Dental lamina• During the fifth week of embryonic development, the oral epithelium thickens along the future dental arches to form the dental lamina. Legend: A, dental lamina; B, Mesenchymal neural crest
Bud stage• Around the eighth week of embryonic development, the mesenchymal neural crest induces the development of tooth buds at ten locations in the upper and lower dental lamina.• During the bud stage the dental lamina grows into the mesenchyme in the shape of a bud.
Cap stage• During the ninth week of embryonic development, the tooth bud differentiates into a cap-shaped enamel organ extending from the dental lamina.• A vestibular lamina develops to separate the gum from the lip/cheek.• During the cap stage, an unequal growth of epithelial cells grows down to form a concavity around the mesenchyme forming the dental papilla.• Other mesenchymal cells encircle the enamel organ forming the dental sac. Legend: A, Enamel organ; B, Dental lamina; C, Vestibular lamina; D, Dental Papilla; E, Dental sac
Bell stage• Cytodifferentiation becomes apparent during the bell stage, when the epithelial cells outlining the enamel organ can be distinguished as the inner enamel epithelium and outer enamel epithelium.• The interior of the enamel organ comprises the stellate reticulum, a cushiony layer which will protect the developing tooth.• The successional lamina, which will give rise to the secondary tooth, arises from the dental lamina. A, Inner enamel epithelium; B, Outer enamel epithelium; C, Stellate reticulum; D, Successional lamina; E, Dental lamina; F, Dental papilla; G, Dental sac.
Cervical loop• The inner enamel epithelium and outer enamel epithelium joint at the cervical loop, that portion of the enamel organ which is growing down into the mesenchyme.• The cells of the inner enamel epithelium will eventually become ameloblasts.• The layer adjacent to the inner enamel epithelium is the stratum intermedium, and will become important in transporting nutrients to the future ameloblasts. Legend: A, Cervical loop; B, Inner enamel epithelium; C, Outer enamel epithelium; D, Stratum intermedium; E, Stellate reticulum
Cytodifferentiation of inner enamel epithelium• The cells of the inner enamel epithelium (which will become ameloblasts) are least differentiated near the cervical loop and most differentiated near the incisal cusp of the tooth. Legend: A, Cervical loop; B, Least differentiated; C, Most differentiated
Odontoblastic differentiation• Preameloblasts initiate the differentiation of odontoblasts which arise from cells in the dental papilla. The odontoblasts are called preodontoblasts before they begin the production of dentin. Legend: A, Preameloblasts; B, Preodontoblasts; C, Stellate reticullum; D, Dental papilla
Deposition of dentin and enamel• Mature, elongated odontoblasts begin the deposition of predentin.• This deprives the preameloblasts of their nutritional source inducing their differentiation into ameloblasts which then begin to deposit enamel.• Predentin is completely organic when it is formed and gradually is mineralized to form dentin.• Enamel is partially mineralized when it is deposited.• Arrows show the direction of movement of ameloblasts and Legend: A, Odontoblasts; B, Predentin; odontoblasts. C, Ameloblasts; D, Enamel; E, Dentin.
Reduced enamel epithelium• Following the formation of the crown , the enamel organ collapses to form the reduced enamel epithelium which covers the tooth through eruption.• The reduced enamel epithelium consists of the mature/protective ameloblasts and remanants of the outer layers of the enamel organ.• Numerous capillaries,which had formed to supply oxygen and nutrients to the ameloblasts following dentin formation, Legend: A, Reduced enamel surround the reduced enamel epithelium; B, Maturative/protective epithelium. ameloblasts; C, Capillary
Immature enamel• Ameloblasts secrete immature enamel which is only partially mineralized. Legend: A, Ameloblasts; B, Immature enamel
Preodontoblast• Prior to dentinogenesis the basement membrane thickens between the preodontoblast and preameloblast.• Processes from the preodontoblasts extend through the basement membrane to come into close association with the preameloblast. Legend: A, Preodontoblast; B, Preameloblast; C, Basement membrane
Odontoblast• Following differentiation of preodontoblasts into odontoblasts, dentin begins to be deposited first as predentin.• The odontoblasts nucleus has moved away from the secretory end of the cell where numerous organelles have accumulated to aid in predentin deposition. Legend: A, Odontoblast nucleus; B, Secretory end of odontoblast; C, Predentin
Ameloblasts• After dentinogenesis begins, the preameloblasts differentiate into ameloblasts which begin to deposit enamel.• Ameloblasts are very tall columnar cells with a nucleus displaced away from the secretory end of the cell. The ameloblasts develop a Tomes process shortly after beginning amelogenesis.• This process is responsible for the production of enamel in the form of rods. Legend: A, Ameloblast nucleus; B, Enamel; C, Tomes process
Maturative ameloblast• When the ameloblast has finished depositing enamel, the Tomes process is lost and a striated border takes its place.• During the maturation stage, there is a loss of organic material and water from the enamel.• The striated border is supposedly responsible for the resorption of these matrix components, as evidenced by numerous dense granules within the apical cytoplasm of the ameloblast. A, Striated border; B, Immature enamel; C, Mature enamel; D, Dense granules
Calcification• Enamel and dentin is fairly evenly calcified in the erupted deciduous tooth (1) but a gradient of calcification can be seen in the developing permanent tooth (2) with the more calcified areas located in the incisal areas (arrow) Legend: A, Enamel; B, Dentin
Developing enamel• Hydroxyapatite crystals are thin in the region of the secreting ameloblast. Legend: A, Hydroxyapatite crystal
More mature enamel• Enamel is made up of elongated groups of hydroxyapatite crystals called rods.• Hydroxyapatite crystals run parallel to the long axis of the rod core (B) and obliquely in the rod sheath (A).• In maturing enamel the hydroxyapatite crystals become thicker. Legend: A, Rod sheath; B, Rod core
Root formation• After complete formation of the crown of the tooth, the root is formed.• An extension of the enamel organ, called the epithelial root sheath of Hertwig, continues to grow apically.• The epithelial root sheath induces the differentiation of odontoblasts which form root dentin.• The apical most portion of the root sheath turns inward toward the radicular pulp cavity (that portion of the pulp cavity inside the root) and is A, Epithelial diaphragm; called the epithelial diaphragm. B, Radicular pulp cavity; C, Dentin; D, Enamel space; E, Alveolar Bone; F, Root
Epithelial root sheath• The epithelial root sheath is made up of inner and outer enamel epithelial layers without the other two interposing layers.• Following the induction of odontoblast and dentin formation, the epitheal root sheath disintegrates forming epithelial rests, small groups of epithelial cells that can remain around the root. A, Radicular pulp cavity; B, Dentin; C, Dental sac; D, Point at which epithelial root sheath begins to disintegrate; E, Epithelial diaphram
Cementum formation• As the epithelial root sheath breaks down, cells from the dental sac migrate to the surface of the root dentin and differentiate into cementoblasts.• These cells lay down cememtum on the surface of the root. A, Cementoblasts; B, Odontoblasts; C, Predentin
Epithelial rests• Remnants of the disintegrated root sheath called epithelial rests can remain for long periods of time following eruption of the tooth.• The first dentin that is formed is called mantle dentin, while the remaining dentin is called circumpulpal dentin.• There is also a small layer interposed between these two dentin layers of less mineralized dentin called globular dentin. A, Epithelial rests; B, Mantle dentin; C, Globular dentin; D, Circumpulpal dentin
First maxillary deciduous molar• This molar is from a 22- week fetus.• The red coloration indicates the formation of the hard tissues.• Enamel and dentin are first formed at the cuspal region and their formation proceeds toward the cervix of the tooth. Legend: A, Cusp of molar
Second maxillary deciduous molar• This molar is from a 19-week fetus.• The first deposited dentin on the mesiobuccal cusp is shown. Legend: A, Dentin on the mesiobuccal cusp
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