WEEK FOUR ONWARDS Flashcards
Outline enamel general characteristics
- hardest biologic tx in body - thickest over cusps/thinnest at cervical margin
- composed of inorganic mineral, organic matter and water
- white w/ low translucency that increases with age = reflects yellow colour of dentine
- composed of keyhole shaped rods made by ameloblasts
- thickest over cusps [2.5mm] and thinnest at cervical margin [knife edge]
outline chemical characteristics of enamel
- by WEIGHT= 96% inorganic material -by weight 4% organic material + water
inorganic
- [crystalline calcium phosphate // hydroxyapatite - HA]
- mineral content ^ from DEJ to surface
- HA crystallites = hexagonal 70nm width and 25nm thick
much bigger than the crystallites in dentine, cementum and bone
- F levels decline from outer to inner layers
organic
- enamelin protein on and in between HA crystals [aids permeability]
- AAs, peptides, lipids
describe enamel prisms [rods] and the THREE types of cross sections
each rod filled w crystals
- those in head follow long axis of rod
- those in tail lie in cross axis to head [65-70d gradual divergence from head crystals]
- each rod = FOUR ameloblasts
-1 forms head, 2 form neck, 1 forms tail
- pattern I
- parallel rows - pattern II
- keyhole pattern [most predominant]
- occupies BULK of enamel - pattern III
- circular
- near DEJ and surface
- interprismatic areas exist between prisms
changes in crystal orientation throughout rod = changes in angle to enamel
- cervical margin = 90d
- occ/incisally = 60d
- fissues 20d
describe the keyhole pattern of enamel rods
-tail located between FOUR heads
- in head = crystals parallel to long axis
- in keyhole = crystals diverge in different directions from head central area
- in tail = crystals 65-70d from head crystals [gradual divergence]
describe the Hunter - Shreger Bands [HSB]
alternating light and dark bands which begin at DEJ and end before reaching enamel surface
due to alternating directs of prisms
- strengthen enamel and prevent cracks
define the incremental lines [stria of retzius] and describe the TWO types
due to rhythmic depo of enamel
- as enamel matrix mineralises it follows the pattern of matrix depo = provides growth lines
periods of activity alternates w period of acquiescene = resulting in incremental lines
1. short periods = cross striations [daily]
2. long period = enamel striae [~weekly]
cross striations
- rods alternating between thick.thin segments = cross striations
- lines at right angles w long axis of prisms
- 2.5-6um apart [2um at cervical enamel]
- 7-10 cros.stri between 2 striae
enamel striae
- lines running oblique across prisms in longitudinal sections
- straie’s ovelapping cusps do not reach surface
- due to metabolic distubrances during mineralisation [eg neonatal line]
- absent in enamel formed before birth
outline what perikymata grooves are
occur as enamel striae reach enamel surface –> series of fine grooves/ridges in circumferential pattern
close together near cervical margin
in prim teeth = only seen in cervical enamel of second molars
describe the dentin enamel junction, its TWO patterns and what structures as visible
- reflects boundary between dentin and enamel
- patterns = scalloped // smooth
- scalloped = beneath cusps and incisal edges
HIGH shearing forces - smooth = at lateral surface
- LOW shearing force
- at the DEJ: spindles, tufts and lamellae are visible
describe enamel spindles
tubules from dentin extending up to 25um –> enamel
believed to be odonotoblastic process that remained between ameloblasts
describe enamel tufts
- junctional structures in inner third of enamel = resembles grass
- travels in same direction as prisms but is several prisms wide
- contains hypomineralised areas
- suggested to travel from residual protein matrix
describe enamel lamellae
- runs through entire thickness of enamel
- appearance = sheet like structural defect
- hypomineralised
- caused by = imcomplete maturation of prism groups during development // cracks after eruption
- contains enamel proteins
define what an enamel pearl is and its cause
- enamel found where it is not meant to be [usually in the furcations of molar roots] - can ^ retention of biofilm = periodontal lesions
- caused by failure of Hertwif epithelial root sheath to separate from dentin in development
- prolonged contact induces odontogenic epithelium to secrete enamel
describe predentin layer
innermost layer of dentin - surrounding pulp [10-40um thickness]
- not mineralised yet
- sec by odontoblasts by golgi app. and mitochon.
- appears pale compared to mineralised dentin
describe translucent dentin
forms w ageing due to tubule occlusion by peritubular dentin [pronounced at root apex]
- used in foresic dentistry in age determination
describe sclerotic dentin
tubular occlusion caused by stimulus [appearance similar to translucent dentine but related to stimulus not age]
- tubules = completely obliterated [^ in amount w age] = pulp permeability eliminated in this case
- believed to be protective mechanism of pulp
describe dead tracts
when dentin damaged = odontoblastic process either dies or retracts = empty tracts [appears dark under light microscope]
with time the empty tubule can be completely filled w minerals
list THREE properties which prevent bacteria from invading dentine through tubules and describe the permeability of coronal dentin
TBCONT..
outward dentinal fluid contains immunoglobin
presence of intratubular deposits of mineral
presence of large collagen fibrils
state the curvature of dentin tubules and describe the FIVE types of structural incremental lines in dentin
primary curvature = long sweeping s shape
secondary curvatures = along length of prim.curv. = gentle, wavy undulations = sec.curv
**Lines of Von Ebner
**- SHORT cross striations across tubules [reflect rhymic deposition]
- finer, more regular incremental lines representing daily deposition [less pronounced than contour lines of owen]
Andresen Lines
- LONG period lines
- 16-20 um apart
- associated w change in **collagen fibril orientation **
- more prominent that von ebner // less pronounced than contour lines of owen
Shreger Lines
- associated w peaks of PRIMARY sigmoid curvatures
**Contour Lines of Owen **
- associated w SECONDARY curvatures
- accentuated incr.growth lines = represent stress/ rate changes in dentin formation
- another type = neonatal lines [marks dentin formed before/after birth]
define coronal, radicular, apical foramina and accessory canals of PULP
**coronal pulp **
- occupies crown of tooth with pulp horns [extend into cusps]
- larger than root pulp + different structure
**radicular pulp
**- extends from cervical regions to apex of tooth
- singular in ant teeth//multiple root pulps in post. teeth
apical foramina
- opening of root pulp –> periodontium
**acc. canals // lateral canals ** **
**- can result blood vessells obstructing dentin fotmation
- OR from break in epithelial root sheath
- occurs in 33% of perm teeth
- opens to PDL
describe what happens to the root canal anatomy w age
large and open apex in immature tooth –> narrows w age
cases of multiple foramina is high –> ^ in complexity and prevalence in multi rooted teeth
List and describe the FOUR functions of pulp
- inductive
- interacts w oral epithelium to initiate tooth formation in early development - formative
- odontoblasts form dentine - protective/defence
- formation of reparative dentine, inflammatory response - nutritive
- carries O2 and nutrition –> tooth
- comms w PDL via apical foramen and acc.canals
- richly vascularised and innervated
describe the pulp composition
- appearance = loose CT
- type 1 collagen fibres
- ground substance, macromolecules and fluid
cells
- mesenchymal cells [potential fibroblasts, macrophages, odontoblasts]
- neurons [trigeminal afferents and sympathetics]
- transient cells
- endothelial cells [blood/lymph]
- LACKS ADIPOSE
- highly organised at periphery
describe the histological organisation of the pulp
beneath predentin = odontogenic zone [pulpal layer]
from superficial –> deep
odontoblastic layer [outermost]
- odon. form single pseudostratified layer of cells attached to predentine surface [single cytoplasmic extensions –> dentinal tubules]
cell free zone [beneath odontoblast layer]
- nerve/ capillary plexus also located here
- not ENTIRELY cell free but much less than upper layer
cell rich zone
- high conc capillaries + axons
- fibroblasts + mesenchymal cells
- not as many cells as odontoblastic layer
central pulp // pulpal core
- bulk
- neurovascular core
describe FOUR pulpal cell types
- odontoblasts
- line perimenter of pulp from time they begin organise to form dentin –> when quiescent/ no longer producing dentin at rapid rate - fibroblasts
- protein producing cell - become smaller w age
- most numerous as they’re located throughout pulp
- in young pulp = produce collagen fibres and ground substance - shwann cells
- form myeline sheath of nerves
- associated w ALL PULP NERVES - endothelial cells
- line capillaries, veins and arteries of pulp
