Development of teeth- Odontogenesis Dr Jamal N. Naim PhD in Orthodontics

Objectives To provide a detailed description of tooth formation and development. To explain different hypothesis about tooth initiation and type determination. To understand the histological aspect of different stages of tooth development. To discuss the formation and development of dental root and supporting tissues. To give a brief comments on related clinical aspects.

Stages of tooth development formation of primary epithelial band down growth of dental lamina development, differentiation & morphogenesis of tooth bud Bud stage Cap stage Bell stage Crown stage dentinogenesis amelogenesis root formation tooth eruption

... ... ... Three processes overlap the development stages Histogenesis differentiation of cells Initiation site of future teeth established Morphogenesis shape of the tooth determined

Stages of tooth development initiation stage – 6th to 7th week bud stage – 8th week cap stage – 9th to 10th weeks bell stage – 11th to 12th weeks Apposition stage – varies per tooth Maturation stage – varies per tooth

... ... ... tooth development occurs in the primitive oral cavity – stomatodeum First signs of formation – day 11 stomatodeum lined by thin epithelium derived from ectoderm embryonic connective tissue – ectomesenchyme development of teeth involves interactions between ectoderm and ecto-mesoderm. mechanisms remain unknown

Primary epithelial Band

Initiation of tooth development Involves epithelial-ectomesenchymal interactions Thickening of the epithelium where tooth formation will occur on the 1st branchial arch

Primary epithelial band appears at ~ 5-6 weeks of development in future maxilla & mandible horseshoe shaped band of thickened epithelium in the position of future dental arches superficial epithelial thickening From Nanci (2003) Ten cate oral histology showing the location of the primary epithelial bands

Dental lamina derived from the primary epithelial band epithelial band divides into two at 7 weeks and grows away from the epithelial surface vestibular lamina (buccally  vestibule) dental lamina (lingually  teeth)

Dental lamina

Tooth formation -initial stage- The dental lamina develops a series of epithelial outgrowths - grow deep into the mesenchyme develops in the future spot for the dental arches will form the midline for these arches arches then form posteriorly from this point the ingrowths represent the future sites for each deciduous tooth

Tooth formation -initial stage- the vestibular lamina cells rapidly enlarge and then degenerate – forms a cleft that becomes the vestibule of the oral cavity The initiation of tooth formation starts around the 37th day of gestation.

Early Dental Lamina Tongue Dental lamina Vestibular lamina ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Late Dental Lamina

Late Dental lamina from: Ten Cate: Oral Histology - Development, Structure and Function

Both deciduous & permanent dentitions arise from dental lamina deciduous teeth arise from the initial development of the dental laminae ~ 13 weeks in utero epithelium proliferates at 10 sites in each dental lamina to form the early tooth germs (from: Berkovitz. Oral Anatomy, Histology and Embryology, Mosby- Wolfe, Inc.)

... ... ... Permanent incisors, canines & premolars form as a result of further proliferation of the dental laminae on the lingual aspect of the deciduous tooth germ. The permanent tooth germ remains dormant for sometimes (from: Berkovitz. Oral Anatomy, Histology and Embryology, Mosby- Wolfe, Inc.)

... ... ... Permanent molar teeth have no deciduous predecessor Permanent molars develop from growth of the dental lamina below the epithelium of the oral cavity posteriorly. from: Ten Cate: Oral Histology - Development, Structure and Function

Tooth type determination Patterning means the determination of specific tooth type at the correct position. Homodont are animals with same shaped teeth Heterodont are the most mammals with different tooth types Two theories for the determination of tooth type

Tooth type determination The field model theory proposes that factors responsible for the determination reside within the ectomesenchyme, but graded fields for each tooth The clone model theory proposes that each tooth is derived from a clone of ectomesenchymal cells programmed by the epithelium to produce a given pattern.

Tooth germ formation bud stage cap stage early bell stage late bell stage rapid change in size & shape crown stage enamel formation root formation cementum formation dentine formation

Bud stage ~8 weeks in utero individual epithelial bud (swellings) on the deep surface of the dental lamina are recognisable little changes in shape or function of epithelial cells ectomesenchyme cells are closely packed around epithelial bud

Bud stage A B (A) Epithelial bud. (B) Ecto- Mesenchymal Cells.

Tongue Bud stage Future dental papilla

Cap stage 11 weeks in utero Proliferation of epithelial bud & invagination of the deeper surface of the epithelial bud forms the cap shape More condensation of ectomesenchyme Increase in morphogenesis central cells of enamel organ spherical while peripheral cells become cuboidal

Cap stage 11 weeks in utero More condensation of ectomesenchyme characterized by continuation of the ingrowth of the oral epithelium into the mesenchyme. tooth bud of the dental lamina proliferates unequally in different parts of the bud forms a cap shaped tissue attached to the remaining dental lamina looks like a cap sitting on a ball of condensing mesenchyme

Cap stage occurs for the primary dentition during the fetal period this stage marks the beginning of histodifferentiation; (differentiation of similar epithelial cells into functionally and morphogically distinct components) the tooth germ also begins to take on form – start of morphodifferentiation

Cap stage a depression forms in the deepest part of each tooth bud and forms the cap or enamel organ (or dental organ) – produces the future enamel (ectodermal origin)

Cap stage below this cap is a condensing mass of mesenchyme – dental papilla – produces the future dentin and pulp tissue (mesenchymal origin)

Cap stage the basement membrane separating the dental organ and the dental papilla becomes the future site for the dentinoenamel junction (DEJ)

Cap stage remaining mesenchyme surrounds the dental/enamel organ and condenses to form the dental sac or the dental follicle

Cap Stage of Tooth Development Dental (enamel) organ Dental papilla dental follicle Tooth germ ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl Oral Histology, 5th edition, A R Ten Cate

Cap Stage ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Cap stage together the enamel organ + dental papilla + dental follicle is considered the developing tooth germ or tooth primordium these primordium will be housed in the developing dental arches and will develop into the primary dentition

Cap stage Enamel knots are clusters of nondividing epithelial cells visible in sections of molar cap stage tooth germs. They play an important role by the cuspal morphogenesis.