enamel and cementum
More cementicles are found in elderly, cementum resorption is characteristic of aging
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acid attacks the mineral at the periphery of the enamel rods and leaves a rough surface
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ameloblasts are hexagonal in cross-section, culomnar shaped w/a secretary-process at on end called Tomes process
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as enamel matures crystals grow in size
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bleaching teeth won't help tet staining because source of prob is dentin, not enamel
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bonding material attaches more firmly to enamel
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cement is less mineralized than enamel and continues to form through life
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cementum has no nerves and is not sensitive
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cementum is lighter in color and softer than dentin, can clean it
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cementum is thinnest near cervix and thickest at apex
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dentin is deposited first and then ameloblasts are elongated
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each ameloblast (6-sided) contributes to 4 rods they appear wavy because of migratory path toward the periphery
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enamel crystals are 4x larger than those in bone, dentin & cementum
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enamel etching: dilute acid is used to alter the surface of the enamel
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enamel is 96% inorganic & 4% water & organic matter (protein called enamelin)
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increase in amount of cementum in apical region usually occurs with age
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no more enamel production. Ameloblast has limited life span
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2 functions of cementum
1 seals tubules of dentin of the root 2 serves as the attachment for the periodontal fibers that suspend the tooth in socket
one enamel rod is formed by
4 ameloblasts
enamel rods are shpaed like
a key-hole
neonatal line
a significant striae of retzius, distinguishes prenatel enamel (few defects) from postnatel enamel
G-gap
a small gap exists between the cementum & enamel (10%) results in exposed dentin & possibly root sensitivity & increased susceptibility to decay
hypercementosis
abnormal thickening of the cementum, usually found in apical region, tooth may fuse to surrounding bone
hunter-schreger bands
alternating light & dark bands in enamel due to configuration of the enamel rods, result of movement of ameloblast
tetracycline stain
appears as dark bands through enamel especially near cervix of tooth. doesn't effecdt enamel
incremental lines (horizontal)
are a result of rhythmic deposition of enamel, end in small ridges on the tooth surface called perikymata
rod sheath
around the periphery of the rod, especially noticeable in the head region of the rod, produced by change in angulation fo crystals formed as ameloblasts move, resist demineraliztion more than rod core
rod less enamel mostly found
at cervicle areas around enamel
rode less enamel less frequently found
at cusp tips
cementicles
calcified ovoid or round nodule, may be free in the pdl, attached or embedded in cementum
root resporption
can be a result of trauma, ex rapid orthodontic tooth movement, hypereruption due to loss of antagonist, traumatic occlusion
cementum is composed of
cells - cementoblasts, cementocytes, fibers and ground substance
cementoclasts
cells that actively resorb cementum, associated with primary teeth; trauma
cell types in cementum
cementoblasts cementocytes cementoclasts
cells from the dental follicle differentiate into
cementoblasts. they begin production of cementum on the newly formed dentin
bone is vascular, has nerves, has cells in lacunae & canaliculi, has incremental lines, more mineralized than cem, less resistant to demineralization & resorption than cem
cementum is avascular, does not have nerve, has cells in lacunae & canaliculi, has incremental lines, less mineralized than bone, is more resistant to demineralization & resorportion than bone
M-meets
cementum meets the enamel (30%)
O-overlaps
cementum overlaps the enamel slightly, (60%)
rod core
center of the enamel rod
cellular cementum
covers apical portion of tooth, much thicker layer, has cells, (cementocytes in lacunae) deposited throughout life, deposited at intervals that produce arrest lines (highly calcified lines similar to those seen in bone)
enamel lamellae
cracks in the surface of the enamel visible to they eye: extend from DEJ to surface of enamel, possible pathway for dental carries to spread not a high risk for fracture, developmental
cross striations
daily appositional lines
enamel rods extyend from
dej to outer enamel surface and run perpendicular to the incisal surface
tetracycline binds to
dentin and bone
when kids take tetracycline, it will disolor
dentin and bone
hydroxyapatite crystals
deposited during the secretory stage are very thin and needlelike.
secretory stage
depostion of enamel matrix that contains both organic and inorganic material
enamel rods
enamel is composed of interlocking rods that help resist masticatory forces & prevent fracture between the rods
Hertwig's epi root sheath degenerates and remnants are called
epethelial rests of mallasez
cementicles originate from
epithelial cells, no consequence to them
enamel spindels
extensions of dentinal tubules into the enamel (shorter than tufts) single extension of odontoblast process into the enamel
amelogenesis
formation of enamel, consists of 2 stages
acellular cementum
formed from cementoblast that originated as fibroblasts in pdl. deposited on surface of intermediate cementum, derived from dental follicle, covers the cervicle 1/2 of root, no cells, does not increase after initial deposition forms at slower rate than cellular cementum
rodless enamel
found on all deciduous teeth and 70% of perm teeth, structureless layer of enamel about 30 microns thick
enamel surface: pits & fissures
from where ameloblasts become crowded between cusps
cementocytes
get nutrients from pdl via canaliculi, orientated towards pdl, all pointed at pdl
enamel tufts
hypomineralized inner ends of some enamel rods, defect in enamel, broader than spindel
pits and fissures cause
incomplete maturation of enamel
3 types of cementum
intermediate acellular cellular
gnarled enamel
is formed by enamel rods that have bent in exaggerated ways and is found under cusp tips, begins near dej
hertwig's epithelial root sheath is formed by
joining of OEE & IEE
enamel permeability: fluid particles & bacteria can pass through enamel by various pathyways and can result in dental carries. these include
lamellae; tufts; cracks; spindles, pits & fissures; space between crystals
enamel fomation begins at
late bell stage
cementoblasts
lay down cementoid (organic mat) becomes mineralized later, become embedded in mineralized matrix as more cementoid is prodcued, they become enclosed in a lacuna & become cementocytes
enamel is composed of
mineral, hydroxyapatite (crystalized clacium phosphate)
striae of retzius (2 e's, enamel)
more prominent growth lines may reflect major interuptions in deposition of enamel related to specific event, car accident
cemental repair
new cementum can be depositied on top of area with a defect, results in reversal line
h-s bands run
perpendicular to dej and extend about 2/3 of way from dej to enamel surface
resorbing stage
removal of most of the water and the organic matter
Cemental variations
root resporption cemental repair hypercementosis cementicles
aging
root surface becomes more irregluar with age due to continued resorption & deposition of cementum
2 stages of amelogenesis
secretory stage resorbing stage
tomes' process
shovel shaped & is responsible for the orientation of the enamel rods. has a specialized end
cementum
small layer of mineralized ct that covers root of teeth.
Enamel is
the most highly mineralized tissue in the body acellular & avascular, unable to remodle or repair. thickest at cusp tips. thinnest near junciton of crown & root
reversal line
the point where resporption stops & deposition begins
cementoenamel junction CEJ
the point where the cementum of the root meets the enamel of the crown, around tooth like a belt along tooth
intermediate cementum
think, noncellular layer deposited by cells of inner epi root sheath. more calcified than the dentin or adjacent cellular cementum
oldest enamel is closest
to DEJ
pits & fissures are more susceptible
to caries due to hypocalcification
