The dental pulp is that loose delicate connective tissue occupying the cavity lying in the center of dentin.
Morphology*The coronal pulp: it is present in the pulp chamber.*The radicular pulp: it is that part of the pulp extending from the cervical region of the crown to the root apex.
Accessory canals:They are commonly seen to extend from radicular pulp laterally through the root dentin to the periodontal ligament. Accessory canalsThey are numerous in the apical third of the root.
Mechanism of formation accessorycanals1- it occurs in areas, where the developing root encounters a large blood vessel, where dentin will be formed around it.2- Early degeneration of the epithelial root sheath of Hertwig before the differentiation of the odontoblasts.3-Lack of complete union of the epithelial diaphragm at the floor of the pulp chamber.
*Apical foramen: The pulp organs are continuouswith the periapical tissue through the apical foramen. The average size of the apical foramen: maxillary teeth : 0.4 mm mandibular teeth : 0.3mm
Dental pain (acute pulpitis)Dental pain occurs in 12% of population.The origin of the dentalpain is difficult to localize. (referred pain)Dental pain is the most unkilling acute painaffecting human being.
Loss of the pulpresults in loss of the pulp functions, but the tooth is still functioning
Histological structure of the pulpThe dental pulp is formed of specialized loose connective tissue:cells fibers intercellular substances blood vessels and nerves
Zones of the pulp peripheral zone Central zone(odontogenic zone). (pulp core). Dentin
Odontogenic zone:a- odontoblasts:Location: Adjacent to the predentin with the cell bodies in the pulp and cell processes in the dentinal tubules. Dentin
B- Cell free zone (the zone of Weil):*It is present beneath the odontoblastic layer.*It is suggested to be the area of mobilizationand replacement of odontoblasts. C- cell rich zone: It is present beneath the cell free zone. It is composed of fibroblasts and undifferentiated mesenchymal cells.
Cell free zone & cell rich zone might be artifacts.
Cells of the pulp1- Progenitor cells: Undifferentiated mesenchymal cells.2- Synthetic cells (formative cells): Odontoblasts and fibroblasts.3- Defensive cells:Macrophages, lymphocytes, eosinophils,mast cells and plasma cells.
1- Progenitor cells: (UMC):They are smaller than fibroblasts but have a similar appearance.They are usually found along the walls of blood vessels.These cells have the potentiality of forming other types of formative or defensive cells.
2-Formative cells: A- OdontoblastsLength: 25-40uDiameter: 5-7uIn the early stages of developmentodontoblasts consist of a single layer ofcolumnar cells .In the later stages of development, theodontoblasts appeared pyriform wherethe broadest part of the cell contains thenucleus
Odontoblasts are longer in the crown cuboidal rootwise, flat at the root apex
The cell membranes of adjacent odontoblasts exhibit junctional complexes. The clear terminal part of the cell body and the adjacent intercellular junction is known as terminal bars. Gap junction desmosome
B- Fibroblasts*These are the most numerous type of pulp cells.*They are spindle in shape.*They have elongated processes whichare link up with those of other pulpalfibroblasts (stellate appearance).*The nucleus stains deep withbasic dye and the cytoplasm ishighly stained and homogenous.
These cells have a double function: formation and degradation of fibers and ground substances. mitochondriaIn young pulp, they are :*Large cells .*With large multiple processes*Centrally located oval nucleus,*Numerous mitochondria, Fibroblast*Well developed Golgi bodies *Well developed RER protein secreting cell
In periods of less activity and aging theyappear smaller and round or spindle-shaped withfew organelles, they are termed fibrocytes. fibroblast fibrocyte
3- Defensive cells:A- Histiocyte (macrophage):They appear irregular in shape with short blunt processes.The nucleus is small, more rounded & darker in staining than fibroblast.They are distributed around the odontoblasts and small blood vessels and capillaries.
In case of inflammation: *Nuclei increase in size and exhibit a prominent nucleolus. *It exhibits granules and vacuoles in their cytoplasm.Ultastructurally,invaginations of plasma membrane with aggregation of vesicles or phagosomes .
*Macrophages are involvedin the elimination of deadcells. *Macrophages removebacteria and interact withother inflammatory cells toprotect the pulp duringinflammation.
B- Plasma cells:These cells are seen during inflammation.The nucleus of this cell is small and appears eccentric in the cytoplasm.The arrangement of chromatin in the nucleus gives the cell a cart wheel appearance,The plasma cells are known to produce antibodies.
C- LymphocytesThey are found in normal pulp and they increase during inflammation.
D-EosinophilsThey are found innormal pulp and theyincrease duringinflammation.
E- Mast cells:*They have a round nucleus and their cytoplasm contains many granules.*They are demonstrated by using specific stains as toluidine blue.*They produce histamine& heparin.
The ground substances of the pulp:*The ground substances consists of acid mucopolysaccharides and neutral glycoprotein.*These substances are the environment that promotes life of the cells.*Glycoseaminoglycans are bulky molecules and hydrophilic, they form gels that fill most of the extracellular space, They contribute to the high tissue fluid pressure of the pulp.
Blood vessels*The pulp is highly vascularized. It issupplied by the inferior and superior alveolar arteries.*As the vessels enter the tooth, their walls become considerably thinner than those surrounding the tooth. D*Along their course they give numerous branches in the radicular pulp that pass peripherally to form a plexus in the odontogenic region.
The rate of blood flow in the pulp of the tooth is four time the rate of blood flow in resting muscle. Laser Doppler Flowmetry It measures the rate of pulpal blood flow
The capillaries adjacent to the odontoblasts arefenestrated. Such capillaries are found in areasof rapid exchange.
Assessment of pulp vitalityCurrent pulp tests assess the function ofnerves in the pulp, by the application of electriccurrent or a rapid change in temperature.Recently, blood flow rate in the pulp is used to measure the degree of the pulp vitality.
Nerves of the pulpThe pulp has an abundant nerve supply which follows the distribution of the blood vessels.Two types of nerve fibers are present: *Sympathetic in nature. They control the contraction of the smooth muscles of the blood vessels.*Sensory nerves.Both contain myelinated and unmyelinated axons.
*As the mylelinated nerves run coronally, they give off side branches and lose their myelin coat. They form then sub-odontoblastic plexus of nerves known as plexus of Rashkow. Few axons extend in-between the odontoblasts to give the nerve endings.*More nerve endings are found in the pulp horns than inother peripheral areas of the coronal or radicular pulp.
Sensory response in the pulp cannot differentiate between heat, touch, pressure or chemicals. This is because the pulp organs lack those types of receptors. Heat, Pain Touch, Pressure, Chemicals
Functions of the pulp1- Inductive: Dental papilla induces the enamel organ formation and also determines the morphology of the tooth.
2- Formative : Pulp organ produces dentin. Odontoblasts develop the organic matrix and function in its calcification.
3- Nutritive : The pulp nourishes the dentin. Nutrition is mediated through the odontoblasts and their processes. Dentin
4- Protective: The sensory nerves in the tooth respond with pain to all stimuli, Pain sensation is a useful alarm system of the pulp.
5- Defensive or reparative: The pulp responds to irritation by producing reparative dentin and mineralizing any affected dentinal tubules. These reparative reactions are an attempt to wall off the pulp from the source of irritation. The presence of macrophages, lymphocytes and leucocytes aid in the process of repair of the pulp.
Age changes in the pulp The size of the pulp The apical foramen The cellular elements decreased The bl. vessels & n. VitalityReticular atrophy: The total affect is the production of a lessened vitality of the pulp tissue and a lessened response to stimulation.
True denticlesTrue denticles are rare & small in size& found near the apical foramen.They consist of irregular dentin containing traces of dentinal tubules and few odontoblasts. odontoblastRemnants of the epithelial root dentinal sheath invade the pulp tissues tubules causing UMC of the pulp to form this irregular type of dentin.
False denticles*They are evidence of dystrophic calcification of the pulp tissue .*They contain no dentinal tubules and can exist in any area of the pulp.*They are formed of degenerated cells or areas of hemorrhage which act as a central nidus for calcification.*Overdoses of vit. D, may favor the formation of numerous denticles.
*Pulp stones are classified according to their location into: free, attached and embedded.*They continue to increase in size and in certain cases they fill up the pulp chamber completely. attached*If pulp stones come close enough to a nerve bundle pain may be elicited. free*The close proximity of pulp stones to blood vessels may cause atrophy of it.
Diffuse pulp calcification*Commonly occurs on top of hyaline degeneration in the root canal and not common in the pulp chamber. *They are irregular calcific deposition in the pulp tissue following the course of blood vessels or collagenous bundle.*Advancing age favors their development.