No abstract

Using human permanent teeth, structural and distribution patterns of the surface ‘prismless’ enamel with the occasional presence of indistinct and/or stunted prism structures were investigated by scanning electron microscopy. The ‘prismless’ enamel was classified into three shapes: step-like, occurring in mid-coronal enamel; band-like, frequently seen in occlusal and fissure enamel, and island-like, found in occlusal and cuspal-coronal enamel. These three ‘prismless’ shapes were formed by two structural patterns. One was determined by prisms which gradually changed into ‘prismless’ structures via indistinct and stunted prisms (prism-dependent; P type), and another, probably a variance of the P type, was characterized by prisms which abruptly changed into ‘prismless’ structures on the incremental lines of Retzius or the fine laminated striations (Retzius-dependent; R type). The P type pattern clearly forming the band and island-like shapes was found in occlusal and cuspal-coronal enamel, whereas the R type pattern forming some of the band-like shapes as well as the step-like shapes might be observed in almost all surface enamel.

Daily toothbrushing with and without an abrasive dentifrice was performed on the ground surfaces of human cervical dentin attached to resin plates, which had been exposed to the oral cavities of 4 subjects for 8 weeks. Brushing with a dentifrice containing calcium hydrogen phosphate as an abrasive caused most of the dentinal tubules to open. The patency of dentinal tubules is thought to induce dentin hypersensitivity. Brushing without a dentifrice, on the other hand, resulted in occlusion of the dentinal tubules with organic pellicle‐containing minerals. Furthermore, abrasion did not occur; however, no bacterial plaque or dental calculus were retained. The occluded tubules which were distributed over the entire dentin surfaces will likely prevent hypersensitivity. Such organic‐mineral materials occluding the tubules can be derived from saliva and embedded by the brushing. We suggest that use of a non‐abrasive dentifrice will prevent or reduce dentin hypersensitivity in the cervical regions. J Periodontol 1994;65:291–296.

Laminar bone or primary plexiform tissue, not Haversian bone, shows an alternative concentric pattern of laminar-bone units or plates around the bone marrow periphery of long bones, although the laminar bone is gradually replaced by osteons during the growth period. One laminar-bone unit is constructed with a hypercalcified line in the center, woven bone on both sides of the line, and lamellar bone with laminated appositional lines. Such a laminar bone showing a homogeneous calcification has been reported in young calves and some young large animals, but it has not been reported in foals although a previous report proposed that the bone structure was distinguishable from plexiform tissue. In this study, we compared young calves with foals by backscattered electron imaging mainly of transverse ground sections of mid-diaphysis. Foals had many hypercalcified lines arranged concentrically around the bone marrow periphery, which were similar to those of young calves. However, rows of cylindrical osteon-like structures with Haversian canal-like canals running along the long-bone axis were arranged between the concentric hypercalcified lines. Each Haversian canal-like structure was enclosed with laminated appositional rings of lamellar bone deposited on the woven bone. In the developing period, the bone units containing the concentric hypercalcified lines were basically equal to the laminar-bone units. The osteon-like structures or ‘pseudo-osteons’ were gradually replaced by ‘true osteons’ during the growth period. The blood vessels in the Haversian canal-like canals of foals ran along the long-bone axis, whereas the blood vessels in the concentrically prolonged bone cavities of young calves ran transversely to obliquely against the long-bone axis. Thus, the long-bone cortex of foals showing an alternative concentric pattern of a row of the osteon-like structures arranged between the hypercalcified lines will be histologically classified into a variety of laminar bone caused by the different arrangement of blood vessels. Such a laminar bone may have a biomechanical structure against physical stress, especially the modified laminar bone of foals with osteon-like structures, when compared with the typical concentric laminar bone of young calves and also Haversian bone possessing variously calcified numerous osteons caused by bone remodeling.

ABSTRACT. Some young large farm animals show a laminar bone formation in the long-bone cortex. Such a laminar bone is gradually replaced by Haversian bone with osteons during their growth periods. In this preliminary study, we observed the transverse ground samples of tibia cortex in young calves, pigs, and sheep by backscattered electron imaging. The cortex bones of all the newborn (NB) animals were basically formed with laminar bone structures. The NB and 1-month-old (1-M) calves had a typical concentric structure of laminar bone, whereas the NB and 1-M pigs showed a wire-netting bone with laminar-bone units. The NB sheep was similar to the calf rather than the pig. In the growth rate of bone volume, sheep was similar to calf up to 6 months after birth (6-M). Such calf and sheep showed a more rapid ratio of bone volume than pig. A few osteons had initially appeared in the innermost layer of the 6-M calf. A 1-year-old (1-Y) calf showed scattered osteons in the bone cortex, but many laminar-bone units were still retained in the outer layer. A 6-M pig had many osteons in the entire cortex but only a few osteons in the outermost layer. In the 6-M sheep, no osteons were observed, whereas a 1-Y sheep showed a relatively small number of osteons mainly in the middle layer but a higher osteon-volume than the 1-Y calf. In the 1-Y sheep, the more widely absorbed areas by bone-remodeling with osteons were observed as compared with the 1-Y calf, and the bone volume was decreased from the 6-M into the 1-Y sheep because of the remarkable bone-absorption. Thus, calf kept on possessing many laminar-bone units for a longer time in the growth period than sheep, while pig showed the earliest bone-remodeling with osteons. These results may be caused by their different body size and withers height in calf and sheep after growing and the difference of the dependence upon mother's body during juvenile period between pig and calf with sheep. The initial region of osteon formation may be distinguishable among their animals, respectively. However, further detailed investigations of their young animals at successive stages will be necessary.

Toothbrushing with and without dentifrice containing abrasive was performed on human enamel pieces attached to resin plates exposed to the oral cavities of 3 human subjects for 8 weeks. The effects on the ground enamel surfaces with engraved scratches were examined by scanning electron and scanning laser microscopy. Brushing with such a dentifrice caused smaller scratches to disappear, large scratches to expand and new microwear to appear; in some samples, prism structures were exposed. Under brushing without dentifrice, these scratches were protected by an organic pellicle with mineral deposits, and also the experimental surface was entirely covered with these membranous deposits. The results indicate that toothbrushing with no dentifrice but saliva induces an organic-mineral protective membrane on the enamel surface. The membrane may increase the enamel resistance to caries. On the other hand, the use of abrasive-containing dentifrice causes slight abrasion with microwear. This roughness may contribute to the formation of dental plaque.

ABSTRACT. The transverse sections of radius diaphysis in an 11-year-old giant Holstein cow with dermal dysplasia of a collagen disorderrelated skin fragility (Cow 1), probably based on increasing turnover of the dermal collagen as reported previously, were morphologically and physico-chemically investigated. Cow 1 had about one and a half times as much as the body weight of normal Holstein cows, aged 5 to 6.5 years with stabilized growth. The bone samples were compared with those of a 12-year-old Holstein cow as controls (Cow 2). It has been reported that the long-bone diaphysis of young calves and some herbivorous dinosaurs are occupied with laminar bone showing a concentric appositional formation, and that such a laminar bone is characteristically seen during the growing period of some farm animals and large dogs that show very rapid growth rates. Cow 1 had a smaller number of osteons than Cow 2 in the outer-half layer of the diaphysis, and showed an intermediate type between Cow 2 and a 1-year-old Holstein ox in the entire layers, although their bone volumes were similar among them. There were no significant differences in Ca and P concentrations and the Vickers microhardness values between the bone matrix of Cow 1 and Cow 2. The bone-collagen fibrils of Cow 1 showed uneven diameters and a disordered arrangement. Thus, there may be some relation in collagen formation between the bone matrix of Cow 1 and the dermis. From the remaining volume of laminar bone, Cow 1, aged 11 years, had probably shown growth until quite recently, so that we consider that Cow 1 became a giant animal, in the same way as some herbivorous dinosaurs.-KEY WORDS: compact bone, delayed osteon formation, giant bovine, histology, laminar bone.J. Vet. Med. Sci. 61(2): 101-106, 1999 In this study, for the purpose of studying the structure of bone matrix and also for comparing with the dermal collagen fibrils [8,10], we investigated the radius diaphysis of the giant cow by using microradiography, backscattered electron (BSE) imaging, image analyzing, electron probe microanalyses including wave-dispersive X-ray (WDX) and energy-dispersive X-ray (EDX), microhardness test, and scanning electron microscopy. As controls, a 12-year-old Holstein cow and a 1-year-old Holstein ox were employed. MATERIALS AND METHODS Animals:The 11-year-old Holstein cow with dermal dysplasia of a collagen disorder-related skin fragility [8] was sacrificed, and the radius was removed. The cow (Cow 1) showed a heavier body weight (about 1,000 kg) [10] than normal Holstein cows (about 650 kg), aged 5 to 6.5 years, thus showing a maximum level in growth [9]. In clinical observations, Cow 1 was found to be in good health except for the dermal dysplasia and her behavior to be normal [11]. For controls, the radius of a 12-year-old normal Holstein cow (Cow 2) and the tibia of a 1-year-old normal Holstein ox (1-year ox) were applied. Their diaphyses were cut transversely into several slices with a diamond wheel and then fixed with 10% buffered formalin, 70% ethanol, or a 4% ...

The surface enamel of human deciduous teeth showing a more negative birefringence by polarized light was investigated by differential interference contrast microscopy and by scanning electron microscopy (SEM) following EDTA etching. Though this surface enamel has been generally called the ‘prismless’ enamel, in this study, the so-called ‘prismless’ enamel was categorized into ‘false’, ‘moderate’, ‘essential’ and ‘complex’ types according to whether they took the form of distinct prisms which bended at the subsurface, indistinct circularly based prisms or not. Based on the SEM observations some types of the ‘prismless’ enamel showed parallel crystallites and no prism boundaries. However, if indistinct prisms showing centripetal crystallites within the circular boundaries are admitted into the prismless enamel, other types except the ‘false’ one will generally belong to it.