Enamel And Cememtum

Front 1

Enamel

Back 1

Most highly mineralized tissue in the body

-acellular and avascular- unable to remodel or repair

Front 2

Enamel

Back 2

Thickest at cusp tips

Thinnest near junction of crown and root

Front 3

Components of enamel

Back 3

96% inorganic- composed of mineral called hydroxyapatite (crystallized calcium phosphate)

-4% water and organic matter (protein called enamelin

Front 4

Amelogenesis

Back 4

Enamel formation begins im late bell stage

Dentin deposited first

Then ameloblasts elongate and begin producing enamel

Front 5

Ameloblasts

Back 5

Columnar shaped with a secretory process at one end called a tome's process

Front 6

Tomes' process

Back 6

Shovel shaped & is responsible for the orientation of the enamel rods

Front 7

Ameloblasts

Back 7

Hexagonal in cross section

Front 8

2 stages of enamel formation

Back 8

1. Secretory stage

2. Resorbing stage

Front 9

Secretory stage

Back 9

Deposition of enamel matrix that contains both organic and inorganic material

Front 10

Resorbing stage

Back 10

Removal of most of the water and the organic matter

Front 11

Hydroxyapatite crystals

Back 11

Depositedd during the secretory stage

Very thin and needle like

As enamel matures, they grow in size

Front 12

Enamel crystals

Back 12

4 times larger than those in bone, dentin and cementum

Front 13

Enamel rods

Back 13

Enamel- composed of interlocking rods

Help resist masticatory forces and prevent fracture between the rods

Front 14

Enamel rods

Back 14

Extend from the DEJ to the outer enamel surface

Run perpendicular to the incisal surface

Front 15

Shape of enamel rods

Back 15

Key hole.

One key hole shaped rod is formed by 4 ameloblasts

Each ameloblasts (6 sided) contributed to 4 rods

Front 16

Enamel rods

Back 16

Appear wavy because of migratory path toward the periphery

Front 17

Hunter-schreger bands

Back 17

Alternating light and dark bands in the enamel due to configuration of the enamel rods

Run perpendicular to the DEJ

Extend about 2/3 of the way from the DEJ to the enamel surface

Front 18

Rod core

Back 18

Center of the enamel rod

Front 19

Rod sheath

Back 19

Around the periphery of the rod

-especially noticeable in the head region of the rod

Produced by a change in the angulation of the crystals formed as ameloblasts move

This resists demineralization more than the rod core

Front 20

Rodless enamel

Back 20

A structureless layer of enamel about 30 microns

Found on all deciduous teeth & 70% of permanent teeth

Found most commonly at the cervical areas of the enamel

Least commonly found over the cusp tips

Front 21

Gnarled enamel

Back 21

Enamel rods bend in exaggerated ways

Begins near the DEJ under the areas of the cusp tips

Front 22

Incremental lines

Back 22

A result in rhythmic deposition of enamel

End in small ridges on the tooth surface called perikymata

Front 23

Cross striations

Back 23

Daily apposition lines

Front 24

Striae of retzius

Back 24

More prominent growth lines

May reflect major interruptions in deposition of enamel

Front 25

Neonatal line

Back 25

A significant striae if retzius

Distinguishes prenatal enamel (fewer defects) from postnatal enamel

Front 26

Enamel spindles

Back 26

Single extension of odontoblast process into the enamel (shorter than tufts)

Front 27

Enamel tufts

Back 27

Hypomineralized inner ends of some enamel rods (defect in enamel) broader than spindles

Front 28

Enamel lamellae

Back 28

Cracks in the surface of the enamel visible to the eye

Extend from the DEJ to the surface of the enamel

Possible pathway for dental caries to spread

Front 29

Pits and fissures

Back 29

Form where ameloblasts become crowded between cusps

-causes incomplete maturation of enamel

More susceptible to caries due to hypocalcification

Front 30

Enamel etching

Back 30

Dilute acid is used to alter the surface of the enamel

Acid attacks the mineral at the periphery of the enamel rods & leaves a rough surface

Bonding material attached more firmly to roughened enamel area

Front 31

Enamel permeability

Back 31

Fluid, particles, and bacteria can pass through enamel by various pathways and can result in dental caries. These include:

- lamellae

- tufts

- cracks

- spindles

- pits and fissures

- spaces between crystals

Front 32

Tetracycline stain

Back 32

Appears as dark bands through enamel, especially near cervix of the tooth

Tetracycline does not affect enamel

Tetracycline binds to dentin and bone

Front 33

Darkened dentin

Back 33

Shows through the more translucent enamel, giving the tooth a darker appearance

-does not usually get good results with bleaching bc the source of the problem is in the dentin

Front 34

Cementum

Back 34

Mineralized connective tissue that covers roots of the teeth

Front 35

Cementum composed of

Back 35

Cells (cementoblasts, cementocytes)

Fibers (collagen)

Ground substance

Front 36

2 functions of cementum

Back 36

1. Seals the tubules of the dentin of the root

2. Serves as the attachment for the periodontal fibers that suspend the tooth in its socket

Front 37

Cementum

Back 37

Thinnest near the cervix of the tooth and thickest at the apex of the tooth

Continues to form throughout life

Less mineralized than enamel and dentin

Front 38

Cementum

Back 38

Lighter in color than dentin and softer than dentin

Has no nerves therefore is not sensitive

Front 39

Bone

Back 39

A vascular tissue (haversian canal, volkmanns canal) cementum is avascular

Front 40

Cementum

Back 40

Does not have nerves, bone has nerves

Both have cells in Lacunae and canaliculi

Front 41

Cementum

Back 41

Less mineralized than bone

Is more resistant to demineralization and resorption than bone

Both have incremental lines

Front 42

Cementogenesis

Back 42

After the crown forms, hertwig's epithelial root sheath is formed by joining of the OEE and the IEE

The sheath forms the outline of the root and induces formation of root dentin

Front 43

Bell stage

Back 43

Front 44

Hertwig's epithelial root sheath

Back 44

Front 45

Epithelial rests of mallasez

Back 45

The sheath degenerates and the remnants are this

Front 46

Dental follicle

Back 46

Cells from here differentiate into cementoblasts

They begin production of cementum on newly formed dentin

Front 47

3 types of cementum are formed

Back 47

1. Intermediate

2. Acellular

3. Cellular

Front 48

Intermediate cementum

Back 48

Thin, noncellular layer deposited by cells of inner epithelial root sheath

More calcified than the dentin or the adjacent cellular cementum

Front 49

Acellular cementum

Back 49

Deposited on the surface if the intermediate cementum

Formed from cementoblasts that originated as fibroblasts in the pdl

(Derived from the dental follicle)

Front 50

Acellular cementum

Back 50

Covers the cervical 1/2 of the root

No cells, does not increase after initial deposition

Forms at a slower rate than cellular cementum

Front 51

Cellular cementum

Back 51

Covers apical portion of the tooth

Much thicker layer

Contains cells (cementocytes)

Front 52

Cellular cementum

Back 52

Deposited throughout life

Deposited at intervals which produces arrest lines (highly calcified lines similar to those seen in bone)

Front 53

Cell types

Back 53

Cementoblasts, cementocytes, cementoclasts

Front 54

Cementoblasts

Back 54

Lay down cementoid (organic material) - becomes mineralized later

They become embedded in mineralized matrix as more cementoid is produced

They become enclosed in a Lacuna and become cementocytes

Front 55

Cementocytes

Back 55

Get their nutrients from the PDL via canaliculi

-(oriented towards the PDL)

Front 56

Cementoclasts

Back 56

Cells that actively resorb cementum

Associated with

-primary teeth

-trauma (caries, injury)

Front 57

Cementoenamel junction (CEJ)

Back 57

Point where cementum of root meets enamel of crown

Front 58

3 variations of CEJ

Back 58

1. O

2. M

3. G

Front 59

O

Back 59

Cementum overlaps the enamel slightly (60%)

Front 60

M

Back 60

Cementum meets the enamel (30%)

Front 61

G

Back 61

A small gap exists between the cementum and the enamel (10%)

Results in exposed dentin and possibly root sensitivity and increased susceptibility to decay

Front 62

Cementoenamel junction

Back 62

Front 63

Root resorption

Back 63

Can be a result of trauma

For example:

-traumatic occlusion

-rapid orthodontic tooth movement

-hypereruption due to loss of antagonist

Front 64

Cemental repair

Back 64

-new cementum can be deposited on top of an area with a defect

Reveral line- the point where resorption stops & deposition begins

Front 65

Hypercementosis

Back 65

-abnormal thickening of the cementum

-usually found in apical region

-tooth may fuse to surrounding bone

Hint 65

Front 66

Cementicles

Back 66

-calcified ovoid or round module

-may be free in the PDL, attached, or embedded in the cementum

-originate from epithelial cells

Front 67

Age related changes

Back 67

Increase in amount of cementum on the apical region usually occurs

Cementum resorption is a characteristic of aging

Root surface becomes more irregular with age due to continued resorption and deposition of cementum

More cementicles Are found in the elderly