Contour lines of Owen• During development of dentin, variations in the metabolism of the organism cause variations in the amount of organic material deposited in the dentin, just as occurs in the enamel.• Changes in the coloration of the dentin are called contour lines of Owen.• The first dentin that is layed down (at the DEJ) forms the mantle layer while subsequent dentin forms the circumpulpal layer.• In the crown of tooth, dentinal tubules from S-shaped primary A, Contour line of Owen; curves. B, Mantle layer of dentin; C, Circumpulpal layer of dentin; D, DEJ
Contour lines of Owen and Stria of Retzius• The contour lines of Owen intercept the dentino-enamel junction and meet an accompanying Stria of Retzius that was formed at the same time. A, Contour line of Owen; B, Stria of Retzius
Lines of vonEbner• Daily alterations in the formation of dentin produce imbrication lines of von Ebner that are approximately 5 µm in length, are seen as banding along the dentinal tubules and are comparable to the cross-striations in enamel.• Arrow indicates the direction of the lines of von Ebner that are perpendicular to the dentinal tubules.
Dentinal tubules• Each odontoblast has a long process that projects through the dentin to the DEJ.• The hole or tube in the dentin through which this process projects is called the dentinal tubule.• The course of the dentinal tubules in the crown of the tooth is S-shaped due to the crowding of the odontoblasts as they get squeezed into a smaller and smaller space within the pulp cavity. A, Primary curve of dentinal tubule;• This curve is called a primary B, DEJ; C, Mantle dentin; curve. D, Circumpulpal dentin
Odontoblasts in an erupted tooth• As the dentin layer forms, the odontoblast become increasingly crowded as they are squeezed into a smaller area.• The single layer of odontoblasts (as occurs in early development) has now changed to stacks of odontoblasts. A, Odontoblasts; B, Predentin; C, Pulp cavity; D, Dentinal tubules
Secondary curves• During the deposition of dentin, the odontoblast makes slight undulations that creates wavy dentinal tubules.• This waviness of the dentinal tubules is called secondary curves. A, Secondary curve of dentinal tubule
Mantle dentin• When viewed in polarized light, mantle dentin (red band), which is about 10 µm wide, can be differentiated from circumpulpal dentin (purple with black dentinal tubules).• This is due to a difference in the collagen fibers in mantle dentin. A, Enamel; B, Circumpulpal dentin; C, Mantle dentin
Globular calcification of dentin• Dentin is calcified after it is formed.• The calcification begins in small spherical areas.• These become larger and fuse with one another to form a calcification front (row of calcification sheres along the A, Odontoblasts; B, Predentin; C, Calcification front; predentin edge). D, Calcified dentin
Calcification pattern of dentin - decalcified section• In mature dentin, globules of well- calcified dentin are apparent (arrow) along with areas of less calcified dentin (white areas). A, Globule of well-calcified dentin
Interglobular dentin in globular layer - ground section• Between the mantle and circumpulpal layers is a layer of dentin in which the calcified globules do not fuse evenly.• This is called the globular layer.• In a ground section of dentin, the less-calcified areas of dentin appear as irregularly shaped crescents called interglobular dentin. A, Interglobular dentin
Globular layer and granular layer• In the root of the tooth, the peripheral border of mantle dentin adjacent to the cementum has a granular appearance and is called the granular layer of Tomes.• The granular layer is a less calcified layer like that of the globular layer.• Generally, interglobular dentin is seen only in the crown, but in this specimen it extends into the root. A, Circumpulpal layer; B, Globular layer; C, Mantle layer; D, Granular layer; E, CEJ; F, Enamel; G, Cementum
Dentinal tubules• Dentinal tubules are the hollow tubes that run through the dentin in which are located the odontoblastic processes.• During formation of dentin, intertubular dentin is layed down between the odontoblastic processes.• Then a second layer of more mineralized dentin is added to "coat" the inside of the tubules.• This layer of dentin is called peritubular dentin or intratubular dentin. A, Peritubular dentin;• In this scanning electron micrograph, B, Intertubular dentin; the peritubular dentin appears white. C, Dentinal tubule
Dentinal tubular branches in root - transmitted and differential interface contrast microscopy• Dentinal tubules generally have lateral branches where odontoblastic processes can communicate with one another.• These branches, as seen here, are most numerous A, Odontoblastic process; in the root of the tooth B, Lateral branches of dentinal tubules
Terminal branching of dentinal tubules• Dentinal tubules are closely spaced but have a large diameter close to the pulp cavity.• Dentinal tubules become more widely spaced in the dentin but have a narrower diameter as they approach the DEJ.• At the DEJ, dentinal tubules branch.• This causes an increased dentity of dentinal tubules in cross-sections of dentin in this region.• In this micrograph, note the scalloped appearance of the DEJ. A, Dentinal tubule; B, DEJ;• The peaks of the scallops point C, Enamel; D, Enamel spindle toward the enamel.
Peritubular and intertubular dentin• In this scanning micrograph of dentin, the dentinal tubules can be seen surrounded by a somewhat loosely packed intertubular dentin and a more dense peritubular dentin. A, Intertubular dentin; B, Peritubular dentin; C, Dentinal tubule
Forms of dentin• Primary dentin, with straight tubules, is laid down before completion of the apical foramen.• Regular secondary dentin is characterized by a slower rate of deposition and an abrupt change in the direction of the dentinal tubules.• Tertiary or irregular secondary (also called irritation, reparative or reactive) dentin is laid down in response to an irritation or damage to the overlying dentin and/or enamel.• This dentin has irregularly arranged and few dentinal tubules. With aging or severe damage, tertiary dentin can totally obliterate the pulp cavity. A, Primary dentin; B, Secondary (regular) dentin; C, Reactive dentin
Dead tracts and blind tracts• When dentin is damaged, odontoblastic processes die or retract leaving empty dentinal tubules.• Areas with empty dentinal tubules are called dead tracts and appear as dark areas in ground sections of tooth.• With time, these dead tracts can become completely filled in mineral.• This region is called blind tracts and appears white in sections of ground tooth.• The dentin in blind tracts is called sclerotic dentin.• The adaptive advantage of blind tracts is the sealing off of the dentinal tubules to prevent bacteria from A, Dead tract; entering the pulp cavity. B, Blind tract (containing sclerotic dentin)
أدعيه قبل المذاكره وبعدها... قبل المذاكرةاللهم أنً اسألك فهم النبٌٌن و حفظ المرسلٌن و المالئكة المقربٌن ، اللهم أجعل ألسنتنا عامرة بذكرك و قلوبنا بخشٌتك و أسرارنا بطاعتك أنك على كل شًء قدٌر .. حسبنا هللا و نعم الوكٌل بعد المذاكرة اللهم أنً استودعتك ما قرأت و ما حفظت و ما تعلمت فرده عند حاجتً الٌه انك على كل شًء قدٌر ، حسبنا هللا و نعم الوكٌل يوم اإلمتحان اللهم أنً توكلت علٌك و سلمت امري الٌك ال ملجأ و منجا منك إال الٌك دخول القاعة رب أدخلنً مدخل صدق و أخرجنً مخرج صدق و أجعل لً من لدنك سلطانا نصٌرا قبل البدء بالحلرب أشرح لً صدري و ٌسر لً أمري و احلل عقدة من لسانً ٌفقه قولً بسم هللا الفتاح ، اللهم ال سهل أال ما جعلته سهال و انت تجعل الحزن اذا شئت سهال ٌا ارحم الراحمٌن أثناء األمتحان ال إله اال انت سبحانك أنً كنت من الظالمٌن ٌا حً ٌا قٌوم برحمتك أستغٌث ، رب ان مسنً الضر أنك أرحم الراحمٌن عند النسيان اللهم ٌا جامع الناس فً ٌوم ال رٌب فٌه أجمعنً و ضالتً بعد األنتهاء الحمد هلل الذي هدانا لهذا و ما كنا لنهتدي لوال أن هدانا هللا
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