Root formation The epithelial cells of inner and outer dental epithelium proliferates from the cervical loop of enamel organ to form a bilaminar structure called hertwigs epithelial root sheath ID: 1009409
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1. Dr. zainab Alhusseini Root formation
2. The epithelial cells of inner and outer dental epithelium proliferates from the cervical loop of enamel organ to form a bilaminar structure called hertwigs epithelial root sheath that outlines the future root and is thus responsible for the shape, length, size, and number of roots and initiates radicular dentin formation.
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4. 1-The development of the roots begins after enamel and dentin formation has reached the future cementoenamel junction. 2-Hertwig’s root sheath consists of the outer and inner enamel epithelia only, and therefore it does not include the stratum intermedium and stellate reticulum. The cells of the inner layer remain short and normally do not produce enamel.
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6. 3- When these cells have induced the differentiation of radicular dental papilla cells into odontoblasts and the first layer of dentin has been laid down, the epithelial root sheath loses its structural continuity and its close relation to the surface of the root.
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8. Cells Rests of Malassez.4-Its remnants persist as an epithelial network of strands or clumps near the external surface of the root. These epithelial remnants are found in the periodontal ligament of erupted teeth
9. 5-There is a pronounced difference in the development of HERS in teeth with one root and in those with two or more roots. Prior to the beginning of root formation, the root sheath forms the epithelial diaphragm .
10. The outer and inner enamel epithelia bend at the future cementoenamel junction into a horizontal plane, narrowing the wide cervical opening of the tooth germ. The plane of the diaphragm remains relatively fixed during the development and growth of the root. The proliferation of the cells of the epithelial diaphragm is accompanied by proliferation of the cells of the connective tissue of the pulp, which occurs in the area adjacent to the diaphragm.
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12. 6-The free end of the diaphragm does not grow into the connective tissue, but the epithelium proliferates coronal to the epithelial diaphragm. The differentiation of odontoblasts and the formation of dentin follow the lengthening of the root sheath. 7-At the same time the connective tissue of the dental sac surrounding the root sheath proliferates and invades the continuous double epithelial layer dividing it into a network of epithelial strands.
13. 8-The epithelium is moved away from the surface of the dentin so that connective tissue cells come into contact with the outer surface of the dentin and differentiate into cementoblasts that deposit a layer of cementum on the surface of the dentin. 9-The rapid sequence of proliferation and destruction of Hertwig’s root sheath explains the fact that it cannot be seen as a continuous layer on the surface of the developing root.
14. 10-In the last stages of root development, the proliferation of the epithelium in the diaphragm breaks after that of the pulpal connective tissue. The wide apical foramen is reduced first to the width of the diaphragmatic opening itself and later is further narrowed by apposition of dentin and cementum to the apex of the root.
15. 11-Differential growth of the epithelial diaphragm in multi- rooted teeth causes the division of the root trunk into two or three roots. During the general growth of the enamel organ the expansion of its cervical opening occurs in such a way that long tongue like extensions of the horizontal diaphragm develop. Two such extensions are found in the germs of lower molars and three in the germs of upper molars.
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17. 12- Before division of the root trunk occurs, the free ends of these horizontal epithelial flaps grow toward each other and fuse. The single cervical opening of the coronal enamel organ is then divided into two or three openings. On the pulpal surface of the dividing epithelial bridges, dentin formation starts and on the periphery of each opening, root development follows in the same way as described for single-rooted teeth.
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19. 13-If cells of the epithelial root sheath remain adherent to the dentin surface, they may differentiate into fully functioning ameloblasts and produce enamel. Such droplets of enamel, called enamel pearls, are sometimes found in the area of furcation of the roots of permanent molars.
20. 14-If the continuity of HERS is broken or is not established prior to dentin formation, a defect in the dentinal wall of the pulp ensues. Such defects are found in the pulpal floor corresponding to the furcation or on any point of the root itself if the fusion of the horizontal extensions of the diaphragm remains incomplete. This accounts for the development of accessory root canals opening on the periodontal surface of the root.
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22. 1-Anodontia is a complete lack of tooth development it is very rare most often occur in hereditary condition called ectodermal dysplasia Developmental disturbances of teeth:
23. 2-hypodontia Congenital missing tooth or teeth it is one of the most common developmental abnormalitiesAbsence of third molar is very common followed in prevalenceby the second premolar and lateral incisor.3-hyperdontia (supernumerary teeth):It is believed to be associated with the remenant of dental lamina or epithelial rest of serres
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25. 4-dilaceration is an abnormal bend on atooth and is nearly always associated with trauma that moves the developing tooth bud5-Regional odontodysplasiaIs rare but is most likely to occur in the maxillary anterior teethThe enamel ,dentin,and pulp of teeth are affected, so the teeth are very brittleOn radiograph the teeth appear more radiolucent than normal so they are described as ghost teeth
26. 6-Amelogenesis imperfecaHeredetary condition characterized by defect in dental enamel formation ,teeth are often free of enamel,small, misshapen and tinted brown 7-Dentinogenesis imperfectHeredetary condition characterized by defect in either dentin matrix formation or mineralization of dentin8-Natal and neonatal teethNatal teeth are present at time of birth,neonatal teeth will erupt during the first 30 days after birthNatal teeth are three times more common than neonatal teeth
27. 9- gemenation Arises when two teeth developed from one tooth bud as a result the patient has extra tooth