Enamel

Question 1

where is enamel

Answer 1

• outside layer of anatomical crown

Question 2

what does enamel originate from

Answer 2

• arises from enamel organ from the epithelium, which arises from the ectoderm

Question 3

what is the hardness of enamel

Answer 3

• hardest tissue in the body
• only calcified tissue to originate from epithelium
• dentin, cementum and bone come from mesenchyme (ectoderm)

Question 4

is enamel living and are imperfections permanent

Answer 4

• non vital = not a living tissue
• no cells, no blood vessels, no nerves
• no sources for repair or growth
• any imperfection during development are permanent (no enamel is laid down after eruption)

Question 5

what is the clinical composition of enamel

Answer 5

• 96% inorganic substance - non vital – hydroxyapatite crystals
• 2.3% water
• 1.7% organic collagen like fibres – laid down by ameloblasts and non calcified

Question 6

what is enamelin

Answer 6

• like keratin protein

Question 7

what is the macroscopic structure of enamel and how does it appear

Answer 7

• macroscopic structure = observation enamel

- appearance = hard, shiny, translucent

Question 8

what is the enamel like in the primary dentition

Answer 8

• clinical crown has thinner enamel and dentin

- whiter due to less denitn

Question 9

what is the enamel like in the secondary dentition

Answer 9

• clinical crown has enamel and cementum/dentin due to recession, abrasion and attrition

Question 10

what is perikymata

Answer 10

• horizontal raised lines from enamel
• results from enamel formation
• mostly on gingival 3rd
• not as obvious in adults -> wear down over time
• indicate the termination of lines of retzius at the surface enamel (result of the layer-upon-layer pattern of enamel matrix formation)
• they are the result of normal enamel apposition

Question 11

what are incremental lines of retzius

Answer 11

• dark brownish lines
• result from the layer-upon-layer pattern of enamel matrix formation
• they curve out and away from DEJ, look like rings of a tree
• normal occurance
• terminate on occlusal surface - perikymata

Question 12

what causes perikymata

Answer 12

• enamel also begins to grow at the incisal edge downwards, so each line is addition to the tooth structure

Question 13

what is the colour of enamel

Answer 13

• varies with age - not completely understood
• yellow-is hue from dentin
• intrinsic/extrinsic stains
• primary teeth more white than secondary

Question 14

what is attrition

Answer 14

• wearing of enamel under friction of use at the incisal edge
• posterior cusps
• changes in dentin where dentin is worn to protect the pulp

Question 15

what are mamelons

Answer 15

• prominences on incisal edge of erupted incisors
• result of how enamel forms
• no clinical significance
• usually wear away, unless overbite or large overjet

Question 16

what are the grooves on posterior teeth

Answer 16

• developmental lines - occlusal, buccal and lingual
• in some -> shallow smooth
• in others -> extend in deep

Question 17

what are fissures

Answer 17

• bottom of the groove
• does not extend to dentin -> ends in enamel
• where you attempt to feel with explorer

Question 18

what are pits

Answer 18

• depressions

- at either end of a groove, always end in enamel

Question 19

what is the exterior surface of enamel called

Answer 19

• enamel cuticle/nasmyth’s membrane

Question 20

what are the 2 coverings (cuticles) of enamel

Answer 20

• primary enamel cuticle: last product of ameloblasts as they flatten out; mineralized
• secondary enamel cuticle: product of reduced enamel epithelium; 4 into 1; not calcified – protection; remains on crown until after eruption

Question 21

what is the dentine-enamel junction

Answer 21

• between dentin and enamel
• not a straight line - mini curvatures
• especially at cusp tips and incisal edge
• allows increased adherence between enamel and dentin
• gives a better stronger fit of enamel on dentin

Question 22

what are enamel rods/prisms

Answer 22

• made by ameloblasts
• deposit enamel matrix (ground substance/fibres/crystals) in a rod and interrod substance arrangement
• tiny rods/prisms extend perpendicular from the DEJ to outer surface
• can have curvatures
• 5-12 million in one tooth
• framework enamel matrix: extremely hard

Question 23

what is the framework for enamel

Answer 23

1. enamel rods (most mineralized)
2. rod sheath -> surrounds enamel rods
3. interrod substance -> cements enamel rod together
   - all 3 structures extremely hard: enamel rod - > interred substance -> rod sheath (least mineralized)

Question 24

what is the bell stage

Answer 24

• ameloblasts lay down gel matrix
• moving away from DEJ toward outer enamel epithelium
• apposition of enamel is done in ‘wave’ sequence (layer-upon-layer)
• first formed at incisal edge
• second wave overlaps first
• moves cervically

Question 25

what is the mineralization stage

Answer 25

• during apposition-depositing of matrix
• ameloblasts deposit minerals (calcium phosphate) -> hydroxyapatite crystals into matrix and partial mineralization occurs

Question 26

what is the maturation stage

Answer 26

• crystals increase in size, tightly packed together

- if lack of growth or packing of crystals - hypocalcification

Question 27

what are bands of hunter-schreger

Answer 27

• alternating light and dark bands
• extend perpendicularly from DEJ to tooth surface
• results from the curvature of the enamel rods (overlapping)

Question 28

what are enamel lamellae

Answer 28

• microscopic space in enamel
• cracks/spaces left between enamel rods
• may be more susceptible to decay - no hydroxyapatite (filled organic material)
• if severe - can extend to surface as visible crack in enamel

Question 29

what are enamel tufts

Answer 29

• ‘clump of grass’ or small burgess at the DEJ and extending shortly into the enamel
• believed to be hypo calcified enamel rods

Question 30

what are enamel spindles

Answer 30

• an odontoblast that is trapped between ameloblasts in early development
• the odontoblast process is caught in the enamel
• it is vital (living tissue)
• thin corkscrew shape

Question 31

what is the dental caries process

Answer 31

• crystal orientation, rod orientation and DEJ orientation determine carious pattern

Question 32

what is the arrangement of enamel rods influence

Answer 32

• influences penetration of decay into enamel
• decay follows lines of enamel rods to the dentin
• decay increases rapidly when reaches the dentin

Question 33

what is the clinical importance of enamel rods

Answer 33

• cause smooth surface caries
• facial, lingual and proximal surfaces
• DEJ is straight, rod orientation straight direction perpendicular to DEJ, so lesion penetrates in straight line to dentin

Question 34

what are pit and fissure caries

Answer 34

• more prone due to plaque retention
• faster -> closer dentin
• rods also perpendicular to DEJ
• however, DEJ very concave beneath fissure -> enamel rods distributed in radial patter or fanning out rods
• clinically - small carious lesions
• microscopically - large progressive carious lesion (broad surface near DEJ)

Question 35

age related changes to enamel

Answer 35

• cusp tips, incisal edges
• excessive wear: less pit and fissure, exposing dentin
• less permeability
• darker colour
• less caries
• increase of fluoride contents at surface
• associated with eating habits and environment of the individual