Development of teeth and its clinical significance
- 2. INTRODUCTION: • Tooth development (ODONTOGENESIS) is the complex process by which teeth form from the embryonic cells, grow, and erupt into the oral cavity. • For human teeth to have healthy oral environment, enamel, dentin, cementum & the periodontium all must develop during appropriate stages of fetal development.
- 3. • Entire primary dentition is initiated between 6th and 7th weeks of embryonic development. • Successional permanent teeth initiated between 20th week in utero and 10th month after birth. • Permanent molars between 20th week in utero (first molar) and 5th year of life (third molar)
- 4. INITIATION OF TOOTH DEVELOPMENT The primitive oral cavity is called stomodeum – lined by stratified squamous epithelium - oral ectoderm. The oral ectoderm contact the endoderm of the foregut to form the buccopharyngeal membrane. At about 27th day of gestation buccopharyngeal membrane ruptures and the primitive oral cavity establishes a connection with the foregut.
- 5. Most of connective tissue cells underlying the oral ectoderm are of neural crest. These cells induce the overlying ectoderm to start tooth development. Which begins in anterior portion of what will be the future maxilla and mandible and proceed posteriorly
- 6. • Connective tissue cells underlying the oral ectoderm induce overlying ectoderm to start tooth development. • Ectomesenchyme proliferation form primary epithelial band in the 6th week of intrauterine life which corresponds in position to future dental arches. • In the 7th week it divides into : • A lingual process called dental lamina • A buccal process called vestibular lamina
- 7. DENTAL LAMINA: • Total activity of dental lamina extends over a period of minimum of 5 years. • As dentine and enamel start to develop dental lamina begins to degenerate separating into clumps but whose thickness of lamina is not perforated. • Breaking upon of dental lamina determines crown pattern. • Degeneration of dental lamina separates developing tooth from oral epithelium as a result of degeneration tooth continues its development within tissues of jaw. • Penetration of lingual epithelium by tooth is unique example of natural break in the epithelium of the body.
- 8. VESTIBULAR LAMINA • Also called as furrow band or vestibular band. • It is horse shoe shaped in growth of epithelium, which develops buccal to dental lamina. • Vestibular band grows deeply into mesenchyme of premature jaws separating lips and cheeks from tooth forming region. • It subsequently thickens and clears at vestibular growth from oral vestibular lamina.
- 13. BUD STAGE • Differentiation of dental lamina leads to formation of round, ovoid swelling at 10 different points corresponding to future position of deciduous teeth. • These are the primordial of enamel organ. • Enamel organ consists of peripherally location low columnar cells and centrally located polygonal cells.
- 14. • Dental papilla is the area of ectomesenchyme condensation subjacent to enamel organ. • Dental sac is the area of ectomesenchyme condensation surrounding the tooth bud and dental papilla. • Cells of dental sac will form cementum and periodontal ligament.
- 16. CAP STAGE: • Characterized by a shallow invagination of deep surface of a bud. • Outer and inner enamel epithelium. • Stellate reticulum: polygonal cells begin to separate as more intercellular fluid is produced and forms cellular network called stellate reticulum. • Enamel knot: cells in center of the enamel organ are densely packed. The knot projects towards the underlying dental papilla. Vertical extension of enamel knot forms enamel cord.
- 17. • Both the structures disappear before enamel formation begins • DENTAL PAPILLA AND DENTAL SAC: dental papilla is for mature organ of dentine and shows active budding of capillaries and mitotic figures. • Dental sac are important for the formation of cementum and periodontal ligaments.
- 19. BELL STAGE: • Stage of Histodifferentiation and Morpho differentiation. • During histodifferentiation some cells of dental organ differentiates into specific form and shape. This is seen in early bell stage. • During morpho differentiation dental organ assumes characteristic shape of tooth. This is seen in late bell stage. • The invagination of epithelium deepens and its margins continue to grow and enamel organ assumes a bell shape.
- 21. • This point is where the cells continue to divide until the tooth crown attains its full size. • The inner epithelium begins at the point where the outer epithelium bends to form the concavity into which the cells of the dental papilla accumulate. • The region where the internal and external dental epithelia meet at the rim of the enamel organ is known as the zone of reflexion or cervical loop. CERVICAL LOOP:
- 22. • Commencement of mineralization & root formation. • Boundary between inner enamel epithelium & odontoblasts–- outlines future DEJ. • 1st formation of dentin. • Proceeds pulpally & apically. • After first layer of dentin is formed, ameloblast which has already differentiated from IEE cells lay down enamel over dentin in future incisal & cuspal areas. • Proceeds coronally & cervically. • Cervical portion of the enamel organ gives rise to Hertwig’s epithelial root sheath. • Outlines the future root. • Responsible for the shape, length, size & number of roots. ADVANCED BELL STAGE:
- 23. APPOSITION: • The tooth germ forms calcified tissues of the tooth. • There is a layer like deposition of an extracellular matrix resulting in additive growth. • There is regular and rhythmic deposition, which is capable of further growth.
- 26. WHAT CAN GO WRONG? • Ectodermal dysplasia: Tooth bud may be absent. • Anodontia: Complete absence of teeth. • Accessory teeth: There may be extra or supernumerary teeth buds. • Neonatal teeth: Teeth are seen to erupt immediately after birth. • Gemination: Two teeth may be fused to each other.
- 27. • Malocclusion: the alignment of upper and lower teeth maybe incorrect. • Hypocalcified/Hypomineralized dentin: if organic matrix is normal but its mineralization is defective. • Enamel hypoplasia: disturbance in the synthesis and secretion of the organic matrix of enamel. • Hutchinson’s incisor: The maxillary central incisors may become notched at the edges in the individuals born with congenital syphilis.
- 28. TIME SCALE OF HUMAN TOOTH DEVELOPMENT: AGE DEVELOPMENT CHARACTERSTICS 42-48 days Dental lamina formation. 55-56 days Bud stage, deciduous incisor canine and molar. 14 weeks Bell stage for deciduous teeth, bud stage for permanent teeth. 18 weeks Dentine and functional ameloblasts in deciduous teeth. 32 weeks Dentine and functional ameloblasts in permanent teeth.
- 29. REFRENCES • Ten Cate’s Oral Histology Development, Structure, and Function Antonio Nanci : 7th edition. • Orban’s Oral Histology and Embryology : 12th edition.
- 30. THANK YOU