Enamel Flashcards
where is enamel
- outside layer of anatomical crown
what does enamel originate from
- arises from enamel organ from the epithelium, which arises from the ectoderm
what is the hardness of enamel
- hardest tissue in the body
- only calcified tissue to originate from epithelium
- dentin, cementum and bone come from mesenchyme (ectoderm)
is enamel living and are imperfections permanent
- 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)
what is the clinical composition of enamel
- 96% inorganic substance - non vital – hydroxyapatite crystals
- 2.3% water
- 1.7% organic collagen like fibres – laid down by ameloblasts and non calcified
what is enamelin
- like keratin protein
what is the macroscopic structure of enamel and how does it appear
- macroscopic structure = observation enamel
- appearance = hard, shiny, translucent
what is the enamel like in the primary dentition
- clinical crown has thinner enamel and dentin
- whiter due to less denitn
what is the enamel like in the secondary dentition
- clinical crown has enamel and cementum/dentin due to recession, abrasion and attrition
what is perikymata
- 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
what are incremental lines of retzius
- 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
what causes perikymata
- enamel also begins to grow at the incisal edge downwards, so each line is addition to the tooth structure
what is the colour of enamel
- varies with age - not completely understood
- yellow-is hue from dentin
- intrinsic/extrinsic stains
- primary teeth more white than secondary
what is attrition
- wearing of enamel under friction of use at the incisal edge
- posterior cusps
- changes in dentin where dentin is worn to protect the pulp
what are mamelons
- prominences on incisal edge of erupted incisors
- result of how enamel forms
- no clinical significance
- usually wear away, unless overbite or large overjet
what are the grooves on posterior teeth
- developmental lines - occlusal, buccal and lingual
- in some -> shallow smooth
- in others -> extend in deep
what are fissures
- bottom of the groove
- does not extend to dentin -> ends in enamel
- where you attempt to feel with explorer
what are pits
- depressions
- at either end of a groove, always end in enamel
what is the exterior surface of enamel called
- enamel cuticle/nasmyth’s membrane
what are the 2 coverings (cuticles) of enamel
- 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
what is the dentine-enamel junction
- 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
what are enamel rods/prisms
- 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
what is the framework for enamel
- 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)
what is the bell stage
- 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