Three‐dimensional wall structure and the innervation of dental pulp blood vessels

Abstract

The involvement of neural components in plasma extravasation and blood flow in the dental pulp has been established by pharmacological and physiological studies. We review here the segmental constitution of pulp vessels and the possible involvement of neural components in both the contractility and permeability of the pulp vessels from a morphological viewpoint. Six vascular segments can be identified based on the morphology of peri-endothelial cells, such as smooth muscle cells and pericytes. These are: muscular arterioles, terminal arterioles, precapillary arterioles, capillaries, postcapillary venules, and collecting or muscular venules. The perivascular nerve forms a mesh with numerous terminal varicosities, some of which attach directly to arteriolar smooth muscle cells. This mesh can be seen by scanning electron microscopy, and indicates the important role of neural components in regulating the pulpal circulation. After administering norepinephrine (0.2 mg/kg/dog), the surface texture of the smooth muscle cells of pulp arterioles reveals marked irregularities, which are correlated with arteriolar contraction. The pericytes in larger postcapillary venules (diameter 20 microm or larger) also show irregularities, whereas no changes are seen in the pericytes of either smaller postcapillary venules or capillaries. The intercellular spaces of pericytes in the postcapillary venules are wide enough for leukocytes to pass through, and the occasional extravasation of leukocytes through venule walls can be seen under electron microscopy. The microvessels of healthy human dental pulp react weakly to selectins, indicating that apparently healthy dental pulp may be weakly inflamed. In rat dental pulp, CGRP-immunoreactive nerves and nerve terminals containing many granular vesicles supply the postcapillary venules more densely than the arterioles, which suggests the involvement of postcapillary venules in neurogenic inflammation in the dental pulp.

Calcium Signalling in Pericytes

“…Based on location and histological characteristics, three different types have been identified: precapillary (arteriolar), capillary and postcapillary (venular) [2]. This topology and morphology has been confirmed by scanning electron microscopy studies of microvessels in different tissues [3,4,23,24,25,26] and recently by live confocal imaging of ureteric microvascular network in situ (fig. 1) [15].…”

The Role of Hypoxia in Orthodontic Tooth Movement

“…However, almost all blood vessels enter a tooth via the apical constriction (Figure 2), making it a trouble spot for pulpal blood supply [52, 53]. Pulpal blood vessels are usually accompanied by other functional structures, such as nerves or lymph vessels [54, 55]. The nociceptive innervation of the pulp is mainly based on A- β -fibers, A- δ -fibers, and C-fibers [56], whereas the vasomotoric nerve fibers of the vegetative nervous system control the muscular tonus of pulpal arterioles and therefore contribute to the regulation of pulpal blood flow [54].…”

“…Pulpal blood vessels are usually accompanied by other functional structures, such as nerves or lymph vessels [54, 55]. The nociceptive innervation of the pulp is mainly based on A- β -fibers, A- δ -fibers, and C-fibers [56], whereas the vasomotoric nerve fibers of the vegetative nervous system control the muscular tonus of pulpal arterioles and therefore contribute to the regulation of pulpal blood flow [54]. Venules of the dental pulp are known to have very thin walls that tend to collapse in case of high pulpal pressure.…”

“…In this context, it is also interesting that vasodilation induced by inflammation mediators, such as PGE 2 , seems to have different effects in the dental pulp as in other tissues. By increasing pulpal pressure and therefore hydraulically inducing secondary vasoconstriction, vasodilation might halt the spread of infections, if induced in a very localized area; however, vasodilation may also facilitate necrosis in cases of generalization [54]. Tripuwabhrut et al [57] induced severe root resorption by applying intermitting tensile loads of 50 g onto 15 first molars in rats for up to 30 days to investigate inflammatory patterns in the dental pulp and the PDL.…”

Nitric Oxide Synthase and PGE2 Reciprocal Interactions in Rat Dental Pulp: Cholinoceptor Modulation

“…A striking feature of dental pulp innervation is its high density relative to that of other tissues in the body (3,4). Dentists have developed many strategies to prevent infection because inflammation frequently leads to necrosis and subsequent loss of dental pulp (2).…”