Dental Pulp-

the tooth has a central pulp cavity (containing
dental pulp) that extends down through the root
of the tooth as the root canal that opens via
the apical foramen. The blood vessels, nerves
etc. of dental pulp enter through this foramen.
This sets up a form of communication between
the pulp and surrounding tissue (important when
inflammation of the pulp spreads to surrounding
bone).-

developmentally and functionally, pulp and dentin
are closely related as both are products of the
neural crest-derived connective tissue that
formed the dental papilla.-

the pulp is a loose connective tissue with an
appearance similar to mucoid CT.
- It contains the components common to all connective tissues:

- cells: fibroblasts and undifferentiated mesenchymal cells as well as other types required
for the maintenance and defense of the tissue (macrophages, lymphocytes etc).

- fibrous matrix: type I and III collagen fibers unbundled and randomly dispersed,
present in greater density around blood vessels and nerves.

- ground substance: proteoglycans, glycoproteins and large amounts of water.-

the large number of undifferentiated mesenchymal cells enables pulp to recruit newly differentiating cells to replace others when they are lost - specifically odontoblasts.-

odontoblasts are pulp cells adjacent to the dentin that are responsible for the secretion of dentin and formation of the layer of dentinal tubules in the crown and root.

Architecture of the Pulp-

the peripheral aspect of the pulp differentiates into a dentin-forming odontoblast layer.-
beneath the odontoblasts is the cell-free zone (of Weil). This region contains numerous bundles of reticular (Korff's) fibers. These fibers pass from the pulp between odontoblasts and have their distal ends incorporated into the matrix of the dentin layer-
numerous capillaries and nerves are found in this zone-
subjacent to the cell-free zone is a cell-rich zone containing fibroblasts (the predominant
cell type of pulp). Fibroblasts of the pulp have demonstrated the ability to degrade collagen as well as form it. -
perivascular cells (undifferentiated mesenchymal cells) are present in the pulp and can give rise to odontoblasts, fibroblasts, or macrophages. Since odontoblasts themselves are incapable of cell division, any dental procedure that relies on the formation of new dentinafter the destruction of odontoblasts, depends on the differentiation of new odontoblasts from multipotential cells in the pulp. -
lymphocytes, plasma cells and eosinophils are other common cell types also present in dental pulp.

Odontogenic Zone of the Pulp Cavity

Vascular Supply to the Pulp this pattern emphasizes the primary function of dental pulp - support and maintenance of the odontoblast layer at the periphery. The odontoblasts in turn maintain the dentin. one or more small arterioles enter the pulp via the apical foramen and ascend through the radicular pulp of the root canal. Once they reach the pulp chamber in the crown they branch out and form a dense capillary network at the periphery, immediately under and sometimes within - the layer of odontoblasts.- reflecting the metabolic activity of this odontoblast layer, the capillaries exhibit numerous pores. Small venules drain the capillary bed and eventually leave as venules via the apical foramen. arteriovenous anastomoses of arteriolar size are present in the pulp. the presence of lymphatic vessels in the pulp has been difficult to establish and most believe there is no lymphatic drainage of the teeth. Tissue fluid would then drain back into the capillary or postcapillary sites of the blood vascular system.

Innervation of the Pulp-

two types of nerve fibers enter the dental pulp via the apical foramen:

1. Autonomic Nerve Fibers. Only sympathetic autonomics are found in the pulp. These fibers extend from the neurons whose cell bodies are found in the superior cervical ganglion. They are unmyelinated and travel with the blood vessels. They function in innervating the smooth muscle cells of the arterioles and therefore regulate blood flow in the capillary network.

2. Afferent (Sensory) Fibers. These arise from the maxillary and mandibular branches of CN V
(trigeminal). They are predominantly
myelinated and may terminate in the central
pulp. From this regions some will send out
small individual fibers that form a plexus
(of Raschkow) just under the odontoblast layer.
From the plexus the fibers extend unmyelinated
towards the odontoblasts. The fibers then
loose their Schwann cell sheath and terminate
as "free endings" near the odontoblasts,
between them or may extend for short distances
into the dentinal tubule. They function in
transmitting pain stimuli from heat, cold or
pressure

Types of Pulp
-
there are two types of dental pulp:

1. Coronal pulp occupies the crown of
the tooth and has six surfaces;
occlusal, mesial, distal, buccal,
lingual and the floor. Pulp horns
are protrusions of the pulp that
extend up into the cusps of the
tooth. With age, the coronal
pulp decreases in volume due to
continued dentin formation. At
the cervix of the tooth the coronal
pulp joins the second type - radicular

2. Radicular pulp extends from the
cervix down to the apex of the
tooth. Molars and premolars
exhibit multiple radicular pulps.
This pulp is tapered and conical and
like coronal pulp, decreases in volume
with age due to dentinogenesis. Pulp
passing through the apical foramen
may be reduced in size by continued
cementum formation.

Age-Related and Pathologic Changes in the Pulp-

certain changes occur with age. Cell death results in a decreased number of cells, the surviving fibroblasts responding by producing more fibrous matrix (increased Type I over II collagen) but less ground substance that contains less water. So with age the pulp becomes:

a) less cellular
b) more fibrous
c) reduced in size due to further dentin deposition-

pulp is surrounded by hard tissue. Minor pathologic events like inflammation that cause swelling elsewhere, result in compression of the pulp leading to intense pain. This generally results in the death of the pulp.

Calcified Bodies in the Pulp (Pulp Stones)-

small calcified bodies are already present in up to 50% of the pulp of newly erupted teeth and in over 90% of older teeth.-

calcified bodies are generally found loose within the pulp but may eventually grow large enough to encroach on adjacent dentin and become attached. These bodies are classified by either their development or histology:

1. Development

- Epithelio-Mesenchymal Interactions. Small groups of epithelial cells become

isolated from the epithelial root sheath during development and end up in the dental papilla. Here they interact with mesenchymal cells resulting in their differentiation into odontoblasts. They form small dentinal structures within the pulp.