Enamel Flashcards
β¦β¦β¦β¦β¦β¦β¦.what is enamel and where is it found
enamel is specialized hard tissue that is unique to teeth covering the dentin of crown
where is the enamel the thickest and where does it taper
enamel thickest over cusps and incisal edges(2.5mm) and thins toward cervical margin (0.5mm)
why cant enamel repair itself if damaged
due to how its avascular ( no blood vessels) and acellular (no cells) so it lacks regenerative ability
is enamel a living tissue
no its nonvital and does not respond to injury like other tissue
how is enamel dynamic
enamel exchange ions with surrounding environment allowing remineralization and demineralization
what gives enamel its hardness
hydroxyapatite crystals make enamel strong and highly resistant to wear
how does ion exchange affect enamel
enamel undergoes ion exchange with saliva , changing its mineral composition over time
what happens if demineralization exceed remineralization
leads to caries and erosion
how can enamel be remineralized to prevent caries
- fluoride ( but not exceeding the minimum dosage to prevent fluorosis)
-calcium phosphate
- fluoride foam trays which is a safer way than giving it systematically by water
why is enamel the hardest
- high in % of inorganic which is 96 % and only 4% organic
- crystal shape of hydroxyapatite very long and very thick crystals
- arrangement of crystals is packed in rods and interrods
why is enamel hardness important
to withstand chewing and grinding forces making enamel highly abrasion resistant
what makes enamel semipermeable
enamel has tiny water filled spaces between crystals allowing small molecules and ions to cross
how do hardness and porosity vary across enamel
enamel is harder and less porous at external surface and cuspal enamel is harder and denser than cervical enamel
why is enamel brittle
enamel lacks collagen so its not flexible , has low shear strength, and is prone to fracture under certain forces
how does enamel thermal property protect the dental pulp
low thermal conductivity and expansion protect the pulp from temperature changes
why is enamel translucent and what color does it appear
high crystal content make enamel translucent and it appears yellowish due to underlying dentine
how does aging affect enamel
becomes more translucent and showing a stronger yellow hue
chemical composition of enamel
mineral: 96%
organic material : β€ 1%
water: 2-3%
how does mineral content of enamel compare to dentine and bone
enamel has higher proportion of mineral components than dentine and bone making it harder
what is the main mineral in enamel what what is the chemical formula
calcium hydroxyapatite
Ca10(PO4)6(OH)2
describe the shape and organization of hydroxyapatite crystals in enamel
crystals are long , large , hexagonal , organized into rods ( prisms) and interrod each with different crystal orientation
does enamel contain organic component and if so what is the structure
yes , it has fine network of organic material surrounding the crystals and thin layers around rods
name the primary proteins found in enamel
amelogenin, enamelin, ameloblastin, tuftelin, dentine sialophosphoprotein
what other types of proteins support enamel formation
enzymes and serum proteins
what role do enamel proteins play in tooth development
the guide tooth morphogenesis and mediate mineralization and hydroxyapatite crystal formation
how are enamel proteins used in dentistry
aid in periodontal regeneration and can stimulate reparative process in enamel and dentine
which cells are responsible for secreting enamel matrix proteins
ameloblasts
what begins to precipitate in enamel matrix after ameloblasts secrete it
hydroxyapatite crystals
what role does amelogenin play in enamel mineralization
provides an ideal substrate for HA crystal formation in an environment rich in calcium and phosphate
how does enamel mineralization different from other tissues in terms of matrix vesicles
it doesnβt involve matrix vesicles it occurs directly in protein matrix
at what mineral content is enamel secreted
enamel secreted as partially calcified tissue with about 30% mineral content and no pre enamel
what happens as enamel matures
its mineral content will increase to about 96% as more amelogenin and parts of enamelin dissolve into enamel fluid enhancing mineralization
whatβs the basic structural unit of enamel
enamel rod or prisms
enamel rods or prisms extend from where
extend from dentine to enamel except near the dentin a thin rodless enamel zone and outermost layer 30-50 micrometer of rodless enamel at enamel surface
describe the shape of enamel rods in cross section
tightly packed
keyhole shape
arranged in horizontal rows
how do enamel rods appear when viewed longitudinally
wavy or sinusoidal form
what is interrod
region around each enamel rod containing crystals orientated differently from those in rod itself
how are crystals orientated in head and tail of enamel rod
head : crystals are parallel to the rod long axis
tail: they diverge about 65 degrees from long axis
why is enamel orientation important in restorative dentistry
cuz enamel unsupported by dentin is prone to fracture so understanding the orientation helps avoid weak stuff
how do enamel rods differ in permanent teeth near CEJ
enamel rod tilt slightly toward root of tooth
what influences the length of enamel rods
thickness of enamel ( rods vary in length according to thickness)
what is the general orientation of enamel rods in relation to enamel surface
usually oriented 90 degrees to enamel surface
how many crystals does each enamel rod contain
each rod contains several million crystals
describe enamel complex arrangement of enamel rods within a tooth crown
its spiral shaped and contribute to enamel strength and resistance properties
what is rod sheath in enamel
layer of organic matrix between enamel crystals mostly located at margins of each enamel rods its primarily made of protein called ameloblastin and other proteins
how are enamel rods arranged in cuspal/ incisal regions
in spiral arrangements ( Gnarled enamel) for added strength with rods twisted or bent in different axis
what is enamel lamellae
defect in enamel that appear as cracks from surface inward containing high level of organic material and allowing bacteria to enter this will initiate caries
what are enamel tufts
small dark branched proteins extending from DEJ into 1/5 to 1/10 of enamel thickness marking areas where rod orientation changes
what are enamel spindles
short dark finger extension from DEJ to enamel and its formed
how is enamel spindles formed
odontoblast process travel through the DEJ into developing enamel and when enamel mineralization occur these processes get trapped within enamel forming enamel spindles
what are striae of retzius
dark striations or lines running from DEJ to enamel surface in cuspal direction
what do striae retzius indicate about enamel formation
each line corresponds to a specific time interval during tooth development, showing when enamel was incrementally added.
what happens when newly differentiated ameloblasts are recruited
they contribute to the secretion of enamel, leading to the formation of Striae Retzius as enamel is deposited in layers
how do striae retzius appear in longitudnal sections
dark lines surrounding tip of dentin
where are striae retzius most prominent
in permanent teeth
what can cause variations in striae retzius
from normal physiological changes in ameloblast activity or functional interruptions such as neonatal line
what is neonatal line
darkened line represents the border between enamel matrix before and after birth
what forms neonatal line
formed due to sudden change in environment after birth leading to metabolic disturbances in ameloblasts
in which teeth is neonatal commonly found
in all deciduous teeth and 1st permanent molars
what are hunter schreger bands
they are optical phenomena observed in enamel appearing as alternating dark and light zones
location of hunter schreger band
seen in longitudinal sections of enamel specifically in inner 2/3 enamel
what causes appearance of hunter schreger bands
caused by groups of enamel rods with different rod orientations creating banding pattern that can change with light direction
how is surface enamel different from subsurface enamel
the chemical and physical characteristics are different surface enamel is less soluble, harder and less porous and they have straie retzius , perikymata and aprismatic enamel
what is perikymata
concentric liner grooves where striae of retzius reach enamel surface
where are perikymata found
paraellel to CEJ and separated by ridges
under which conditions are perikymata present
where enamel has not been abraded or eroded such as in cervical areas
