Enamel and Cementum Flashcards
During Amelogenesis, what’s the secretory process short shovel or spoon shape?
Tome’s Process
What are two major phases ameloblasts pass through?
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)
Enamel Rods
- 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
Enamel Rods & ameloblasts
- 4 ameloblasts contribute to each rod or prism
- each rod arises from 4 ameloblasts
- thin sheath surrounds each rod
Rod Core vs Rod Sheath
RC- lighter band; represents outer covering (RS)
RS- outer covering; darker band
difference in color is density of hydroxyapatite crystals
Gnarled Enamel
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
Striae (Stripes) of Retzius
incremental lines following the shape of crown that results from enamel deposited incrementally
Hunter-Schreger Bands
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)
Perikymata
- 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)
Enamel Lamellae
- 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
Enamel Tufts
- doesn’t occur at enamel surface
- ords are orientated slightly away from each other at DEJ
- fills w/ material; vulnerable to caries
Enamel Spindles
- @ 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
What’s difference betweeen Enamel Tuft and Enamel Lamellae
ET remains at DEJ/ has a fuzzy appearance while EL extends towards the outer surface of the enamel
Tetracyline STaining
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
What’s the least mineralized structure?
cementum
Cementocytes
cellular cementum where cementoblasts have been incorporated into a matrix
Cellular vs acellular cementum
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
Cementum is 1/2 the anchor for the periodontal ligament, which contains what 2 types of fibers?
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
Sharpey’s Fibers
Group II Fibers that are inserted into cementum
Cementum Abnormalities:
1) Reversal Lines
2) Cementicles
3) Arrest or Resting Lines
4) Hypercementosis
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
