a central area of the exposed surfaces the dentinal tubules were occluded, whereas peripherally most tubules were open. Deposits, apparently dental plaque, were observed on the exposed dentin as uneven, but often continuous, layers covering whole areas of the surfaces. Loss of dentin within delimited areas of the surfaces was observed. The resulting defects could hardly be related to attrition, and it seemed that they were caused by erosive or caries-like processes. The dentin subjacent to the attrited surfaces was characterized by mineralized inclusions in the dentinal tubules. The inclusions consisted of irregularly rod-shaped crystals forming a meshwork on the tubule walls. Other crystals were formed as prisms, seemingly rhombohedrons. Crystals which were hexagonal in cross-section were also seen. The exposure of the dentin also seemed to have influence on the organic content of the tubules. Thus, it appeared that ground substance was removed from the intratubular fibers permitting the observation of cross-banding typical of collagen at their surfaces. In some tubules the fibers seemed to be covered by mineral.     

In vitro study of the giant tubule collagen formation in bovine dentin by [3H]- proline incorporation

Abstract – Unerupted permanent bovine incisors studied by routine autoradiography using radioactive proline incorporation revealed collagen formation within the giant tubules situated in the incisal dentin. A high [³H]-proline labeling was seen within the pulpal vascularized portion of the giant tubules, as well as in association with groups of cells immediately incisal to the blood vessel loops. The incisal portion of the giant tubules showed no or insignificant [³H] -proline labeling.     

Scanning electron microscope observations on collagen fibers in human dentin and pulp

Abstract – Human permanent teeth were examined in the scanning electron microscope after demineralization and exposure to preparative procedures based on hydrogen peroxide, trypsin, and EDTA. These substances removed the inorganic material, the cellular structures, the homogeneous connective tissue ground substance, and interfibrillar matrix. The remaining tissue components comprised a network of distinct collagen fibers whose organization was related to the type of tissue in which these were incorporated. A similar or identical method has not been developed or applied to teeth previously. Dentin and predentin comprised a compact mass of fibers which basically were parallel to the continuously growing interior surface of the predentin, or arranged at an acute angle to this plane. Collagen fibers in the pulp were numerous, but lacked any particular orientation in most areas. Interodontoblastic fibers crossed the odontoblastic zone at a right angle to the pulp chamber wall and mingled with collagen fibers in predentin. When previously published findings of ours are taken into account, it is possible to conclude that other factors than the organization of the collagen fibers are responsible for the stainability of these fibers in predentin and in interglobular dentin with silver methenamine, and that aldehyde groups on collagen fibers in predentin may be actively and directly involved in the mineralization of the dentin.     

Transmission electron microscopic study of giant tubules in bovine dentin

Giant tubules in the axiomesiodistally extended incisal dentin of unerupted permanent bovine incisors from 1/2-1 1/2-yr-old calves were studied by TEM. The pulpal portion of each giant tubule contained two capillaries forming a loop incisally. The capillaries consisted of a delicate, continuous, or fenestrated endothelium and often had a pericyte coating. Cells with a rich RER, mitochondria, and Golgi apparatus dominated along and just incisal to the vessels. Extravasated erythrocytes and occasional macrophages were also seen in the latter location. It was suggested that the pulpal retraction of the giant tubule vessels during primary dentinogenesis might be the result of an intermittent sequestration of the most incisal portion of the loop, concomitant with endothelial proliferation in the pulpal portion of the capillaries. The major portion of the giant tubules, incisal to the vessels, contained a dense matrix of more or less axially oriented unmineralized 0.07-0.1-micron-thick collagen fibrils and single cells showing gradually increasing degenerative and necrotic changes in an incisal direction. Longitudinal sections of the mineralized tubular walls revealed transversely cut collagen fibrils. The incisally located giant tubule origins were circumvented by dentinal tubules and contained 0.10-0.22-micron-thick, densely packed collagen fibrils with an electron dense perifibrillar zone.     

Closing of dentinal tubules by glutardialdehyde treatment, a scanning electron microscopy study

The properties of dentin are strongly influenced by the so-called smear layer. This layer is always present on the dentin surface after cutting, drilling, sawing, etc. The smear layer can be removed by various chemical treatments, such as those of acid etching or ethylenediaminetetraacetic acid (EDTA). These treatments remove the smear layer and open the tubules. In this paper, the effect on the smear layer of human dentin of treatment with a 2% glutardialdehyde (GDA) solution at pH 3.5 for 2 min and a 0.5-M EDTA solution at pH 7.4 for 4 min was investigated by scanning electron microscope (SEM). The dentin samples were dried by air or critical-point drying before SEM photography was employed. The number of open dentin tubules was quantified on micrographs of EDTA- and GDA+EDTA -treated dentin. The results show that the GDA treatment fixed part of the smear layer and the superficial dentin surface in such a way that at least 50% of the tubules remained closed after EDTA treatment. By closing the dentinal tubules, the GDA-fixed layer might have a positive effect on dentin hypersensitivity, root caries, and bonding of composite to dentin.