Hierarchical Structure and Function of Teeth

Question 1

tooth structure

Answer 1

crown and root

crown:
top layer = enamel (0.1-2mm thick)
underlying material is dentine
pulp: nerves, blood vessels and odontoblasts

root:
dentine covered w/ cementum
alveolus: located in a deep socket
periodontal ligament: fixes root firmly into alveolar bone

Question 2

tissues in teeth

Answer 2

7

enamel, dentine, pulp, periodontal ligament, alveolar bone, gingiva (gum)

Question 3

enamel

Answer 3

Highly calcified (96% mineral, 1% organic, 3% water, no living cells)
Hexagonal crystals: densely and perpendicular packed = hydroxyapatite crystals 
Packed in rods/prisms (protein), has keyway interlocking structure, surrounds individual crystals
rods: 5μm diameter. runs from EDJ to tooth surface

Properties: 
anisotropic
\+ hardness
\+ abrasion & wear resistance
- brittle

Question 4

Dentine

Answer 4

Calcified tissue
Similar to cortical bone, but more cross linked
70% inorganic (apatite), 20% organic (collagen), 10% water
Porous: made from S shaped dentine tubules
tubules: pulp to enamel, contains odontoblasts

as distance increases from pulp = decrease in number and diameter of dentinal tubules

significant water & collagen content

Question 5

Collagen

Answer 5

25% protein content in mammals
Fibrous , structural protein: triple helix of 3 amino acid sequence or polypeptide chains, combination of amino acids = diff collagen types .
28 types
+ gd tensile strength
main component of cartilage, ligaments, bone and teeth

Question 6

DEJ (dentine enamel junction)

Answer 6

2 dissimilar materials:
enamel (hard, brittle)
dentine (softer, tougher)
scalloped structure

Question 7

stress transfer

Answer 7

tooth entire of enamel: hard, ceramic wear/corrosion resistant coating material –> failure if only made from enamel. = overlaid on softer but tougher substrate of dentine
prismatic structure of enamel: long thin apatite crystals = orientated perpendicular to surface = transfer stresses from enamel to underlying dentine
Stresses follow stiffer component in a structure
apatite crystals fan out = distributing stress onto dentine

Question 8

pulp

Answer 8

highly vascularised connective tissue
nerves and blood vessels
fibroblasts
type 1 & 3 collagen
ground substance (proteoglycans & glycoproteins)

Question 9

Cemetum

Answer 9

covers dentine from below gum line
calcified connective tissue
thickness: 10μm gum line. 150μm tip of tooth

Question 10

Gingiva

Answer 10

joins onto tooth at dentogingival junction
prevents fluid ingress into jaw
endothethial tissue
permeable to molecules

Question 11

Periodontal ligament

Answer 11

connective tissue
attaches teeth to cementum to alveolar bone
tendon like tissue: orientated perpendicular to tooth
0.2mm in width (decreases w/ ages)
Composition: fibroblasts, type 1 & 3 collagen, ground substance (proteoglycans & glycoproteins), highly vascularised
shock absorber: application of large compressive forces to teeth, w/out destruction to bone, simulates bone growth (wolffes law)
method for sensation
orthodontic treatment:
compression = resorption of old bone
tensile loads= deposition of new bone

Question 12

tooth mineral

Answer 12

apatites = group of calcium phosphates, basis of mineral phase of tooth & bone
debate: apatite mineral phase in tooth and bone

Question 13

apatites importance

Answer 13

loss of tooth & bone mineral = 3 major diseases
osteoporosis
tooth decay or carries
periodontal disease

apatisers:
lasers
flurorescent lights
radioactive waste entrapment

Question 14

hydroxyapatie (HA)

Answer 14

Ca10(PO4)6(OH)2
tooth & bone mineral
crystal structure:
central coloumn of OH- ions in c line
equilateral triangle: PO4- ions around oh-
hexagon of CaI ions
hexagonal structures rotated 60degrees

Question 15

biological apaties

Answer 15

non stoichiometric substituted apatite
Sr, Mg2+, Mn2+ substituted for Ca2+
F-, CO3 2- –> oh- = fluroapatite (FA)
CO3 2- –> PO4 3-

fluroine: food, water, toothpaste

Question 16

HA vs FA

Answer 16

partial susbstitution: f- for oh- = hydroxy-fluroapatie Ca10(PO4)6Fx(OH)y
oh- too large to pack into ideal hexagonal apatie lattice= displaced off c axis
crystal structure of HA: distorted hexagonal or monoclinic structure
f- is smaller = fits into site = f- readily exchanged for hydrolysis, hexagonal crystal structure, FA chemically & thermodynamically stable than HA, more resistant to dissolution in acidic solution

Question 17

apatite

Answer 17

5Ca2+ + 3PO43- + OH- Ca5(PO4)3OH. f- –> co3 2-