Oral Biology I BDS123 Lecture Notes Fall 2024 PDF

Course Title: Oral Biology I Course Code: BDS123 Topic of Lecture: Tooth development Lecturer: Prof Samah Mehanny F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e F a l l 2 0 2 4 O...

Course Title: Oral Biology I Course Code: BDS123 Topic of Lecture: Tooth development Lecturer: Prof Samah Mehanny F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e F a l l 2 0 2 4 Oral Biology and its importance By providing a focus for the traditional basic health sciences, oral biology has laid a foundation for the further development and expansion of the knowledge base upon which the clinical subjects of the dental curriculum and dental practice necessarily rest. Oral biology Prepared by Prof Samah Mehanny  Topics to be studied this semester: -Tooth development -Enamel structure and amelogenesis -Dentin structure and Dentinogensis -Cementum structure and cementogenesis -Pulp structure -PDL structure -Alveolar bone and osteointegration -Radiographic interpretation to the maxillary and mandibular landmarks Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Before going through the stages of tooth development please search for; What’s meant by dental congenital anomalies? Prepared by Prof Samah Mehanny  Congenital Dental Anomalies Supernumerary teeth Teeth fusion Macrodontia Microdontia Prepared by Prof Samah Mehanny  Tooth development or odontogenesis takes place in many stages, which occur in a stepwise fashion for both dentitions. Odontogenesis is a continuous process, and there is no clear-cut beginning or ending points between its stages. Prepared by Prof Samah Mehanny  We can describe odontogenesis in two ways; Morphological stages; Dental lamina formation, bud, cap, and bell. Physiological stages; Induction, proliferation, morpho-differentiation, histo-differentiation, apposition, and maturation. Molecular basis of tooth development Sonic hedgehog (Shh) and different types of growth factors are responsible for the development of teeth, their numbers, and their certain morphology. Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny  Dental placode Prepared by Prof Samah Mehanny Watch the following video, then figure out what are the morphological stages of tooth development. Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Morphological stages of tooth development: Crown formation. 1-Dental lamina initiation. 2- The bud stage. Prepared by Prof Samah Mehanny 3- The cap stage. 4- The early bell stage. 5- The late (advanced) bell stage. (Apposition and maturation stage). Prepared by Prof Samah Mehanny 1-Dental lamina initiation. Oral epithelium Oral cavity Primary epithelial band Ectomesenchyme Prepared by Prof Samah Mehanny  Vestibular lamina Dental lamina Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Kindly search also for; What’s meant by the signaling molecule Sonic hedgehog and its role in odontogenesis? Prepared by Prof Samah Mehanny *The signaling molecule Sonic hedgehog (Shh) is secreted by the odontogenic epithelium. *Shh gradually diffuses to the dental ectomesenchyme. Int J Mol Sci. 2020 Mar; 21(5): 1587. Sonic Hedgehog Signaling and Tooth Development Prepared by Prof Samah Mehanny -At the age of 5 wiu the odontogenic epithelium (rich in Shh signaling molecules) covers mesenchymal tissues. -The mesenchymal cells tend to ectomesenchymal cells arise from neural crest cells. -The odontogenic epithelium sends inductive messages converting the neural crest cells into odontogenic cells. Prepared by Prof Samah Mehanny - At the age of 6 wiu, By shifting the mitotic spindles of the odontogenic epithelium it will proliferate to form a primary epithelial band (U-shaped band). - Then this primary band is bifurcated into general (main) dental and vestibular laminae. - The main dental lamina gives rise the deciduous dentition. - Posterior (distal) proliferation to the main dental lamina gives rise to permanent molars. - Lingual to the deciduous dentition, successional dental laminae proliferate that are responsible for successors. (successional dental lamina). - The vestibular lamina will eventually form the vestibular mucosa in the oral cavity. Prepared by Prof Samah Mehanny  Oral cavity Oral epithelium **** Thus the physiological processes are induction and proliferation. Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny 2- Bud stage. Dental At the site of the future tooth, the lamina facial aspect of the dental lamina is induced to give dental placodes Bud for each tooth in the form of bud by the influence of neural crest cells (Induction) that penetrates growing ectomesenchyme (Proliferation). Proliferating ectomesenchyme. Thus the main physiological processes are Induction and Proliferation. Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Virtual microscope link https://www.anatomicum.com/en/?articleid=58 Prepared by Prof Samah Mehanny 3- Cap stage. “Differential growth” Prepared by Prof Samah Mehanny The ectomesenchyme then sends signals that trigger localized proliferation. Bud then shows unequal growth leading to the Enamel organ formation of a cap shape which is Dental called an enamel organ. papilla The growing ectomesenchyme will be divided into dental papilla Dental sac (inside the concavity of the cap) and dental sac (surrounding the cap). The basement membrane still separates the epithelium from the C.T Prepared by Prof Samah Mehanny  Enamel organ Dental papilla Dental sac Enamel organ, dental papilla and dental sac are called Tooth Germ. Enamel organ Enamel Dental papilla Dentin and pulp (Calcified and non-calcified parts) Dental sac (Calcified Cementum, alveolar bone and PDL and non-calcified parts) Prepared by Prof Samah Mehanny The main physiological process involved in this stage is: Proliferation (growth of enamel organ, dental papilla and dental sac). This results in the organization of the cells into outer and inner enamel epithelium and stellate reticulum. Outer D. E. Stellate R. Inner D. E. Prepared by Prof Samah Mehanny Polygonal cells….change to.. Prepared by Prof Samah Mehanny Stellate reticulum cells ………………. …… ……… ………………….. ……………….. Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny -The polygonal central cells of the enamel organ are termed the stellate reticulum. -These cells synthesize and secrete glycosaminoglycans into the extracellular compartment between them. The glycosaminoglycans are hydrophilic and so pull water into the enamel organ. -The increasing amount of fluid increases the volume of the extracellular compartment of the enamel organ and the central cells are forced apart. Prepared by Prof Samah Mehanny  Because the stellate reticulum cells retain connections with each other through their desmosomal contacts, these polygonal cells stellate reticulum become star shaped Prepared by Prof Samah Mehanny  Transitory structures: Earlier during tooth development two transitory structures may be seen named as the enamel knot and enamel cord. Prepared by Prof Samah Mehanny  Enamel knot -Enamel knots are clusters of non-dividing epithelial cells that appear in the cap stage and bulge into the dental papilla, at the center of the enamel organ. -They are non-dividing cells. -The enamel knots disappear in the bell stage by apoptosis. -The enamel knot is a signaling center that controls cuspal morphogenesis. Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny  Enamel cord The enamel cord is a strand of cells seen at the early bell stage extending from the stratum intermedium to the outer enamel epithelium. When it completely divides the stellate reticulum into two parts, it is termed the enamel septum. It has been suggested that the enamel cord may be:- Involved in the process by which the cap stage is transformed into the bell stage (act as a mechanical tie) Prepared by Prof Samah Mehanny  Enamel cord Stratum intermedium Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Prepared by Prof Samah Mehanny Thank you Prepared by Prof Samah Mehanny