Tooth development Flashcards
When do deciduous teeth start to develop?
Between 6-8 weeks in utero
When do successional teeth begin to develop?
20 weeks in utero to 10 months after birth
Which teeth are not successional?
Permanent molars
When does the 1st molar begin to develop?
20 weeks in utero
When does the 2nd molar begin to develop?
After birth
When does the 3rd molar begin to develop?
4-5 y/o
What are the 3 phases of tooth development?
- initiation
- morphogenesis
- histogenesis
What is initiation?
The first initial events of tooth development
What is morphogenesis?
The change in shape of the tooth as the tooth develops (how become an incisor or molar etc.)
What is histogenesis?
Differentiation of the cells responsible for making the tissue of the tooth e.g. into ameloblasts
Interactions between which two types of cells does tooth development heavily rely upon?
Epithelial cells and ectomesenchymal (derived from neural crest) cells
What type of cells are neural crest cells?
Pluripotent
Where are ameloblasts derived from?
Epithelial derived
What is the fate of an individual cells determined by?
The environment into which it migrates and a combination of homeobox gene expression
What is the role of epithelium and mesenchyme in tooth development?
Epithelium is instructive in very early events (type of tissue), then mesenchyme takes over (tooth specificity)
Skin mesenchyme + dental epithelium forms:
skin
Dental mesenchyme + skin epithelium forms:
tooth
Incisor germ mesenchyme + molar epithelium forms:
incisor
Molar germ mesenchyme + incisors epithelium forms:
molar
What does the dental follicle become in a fully developed tooth?
The periodontal ligament
What does the dental papilla become in a fully developed tooth?
The dental pulp
Which transcription factors/ signalling molecules are involved in tooth development?
Pitx-2 = initiates tooth development, Sonic hedgehog (Wnt) = increases cell proliferation, Pax9 & Msx1 = needed for the early tooth genre ti progress from the bud stage
What are the homeobox genes?
The different gene expressions needed to form different types of teeth
What are the homeobox genes for incisors?
Msx1, Msx2 & Alx3
What are the homeobox genes for molars?
Dlx1, Dlx2 & Barx 1
What was shown by experiments removing 1 or other of the genes Dlx1 or Dlx2?
Absence of maxillary molars
What happens by the 6-7th week of development?
A thickening of the oral epithelium occurs = invaginate into mesenchyme and divides into the buccal vestibular lamina (hollows out to form buccal vestibule) and the lingual dental lamina (tooth)
What is a placode?
A swelling within which teeth develop
Where are successional placodes placed?
Lingual to developing tooth buds (except tooth that dont have predecessors = molars)
What are the 3 tooth germ stages of development?
Bud, Cap and Bell (early and late)
n.b. = a continuum
At what time is the tooth in cap stage?
By 11th-12th week
By what time is the tooth in early bell stage?
By the 14th week
What does the inner epithelial layer do in the early bell stage?
Maps out the occlusal pattern of the tooth crown
How do we protect the tooth germ?
The stellate reticulum produces glycosaminoglycans = jelly like ECM in the cap stage = protects against pressure which would change the shape of the tooth
What are remnants of the dental lamina in the early bell stage called and what can they cause?
Epithelial pearls of serres -> may be involved in aetiology of cysts and tumours
Which occurs first, dentine or enamel formation?
Dentine formation always just precedes enamel formation
Where does dentine and enamel formation start?
Future cusp tip or incisal edge (proceeds apically)
What is an enamel knot?
A little accumulation of cells usually in the centre of where an incisal tip or cusp is developing (may have >1 in a tooth germ) = thought to be a centre for production of signalling molecules (disappears in early bell stage)