Enamel Flashcards
1
Q
where is enamel
A
- outside layer of anatomical crown
2
Q
what does enamel originate from
A
- arises from enamel organ from the epithelium, which arises from the ectoderm
3
Q
what is the hardness of enamel
A
- hardest tissue in the body
- only calcified tissue to originate from epithelium
- dentin, cementum and bone come from mesenchyme (ectoderm)
4
Q
is enamel living and are imperfections permanent
A
- 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)
5
Q
what is the clinical composition of enamel
A
- 96% inorganic substance - non vital – hydroxyapatite crystals
- 2.3% water
- 1.7% organic collagen like fibres – laid down by ameloblasts and non calcified
6
Q
what is enamelin
A
- like keratin protein
7
Q
what is the macroscopic structure of enamel and how does it appear
A
- macroscopic structure = observation enamel
- appearance = hard, shiny, translucent
8
Q
what is the enamel like in the primary dentition
A
- clinical crown has thinner enamel and dentin
- whiter due to less denitn
9
Q
what is the enamel like in the secondary dentition
A
- clinical crown has enamel and cementum/dentin due to recession, abrasion and attrition
10
Q
what is perikymata
A
- 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
11
Q
what are incremental lines of retzius
A
- 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
12
Q
what causes perikymata
A
- enamel also begins to grow at the incisal edge downwards, so each line is addition to the tooth structure
13
Q
what is the colour of enamel
A
- varies with age - not completely understood
- yellow-is hue from dentin
- intrinsic/extrinsic stains
- primary teeth more white than secondary
14
Q
what is attrition
A
- wearing of enamel under friction of use at the incisal edge
- posterior cusps
- changes in dentin where dentin is worn to protect the pulp
15
Q
what are mamelons
A
- prominences on incisal edge of erupted incisors
- result of how enamel forms
- no clinical significance
- usually wear away, unless overbite or large overjet
16
Q
what are the grooves on posterior teeth
A
- developmental lines - occlusal, buccal and lingual
- in some -> shallow smooth
- in others -> extend in deep
17
Q
what are fissures
A
- bottom of the groove
- does not extend to dentin -> ends in enamel
- where you attempt to feel with explorer
18
Q
what are pits
A
- depressions
- at either end of a groove, always end in enamel
19
Q
what is the exterior surface of enamel called
A
- enamel cuticle/nasmyth’s membrane
20
Q
what are the 2 coverings (cuticles) of enamel
A
- 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
21
Q
what is the dentine-enamel junction
A
- 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
22
Q
what are enamel rods/prisms
A
- 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
23
Q
what is the framework for enamel
A
- enamel rods (most mineralized)
- rod sheath -> surrounds enamel rods
- interrod substance -> cements enamel rod together
- all 3 structures extremely hard: enamel rod - > interred substance -> rod sheath (least mineralized)
24
Q
what is the bell stage
A
- 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
25
Q
what is the mineralization stage
A
- during apposition-depositing of matrix
- ameloblasts deposit minerals (calcium phosphate) -> hydroxyapatite crystals into matrix and partial mineralization occurs
26
Q
what is the maturation stage
A
- crystals increase in size, tightly packed together
- if lack of growth or packing of crystals - hypocalcification
27
Q
what are bands of hunter-schreger
A
- alternating light and dark bands
- extend perpendicularly from DEJ to tooth surface
- results from the curvature of the enamel rods (overlapping)
28
Q
what are enamel lamellae
A
- 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
29
Q
what are enamel tufts
A
- ‘clump of grass’ or small burgess at the DEJ and extending shortly into the enamel
- believed to be hypo calcified enamel rods
30
Q
what are enamel spindles
A
- 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
31
Q
what is the dental caries process
A
- crystal orientation, rod orientation and DEJ orientation determine carious pattern
32
Q
what is the arrangement of enamel rods influence
A
- influences penetration of decay into enamel
- decay follows lines of enamel rods to the dentin
- decay increases rapidly when reaches the dentin
33
Q
what is the clinical importance of enamel rods
A
- 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
34
Q
what are pit and fissure caries
A
- 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)
35
Q
age related changes to enamel
A
- 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
