Exam 3 - Enamel Davenport

Question 1

Hardest substance in the human body

Answer 1

Enamel

Hard as mild steel

Question 2

Physical characteristics of enamel

Answer 2

• elicit sparks when struck with flint
• withstands tremendous mechanical forces
• brittle
• translucent (light yellow to grayish white)
• variable thickness (max 2.5mm)
• acellular/avascular
• no collagen

Question 3

True or false: enamel is considered an active chemical system

Answer 3

True - participates in a variety of chemical reactions

Question 4

Most highly mineralized tissue

Answer 4

Enamel (96% inorganic material)

Question 5

Enamel - inorganic material

Answer 5

Hydroxyapatite (crystalline calcium phosphate)

Question 6

___ can strengthen hydroxyapatite

Answer 6

Fluoride (fluorapatite)

Question 7

During maturation of enamel, some organic material is:

Answer 7

Reabsorbed

Question 8

True or false: apatites are precipitated on a fibrillar substrate

Answer 8

False - they are not

Question 9

Enamel is made of 4%:

Answer 9

water and organic material (1% protein)

Question 10

Enamel is a ____ substance

Answer 10

Interprismatic

Question 11

Enamel rod is thought to be ____ shaped

Answer 11

Cylindrical (keyhole shape discontinued)

Question 12

Initial layer of enamel is:

Answer 12

Aprismatic

Question 13

Rod crystals are oriented in:

Answer 13

The same direction

Question 14

The long axis of the crystals is ____ to the long axis of the enamel rod

Answer 14

Parallel

Question 15

Does interrod substance have a specific orientation?

Answer 15

Does not appear so, but slightly perpendicular to the long axis of the enamel rod

Question 16

Rod sheath

Answer 16

optical/refractive phenomenon between the interrod substance and the enamel rod caused by the differences in hydroxyapatite crystal orientation

Question 17

Crystallites are ____ in the rod than the interrod substance

Answer 17

Larger and more compact

Question 18

Interrod substance looks like:

Answer 18

Honeycomb; crystals more haphazard

Question 19

Successive enamel rods are off by _____ which contributes to a stacking in a structurally sound manner

Answer 19

2 or 4 degrees

Question 20

Enamel rods are more ____ at cusps and _____ at cervix

Answer 20

Vertical; horizontal

Question 21

Enamel rods run generally ____ to long axis of the tooth

Answer 21

Perpendicular

Question 22

Enamel rods ____ as they run toward the surface

Answer 22

Undulate

Question 23

Rod heads are always oriented:

Answer 23

Coronally

Question 24

Rod structure allows:

Answer 24

Interlocking arrangement

Question 25

Rate of enamel maturation depends on:

Answer 25

Nutrients available

Question 26

Striae of Rezius

Answer 26

- Incremental growth lines (dark bands in longitudinal section, concentric rings in cross section) - phasic episodes of mineral maturation

Question 27

Accentuated lines of Striae of Retzius represents:

Answer 27

Systemic disturbances

Question 28

Darker bands of Striae of Retzius means:

Answer 28

Less mineralized

Question 29

What is the neonatal line?

Answer 29

Accentuated Stria of Retzius reflecting marked physiologic change at birth

Question 30

How often is Striae of Retzius laid down?

Answer 30

Weekly (circaseptimanian)

Question 31

Enamel cross striations

Answer 31

Indicates daily circadian variation in secretory activity of ameloblasts

Question 32

Enamel cross striations result from:

Answer 32

- Temporary constriction of Tomes' process - corresponding increase in the secretory face forming interrod substance

Question 33

Hunter Schreger bands

Answer 33

Optical phenomenon produced strictly by the **change in orientation of rod direction**

Question 34

Gnarled enamel

Answer 34

- found at cusp tips - rods appear twisted around each other in a complex pattern

Question 35

Enamel tufts are analagous to

Answer 35

Geologic faults

Question 36

Enamel tufts project from ___ for a ___ distance

Answer 36

DEJ; short (1/3-1/2 enamel thickness)

Question 37

Enamel tufts are hyper or hypomineralized?

Answer 37

Hypomineralized - increased concentration of enamel protein

Question 38

Enamel ____ can be microscopically confused with cracks

Answer 38

Lamellae

Question 39

What are enamel lamellae?

Answer 39

Linear, longitudinally oriented defects which are **highly organic (hypomineralized enamel)**

Question 40

True or false: enamel lamellae exacerbate caries development

Answer 40

False - do not

Question 41

Enamel lamellae have a different _____ than the rest of enamel

Answer 41

refractive index

Question 42

_____ are physical defects extending from surface for varying depths

Answer 42

Enamel cracks

Question 43

True or false: Enamel cracks have a developmental origin

Answer 43

False - physical defect

Question 44

What is the dentinoenamel junction?

Answer 44

Series of ridges that increases surface area and facilitates adhesion

Question 45

What are enamel spindles?

Answer 45

Newly formed odontoblast process that push between adjoining ameloblasts, become entrapped in enamel matrix when it mineralizes

Question 46

Carious lesion forms a ____ shape through the enamel and then ___ at the DEJ, then forms a _____ through the dentin

Answer 46

Conical; Spreads; Conical lesion

Question 47

What are perikymata?

Answer 47

Extensions of Striae of Retzius from the DEJ to the outer surface of enamel

Question 48

Perikymata run in what direction?

Answer 48

Circumferentially horizontal lines across the face of the crown (where Striae of Retzius ends on surface of tooth)

Question 49

Surface structure of unerupted teeth

Answer 49

- Structureless cuticle of organic material - Subsurface layer of loosely packed crystals

Question 50

Surface structure of erupted teeth

Answer 50

- cuticle and subsurface layer is lost - Salivary pellicle

Question 51

Age changes of enamel

Answer 51

- Becomes worn - Discoloration - Reduced permeability - Modifications of surface layer

Question 52

Amelogenesis imperfecta causes:

Answer 52

Disruption to the structure and clinical appearance of tooth enamel

Question 53

Amelogenesis imperfecta - phenotypic classifications

Answer 53

- hypoplastic - hypocalcified - hypomature

Question 54

Amelogenesis imperfecta is acquired via:

Answer 54

- X-linked autosomal dominant - Autosomal recessive

Question 55

Best fix for amelogenesis imperfecta

Answer 55

Crown the teeth

Question 56

What are some environmental effects that affect enamel?

Answer 56

- febrile diseases (bands of malformed enamel) - Tetracycline induced disturbances - fluoride concentrations over 5ppm can cause **mottled enamel/toxic to secretory ameloblasts**

Question 57

Tetracycline can get incorporated into:

Answer 57

Bone, dentin, enamel

Question 58

Fluoridation effects on enamel

Answer 58

- crystals more resistant to acid demineralization - toxic to secretory ameloblasts in high concentrations (mottling of enamel) - enhances calcium phosphate/remineralization

Question 59

Acid etching

Answer 59

- involved in use of fissure sealants, orthodontics - removes plaque and other debris - increases porosity of exposed surface

Question 60

Ionic substitutions to biological apatites may alter:

Answer 60

- chemical properties - physical properties - chemical reactivity - hardness

Question 61

What ionic substitutions can occur on apatites?

Answer 61

- substitution of calcium ions - substitution of phosphate ions - substitution of hydroxyl ions

Question 62

Enamel is a dynamic system which participates in what kind of interractions?

Answer 62

- solute and ion transport from saliva to dentin - ion exchange with saliva - demineralization/remineralization - reactions with bacteria and other surface organic compounds

Question 63

____ is in equilibrium with oral fluid/saliva

Answer 63

Enamel

Question 64

Saliva is super saturated with:

Answer 64

Calcium and phosphate