Tooth Development

Question 1

How many teeth in each quadrant in primary dentition

Answer 1

5 teeth in each quadrant: 2 incisors (A, B), 1 canine (C) and 2 molars (D, E)

Question 2

Describe primary dentition

Answer 2

Tooth types and shapes (morphology) symmetrical across the midline (i.e. within a jaw) but not between jaws e.g. upper A not a mirror-image of lower A, but slightly different in shape

Same tooth types (i.e. A-E) in lower arch (mandible) but tooth shape not exactly the same as upper jaw (maxilla), although again symmetrical within a jaw

Question 3

How many teeth in each quadrant in permanent dentition

Answer 3

8 teeth in each quadrant:
2 incisors (1, 2), 1 canine (3), 2 premolars (4, 5), 3 molars (6, 7, 8)

Question 4

Describe the stages of tooth development

Answer 4

• Initiation – starts tooth formation and ensures the right number of teeth in the correct location in the jaws
• Morphodifferentiation - formation of teeth of the correct shape
• Cytodifferentiation – differentiation of cells to produce specific dental tissues

Question 5

What are the 2 phases of tooth formation

Answer 5

crown formed first then root formation

Question 6

Tooth structure

Answer 6

Question 7

Describe Stage 1:
Initiation of Tooth Development

Answer 7

The first overt sign of tooth development is appearance of a thickened band of ectoderm along each dental arch – the primary epithelial band

The primary epithelial bands appear about 7 weeks post-fertilisation (in utero, after maxillary arch has developed) = end of the embryonic period

Question 8

What is the role of the primary epithelial band in initiation of tooth development

Answer 8

The primary epithelial band induces condensation of ectomesenchymal cells beneath the band
i.e. cells gathering around, due to signals from ectoderm

(Ectomesenchyme = fibroblasts)

Question 9

When is oral ectoderm dominant

Answer 9

Oral ectoderm is dominant during initiation:
only oral ectoderm will form teeth in combination with first arch ectomesenchyme (but experimentally the ectomesenchyme can come from any region of the head)

Question 10

is subsequent development after oral ectoderm has formed teeth ectomesenchyme site specific

Answer 10

Subsequent development is not site specific:
tooth development will continue if oral ectoderm and head ectomesenchyme transplanted elsewhere

Question 11

Describe growth factor and genetic involvement with initiation of tooth development

Answer 11

BMPs and FGFs (signalling molecules) expressed by ectoderm interact with underlying first arch ectomesenchyme to form correct NUMBER of tooth buds in each quadrant

DLX gene coding also involved in antero-posterior positioning and differentiation of tissues along maxillary and mandibular arches; gradient

Expression of homeobox genes at specific parts of each arch determine TYPE OF TOOTH

Question 12

Describe genetic involvement in initiation of tooth development

Answer 12

• Genes grt proteins that can be gene-regulating
• effect on DNA
• grt further gene and further protein expression
• Certain genes at specific times in certain places determines tooth type that results
• ↑ factors as years↑

Question 13

What happens if initiation stage is disrupted

Answer 13

If initiation stage disrupted
Anodontia (no teeth) – very rare
Hypodontia (a few teeth don`t develop) – relatively common and occurs at end of expression domain so most commonly affects second incisors, second premolars and third molars (wisdom teeth)

-Hyperdontia (extra teeth: supernumerary)
extra atypically shaped teeth (accessory) or extra “normal” teeth (supplemental teeth)