Pulp

PULP of the tooth-tooth pulp, "tooth marrow" (Zahnmark)-fills the crown and root cavities of the tooth and serves for the nutrition of the tooth and the formation of dentin. The pulp of the tooth together with the dentin corresponds in the early stage of embryonic development to the dental papilla, consisting of round and large elongated mesodermal cells with long thread-like processes intertwined with each other, embedded in its gelatinous substance with numerous collagen fibers. The tooth germ is composed of two elements-the enamel organ of ectodermal origin and the dental papilla of mesodermal origin. The enamel organ forms enamel, and from the dental papilla dentin and the pulp of the tooth are formed. Initially, the peripheral cells of the dental papilla do not differ from the central ones, only later the peripheral cells elongate and arrange themselves in a row resembling cylindrical epithelium, forming a layer of odontoblasts. The latter are highly differentiated cells of connective tissue and, although completely resembling cells of cylindrical epithelium, differ from them by their numerous processes, among which the peripheral ones, directed toward the dentin and called Tomes' processes, reach considerable size and penetrate into the dentinal tubules of the developing tooth. Tomes' processes, penetrating the dentinal tubules throughout their entire length, play a major role in the exchange of substances and in conducting the sensitivity of dentin. The pulp as a whole, deprived of its bony case, corresponds to the shape of the tooth. In it, the coronal part and the root part are distinguished. In single-rooted teeth, the coronal and root pulp form one trunk, in reduced volume repeating the shape of the tooth. In multi-rooted teeth, the pulp splits in the bifurcation area according to the number of roots. The mass of pulp tissue, its entire volume in a young tooth is greater than in the teeth of elderly people. The tissue filling the tooth cavity decreases throughout life, as the pulp gradually exhausts itself in the formation of newer and newer layers of dentin (dentin-like tissue), which narrow the tooth cavity-both the coronal and the non-rootal-until their almost complete obliteration. In the initial periods of development and dentin formation, the pulp resembles mucous tissue, but only with a large mass of finest, long fibers, small vessels, and nerve fibers. Recent research by Krauss has proven the collagenous nature of the pulp fibers. Behind the layer of odontoblasts there is a light, poor in cells band almost as wide as the odontoblast zone, called after the author Weil's zone (Weilsche Zone). Some deny its existence and believe that this light, almost acellular band is an artificial product of tooth fixation. Now the erroneousness of such an interpretation has been proven. Behind Weil's layer there is a band formed by ordinary pulp cells very densely, but without any order. In young pulp, three forms of cells can be distinguished-stellate with large processes, round, and spindle-shaped. Then wandering cells are constantly encountered, mostly of round shape, with intensely staining nuclei. The vessels of the pulp penetrate through the apical foramen and through the delta-like branches of the apical part of the root. Entering by several large branches, the vessels rise along the root part of the pulp to the coronal, branch into smaller ones, and, heading toward the periphery, form a network of capillaries in the cell-rich layer, sometimes in Weil's layer and in the odontoblast layer. The terminal branches of the pulp pass into the venous network. Arterial vessels in structure approach capillaries. The intima consists of even endothelial cells without elastic fibers; the medial layer is of a very thin muscular ring, followed by connective tissue cells of the pulp and fibers located around the vessel. As for the lymph vessels of the pulp, this question is currently controversial, although there are all grounds to recognize the presence of lymph vessels in the pulp. Nerves enter the pulp together with vessels and almost always go next to them. Going upward, the main trunks divide into small nerve bundles, accompanied by vessels. Often a vessel is completely included in the nerve trunk. The nerve bundles break up into individual nerve fibers, penetrating especially densely throughout the periphery, Weil's layer, and the odontoblast layer. To this day, the dispute about the innervation of dentin continues. Romer, Dependorf, Dick, Tojoda insist on the presence of nerve endings in dentin; Walkhoff believes that the elements perceiving irritation are the processes of odontoblasts, transmitting irritation to them. Using the silvering method, Dick and Tojoda managed to detect nerve endings in the dentinal tubules and in the mass of dentin. At the time of tooth eruption, the pulp in volume and morphological structure differs from the pulp of a tooth in a functioning masticatory apparatus. The volume of the pulp decreases in the coronal and in the root part due to the growth and deposition of new layers of dentin. Often already in middle age we find root canals in which the pulp is completely replaced by irregular dentin, obliterating the canal so much that only a narrow small slit remains from it. The described structure of the pulp changes very early. Its delicate structure, allowing one to compare the tissue of tooth pulp with embryonic tissue, gradually takes on a more pronounced fibrous character with a simultaneous decrease in the number of cellular elements. The coronal part of the pulp retains its normal initial structure longer. The root part of the pulp early becomes impregnated with lime salts. The view has been established, based on a number of studies, that normal pulp is difficult to find even in the teeth of young individuals. Various degrees of degeneration of the odontoblast layer are encountered even in clinically healthy teeth. Even in impacted teeth-pulp is found to be severely degeneratively changed. The following explanation is given for this: the function of odontoblasts is exhausted with the final formation of the tooth and root, and then the rest of odontoblasts and reverse development sets in. This thought is not quite correct. We know that the pulp continues to deposit dentin throughout life and odontoblasts, having lost their cylindrical shape, also produce dentin. Moreover, under the influence of irritation, ordinary pulp cells can turn into odontoblasts, which contribute to the deposition of dentin-like tissue (Feldman, Fischer).- Regressive changes of the pulp are often observed. According to the authors, they are the result of a violation of metabolism, caused by general sufferings of the body and external irritations acting on the tooth. The latter can be the result of severe overload, abrasion and wear of the tooth. General damage to the vascular system immediately affects the vascular system and parenchyma of the pulp. The anatomical conditions of the pulp do not favor the biological processes of the pulp. Included in a bony case, it maintains connection with the tissues surrounding it only through a small "opening" (foramen apicale) and a small number of the smallest openings (regio ramificationis), which more and more narrow, obliterate. Such a circumstance undoubtedly affects the correct metabolism and is partly the result of such frequent regressive changes of the pulp. Clinically, regressive changes of the pulp are almost not expressed. Only in those cases where there is severe abrasion of the chewing surface, pains from temperature, chemical irritations appear and independent pains are also possible. When the pulp is petrified, the action of arsenic acid, the passage into the root canal, etc., is hindered. The following regressive changes of the pulp are encountered: the most common form of pulp degeneration is petrification of the pulp or calcareous degeneration-diffuse deposition of lime in the form of a homogeneous mass impregnating vessels, nerves and intercellular substance and fusing them into one amorphous mass.- Hyaline degeneration of the pulp is expressed in the compaction of the delicate connective tissue basis of the pulp as a result of the deposition of hyaline mass. The latter is deposited in the form of lumps, strips along the vessels and nerves. Hyaline degeneration of the pulp is often the result of chronic inflammation of the pulp.- Amyloid degeneration of the pulp is encountered less often. It is isolated or as a result of general amyloidosis and is expressed in the impregnation of pulp tissue with amyloid.- Fatty degeneration of the pulp is often accompanied by caries and chronic inflammation of the pulp. In addition to these causes, we encounter pathological deposition of fat in the cells of pulp tissue as a result of violation of tissue metabolism. Droplets of fat are deposited in the endothelial cells of vessels, in nerve elements and in the mesenchymal cells of the pulp.- Vacuolar degeneration of the pulp affects first of all the layer of odontoblasts and can be the result of caries and chronic inflammation of the pulp. The cellular elements of the pulp are also subject to vacuolar degeneration. A frequent cause of vacuolar degeneration is disturbance of nutrition and lesions of the paradentium-paradentosis. Atrophic degeneration of the pulp is expressed in a decrease in the number of cellular elements, interstitial substance and a decrease in the entire mass of the pulp. Atrophy of the pulp is not always an expression of the age of the individual.

Atrophy of the P. is found in comparatively young teeth and not always as a result of inactivity of the tooth, but more often as a result of impaired nutrition of the P., caused by unfavorable anatomical conditions of the tooth. Atrophic degeneration of odontoblasts is a not infrequent phenomenon and accompanies a whole series of lesions of the P. It can also be the beginning of the manifestation of various harmful factors acting on the P., as for example, medications used for disinfection of the carious cavity, some filling materials, etc. Complete atrophy of the P. is expressed in the depletion of the P. tissue by cells, primarily in the disappearance of odontoblasts, reduction in the number of vessels, especially capillaries, and in the appearance in the interstitial substance of thin short fibers, as if scattered on the surface. Reticular atrophy usually begins with odontoblasts. Cellular elements sharply decrease. A fine-meshed and coarse-meshed network appears, capturing larger or smaller areas of the P. The described forms of degeneration of the pulp do not cause any subjective complaints and are not diagnosed clinically. Until recently, it was believed that not only the inflamed, but also the damaged or accidentally exposed pulp tissue cannot be saved, and therefore in such cases it was devitalized with subsequent amputation or extirpation. Feldman managed to prove that the pulp can be preserved in many cases if it is not cauterized with strongly acting antiseptics. By covering the P. with dentin sawdust, Feldman obtained its metaplasia into dentin-like or bone-like tissue.