TOOTH GERM - PHYSIOLOGICAL STAGES IN THE DEVELOPMENT OF TEETH.
Teeth have ectodermal and mesodermal origin
- Mesoderm is the 4th embryonic leaf: ectomesenchyme is also involved
- Ectomesenchyme epithelium is a combination of neural crest cells and mesenchyme
In tooth development, interaction of oral ectoderm and ectomesenchyme initiate the process
Cellular interaction leads to formation of dentin, enamel, cementum and the crown
Two Stages of Development
Morphological Stages:
- Dental lamina
- Bud Stage
- Cap Stage
- Early Bell Stage
- Advanced Bell Stage
- Formation of Enamel and Dentin Matrix
Physiological Stages:
- Initiation
- Proliferation
- Histodifferentiation
- Morphodifferentiation
- Apposition
- Maturation
- Eruption
Initiation
- Newly formed stomodeum is lined by a primitive 2 or 3-cell thick layered epithelium covering an embryonic tissue that is now called Ectomesenchyme (neural crest cells+ mesenchyme)
- Ectomesenchyme consists of a few spindle shaped cells separated by a gelatinous ground substance
- Formation of primary epithelial thickening dental lamina, tooth bud and cap, bell stage cannot take place without dentally active ectomesenchyme which becomes concentrated in regions of presumptive tooth development
- Inner epithelium of enamel organ induces ectomesenchyme of dental papilla to become orientated towards the intervening basal lamina and differentiate into odontoblasts
Stages of Initiation:
- Primary Epithelial Band
- Continuous band of thickened epithelium forms around the mouth in presumptive upper and lower jaws ↳ change in orientation of mitotic spindle & cleavage plane of dividing cells
- Bands are roughly horseshoe shaped and correspond to position of future dental arches of jaw
- Each band of epithelium gives rise to Vestibular Lamina and Dental lamina
- Vestibular lamina (lip furrow band)
- Vestibule forms as a result of proliferation of vestibular lamina into ectomesenchyme
- Cells rapidly enlarge and then degenerate to form a cleft that becomes the vestibule between the cheek and tooth bearing area
- Dental lamina
- Located orally to vestibular lamina
- Within dental lamina, continued and localized proliferative activity leads to formation of a series of epithelial outgrowth into ectomesenchyme at sites corresponding to positions of future primary teeth