Lesson 8 - Part 1

Question 1

Describe the physical properties of enamel

Answer 1

1. 96% Inorganic mineral - 4% water and organic matter
2. Crystalline formation - Calcium hydroxyapatite (crystalline calcium phosphate)
3. trace: magnesium, potassium, sodium and fluoride
4. Organic matter: ENAMELIN - protein (similar to keratin in skin)
5. Enamelin between and on crystals makes enamel permeable

Question 2

Describe the natural colour of enamel

Answer 2

1. Grayish white to Slightly yellow
2. Due to translucency and underlying yellow dentin

Question 3

Describe enamel rod structure

Answer 3

1. Enamel rods extend from the DEJ to the outer surface
2. Enamel rods nearly perpendicular to the DEJ
3. Enamel rods nearly perpendicular to the surface
4. Enamel rods curve slightly toward the surface
5. Rod groups intertwine preventing separation
6. Cross-section of rod is keyhole shape divided into head and tail portions

Question 4

What is Gnarled Enamel?

Answer 4

In the cusp tips, enamel rods are twisted

Question 5

Describe the Interlocking of enamel rods

Answer 5

1. Enamel rods interlocked with adjacent rods
2. Prevents fracture, splitting and separation of enamel

Question 6

Describe Enamel rod crystals

Answer 6

1. Each rod is filled with crystals (minerals)
2. Maturation stage of enamel formation causes crystal growth and increased density (each crystal 30X larger than crystals in dentin)
3. Crystalline orientation varies in the head/tail of the rod

Question 7

Describe acid etch of enamel

Answer 7

1. Rod core rich in coronated apatite & more susceptible to demineralization
2. Rod sheath is rich in hydroxyapatite and more resistant to demineralization
3. Acid etching technique based on variables of the rod sheath and core
4. Rod core crystals demineralize at faster rate than rod sheath
5. Allows for attachment of sealant

Question 8

Describe the Line of Retzius (growth lines)

Answer 8

1. Hesitation in deposition of enamel creates lines marking the path of the ameloblasts
2. Spaces between the crystals entrap air molecules, accentuating these lines
3. Line of Retzius: growth lines , hesitation lines of ameloblasts

Question 9

Describe Incremental growth lines

Answer 9

1. Apposition of enamel creates incremental growth lines
2. Maturation of enamel follows the pattern of matrix deposition (apposition)
3. Incremental growth lines can be accentuated by variations in mineral deposited

Question 10

Describe the Neonatal Line

Answer 10

1. Most primary teeth
2. Accentuated line of Retzius
3. Environmental and nutritional changes at birth creating accentuated incremental line
4. Neonatal enamel has fewer defects than postnatal enamel
5. Postnatal enamel has more spaces between rods resulting in increase staining with pigment

Question 11

Describe imbrication lines

Answer 11

1. Hesitation lines on the surface of the enamel created by variable activity of ameloblasts
2. Creating ridges on the surface enamel: termination of line of retzius on the surface
3. Clinically: Grooves and ridges on the surfaces of enamel
4. Most prominent on facial near cervical region

Question 12

Describe Enamel Spindles

Answer 12

1. Extensions of the odontoblastic process that pass through the DEJ into the enamel
2. Enamel forms around the odontoblastic process

Question 13

Describe the structure of the Dentinoenamel junction

Answer 13

1. Enamel spindles Extensions of the odontoblast/dentinal tubule that pass through the DEJ
2. Extensions become embedded in forming enamel
3. Scalloped DEJ: allowing increased adherence

Question 14

Enamel caries follow the __________

Answer 14

enamel rod structure

Question 15

How can the dentist determine the clinical treatment of enamel?

Answer 15

1. Microscopic features must be taken into consideration during clinical treatment of enamel
2. Direction of enamel rod must be considered
3. Decay and adjacent preparations removed so all enamel rods remain supported by other rods