Oral Histology - Development of Teeth (Odontogenesis) Lecture Notes PDF

Oral histology Development of teeth (odontogenesis) Lec. 1 by dr. shadan muhamad  Background : The development of the tooth involves many complex biological processes, including epithelial mesenchymal interactions, morphogenesis and mineralization. In h...

Oral histology Development of teeth (odontogenesis) Lec. 1 by dr. shadan muhamad  Background : The development of the tooth involves many complex biological processes, including epithelial mesenchymal interactions, morphogenesis and mineralization. In human beings, 20 deciduous and 32 permanent teeth develop from the interaction between the oral epithelium cells and the underlying mesenchymal cells. The basic developmental process is similar for all teeth but each developing tooth develops as an anatomically distinct unit.  Cont. Mammalian teeth develop from oral epithelium (ectoderm) and neural crest cells derived mesenchyme (mesoderm). Neural crest cells are migrate (at 3rd weeks of the embryo) from lateral parts of neural tube and enter in the underlying mesenchyme ,now it’s termed as ectomesenchyme. Vitamins, minerals and hormones affect tooth  Cont. Vitamin A is important for epithelial growth, Vitamin C = = for connective tissue development , Vitamin D is essential for calcification  Developmental phases of tooth : Tooth development is divided into three overlapping developmental phases ,these are: 1- Initiation : In this phase, the sites of future teeth are established with the appearance of tooth germs along an invagination of oral epithelium called dental lamina.  2- morphogenesis : In this phase, the shape of the teeth are determined by a combination of cell proliferation and cell movement. 3- Histogenesis : Differentiation of cell begun during (morphogenesis) proceed to give rise to the fully formed dental tissues,both mineralized (as enamel ,dentin and cementum) and unminaralized (as pulp and periodental ligament ). Development of tooth germ Primary epithelial band : After 37 days of development, a continuous band of thickened epithelium forms around the mouth in the presumptive upper and lower jaws. These bands are horse shoe-shaped and correspond in position to the future dental arches of the upper and lower jaws. Each band of epithelium, called the primary epithelial band, quickly gives rise to two subdivisions.  Cont. These are: 1- The dental lamina, which forms first, 2- The vestibular lamina, which forms shortly afterward and is positioned just in front of the dental lamina. Dental lamina  Dental Lamina : The dental lamina is a band of epithelium that has invaded the underlying ectomesenchyme along both the horse shoe-shaped future dental arches. Deciduous dentition develops directly from the dental lamina at the eighth week of fetal life, while the permanent molars develop from a distal extension of the dental lamina.  Cont. Along the lamina 20 areas of enlargement next appear,which are the forming buds of 20 primary teeth ,and the lamina continues to develop the 32 permenant tooth buds. The lingual extension of dental lamina is called successional lamina ,it is responsible for the development of permanent incisors, canine and premolars.  Cont. The successional lamina is active from the fifth month in utero (for the permanent central incisor) to ten months of age (second premolar).  Bud stage. (1) enamel organ (2) the dental lamina, (3) Successional dental lamina, (4) Primary epithelial Band,  Vestibular Lamina : The vestibule forms as a result of the proliferation of the vestibular lamina into the ectomesenchyme soon after formation of the dental lamina. The cells of the vestibular lamina rapidly enlarge and then degenerate to form a cleft that becomes the vestibule between the cheek and the tooth- bearing area.  DEVELOPMENTAL STAGES OF TOOTH Tooth formation is a continuous process. It is characterized by a series of stages. Each tooth develops through successive bud, cap and bell stages, continues to change. During these the dental lamina breaks up and the tooth bud loses its connection with the epithelium of the primitive oral cavity. Interaction of the first arch epithelium and neural crest cell results in the development of tooth.  CONT. All teeth pass through similar stages of tooth development. These stages: A. Bud stage - Initiation B. Cap stage - Proliferation C. Bell stage – a. Early - Histodifferentiation b. Advanced – Morphodifferentiation The name of the stages is based on the shape of the epithelial part of the tooth germ that is epithelial enamel organ. 1- Bud Stage (Initiation) : Bud stage is the initial stage of tooth development. The basement membrane separates the epithelium of dental lamina from the ectomesenchyme. Ten small, round or ovoid swellings develop superficial to the basement membrane called as tooth buds. Tooth buds are the precursors of enamel organs. The epithelium of the tooth bud forms the enamel. Tooth development – bud stage  Cont. The supporting ectomesenchymal cells are densely packed under the lining epithelium and around the epithelial bud. The enamel organ of bud stage contains two types of cells : 1. Polygonal cells, which are centrally situated. 2. Low columnar cells, which are peripherally situated.  Cont. The centrally situated cells rapidly divide and grow and condensed and formed the dental papilla. Tooth pulp and dentin are formed from dental papilla. The ectomesenchyme that surrounds the tooth bud and dental papilla forms the dental sac. Cementum and periodontal ligament are formed from the dental sac. Thank you