Dental Enamel PDF

Dental Enamel I. Definitions: - It is the ectodermal tissue covering the anatomical 3- Hunter Schreger’s bands; crown of the teeth. It is the most highly mineralized They are alternating dark and light bands.They are tissue in the...

Dental Enamel I. Definitions: - It is the ectodermal tissue covering the anatomical 3- Hunter Schreger’s bands; crown of the teeth. It is the most highly mineralized They are alternating dark and light bands.They are tissue in the human body. present at the middle and cervical thirds of the crown and absent in the region of gnarled enamel - It is an acellular, inert, nonvital and insensitive tissue. ( The occlusal or incisal third of the crown). IV. Chemical properties of dental enamel: 4- Primary enamel cuticle (Nasmyth’s membrane); - Dental enamel is composed of nearly 96% inorganic It is a delicate organic membrane that covers the crown material supported by 4% organic material and water surface of the newly erupted teeth. - The inorganic components of dental enamel consist mainly of hydroxyl apatite {3 Ca3(PO4)2.Ca(OH)2} -Its thickness is about 0.2 micron. -The primary enamel cuticle is gradually worn off from V. Histological structure of dental enamel: the surface exposed to mastication or tooth brushing but 1- Enamel prisms (Enamel rods); it may remain for life of the tooth in sheltered areas, as in - The unit structure of enamel is enamel prism / rod. the gingival sulcus and depths of pits and fissures. - The direction of enamel rods in general perpendicular to 5- Incremental lines of dental enamel; the dentin surface. i- Cross striations: - The course of individual enamel rods is wavy from the Dark transverse lines that give the enamel rods a amelodentinal junction outwards but just before they striated appearance. reach the outer surface of the enamel, they become ii- Brown striae of Retzius: They appear as brown bands straight. in ground section of enamel. - Enamel rods are separated interprismatic substance iii- Neonatal line: It is present only in the deciduous teeth and first III.Physical properties of dental enamel: permanent molars. It separates formed enamel before i- Color: ranges from yellowish-white to grayish-white. birth from formed enamel after birth. ii- Thickness: The thickness of dental enamel is variable over the entire surface of the crown where it is the 6-The amelodentinal junction; thickest in the cusps and incisal edge, and it thins down In ground sections,the amelodentinal junction appears to to a knife edge at the cervical margin. be scalloped in permanent teeth and smooth in deciduous teeth. iii- Hardness: Dental enamel is the hardest calcified 7- Enamel lamellae; tissue in the human body due to ; They are a thin leaf or sheet like structures that extend : - Its high content of mineral salts and - to its crystallites arrangement. - from the enamel surface to a considerable distance in the enamel , or iv- Density: The density of dental enamel decreases from the outer surface to the amelodentinal junction. - reaching to the amelodentinal junction, or Permanent teeth have more density than the deciduous. - they may extend into the dentin. v- Permeability: 8- Enamel tufts; Dental enamel has a certain degree of permeability. They are a ribbon like structures that extend from the 2- Gnarled enamel; amelodentinal junction to about 1/5 - 1/3 of the enamel It is a part of dental enamel that is present in areas thickness. where the enamel rods are twisted and braided together to give maximum strength to these areas. 9- Enamel spindles; They are the endings of odontoblastic processes that It is present at the occlusal or incisal third of the crown extended between the inner enamel epithelium before and absent in the region of Hunter Schreger’s bands hard dental tissues are formed. Clinical Oral Histology 1 Level: 2 Dr.Basem Muthanna.  Dental Dentin 3- Periodontoblastic space; I. Definition: It intervenes between the wall of the dentinal tubule and It forms the main bulk of the tooth.Dentin of the crown is the odontoblastic processes.This space contains tissue covered by the enamel, while dentin of the root is fluid,dentinal lymph and collagen fibers. covered by cementum. 4- Peritubular dentin; III. Physical properties of dental dentin It is a highly calcified zone surrounding the odontoblastic i- Color: It is a yellowish in color. processes and forming the walls of dentinal tubules. ii- Thickness: The thickness of dental dentin varies from 5-Intertubular dentin; 3-10 mm or even more. It is the main body of the dentin and located between the dentinal tubules. iii- Hardness: Dentin is less hardness than enamel. 6-Interglobular dentin It is described as areas of unmineralized or iv- Elasticity: Dentin is more elasticity than enamel. hypomineralized dentin that persists with mature dentin. IV. Chemical properties of dental dentin: 7- Granular layer of Tomes; Dental dentin has a considerably higher organic content It is always present immediately adjacent to the than enamel. By weight the organic material and water is cementum. It is a constant feature of the root dentin about 25-30% and the remaining 70-75% is an inorganic.This granular appearance is produced by minute areas material. of interglobular dentin. V. Histological structure of dental dentin; 8-Incremental lines of dental dentin; Dental dentin is composed of the following: i-Incremental lines of Von Ebner: 1- Dentinal tubules; They are formed due to periods of activity alternating - The unit structure of dental dentin is dentinal tubule. with periods of rest.They appear as fine lines which in Dentinal tubules are closely packed and traverse the cross sections run at right angles to the dentinal tubules. entire thickness of ii-Contour lines of Owen:They present as areas of dentin. hypocalcification and become more accentuated in disturbances of calcification process. - Dentinal tubules contain the odontoblastic processs in the central areas. iii-Neonatal line: It is present only in the deciduous teeth and first - At the middle and cervical thirds of the crown, the permanent molars.It separates formed dentin before dentinal tubules in their course from the pulp to the outer birth from formed dentin after birth. dentin surface take S shaped course. While in the root 9- The dentinoenamel junction; portion and under the cusps or incisal edges, the dentinal In ground sections,the dentinoenamel junction appears to tubules take a straighter course. be scalloped in permanent teeth and smooth in deciduous teeth. 2- Odontoblastic processes; - They are cytoplasmic processes of the odontoblasts 10- The dentinocemental junction; (Tomes fibers) and present in the center of the dentinal It is usually smooth in permanent teeth and scalloped in tubules. deciduous teeth. - In the crown, some of Tomes fibers pass the 11-The nerve fibers of dental dentin; dentinoenamel junction and terminate in the enamel as The nerve fibers enter the pulp and divided into many enamel spindles. However, many of Tomes fibers in the branches till reaching near the odontoblasts where they root dentin terminate as the granular layer of Tomes. lose their myelline sheath and form a plexus of nerves called plexus of Raschkow or subodontoblastic plexus giving intratubular nerves in the dentin. Clinical Oral Histology 1 Level: 2. dr.Basem Muthanna  Dental Cementum I. Definitions: 4-Incremental lines of Salter; i-It is a calcified dental tissue covering the anatomical part Both cellular and acellular cementum are separated by of the roots of the teeth. incremental lines which indicate to periodic formation. ii-It begins at the cemento-enamel junction and continues They are highly mineralized areas. to the apex. In acellular cementum: III. Physical properties of dental cementum; incremental lines of Salter are relatively close together, thinner and regular lines. However, in cellular cementum : i- Color: It is a light yellow in color. they are relatively wide apart, thicker and irregular lines. ii- Thickness: The thickness of cementum at the cervical area 5-The cementodentinal junction; is about 20-50 microns and it gradually increases in It is usually smooth in permanent teeth and scalloped in thickness till it reaches its maximum about 150-200 deciduous teeth. microns at the apex and the bifurcation of the root. iii- Hardness: Cementum is less hardness than enamel 6-The cementoenamel junction; and dentin. The relation between cementum and enamel at the cervical region of the teeth is variable as follows: iv- Elasticity: Cementum is more elasticity than enamel and dentin. 6.a- In 30% of all teeth: Cementum meets the cervical end.III.Chemical properties of dental Cementum: of enamel in a relatively sharpline. Dental cementum contains: - 45-50 % inorganic materials and 6.b- In 10% of all teeth: The cementoenamel junction -50-55 % organic materials. consists only of a layer of dentin without enamel and cementum when the epithelial root sheath of Hertwig is delayed in its separation from the dentin. V.Histological structure of dental cementum: Dental cementum is composed of the following: 6.c- In 60% of all teeth: 1-Acellular cementum Cementum overlaps the cervical end of enamel for a It does not contain cells (cementocytes). It covers the short distance root dentin in the coronal and middle thirds of the roots.It is sometimes termed as primary cementum. VI. Functions of dental cementum : 2- Cellular cementum: 1- Supportive function: It covers the root dentin in the apical third of the roots It furnishes a medium for the attachment of and is sometimes termed secondary cementum. It is collagen fibers of the periodontal ligament to the also found in the interradicular areas. It contains cells alveolar bone. (cementocytes).The cementocytes are cells incorporated into cellular cementum.Cementocyte has: 2- Compensative function: - granular cytoplasm and Deposition of cementum at the apical part of the root - faintly stained nucleus, can compensate to some extent for the loss of dental - the body of cell lies in space called lacunae. enamel that may occur from occlusal wear. 3- Intermediate cementum: 3- Reparative function: Sometimes dentin is separated from cementum by a It serves as major reparative tissue for root surface zone known as the intermediate cementum layer.This damage as fracture or resorption where it can be repaired layer does not resemble either dentin or cementum. by deposition of new cementum. Usually it is present in the middle and apical thirds of the VII. Age changes of dental cementum; roots of permanent molars and premolars. 1- Hypercementosis. 2- Permeability. Clinical Oral Histology 1 Level: 2 dr.Basem Muthanna  1.Tooth Development Clinical Oral Histology Level: 2 dr.Basem Muthanna  II. Dental Enamel Clinical Oral Histology Level: 2 dr.Basem Muthanna  III. Dental Dentin Clinical Oral Histology Level: 2 dr.Basem Muthanna  IV. Dental Cementum & V. Dental Pulp Dental Cementum Dental Pulp Clinical Oral Histology Level: 2 dr.Basem Muthanna