Dental Pulp

Dental pulp is an unmineralized oral tissue composed of soft connective tissue, vascular, lymphatic and nervous elements that occupies the central pulp cavity of each tooth. Pulp has a soft, gelatinous consistency; The pulp cavity extends down through the root of the tooth as the root canal which opens into the periodontium via the apical foramen. The blood vessels, nerves etc. of dental pulp enter and leave the tooth through this foramen. This sets up a form of communication between the pulp and surrounding tissue - clinically important in the spread of inflammation from the pulp out into the surrounding periodontium.

Histology of Dental Pulp: Cells: fibroblasts and undifferentiated mesenchymal cells as well as other cell types (macrophages, lymphocytes, etc.) required for the maintenance and defense of the tissue . Fibrous matrix: collagen fibers, type I and II, are present in an unbundled and randomly dispersed fashion, higher in density around blood vessels and nerves. Type I collagen is thought to be produced by the odontoblasts as dentin, secreted by these cells, is composed of type I collagen. Type II is probably produced by the pulp fibroblasts as this type increases in frequency with the age of the tooth. Older pulp contains more collagen of both the bundled and diffuse types.

Ground substance: the environment that surrounds both cells and fibers of the pulp is rich in proteoglycans, glycoproteins and large amounts of water

Architecture of the Pulp (1)The peripheral aspect of dental pulp, referred to as the odontogenic zone, differentiates into a layer of dentin-forming odontoblasts (A). (2) Immediately subjacent to the odontoblast layer is the cell-free zone (of Weil). This region contains numerous bundles of reticular (Korff's) fibers (B). These fibers pass from the central pulp region, across the cell-free zone and between the odontoblasts, their distal ends incorporated into the matrix of the dentin layer. Numerous capillaries (C) and nerves (D) are also found in this zone.

(3) Just under the cell-free zone is the cell-rich zone containing numerous fibroblasts (E) - 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 dentin (F) after destruction of odontoblasts, depends on the differentiation of new odontoblasts from these multipotential cells of the pulp. Lymphocytes, plasma cells and eosinophils are other cell types also common in dental pulp. (4) Medial to the cell-rich zone is the deep pulp cavity that contains subodontoblastic plexus (of Raschkow; parietal layer) of nerves (G).

2--Vascular Supply to the Pulp: Extensive vascular present in dental pulp . its primary function -  support and mainten ance of the peripheral odontoblast layer. The odontoblasts in turn maintain the overlying layer of dentin

3-Innervation of the Pulp: Autonomic Nerve Fibers. They are unmyelinated fibers and travel with the blood vessels. They innervate the smooth muscle cells of the arterioles and therefore function in regulation of blood flow in the capillary network.   Afferent (Sensory) FibersThey are predominantly myelinated fibers and may terminate in the central pulp. From this region some will send out small individual fibers that form the subodontoblastic plexus (of Raschkow) just under the odontoblast layer. They function in transmitting pain stimuli from heat, cold or pressure.

Types of Pulp 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, pulp horns diminish and the coronal pulp decreases in volume due to continued (secondary) dentin formation - often the result of continued masticatory trauma. At the cervix of the tooth the coronal pulp joins the second type.

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. In a fashion similar to coronal pulp, it also decreases in volume with age due to continued dentinogenesis. Pulp passing through the apical foramen may be reduced by continued cementum formation.

Age-Related and Pathologic Changes in the Pulp Specific changes occur in dental pulp with age. Cell death results in a decreased number of cells. The surviving fibroblasts respond by producing more fibrous matrix (increased type I over type II collagen) but less ground substance that contains less water. So with age the pulp becomes: a) less cellular b) more fibrous c) overall reduction in volume due to the continued deposition of dentin (secondary/reactive)

Stages in Pulp Aging Some attrition of the pulp as the result of normal aging as well as trauma from wearing of the enamel at the cusp the changes in pulp cavity size by middle age. The pulp horn continues to be reduced in response to increased wearing of the overlying enamel An overall reduction in pulp cavity dimensions through the continued deposition of normal secondary dentin has occurred. Histology of the pulp reveals a decreased cellularity coupled with increased fibrosis.

Aging decreases the ability of dental pulp to respond to injury and repair itself. The fact that the pulp is surrounded by mineralized dentin makes relatively minor pathologic events like inflammation, that cause swelling elsewhere, lead to a 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 present in up to 50% of the pulp of newly erupted teeth and in over 90% of older teeth. These 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

Causes : 1-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

2-Calcific Degenerations. Spontaneous calcification of pulp components (collagen fibers, ground substance, cell debris, etc.) may expand or induce pulpal cells into osteoblasts. These cells then produce concentric layers of calcifying matrix on the surface of the mass - but no cells become entrapped. Diffuse Calcification. A variation of the above whereby seriously degenerated pulp undergoes calcification in a number of locations. These bodies resemble calcific degenerations except for their smaller size and increased number.

Histology Calcified bodies in the pulp may be composed of dentin, irregularly calcified tissue, or both. A calcified body containing tubular dentin is referred to as a "true" pulp stone or denticle . True pulp stones exhibit radiating striations reminiscent of dentinal tubules. Usually those bodies formed by an epithelio- mesenchymal interaction, are true pulp stones.

Irregularly calcified tissue generally does not bear much resemblance to any known tissue and as such is referred to as a "false" pulp stone or denticle . False pulp stones generally exhibit either a hyaline-like homogeneous morphology or appear to be composed of concentric lamellae.

Functions of Dental Pulp: The primary function of dental pulp is providing vitality to the tooth. Loss of the pulp following a root canal) does not mean the tooth will be lost. The tooth then functions without pain but, it has lost the protective mechanism that pulp provides.

Dental pulp also has several other functions: inductive: very early in development the future pulp interacts with surrounding tissues and initiates tooth formation.  formative: the odontoblasts of the outer layer of the pulp organ form the dentin that surrounds and protects. protective: pulp responds to stimuli like heat, cold, pressure, operative cutting procedures of the dentin, caries, etc.. A direct response to cutting procedures, caries, extreme pressure, etc., involves the formation of reactive (secondary) dentin by the odontoblast layer of the pulp. Formation of sclerotic dentin, in the process of obliterating the dentinal tubules, is also protective to the pulp, helping to maintain the vitality of the tooth.