Tooth Development 2023-2024 till Cap Stage PDF

Tooth development Odontogenesis  Tooth development Starts as early as 5th to 6th week of I.U.L. The developing tooth passes though different stages as it changes in shape & size The stages are continuous with no sharp cut between the end of one and the sta...

Tooth development Odontogenesis  Tooth development Starts as early as 5th to 6th week of I.U.L. The developing tooth passes though different stages as it changes in shape & size The stages are continuous with no sharp cut between the end of one and the start of another. There is no difference between deciduous & permanent teeth in the stages of development Except In number and the chronology All parts of the tooth develop from the mesoderm except enamel is ectodermal in origin Human embryo during the early development is formed basically Three germ layers which are made of three main types of basic tissues that make the whole body Outside cover (skin , nails, mucous membrane, enamel. etc. Internal support Bone, muscles, cartilage, c.t., dentin etc. Lining of stomach, intestine, urinary bladder… etc. The human embryo very early develops as a pear-shaped disc formed first of two layers (ectoderm and endoderm) then soon a third layer develops in between these 2 layers giving rise to a trilaminar embryonic disc ( ectoderm, endoderm & mesoderm)  at 5 W I.U.L. Embryo Primitive oral cavity Stomodeum  5 w.I.U.L Embryo Flat cells Columnar ECTODERM cells MESODERM Basement membrane The primitive oral cavity is lined by two layers of cells (basal columnar & superficial flattened) composing the ectodermal part of the lining (epithelium) The epithelium lies over the mesoderm and separated from it by basement membrane. Neural crest At 6 w.I.U.L Embryo cells Ecto-mesenchyme Early during development of the central nervous system cells of nervous origin separate from the developing ectoderm of the nervous system and travel in the mesoderm to different parts of the body. These are known as neural crest cells  Neural crest cells They are ectodermal in origin ( from the nervous system) and migrate to the underlying mesenchymal tissue to initiate the development of different organs including the teeth except enamel. Due to the presence of the neural crest cells (ectodermal in origin) in the underlying mesenchyme, this primitive mesenchyme is termed ectomesenchyme (embryonic CT). Different stages of tooth development 1. The stage of dental lamina. 2. The bud stage. 3. The cap stage. 4. The bell stage which is divided into: Early bell stage (before hard tissue formation). Late or advanced bell stage (starts as the 1st layer of dentin is formed). Tooth development starts with thickening of the oral epithelium forming “ The Primary Epithelial Band”  Under the influence of neural crest cells 6 w.I.U.L Ecto-mesenchyme An early Ecto-mesenchyme induction process in dental arch development Under the effect of ectomesenchyme the basal cells proliferate at a faster rate than the adjacent cells forming separate islands that invaginate the underlying ectomesenchyme  Ecto-mesenchyme Primary epithelial band These islands grow toward each other and coalesce to form an arch shaped ectodermal band called primary epithelial band which outlines the future developing jaw. Each Primary Epithelial Band soon splits into two laminae  The vestibular lamina is responsible for the formation of the oral vestibule Which is the area between the teeth, lips and cheeks At 7th W.I.U.L. The primary epithelial band divides into two laminae; Dental lamina. (Lingual) Vestibular lamina (Facial) The vestibular lamina The epithelial cells of the vestibular lamina proliferate into the underlying primitive mesenchyme. Then the central cells of this lamina disintegrate to form the vestibule which is the space between the maxilla and the mandible on one side and the lips and the cheeks on the other side  Morphological stages of tooth development 1- Dental lamina. 2- Bud stage. 3- Cap stage. 4- Bell stage A- Early bell stage. B- Late bell stage. Dental lamina  Oral Oral Oral cavity cavity Oral cavity epithelium *** * Neural crest cells induce proliferation of the basal cell layer of oral epithelium leading to the formation of dental lamina which is an epithelial growth in the underlying ecto- mesenchyme. Both tissues are separated by a basement membrane. Dental lamina It is the lingual side division of the primary epithelial band which is a sheet-like structure the future arch shape. From this lamina extending along the entire free margin of the future jaw different teeth germs originate  Labial Lingual Histologically , the dental lamina is composed of peripherally low columnar cells on the basement membrane and centrally located polygonal (polyhedral) cells. Dental Lamina stage Bud stage  The buds of deciduous anterior teeth appear first, followed by that of the canine and molars. The cells of dental organ have a uniform size and shape.  Labial Deciduous teeth develop by proliferation of the dental lamina on its labial surface at 10 sites in each jaw.(each at its own date) The cells at these sites will divide at a faster rate than the adjacent cells to form ectodermal rounded masses or bud shape epithelial structure called enamel (dental) organ. From the facial side ;10 ectodermal swellings for Facial deciduous teeth in each jaw side appear having the bud shape Lingual which is called the dental side (enamel) organ. The supporting ectomesenchymal cells beneath the epithelial bud are called dental papilla Dental sac (dental follicle) encircles the enamel organ and dental papilla. Dental organ + Dental papilla + Dental sac = Tooth germ.  Bud stage L L I A N B G U I A A L L Dental Organ Dental Papilla Tooth germ Dental Sac Histologically, the dental organ is composed of: Basal or Peripheral cells (cuboidal). Central cells (polyhedral) secrete glyocsaminoglycans extra-cellulary. The ectomesenchymal cells situated beneath the enamel organ (bud) become condensed→ Growing ectomesenchyme (dental papilla) The connective tissue beneath and around the enamel organ and dental papilla forming what is called dental sac (follicle). A basement membrane remains between the bud and the growing underlying ectomesenchyme. 36_bb Peripheral Central cells cells Growing ectomesenchyme Bud stage Cap stage Un equal growth Differential growth  Cap “Differential Growth” stage The dental organ increases in size and changes in shape from a bud like to a cap like dental organ due to formation of a deep concavity in its inner surface enclosing the dental papilla, while its outer surface remains convex.  Cap stage 1-Dental Organ TOOTH 2- Dental GERM Papilla 3-Dental Sac Histological structures in cap stage 1. Dental lamina 2. Dental organ ❑ Outer enamel epithelium ❑ Inner enamel epithelium ❑ Stellate reticulum ❑ Transient structures: ❖ Enamel knot ❖ Enamel cord 3. Dental papilla 4. Dental sac 1- Dental lamina: There is a broad connection between dental organ and dental lamina. 2- Dental (Enamel) organ: Outer Enamel Epith. Inner Dental Epith The basement membrane separates the whole surfaces of the dental organ from the surrounding mesenchymal tissue 2- Dental (Enamel) organ: Stellate reticulum. They are star shaped cells with long processes anastomose with each other and with the outer and inner enamel epithelia by DESMOSOMES. The intercellular spaces are rich in GYCOSAMINO-GLYCANS  How do polyhedral cells change to stellate reticulum cells? The secreted dense material (glycosamino-glycans) elevates the osmotic pressure inside the enamel organ leading to water suction from outside the organ. The water fills the intercellular spaces between polyhedral cells which compresses their membranes converting the cells into star-shaped cells. The junctions between cells make them look like a network of stars 2- Dental (Enamel) organ: Non-dividing cells Enamel Cord Enamel Knot Transient structure: Disappears before enamel formation. a-Enamel Knot b-Enamel Cord 3- Dental papilla: Is a condensation of Ectomesenchyme. It is separated from the inner enamel epithelium by a basement membrane. Cell Free Zone. 4- Dental sac: is an ectomesnenchymal condensation of cells surrounding both dental organ and dental papilla  Cell free zone Cytoplasmic process Argirophilic fibers Outer Dental Enamel Epith. cord Enamel Stellate Knot Reticulum Inner Dental Dental Epith. Papilla Q Complete: The second stage of odontogensis is called the.................. Q Complete: The connective tissue-beneath-and around the enamel organ and dental papilla is called.............................. Q Complete: The dental organ is..................... in origin, while both dental papilla and dental sac are.......................... in origin. Thank you