Neurophysiology of pulp

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1. NEUROPHYSIOLOGY OF DENTAL PULP CONTENTS INTRODUCTION DEVELOPMENT ANATOMY o General features o Pulps of maxillary teeth o Pulps of mandibular teeth o Coronal pulp o Radicular pulp o Apical foramen o Accessory canals STRUCTURAL FEATURES FUNCTIONS o Inductive o Formative o Nutritive o Protective o Defensive VASCULAR SUPPLY INNERVATION CLINICAL CONSIDERATIONS THE FUTURE CONCLUSION REFERENCES 2. INTRODUCTION : Rapid advances in the basic sciences and the development of sophisticated instrumentation have had a profound effect on one know ledge of every organ in the body. The dental pulp is no exception. There are some technical difficulties in deriving information on the dental pulp an organ or tissue that is difficult to see because it is encased by the hardest materials in the body. WHY MAKE SUCH A BIG ISSUE ABOUT A LITTLE TISSUE? This is because this little tissue has created a big issue. The best root filling is the healthy pulp. The pulp is a soft tissue of mesenchymal origin with specialized cells, the odontoblasts arranged peripherally in direct contact with the dentin matrix. It is enclosed by the rigid mineralized dentin and this admits its ability to increase in volume during episodes of vasodilatation and increased tissue presence. Following tooth development, pulp retains its ability to produce dentin throughout life. This enables vital pulp to partially compensate for the losses of enamel or dentin caused by mechanical trauma or disease etc. Thus, knowledge about pulp provides a firm biological basis for clinical decision making. 3. DEVELOPMENT Pulp is basically derived from the cephalic neural crest. During the sixth week of embryonic life, tooth formation begins with the development of the primary epithelial bands in the upper and lower jaws. This continuous horse-shaped bands of thickened epithelium cry quickly divides into o Vestibular lamina o Dental lamina Within the dental lamina, continued and localized proliferative activity leads to the formation of series of epithelial ingrowths into the ectomesenchyme. (primitive 2 or 3 cell thick layered epithelial covering an embryonic connective tissue) at sites corresponding to future deciduous teeth. From this point, tooth development proceeds in 3 stages Bud Cap and Bell Bud stage Cap stage Bell stage 4. Bud stage : Is represented by the first epithelial ingrowths or incursions into the ectomesenchyme of the jaw. Cap stage : Further proliferation into the ectomesenchyme and cellular density increases immediately adjacent to the epithelial ingrowth. This process is classically referred to as condensation of the ectomesenchyme. The epithelial ingrowth, which superficially resembles a cap sitting on a ball of condensed ectomesenchyme is called enamel or dental organ eventually forms enamel of the tooth. The ball of condensed ectomesenchyme cells called DENTAL PAPILLA forms dentin and pulp. DENTAL PAPILLA 5. Bell stage : Continued growth leads to the enamel organ resembling a bell as the undersurface deepens. The cells within the dentin papilla undergo cytodifferentiation into a peripheral layer of odontoblasts and a central mass of fibroblasts. This change is induced by signals originating in the internal enamel epithelium. Once the odontoblasts begin to lay down dentin, the dental papilla becomes by convention, the dental pulp. Vascularization of the developing pulp also starts during this stage, with branches entering the base of the papilla. The vascularization of the odontoblast layer increases as dentin is progressively laid down. Pioneer nerve fibers approach the developing tooth during bud-cap stage but they penetrate the dental papilla after dentin begins. Here, we see the life cycle of the ameloblast related to that of the odontoblast. 6. 1) The ameloblast begins to differentiate first 2) The peripheral ectomesenchymal cells divide, with some daughter cells migrating below the odontoblast layer. 3) Acting from a signal from the ameloblast, the pre-odontoblasts begins to differentiate. 4) Synthetic organelles begin to increase in size and number. 5) Cell becomes polarized, nucleus moves basally. Number of odontoblastic process begin to form and begins to secrete matrix. 6) Odontoblast retracts as matrix is being laid down, leaving behind a single main process. 7) Once the first layer of dentin is laid down, the differentiated ameloblast begins to deposit matrix. ANATOMY : General features : The dental pulp occupies the center of each tooth and shapes itself to a miniaturization of the tooth. Every person normally has a total of 52 pulp organs, 32 in the permanent teeth and 20 in deciduous dentition. The residence of the pulp is called the pulp cavity surrounded by dentin on all sides except at the apical foramen. Total volumes of all the permanent teeth pulp organs is 0.38cc. Mean volume of a single adult human pulp is 0.02cc. Molar pulps are 3-4 times larger than incisor pulps. 7. The pulp cavity may be divided into a coronal portion the pulp chamber and a radicular portion the root canal. In single rooted teeth, the pulp chamber gradually merges into the root canal, but in multirooted teeth, there is a single pulp chamber and more than one root canal. There are canal orifices which are openings in the floor of the pulp chamber leading into the root canals. They are not separate structures but are continuous with both the pulp chamber and root canals. Coronal pulp : The pulp chamber has a roof, floor, mesial, buccal, lingual and distal surfaces. There are pulp horns which are acc extending of the pulp chamber directly under a cusp or developmental lobe. The number of these of these horns, thus depends on the cuspal number. Radicular pulp : Or the root canal is that portion of the pulp cavity from the canal orifice to the apical foramen. They are not always straight, and vary in size, shape and number. It may divided for convenience into the coronal, middle and apical third portions. The radicular portions of the pulp are continuous with the periapical connective tissue through the apical foramen. Apical foramen : Is an aperture at or near the apex of a root through which the blood vessels and nerves of the pulp enter or leave the pulp cavity. The anatomy of this is partially determined by the number and location of apical blood vessels present at the time of formation of the apex. The average size of the apical foramen of maxillary teeth in adults is 0.4mm, in mandibular teeth it is 0.3mm. In young, incompletely developed 8. teeth the apical foramen is funnel shaped, with the wider portion extending outward. The mouth of the funnel is filled with periodontal tissue that is later replaced by dentin and cementum. As the root develops, the apical foramen becomes narrower. The inner surface of the root apex becomes lined with cementum, which may extend for a short distance into the root canal (1mm-1.5mm). Also, the apical foramen is not always the most constricted portion of the root canal. Constrictions can and do occur before the extremity of the root is reached. And the apical foramen is not always in the center of the root apex. It may exit on the mesial, distal, labial or lingual surface of the root, usually slightly eccentrically. Anatomic studies have shown that the apical foramen coincides within the anatomic apex in only 17 to 46% of the cases and it is located on an average of 0.4 to 0.7mm away from the anatomic apex. As a general rule, the root apex is completely formed about 2-3 years after eruption of the tooth. Accessory canals : Occasionally, during formation of the root sheath, a break develops in the continuity of the sheath, producing a small gap. When this occurs, dentinogenesis does not take place opposite the defect. The result is a small accessory canal. They can become established anywhere along the root but are found to be most numerous in the apical third. They create a periodontal-endodontic pathway of communication and a possible portal of entry in to the pulp if the periodontal tissues lose their integrity (in case of periodontal disease) Accessory foramina are also present, which are openings of the accessory and lateral canals in the root surface. 9. Pulps of maxillary teeth : In the central incisor pulp is somewhat shovel shaped with 3 pulp horns which are short lateral incisor has 2 pulp horns and the longest pulp is cuspid with an elliptical cross section buccolingually, with 1 pulp horn. First premolar has large pulp chamber occlusocervically dividing into 2 smooth funnel shaped root. The second premolar is similar but has only one root which tapers at about its midpoint. Molars : The pulp chamber of maxillary first molar is the largest in the dental arch, with 4 pulp horns mesiobuccal, distobuccal, mesiopalatal and disto palatal. The arrangement of the pulp horns gives the pulpal root a rhomboidal shape is cross section, while the pulpal floor is triangular in cross section. There are usually 3 roots with usually 3 canals situated in, mesiobuccal, distobuccal and palatal. The mesiobuccal canal is the narrowest of the three. The palatal root canal is the largest having the largest diameter of the three. Maxillary second molars have a pulp chamber similar to the first molar except that it is narrower mesiodistally and the 3 root canals are more closely grouped. Pulps of mandibular teeth : The pulp chamber of central incisors in small and flat mesiodistally. The three distinct pulp horns present in a recently erupted tooth become calcified and disappear early in life due to constant masticatory stimulus. Mandibular lateral incisor is parallel to central incisor but only larger in dimension. The mandibular cuspid resembles the maxillary cuspid with smaller dimensions. Only one pulp horn is present in the adult tooth. 10. Mandibular first premolar has a pulp chamber that is narrow mesiodistally but wider buccolingually. It has a prominent buccal pulp hor