The dental pulp is that loose delicate connective tissue occupying the cavity lying in the center of dentin.
Regions of the pulp cavity • The pulp cavity can be divided into two main regions: the coronal pulp is located within the crown of the tooth and the radicular pulp is located within the root. A, Coronal pulp; B, Radicular pulp
Morphlogy*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.*Apical foramen: The the periapical tissue through the apical foramen.The average size of the apical pulp organs are continuous with foramen of the maxillary teeth in the adult is 0.4 mm, while in the mandibular teeth it is 0.3 mm in diameter.
Accessory canals:They are commonly seen to extend from the radicular pulp latrally through the root dentin to the periodontal ligament. Accessory canalsThey are numerous in the apical third of the root.
Mechanism of accessory canals formation: Mechanism of accessory canals formation:1- it occurs in areas, where the developing root encounters a large blood vessel, where dentin will be formed around it, then making the lateral canal .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.
Zones of the pulp peripheral zone Central zone(odontogenic zone). (pulp core). Dentin
Dentin Odontoblasts layerPredentin Cell rich zone Pulp core Cell free 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 mobilization andreplacement of odontoblasts. C- cell rich zone: It is present beneath the cell free zone. It is composed of fibroblasts and undifferentiated mesenchymal cells.
Histological Structures of the PulpThe dental pulp is formed of specialize loose connective tissue contain :1) Cellular elements : a. Formative cells : Odontoblast, Fibroblast . b. Progenitor cells : Undifferentiated mesenchymal cells . c. Defensive cells : Macrophages, neutrophils, eosinophils, basophils, mast cells , plasma cells and Lymphocytes.
2) Fibrillar elements : a. collagen bundles b. fine collagen fiber3) Ground substance: Act as a medium totransport nutrients to cells and metabolites of thecell to the blood vessels.4) Neurovascular elements : Blood vessels,nerves, lymph vessels
1- Formative cells :a- odontoblasts: 5-7u in the diameter 25-40u in length. In the early stage of development odontoblasts consist of a single layer of columnar cells .In the later stages of development, the odontoblastic layer appeared pyriform where the broadest part of the cell contains the nucleusThey are longer in the crown and then become cuboidal rootwise, at the root apex, they may be almost flattened.
The cell membranes of adjacent odontoblasts exhibit junctional complexes. Gap junction desmosome
b- FibroblastsThese are the most numerous type of cells.They are spindle in shape.They have elongated processes which are widely separated and link up with those of other pulpal fibroblasts (stellate appearance).The nucleus stains deep with basic dye and the cytoplasm is highly stained and homogenous.
These cells have a dual function: synthesize and degradation of fibers and ground substances in the same cell . mitochondria In young pulp, they are : *large cells *with large multiple processes *centrally located oval nucleus, Fibroblast (protein secreting cell). *numerous mitochondria, *well developed Golgi bodies *well developed RER
in periods of less activity and aging thesecells appear smaller and round or spindle-shaped with few organelles , they aretermed fibrocytes. fibroblast fibrocyte
2- Defensive cells:A- Histiocyte ( macrophage ) :In light microscope, the cells appear irregular in shape with short blunt processes.The nucleus is small, more rounded and darker in staining than fibroblast. Their presence is disclosed by intra-vital dyes such trypan blue.These cells are distrbuted 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 cytoplasmInvaginations of plasma membrane are noted ultastructurally with aggregation of vesicles or phagosomes .
b- Plasma cells:These cells are seen during inflammation.The arrangement of chromatin gives the nucleus a cart wheel appearance.The mature type exhibits a typical small eccentric nucleus and more abundant cytoplasm.The plasma cells are known to produce antibodies.
c- LymphocytesThey are found in normal pulp and they increase during inflammation.
c- EosinophilsThey are found innormal pulp and theyincrease duringinflammation.
d- 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 histamin & heparin.
3- Progenitor cells:(The undifferentiated mesenchymal cells):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 connective tissue cells.
Fibers of the pulpIn young pulp the fibers are relatively sparse and delicate throughout the pulp and gradually the bundles increase in size with advancing age.In older pulp two patterns of collagen distribution can be seen: one is a diffuse collagen network with no definite orientation, the second is bundles of collagen.There are no elastic fibers in the pulp except those present in the walls of the larger blood vessels.
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
Vascularity and Nerves of the Pulp The pulp organ is extensively vascular with vessels arising from the external carotids to the superior or inferior alveolar arteries. It drain by the same vein. Blood flow is more rapid in the pulp than in most area of the body, and the blood pressure is quite high. The walls of the pulpal vessels become very thin as their enter the pulp. Nerves : Several large nerves enter the apical canal of each Molar and Premolar and single ones enter the anterior teeth. This trunks transverse the radicular pulp, proceed to the coronal area and branch peripherally.
• Structure of Tooth A - crown B - enamel C - dentine D - gum E - tooth pulp F - cement H - nerves & blood vessels
Nerve Plexus of Raschkow• Sensory nerve fibers that originate from inferior and superior alveolar nerves innervate the odontoblastic layer of the pulp cavity. These nerves enter the tooth through the apical foramen as myelinated nerve bundles. They branch to form the subodontoblastic nerve plexus of Raschkow which is separated from the odontoblasts by a cell-free zone of Weil. In addition to the sensory nerves, sympathetic nerve bundles also enter the tooth to innervate blood vessels.
A, Odontoblasts; B, Cell-free zone of Weil; C, Nerve plexus of Raschkow
Vascular supply of pulp cavity• The pulp cavity receives blood from one artery that enters the apical foramen and courses directly to the coronal pulp. Within the coronal pulp numerous arterial branches form a interconnected network of blood vessels. The smallest capillary loops are in the subodontoblastic zone.
Clinically Importance features of the Dental Pulp With age the pulp becomes less cellular. The number of cells in the dental pulp decreases as cell death occurs with age. The volume of the pulp chamber with continued deposition of secondary dentine. In older teeth, the pulp chamber decreases in size; in some cases the pulp chamber can be obliterated. An increase in calcification in the pulp occurs with age. An increase in calcification in the pulp occurs with age.
Age changes in 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.
Retrogressive and age changes : 1) Cellular changes : during the time of teeth development the pulps of the teeth are highly cellular , extensively vascular, and the cells show high mitotic rate . Further more the fibroblasts and odontoblasts are actively synthesizing cells , while the ground substance is found in a profuse amount. However, in aged pulp, the cells become decreased in number and the cell organelles ( endoplasmic reticulum, Golgi and mitochondria ) also reduced in number and size .The fibroblasts appear round with short processes and termed fibrocytes . The odontoblasts enter their quiescent stage and their activity becomes restricted .2) Fibrosis : by aging, the pulp shows accumulation of diffuse fibrillar components especially in the coronal part .3) Neurovascular changes : with aging the blood vessels as will as the nerves undergo reduction in number and size . the blood vessels undergo arteriosclerosis, resulting in diminished blood supply to the pulp cells .The degenerative changes of the vessel wall include the three layers of the vessels . The nerves undergo progressive mineralization of the nerve sheath or the nerve itself .4) Reduction in pulp size : this occur due to continuous deposition of secondary dentin through the life span of the tooth , and may eventually leads to pulp obliteration .5) Dystrophic calcification and pulp denticles :
True denticles True 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.*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.*The close proximity of pulp stones free 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.
A, False pulp stone; B, Pulp cavityFalse pulp stone
Functions of the pulpFunctions of the pulp 1- 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-Reparative: through the formation of highly mineralized reparative dentin at the site of injury to seal off the pulp from the source of irritation . Also the pulp may mineralize the affected dentinal tubules by forming sclerotic dentin .4-Defensive : pulp inflammation represents other aspect of its response to irritation. In this condition, the defensive cells of the pulp will be increased and activated to repair and heal the inflamed pulp and phagocytoses the invading bacteria and their toxin .
5- Protective: : any environmental irritating stimuli always elicit pain as a response .6- Nutritive : the extensive pulp vasculature ensures an excellent nourishment to the odontoblasts for the continuously forming secondary dentin . This is provided through the capillaries found in the odontogenic zone .