Dental Histology

Front 1

what are enamel rods

Back 1

-basic unit of enamel
-Rods are made of crystallites of hydroxyapatite that form at right angles to the membranes of Tomes' processes (cell processes of ameloblasts). Crystallites are extracellular and their orientation results in the rod structure seen by LM

Front 2

Prismless enamel

Back 2

First and last enamel formed has no rod structure because ameloblasts have no tomes processes when laying down enamel at these points

Front 3

reciprocal induction

Back 3

Inner enamel epithelium (IEM) surround ectomesenchyme and induce the ectomesenchyme cells to differentiate into odontoblasts. Odontoblasts then lay down the Dentine and the completion of this induces the IEM cells to differentiate into ameloblasts which then lay down the enamel. Odontoblasts reciprocate therefore dentine is always layed down before enamel.

Front 4

Tomes processes

Back 4

cell processes of ameloblasts

Front 5

Formation of enamel rods

Back 5

Rods are made of crystallites of hydroxyapatite that form at right angles to the membranes of Tomes' processes

Front 6

Prismless enamel

Back 6

First and last enamel formed has no rod structure because ameloblasts have no tomes processes when laying down enamel at these points

Front 7

interrods

Back 7

-lateral parts of adjacent ameloblasts form interrods which are like a walled area within which is a pit surrounding a tomes process
-one ameloblast forms one rod and also contributes to the surrounding interrod

Front 8

Rod sheath

Back 8

enamel protein that lies in the gap between the forming rod and the interrod

Front 9

etching of enamel- what is the purpose of it and what does it look like under SEM

Back 9

used to remove plaque and assist in bonding of resins
different patterns will be seen if the rods dissolve or the interrods dissolve

Front 10

immunoelectron microscopy

Back 10

involves labelling an antigen with an antibody then using a second antibody with a tag to allow it to be seen with an TEM. Only way to find out what proteins are in ultra structural features

Front 11

amelogenin

Back 11

main enamel protein (90%)that regulates growth of crystals.
secretery granules travel along tomes processes and release it to rod

Front 12

enamelin

Back 12

enamel protein that assists crystal nucleation

Front 13

amelogenesis imperfecta

Back 13

Various genetic mutations cause different defects in enamel development eg hypoplasia. Mutation of enamelin gene has been id as one cause of enamel defects

Front 14

fluorosis

Back 14

Mottling of the enamel due to high levels of fluoride which causes metabolic inhibition

Front 15

adequate levels of fluoride in diet during tooth development is recommended because...

Back 15

Fluoride in adequate levels make crystals resistant to acid as fluoride is incorporated in the hydroxyapatite

Front 16

Short term incremental lines

Back 16

Periodic cross striations on the rods at around 4µm intervals caused by ameloblasts taking a daily rest period

Front 17

At what rate do ameloblasts lay down enamel

Back 17

4µm per day

Front 18

Srtiae of retzius

Back 18

incremental growth lines seen in enamel and are results of enamel's development. When viewed microscopically in cross-section, they appear as concentric rings. In a longitudinal section, they appear as a series of dark bands similar to the annual rings on a tree.Darker lines result from systemic disturbances. The neonatal line is the darkest band which represents the disrupted enamel formation after the stress of being born.
-The formation of the striae of Retzius result from a constriction of Tomes' processes in conjunction with an increasing process of interrod enamel development.

Front 19

perikymata

Back 19

-incremental growth lines that appear on the surface of enamel as a series of grooves. They may disappear as the enamel wears over a period of time.
-They are thought to indicate the termination of striae of Retzius at the surface of enamel.

Front 20

hunter-schreger bands

Back 20

alternating left and right groups of enamel rods that produces a banded appearance in reflected light- can’t see with class microscopes

Front 21

Enamel Tufts

Back 21

hypomineralised rods causing small, branching defects that are found only at the dentinoenamel junction. complex cours of tuft helps to withstand occlusal forces
Best seen in TS

Front 22

Enamel Spindles

Back 22

short, linear defects, found at the dentinoenamel junction (DEJ) and extend into the enamel, often being more prevelant at the cusp tips. They are formed by entrapment of odontoblast processess between ameloblasts prior to and during amelogenesis so they cannot be found at the enamel surface protruding inward, as enamel lamellae are often located. Best seen in the LS

Front 23

Enamel Lamellae

Back 23

-Dark leaf like structures running in the LS from the enamel surface to the DEJ. May be confused with cracks but are said to develop in planes of tension.

Front 24

What are the features of the DEJ

Back 24

scalloped appearance with the concavity facing the surface of the tooth more pronounced in the cusps promoting cohesion between the enamel and the Dentine. Prismless enamel, tufts and spindles and dichotomous branching of dentinal tubules are also all found at the DEJ

Front 25

The aquired enamel pellicle

Back 25

defined as a structure which is a acellular and essentially bacteria free and is only deposited after eruption of teeth and the loss of the enamel cuticle

Front 26

dentine

Back 26

ablitity to keep growing
odontoblasts with single processthat lie in dentinal tubules
cel bodies lie alone pupal surface

Front 27

predentine

Back 27

organic matrix that is layed down first before mineral salts are deposited within it
usually one day before it gets mineralised

Front 28

Dentine Matrix

Back 28

glycosaminoglycans and collagen fibrils

Front 29

where are glycosaminoglycans present

Back 29

where calcification of dentine is occuring and where dentine is highly mineralised

Front 30

collagenous component of dentine

Back 30

forms supporting lattice work around and between dentinal tubules

Front 31

inorganic component of dentine

Back 31

hydroxyapitite crystals similar to that in cementum but smaller than those found in ename

Front 32

dentinal tubules

Back 32

small canal like spaces that are filled with tissue fluid and the processes of odontoblasts.
sigmoid shaped path

Front 33

odontoblastic processes

Back 33

cytoplasmic extensions start of thin at DEJ but get thicker at pupal surface 3microM
give of lateral branches along their coursewhich contact neighbouring processes

Front 34

dichotomous branching

Back 34

found at DEJ or CDJ caused by odontoblasts having 2 processes when they start laying down enamel
more common in root than coronal dentine

Front 35

periodontoblastic space

Back 35

space between the process and the surrounding mineralised material. contains glycosaminoglycans, tissue fluid, collagen fibrils

Front 36

peritubular dentine

Back 36

highly mineralised zone surrounding the tubule. layed down after intertubular dentine.
thicker at DEJ and CDJ where tubules are thinner

Front 37

intertubular dentine

Back 37

main body of dentine
layed down before peritubular dentine.
lots of collagen
amorphous substance

Front 38

mantle dentine

Back 38

first formed dentine that lies at the DEJ or CDJ

Front 39

primary dentine

Back 39

bulk of dentine that is layed down till root formation is complete

Front 40

secondary dentine

Back 40

formed after root finished
reduce the size of pulp cavity
tubules reduced and bens sharply at transition from primary to secondary

Front 41

Reparative / Tertiary Dentine

Back 41

Formed in respose to noxious stimuli such as caries, abrasion, cavity preparation or erosion.
Formed by differentiated cells from the pulp moving through the cell-free zone of weil and differentiating into odontoblasts
Tubules are sealed of at the top of the reparative dentine.

Front 42

dead tract

Back 42

reparative dentine seals of pulp leaving dentine empty or containg bacteria and therefore appear black in transmitted light and white in reflected light

Front 43

osteodentin

Back 43

When reparative dentine is laid down quickly the dentinal tubules are irregularly arranged and cells can become trapped within it that gives it an appearance similar to bone but the trapped cells are not thought to be functional

Front 44

reactionary Dentine

Back 44

Dentine laid down by pre-existing odontoblasts that survived the noxious stimuli

Front 45

Sclerotic / Transparent Dentine

Back 45

Tubules are completed occluded by deposition of calcium salts causing it to have the same refractive index as the intertubular dentine making it transparent.
May be due to aging especially in the roots or as a defensive reaction to seal of tubules (localised to beneath dead tracts)

Front 46

Interglobular Dentine

Back 46

Unmineralised or hypomineralised dentine that lies within calcified globules.
Calcified globules generally form in the coronal dentine where rapid mineralization occurs

Front 47

Granular Layer of Tomes

Back 47

A granular layer in the peripheral layer of the dentine close to the DEJ

Front 48

Incremental Lines of Von Ebner

Back 48

Run at right angles to tubules representing intervals of approx 5 days making them about 20µm in width

Front 49

Contour lines of Owen

Back 49

Accentuated incremental lines due to physiological disturbances similar to striae of Retzius

Front 50

Pulp chamber / cavity

Back 50

Composed of 1)structural 2)vascular 3)nervous component
Reduced occluso-cervically in size overtime due to secondary dentine
Can contain pulp stones or reparative dentine

Front 51

what is found in the structural component of the pulp composition

Back 51

Odontoblasts, osontoclasts, undifferentiated cells,fibroblasts, macrophages, collagen, reticular fibres

Front 52

what is the vascular composition of the pulp

Back 52

terminal arterioles, arterioles, capillaries, arterio-venous anastomoses, venules

Front 53

odontoclasts

Back 53

Resorb dental hard tissue such as in the deciduous tooth under pressure from erupting adult tooth or resorbing dentine under conditions of chronic inflammation

Front 54

how does the shape of odontoblasts relate to their activity and position within the pulp

Back 54

Active / roof and sides of pulp chamber= columnar
Medium activity / middle of root= cuboidal
Inactive / close to apex= flat and spindally

Front 55

undifferentiated cells

Back 55

Can differentiate into odontoblasts or fibroblasts
Close to and part of subodontoblastic zone

Front 56

reticular fibres

Back 56

Finer than collagen fibres and stain black with the silver impregnation technique (agyrophilic) due to polysaccharide component

Front 57

macrophages

Back 57

Sparse in the normal pulp but nurmerous in inflammatory sites

Front 58

odontoclasts

Back 58

Resorb dental hard tissue such as in the deciduous tooth under pressure from erupting adult tooth or resorbing dentine under conditions of chronic inflammation
Undifferentiated cells
Can differentiate into odontoblasts or fibroblasts
Close to and part of subodontoblastic zone

Front 59

Nerve innervation of blood vessels in pulp

Back 59

Innervated by vasomotor (vaso-constrict or dialate) fibres derived from autonomic ganglia

Front 60

Subodontoblastic plexus of rachkow

Back 60

unmyelinated nerve branches in the subodontoblastic region

Front 61

Subodontoblastic layer / Cell-free zone of weil

Back 61

Just below layer of odontoblast cell bodies
Contains cytoplasmic processes of cells and nerve endings arising from the plexus of Raschkow
This zone is inconspicuous during early dentinogenesis because it is through this zone that new odontoblasts are recruited

Front 62

Nerve innervation of the dentine

Back 62

1)Recurrent Fibre – plexus of Raschkow -> predentine -> plexus of Raschkow
2)Predentine Nerve Fibre - plexus of Raschkow -> predentine
3)Intratubular Nerve Fibre – Plexus of Raschkow -> dentinal tubule

Front 63

Nervous component of pulp

Back 63

Myelinated except in subodontoblastic zone
Subodontoblastic plexus of Raschkow or parietal plexus
2 types of nervous tissue unmyelinated and myelinated (said to be pain fibres)

Front 64

Nerve innervation of blood vessels in pulp

Back 64

Innervated by vasomotor (vaso-constrict or dialate) fibres derived from autonomic ganglia

Front 65

what does the periodontium consist of

Back 65

- cementum
- PDL
- alveolar bone
- part of the gingiva with the gingival fibres

Front 66

acellular cementum

Back 66

no cementocytes only cementoblasts on the surface
found nearest the CEJ

Front 67

cellular cementum

Back 67

cementocytes within lacunae + cementoblasts at surface
found more apically and can be thich at the apex or interradicularly
contributes to the continual erryption of the teeth
appears granular due to cementocytes in the lacunae

Front 68

what are the three tyes of CEJ's and their prevalence

Back 68

1. cementum overlaps enamel (60%)
2. edge to edge (30%)
3. dentine exposed (10%) can cause caries and hypersensitivity

Front 69

what do cementoblasts do

Back 69

lay down unmineralised matrix (cementoid)

Front 70

what are sharpeys fibres

Back 70

bundles of collagen fibres that insert into the cementum and into the bone
produced by fibroblasts of the PDL
cementoblasts add collagen fibres and mineralise around them to maintain good attachment

Front 71

what are extrinsic fibres

Back 71

sharpey's fibres produced by fibroblasts of the PDL

Front 72

what are intrinsic fibres

Back 72

collagen fibres produced by cementoblasts - less oriented