Enamel and Cementum

Question 1

During Amelogenesis, what’s the secretory process short shovel or spoon shape?

Answer 1

Tome’s Process

Question 2

What are two major phases ameloblasts pass through?

Answer 2

1) Secretory Phase- deposit of enamel matrix containing enamelin; Tome’s process evident
2) Resorbing Stage- removal of H2O/ organic components from EM; TP not visible; border has ruffled appearance (increased surface area aids in resorption- mitochondria aids active process)

Question 3

Enamel Rods

Answer 3

• structural units of enamel
• paced with calcium hydroxyapatite crystals
• orientation related to Tome’s Process
• prisms run form DEJ to the outer edge of the enamel surface

Question 4

Enamel Rods & ameloblasts

Answer 4

• 4 ameloblasts contribute to each rod or prism
• each rod arises from 4 ameloblasts
• thin sheath surrounds each rod

Question 5

Rod Core vs Rod Sheath

Answer 5

RC- lighter band; represents outer covering (RS)
RS- outer covering; darker band

difference in color is density of hydroxyapatite crystals

Question 6

Gnarled Enamel

Answer 6

enamel rods deposited from DEJ outward in a manner perpendicular to a line tangential to enamel surface, which allows for best geometry for tight packing of rods

GE- areas not conducive to this geometry so rods become bent; more vulnerable to caries

Question 7

Striae (Stripes) of Retzius

Answer 7

incremental lines following the shape of crown that results from enamel deposited incrementally

Question 8

Hunter-Schreger Bands

Answer 8

high minieral crystal structure of rods are visible of polarized light; HS bands are imperfect bands (bent crystals) that block polarized light, creating light/ dark bands (normal crystal pass polarized light)

Question 9

Perikymata

Answer 9

• end of incremental lines (Stiae of Retzius) visible to outer enamel surface
• produced by hesitation of ameloblasts before next group of rods contacts the enamel surface
• disappear due to attrition
• end point of secretory phase (lack of ameleoblasts)

Question 10

Enamel Lamellae

Answer 10

• cracks in enamel
• can occur due to deffective crystallization during mineralization
• can occur from impact or thermal pressures
• cracks fill w/ material; vulnerable to caries

Question 11

Enamel Tufts

Answer 11

• doesn’t occur at enamel surface
• ords are orientated slightly away from each other at DEJ
• fills w/ material; vulnerable to caries

Question 12

Enamel Spindles

Answer 12

• @ DEJ; odontoblasts process have exteneed beyond dentin into enamel
• become trapped due to failure to w/draw into dentinal tubule prior to amelogenesis
• in some cases, can secrete funtional denitn

Question 13

What’s difference betweeen Enamel Tuft and Enamel Lamellae

Answer 13

ET remains at DEJ/ has a fuzzy appearance while EL extends towards the outer surface of the enamel

Question 14

Tetracyline STaining

Answer 14

Tetracylin staining has high affinity for dentin/ bone that are still developing

• dentin stained w/ T. shows dark bands through translucent enamel
• clinically not an issue

Question 15

What’s the least mineralized structure?

Answer 15

cementum

Question 16

Cementocytes

Answer 16

cellular cementum where cementoblasts have been incorporated into a matrix

Question 17

Cellular vs acellular cementum

Answer 17

CC- found more apical area of root; thickens towards the apex/ thickens with age and trauma; forms quicker

AC- found more cervical areas of root; intermediate cementum; never thickens; forms slowly; covered by a layer of CC

Question 18

Cementum is 1/2 the anchor for the periodontal ligament, which contains what 2 types of fibers?

Answer 18

1) Group I Fibers- fibers from cementoblasts that forms the fibrous part of cementum; runs parallel to long axis of root and is contained w/in cementum
2) Group II Fibers- fibers from dental sac cells that compromises the PDL; it inserts into the cementum at right angles to the CEJ and to GIF; sharpey’s fibers

Question 19

Sharpey’s Fibers

Answer 19

Group II Fibers that are inserted into cementum

Question 20

Cementum Abnormalities:

1) Reversal Lines
2) Cementicles
3) Arrest or Resting Lines
4) Hypercementosis

Answer 20

1) RL- lines that reflect active areas of resorption (remodeling); occurs with extreme movement of teeth
2) C- calcified nodules; results from cellular debris; mostly found in PDL
3) A/RL- a banding pattern of periods of deposition/ non-deposition (of cementum)
4) H- abnormal thickening near the apical region; caused by chronic inflammation, loss of opposing teeth & hypereruption