Microvascular patterns of the dental pulp of the upper major incisor of the rabbit

Capillary changes with fenestrations in the contralateral soleus muscle of the rat following unilateral limb immobilization

Using electron microscopy, we examined structural changes in the capillaries of the immobilized and contralateral soleus muscles in the rat after the unilateral limb had been immobilized for 4 weeks. Individual contralateral muscle fibers showed a normal structure, compared with the structure in the immobilized muscle fibers. Most capillaries in the contralateral muscle were of the continuous type. However, about 5% of the examined capillaries in these muscles in each rat had fenestrations. The non-nuclear portions of the endothelial cells in these capillaries were extremely thin and were perforated by several fenestrations that were bridged by a single-layered diaphragm. The fenestration of capillaries in the contralateral muscle may have been caused by some the unilateral limb immobilization.

Distribution and organization of peripheral capillaries in dental pulp and their relationship to odontoblasts

BACKGROUND

Developmental and chronological changes in the peripheral capillaries of the dental pulp and their relationship to odontoblasts during dentin formation has not been sufficiently detailed. This study aims to elucidate the morphological changes of the peripheral capillaries in relation to the life cycle of odontoblasts.

METHODS

Peripheral capillaries of the dental pulp were examined in the labial region of rat incisors and in the crown region of rat molars by using light, transmission, and scanning electron microscopy.

RESULTS

Before the start of dentin formation, continuous capillaries formed a coarse vascular network under the odontoblast layer. With the start of dentin deposition, capillaries began to invade into the odontoblast layer and finally located close to the predentin, where they formed a dense vascular network consisting of fenestrated capillaries. In the incisors, dentin was formed actively even near the incisal tip, and fenestrated capillaries continued to locate in the odontoblast layer. In the molars, however, the activity of dentin deposition gradually decreased with the advance of dentin formation, and the fenestrated capillaries altered to continuous capillaries and withdrew from the predentin border to the odontoblastic-pulpal border shortly before the cessation of active dentin deposition.

CONCLUSIONS

It is concluded that the changes in the peripheral capillaries are closely related to the secretory activity of the odontoblasts. To facilitate a rapid and sufficient supply of raw materials from the bloodstream to the calcifying front, peripheral capillaries first approach the odontoblasts, invade into the odontoblast layer close to the predentin with increases in density, and finally alter the endothelium from the continuous to the fenestrated type in compliance with the nutritional requirements of the odontoblasts, which lay down the dentin. When the activity of odontoblasts decreases, capillaries first alter the endothelium from the fenestrated to the continuous type, then retreat from the odontoblast layer, and finally locate below the odontoblast layer.

Fate of odontoblasts and blood capillaries in the incisal region of the rat incisor pulp

Transmission electron microscopy of thin sections of the rat incisor pulp revealed that in the middle region of the incisor there were fenestrated capillaries in the "predentinal plexus" and that this region contained the tallest odontoblasts. The odontoblasts gradually became shortened in the incisal part of this region; the fenestrated capillaries in the predentinal plexus changed to continuous type capillaries. Almost all the odontoblasts had degenerated near the incisal end of the tooth. The predentinal plexus disappeared in this region, but the "subodontoblastic capillary plexus" persisted. In a specific region just beneath the worn incisal end, numerous macrophages and polymorphonuclear neutrophils appeared and scavenged the degenerating cells, possibly including the odontoblasts.