Tooth Biology

Question 2

Enamel:

organic/inorganic/water components and their %

Answer 2

Enamel

• very organized
• predictable bonding

inorganic: 90s% (96%) Ca-hydroxyapatite

organic: 1-2% glycoproteins, enamelins and tuftleins

water: 4-12% (4% water+organic)

Question 3

1. Cells that produce enamel?
2. Basic development of enamel?
3. Tree-like rings are called?

Answer 3

1. ameloblasts
2. develops from enamel matrix protein amelogenin;

amelogenin is degraded and removed by proteinases to form mineral-enriched tooth enamel;

successive rod segments of hypocalcification and normally calcified enamel (reflect metabolism during formation)

3. tree-like rings: Striae of Retzius -ameloblasts die before tooth erupts- enamel cannot be repaired

Question 4

Dentin:

organic/inorganic/water component and %

Answer 4

• Dentin-
  inorganic: 50-75% Ca hydroxyapatite (depends on depth/proximity to pulp)
  organic: 20-30% Type I collagen fibrils, ground substance
• noncollagenous matrix proteins pack space between collagen fibrils and between tubules (mixed in with HA crystals)
  water: 10%-25%

Question 5

1. Cells that produce dentin?
   - where are they located?
2. Tree-like rings are called?

Answer 5

1. Odontoblasts -maintain their association with dentin for life

• dentin can self-repair
• cell bodies aligned along the inner aspect of the dentin, against a layer of predentin, forming the peripheral boundary of the pulp
• Cytoplasmic extensions (odontoblastic processes) into dentin tubules

2. Contour Lines of Owen: Along length of tubules, odontoblasts lay down alternating regions of normal calcification and hypocalcification (reflective of mother/child metabolism)

Question 6

Types of dentin

Answer 6

1. Mantle dentin: outermost layer near enamel or cementum

2. Primary dentin (circumpulpal dentin)- most of tooth

3. Secondary dentin: along entire pulp-dentin border, develops after root formation is complete- continuing, slow deposition of dentin; less regular tubular structure- asymmetric deposition; recession in size and shape of pulp; readily becomes sclerotic dentin

4. Predentin: unmineralized matrix; lines innermost (pulpal) portion- principally collagen Type I; layer directly adjacent to odontoblasts

5. Tertiary dentin (reactive/reparative): produced in reaction to stimuli (attrition, caries, restoration)

• produced only by cells directly affected by the stimulus
• regular/irregular architecture dependent of intensity and duration of stimulus

Question 7

Three zones + core of the pulp

Answer 7

1. Odontoblastic zone: single layer of odontoblasts- processes extend into dentin tubules
2. Cell-free zone: deep to odontoblastic zone- devoid of cells
3. Cell-rich zone: fibroblasts, mesenchymal cells; immediately surrounds pulp core
4. Pulp core: loose CT (but lacks adipose cells) and nerve tissue; highly vascularized; sometimes pulp stones (calcified denticles)

Question 8

1. &2. 2 types of nerve fibers in pulp core
2. Pain fibers- type? called? Distribution?

Answer 8

1. Sympathetic (vasomotor) fibers- control luminal diameters of blood vessels
2. Sensory fibers: transmission of pain sensation
3. Thin myelinated fibers form Raschkow plexus- just deep to cell rich zone; fibers extend through cell-free zone, lose their myelinated and penetrate space bw odontoblasts and enter tubules or synapse on the odontoblasts or their processes instead of directly entering the tubule

Question 9

4 Functions of the pulp

Answer 9

1. Formative: produces the dentin that surrounds it
2. Nutritive: nourishes avascular dentin
3. Protective: carries nerves that give dentin sensitivity
4. Reparative: produces new dentin PRN

Question 10

Function of dentin NOT COMPLETE

Answer 10

1. Elasticity provides flexibility and prevents fx of overlying brittle enamel

Question 11

Histology of dentin

Define:

Dentin Tubules (general)

Peritubular dentin

Intertubular dentin

Interglobular dentin

Sclerotic Dentin

Dead Tracks

Incremental Growth lines and Contour Lines of Owen

Granular layer of Tomes

Answer 11

1. Dentinal tubules: contain odontoblastic processes, peritubular dentin, extracellular fluid (+water), very little collagen

• The closer to the pulp
• the dentin tubules become wider
• more numerous - 59K-79 K per square mm at pulpal surface
• Intertubular dentin is less organized

2. Peritubular dentin- hypermineralized dentin that lines inner dentin tubules

3. Intertubular dentin- random, tightly interwoven network of Type I collagen fibrils, ground substance and apatite crystals

-noncollagenous matrix proteins pack space between collagen fibrils and between tubules

4. Interglobular dentin- areas of deficient calcification- hypomineralized (i.e. from exposure to High F or vit D deficiency)

5. Sclerotic dentin- tubules filled with calcified material

• Dentin becomes translucent
• reduce overall permeability of the dentin to protect pulp
• thought to be a physiologic response and that occlusion is achieved by continued deposition of peritubular dentin

6. Dead Tracks-empty tubules that are sealed off by reparative dentin: from infection/bacteria or as a normal physiological process when odontoblasts die

7. Incremental growth lines (daily deposition increments) and Contour Lines of Owen (lines of deficiencies of mineralization during tooth formation)

8. Granular layer of Tomes: only on root portion near CDJ