Tooth Development PDF

TOOTH DEVELOPMENT Dr. Hagar Sherif (BDS, MSc, PhD) Lecturer of Oral Biology, Faculty of Dentistry, Alexandria University, Egypt. Tooth Development (odontogenesis) ◦ Odontogenesis ◦ “Odon” is a Greek word meaning tooth ◦ ‘Genesis’ is a Greek word meaning creation ◦ It is...

TOOTH DEVELOPMENT Dr. Hagar Sherif (BDS, MSc, PhD) Lecturer of Oral Biology, Faculty of Dentistry, Alexandria University, Egypt. Tooth Development (odontogenesis) ◦ Odontogenesis ◦ “Odon” is a Greek word meaning tooth ◦ ‘Genesis’ is a Greek word meaning creation ◦ It is a medical term describing the process of tooth formation and eruption.  Permanent set Dental Arch Deciduous set The oral Cavity Vestibule  The primitive oral cavity ◦ The primitive oral cavity is lined by ectoderm (epithelium) covering an embryonic connective tissue termed ectomesenchyme; both separated by a basement membrane. Oral epithelium Basement membrane Ectomesenchyme Why called ectomesenchyme? ◦ Because the origin of the contained cells is ectodermal “Neural crest cells” ◦ These are cells that migrate from the ectodermal neural tube to the head and neck mesoderm to form very important structures (face and teeth). The mesoderm is now called ectomesenchyme. Formation of the future Dental arch ◦ After 37 days of development (6th week of intrauterine life), a continuous band of odontogenic epithelium forms in the presumptive upper and lower jaws. These bands are roughly horseshoe-shaped and correspond in position to the future dental arches of the upper and lower jaws. ◦ Each band of epithelium, is called the primary epithelial band.  Primary Epithelial Band Sagittal section through the head of an embryo.  Primary epithelial band By the 7th week, the primary epithelial band divides into a buccally located vestibular lamina and a lingually situated dental lamina Buccal vestibular lamina Lingual dental lamina vestibular lamina vestibule The cells of the vestibular lamina rapidly enlarge and then degenerate to the vestibule between the cheek and the tooth-bearing area. dental lamina 10 buds 10 mandibular and 10 maxillary Dental lamina contributes to the development of teeth, at sites corresponding to the positions of the future deciduous teeth.  Dental Lamina This lamina contributes to the development of the teeth. The teeth develop as a result of the interaction between oral epithelium and underlying ectomesenchyme that go in many stages.  Vestibular lamina the vestibular lamina, which forms shortly afterward and is positioned just in front of the dental lamina. The vestibular lamina contributes to the development of the vestibule of the mouth, separating the lips and cheeks from the tooth-bearing regions. Dental lamina Vestibular lamina Ectomesenchymal Condensation  Vestibular lamina Before degeneration After degeneration Initiation of the Tooth  Stages of tooth development ◦ From this point, tooth development proceeds in three stages: the bud, cap, and bell. These terms are descriptive of the morphology of the developing tooth germ Primitive oral cavity  Molecular Regulation of Tooth Formation ◦ Numerous genes regulate tooth development ◦ The reciprocal and sequential interactions between dental mesenchyme and epithelium constitute the core of the molecular program. The interactions are mediated by the conserved signal molecules, which in turn regulate the expression of numerous other genes important for the developing tooth. Initiation of the Tooth development ◦ Odontogenesis is initiated first by factors resident in the first arch epithelium influencing ectomesenchyme To date, more than 90 genes have been identified during the initiation of tooth development.  Homeobox genes Constitute a large family of genes that are important in controlling embryonic development.  These genes are involved in the regulation of the key events in tooth development: ◦ Initiation: the onset of tooth formation ◦ Odontogenic pattern: determination of tooth type and position. Defects in these pathways could lead to missing teeth (oligodontia: congenital absence of six or more teeth) and misshapen teeth. On the other hand, overactivation leads to extra teeth with aberrant morphology. To date, the earliest mesenchymal markers for tooth formation are the LIM- homeobox (Lhx) domain genes, Lhx-6 and Lhx-7. Both of these genes are expressed in ectomesenchyme as early as day 9 of gestation. Fibroblast growth factor-8 (Fgf-8); this growth factor is expressed at the proper place and time to induce Lhx-6 and Lhx-7 expression. Pax-9 gene is one of the earliest mesenchymal genes that define the localization of tooth germs. Pax-9 gene expression colocalizes with the exact sites where tooth germs appear. Pax-9 is induced by Fgf-8 and is repressed by bone morphogenetic proteins (BMP-2 and BMP-4). Wnt is the inducer of tooth initiation. Cbfa1, expression in dental mesenchyme regulates key epithelial– mesenchymal interactions that control advancing morphogenesis and histodifferentiation  CLINICAL CONSIDERATION  Initiation Lack of initiation results in the absence of Abnormal initiation (hyperactivity of a tooth, a condition called hypodontia. dental lamina) results in hyperdontia This can involve a single tooth or multiple or supernumerary teeth teeth (oligodontia) or the entire dentition (complete anodontia). The teeth commonly absent are the upper lateral incisors, third molars, and lower second premolars.  Hypodontia It is a failure of one or more teeth to develop and is a relatively common anomaly in human populations Oligodontia, more than 6 teeth congenitally missing e.g. all third molars absent. Supernumerary teeth Supernumerary teeth are teeth present in addition to the normal dentition and can occur within either dentition. It is more common in permanent dentition When located in the midline of the anterior maxilla these teeth are known as mesiodens. Supplemental Tuberculate  Abnormalities of tooth form ◦ Microdontia ◦ Macrodontia ◦ Gemination ◦ Fusion Transposition Dental transposition is the complete positional interchange of two adjacent teeth or the development or eruption of a tooth in a position normally occupied by a non-adjacent tooth.