L5: Teeth

Question 1

Name the hard components of teeth

Answer 1

dentin

enamel

cementum

Question 2

What is dentin

Answer 2

matrix mainly of collagen fibers and GAGs (20% of
dentin), becomes impregnated with hydroxyapatite crystals (80% of dentin) so similar to bone but harder (bone consists of 65% hydroxyapatite, 35% organic matrix)

• Forms the bulk of the tooth volume

Question 3

What is enamel?

Answer 3

matrix composed of protein (enamelin) but calcium
phosphate crystals make up ~98-99% of enamel substance, so enamel is the hardest substance within the body

• Forms the crown of the tooth
• Composed of units called enamel prisms (or rods) that lay perpendicular to the surface of the dentin; between rods is interprismatic substance; both are formed from apatite crystals

Question 4

What is cementum

Answer 4

histologically similar to bone

upper 1/3 is acellular

lower 2/3 is cellular

(cells-cementocytes)

• Covers outside of root
• cementum is a labile tissue, susceptible to resorption or hyperplasia under certain conditions, but only in lower cellular portion.

Question 5

Dental pulp

Answer 5

fills pulp cavity and root canals

– Consists of CT similar to mesenchymal CT with fine
collagen fibrils

– Also contains many blood vessels and nerves

Question 6

Periodontal membrane

Answer 6

dense regular CT attaches tooth in socket of underlying alveolar bone

Sharpey’s fibers extend into both bone and cementum to anchor tooth to bone

Question 7

Why is there no capacity for remodeling in teeth?

Answer 7

Since hard components of the tooth are acellular
(except for the lower portion of cementum) and
cells are responsible for remodeling in bone and
cementum, there is no capacity for remodeling in
teeth. Consequently, there is no capacity for repair
if damaged (except, of course, for the dentist!).

Question 8

Describe the development of teeth

Answer 8

Begins as epidermal invagination into dermis (as in all other skin derivatives)

• Develop tooth bud - 5 in each half jaw in humans
(“milk teeth”)

• Secondary tooth buds develop ventrolaterally (labial
side) - 8 in each half jaw in humans (permanent teeth)

• Formation of enamel organ with outer and inner
enamel epithelia investing enamel pulp

• Inner enamel epithelium → Ameloblasts (ectodermal origin) Adjacent mesenchyme cells (from neura crest) → Odontoblasts

• Ameloblasts secrete enamel; Odontoblasts secrete
dentin

Question 9

Ameloblasts

Answer 9

ectodermal origin

secrete enamel

Question 10

odontoblasts

Answer 10

from mesenchyme cells

from neural crest

secrete dentin

Question 11

How is the organic matrix of teeth secreted during development?

Answer 11

Ameloblasts and Odontoblasts secrete organic matrix between each other, which subsequently becomes calcified as enamel and dentin. Cells move apart from each other as enamel and dentin are produced.