Lecture 13 Dental Structures (copy)

at what week of gestation does tooth formation begin?

week 6

mesenchymal cell differentiation in developing jaws of embryo

upr/lwr jaw develop from max. and mand. processes of 1st pharyngeal arches respectively

stages of early tooth development

bud, cap, bell

dental lamina

growth from the oral epithelium that gives rise to the tooth buds

Thickened band of oral epithelium that follows the curve of each developing arch

beginning of tooth development

forms max and mand arch (at same time)

where are buds first seen?

along dental lamina; buds will eventually become teeth

bud stage

first stage to create each single tooth

the first stage of odontogenesis, initiation of the tooth begins

second stage of tooth development marked by growth of dental lamina into buds

bud

mesenchymal cells move towards bud

bud folds inward (leading to cap stage)

what is the beginning of the cap stage?

when the ingrowth is seen, proliferation of cells and the bud folds inward; beginning of dental structure formation

enamel organ

cap or bell-shaped part of tooth germ that produces enamel

part of a developing tooth destined to produce enamel

forms when the bud bends inwards

shifts/modifies shape for each tooth at bud stage

dental papilla

dental follicle

outer protection until tooth formation

basement membrane

separates papilla from enamel organ

inner enamel epithelium

outer enamel epithelium

enamel knot

stellate reticulum

cervical loupes

what 4 structures are all present in the bell stage?

outer enamel epithelium

stellate reticulum

enamel knot

inner enamel epithelium

cervical loupes

begin to form shape of tooth's crown as like a mold

enamel

dentin

at what stage is enamel and dentin formed?

late bell stage

mold forms --> then see enamel and dentin

what signifies the end of bell stage?

shape of each tooth is created; develops differently

shrinks enough to break away from dental lamina --> becomes own tooth

enamel

outermost layer of crown; protects entire tooth

cementum

along the root between teh CEJ and apex

amelogenesis

formation of enamel by ameloblasts

tome's process function

secrete enamel

what do ameloblast cells secrete?

hydroxyapatite- main mineral to form enamel and make layers

Tome's process

45º at cell edges

90º at cell center

creates rod/inter-rod formation

enamel formation looks like a honeycomb; daily growth

maturation stage

enamel fully calcified

secretes minerals and absorbs proteins

enamel hardens and is fully formed

during enamel formation, after teh cells elongate, what do the cells of the inner enamel epithelium differentiate into?

ameloblasts --> cells that form enamel

secretion/formation of enamel after the nucleus shifts to the upper part of cells

Tome's process

distal end of the ameloblast cells bend at 45º inclination at distal end of cell

secretes enamel

what is the function of the Tome's process?

secrete enamel

hydroxyapatite

main crystal to form enamel after calcification; secreted by ameloblasts

describe the structure of the Tome's process layers of enamel

creates layers of enamel

40º at cell edges

90º at cell center

angulation during hydroxyapatite crystals

forms rod/inter-rod enamel formation

enamel formation creates what greater shape?

honeycomb due to different-angulations of hydroyapatite

Stria of Retzius

Incremental lines of growth formed by ameloblasts

- Represent weekly changes in enamel formation

- Stria may also represent growth of the enamel organ

May be caused by incremental pattern of enamel secretion during tooth development

composition of enamel

inorganic 88%

organic 2%

water 10%

describe the arrangement of enamel rods

arranged parallel in a direction perpendicular to the dentin-enamel junction from dentin to the outer enamel surface

microstructure of enamel: inorganic

Enamel consists of hydroxyapatite crystallites 25 m thick, 100 m wide and 500-1000 nm long

Crystallites are arranged into 5 m diameter rods that are encapsulated by 1 um thick protein rich sheaths.

Enamel rods are arranged parallel in a direction perpendicular to the dentin-enamel junction from dentin to the outer enamel surface.

Within the rod units, the directional arrangement of the apatite crystallites varies. Crystallites in the central part of the rod are parallel to the rod axis while those near the edge of the rod usually have an angle of near 15°-45° to the longitudinal axis of the rods.

describe the arrangement of crystallites in the central part of the rod

parallel to the rod axis while those near the edge of the rod usually have an angle of near 15°-45° to the longitudinal axis of the rods.

what is the significant of rod edges beign 15-45º inclined to the longitudinal axis?

lessens enamel stress when eating

enamel rods

hold proteins and water

inter rod

enamel rods at 45º/15º perpendicular to others

microstructure of enamel: organic

.Enamel organic components consists of proteins and enzymes

• Proteins: Amelogenin, Ameloblastin, Enamelin, and Tuftlelin

• Enzymes: Mettaloproteinases (MMP), Proteinase, Phosphatase

proteins in organic matrix of enamel

Amelogenin, Ameloblastin, Enamelin, and Tuftlelin

enzymes in protein matrix of enamel

Mettaloproteinases (MMP), Proteinase, Phosphatase

what component of enamel regulates enamel growth?

organic proteins and enzymes

enamel thickness along the tooth

incisal 1/3 > middle 1/3 > cervical 1/3

Striae of Retzius

tooth growth in lines

incremental growth lines or bands seen in tooth enamel. They represent the incremental pattern of enamel, the successive apposition of different layers of enamel during crown formation

• identifies enamel growth

• enamel grows in layers/increments during crown formation

perikymata

external manifestation of the striae of Retzius showing as wavy transverse lines 30-100 microns apart

wavy transversal lines on external surface

enamel cross-striations

demarcate the amount of enamel deposited by ameloblasts in a single day. The average rate is approximately 4 um/day in humans.

The average distances between cross-striations in human teeth are about 2.5 um at the DEJ and 6.5 um at the enamel surface.

can calculate average growth rate for an individual

When tooth forms from DEJ to outer tooth surface --> closer together at DEJ, growth increases as move towards outer enamel surface

cross-striations

enamel rods

retzius line (purple lines)

outer enamel surface

enamel rods are // to each other when move from outer to inner surface enamel rods change direction into "S" or

wave shape --> decussation

decussation

wave shape of enamel these bands are seen in places of increased functional demand

Hunter-Schreger bands (HSB)

composes set of 10 or more layers of enamel rods

is related to the synchronous decussation of enamel rods in the horizontal plane and is probably caused by reflection of light by inter-prismatic material

are most concentrated in regions exposed to the greatest functional demand, such as the occlusal surfaces of posterior teeth for chewing and the surfaces of maxillary and mandibular canines for guiding mandibular movement

where are HSBs most commonly found?

most concentrated in regions exposed to the greatest functional demand, such as the occlusal surfaces of posterior teeth for chewing and the surfaces of maxillary and mandibular canines for guiding mandibular movement

area with more stress/occlusal contact has more HSB to protect the tooth

difference in inclination on areas with more stress

what is the name of the bands with different inclinations of enamle?

HSB

• difference in inclinations of enamel rods especially on areas with high stress

describe the change of rod arrangement as you move from outer to inner enamel

outer enamel has parallel enamel rods

enamel rods deviate from original parallel path as you move downward

inner enamel has decussation

outer enamel

enamel rods are mostly oriented parallel to each other and perpendicular to the DEJ

where is aprismatic enamel found?

in outer enamel

what area of enamel has the highest modulus of elasticity?

outer enamel

• very rigid, strong (tears food) bc of inclination of // enamel rods

• handles lots of occlusion

aprismatic enamel

outer enamel

ameloblasts secrete hydroxyapatite and in the last layer pack lots of hydroxyapaite and make the area dense

when ameloblasts secrete hydroxyapatite, area with densely packed hydroxyapatite but dont' have rod/inter-rod formation

inner enamel

Closer to the DEJ, the enamel rods decussate (wave pattern) in layers (or bands)

Area of enamel with lower modulus of elasticity compared to that of the outer enamel

• still rigid, out not as much as much as outer surface

Increased organic content

Contains enamel tufts

describe how enamel decussation prevents crack propagation

hard for crack to propagate if at 90º with enamel decussation

crack initiates here, enamel turns 90º so crack can't propagate

fracture/crack initiates between the // enamel, so the crack would fracture in half

enamel decussation

•Decussation: constitute a structural reinforcement of teeth

• Decussation is caused by crossing enamel rods bundle within alternating bands that follows a sinusoidal path

• Prevent crack propagation --> hard for crack to propagate if at 90º with enamel decussation; crack initiates here, enamel turns 90º so crack can't propagate

structural hierarchy of enamel

(levels of enamel protection)

enamel patterns

enamel types

• outer enamel // to each other

• inner enamel- decussation (strength)

multiple prisms

• enamel rods, rod/iner-rod formation

multiple crystallites

single crystallites

bridging

if crack is too strong and progresses to a different area enamel tries to prevent this

in addition to decussation what helps prevent a crack/fracture from propagating?

rod/inter-rod

where are enamel tufts located?

on inner enamel, extend outward from the DEJ

enamel tufts

Brush-like structures extending outward from the dentin enamel junction (DEJ).

They are hypomineralized regions containing increased residual enamel matrix proteins, thought to be due to changes in direction of adjacent enamel rods originating from different areas of the scalloped dentin enamel junction.

May assist in the resilience of enamel bc of amount of proteins

inner enamel has enamel decussation and protein-rich

or hypo-mineralized structures => enamel tufts

can be a problem if too long and reach enamel surface

enamel lamellae

Fissure-like linear enamel defects containing proteins proteoglycans, and lipids.

Enamel lamellae extends along the longitudinal axis of the tooth perpendicular to the dentin enamel junction.

fluorosis

too much F- exposure

competes with calcium from hydroxyapatite and form fluoroapatite which weakens enamel } all during tooth formation

dental fluorosis

Increased enamel porosity along the striae of Retzius.

Hypomineralized lesions that extend throughout the enamel.

Pits, bands, attrition, abrasion and loss of extensive areas occur post eruptively.

too much exposure to F- during tooth development

results in staining

possible to remove stains, minimally invasive

dentin > ? > enamel tufts > ?

(outer to inner)

dentin > DEJ > enamel tufts > inner enamel

amelogenesis imperfecta

Caused by mutations in the AMELX, ENAM, MMP20, and FAM83H genes.

can be treated minimally invasively

Types: Hypomaturation (defect in the final growth and development of the tooth enamel),

Hypocalcification (defect in the initial stage of enamel or tooth formation followed by defective tooth growth), and

Hypoplastic (defects in the amount of enamel)

types of amelogenesis imperfecta

Hypomaturation (defect in the final growth and development of the tooth enamel)

Hypocalcification (defect in the initial stage of enamel formation followed by defective tooth growth)

Hypoplastic (defects in the amount of enamel)

Hypomaturation

defect in the final growth and development of the tooth enamel

Hypocalcification

defect in the initial stage of enamel formation followed by defective tooth growth

Hypoplastic

defects in the amount of enamel

what is the majority of the tooth made of?

dentin

microstructure of DEJ

• The dentin-enamel junction (DEJ) unites two dissimilar calcified tissues: enamel and dentin

(even though they're made of the same thing)

• Three-dimensional scalloped appearance has concavity towards dentin with its convexities directed toward the dentin and concavities

directed toward the enamel.

• Scallop size: 30 um on incisors and 43 um on molars

• Prevent enamel cracks from propagating across the interface, thus preventing catastrophic tooth fractures

• absorbs stress, disipates load

what is the significance of the scalloped pattern of the DEJ?

helps the DEJ (mix of collagen, hydroxyapatite) absorb stressful loads

enamel has lower elasticity than dentin; more rigid, organized

dentin- dentinal tubules have more organic components

scalloping- small area of wave patterns that differentiates enamel and dentin

makes the dentin side of DEJ more elastic

composition of dentin

30% organic (collagen)

20% water

50% inorganic (hydroxyapatite)

microstructure of dentin: organic

Type I Collagen (90%; majority is Type I) (small amounts of Type IlI and Type V collagen are present - 1-3%)

• Non-collagenous components (10%): phosphorylated and non-phosphorylated proteins, proteoglycans, lipids, growth factors

• Proteins: Amelogenin, Osteonectin, Osteocalcin

• Enzymes: to control dentin growth; Matrix Mettaloproteinases (MMP-1, -2, -3, and -9), tissue inhibitors of metalloproteinases (TIMPS), Acid & alkaline phosphates

what is most of dentin?

30% is collagen (type I at 90%, type III and V are also present)

50% hydroxyapatite

microstructure of dentin: inorganic

Crystallites: 2-5 nm in thickness and 60m in length and randomly fill interfibrillar spaces

Intertubular crystallites have a needle like appearance. They are located either at the surface the collagen fibrils, and parallel with the collagen fibril axis.

what goes between collagen fibers?

hydroxyapatite

what is dentin a mix of?

collagen and hydroxyapatite

dentin consists of:

dentinal tubules

peritubular dentin

intertubular dentin

dentinal tubules

odontoblast cells --> living part of the tooth

(blue)

peritubular dentin

calcified, heavily densed dentin

protects dentinal tubule

(green)

intertubular dentin

less calcified dentin in between the peritubular dentin

(pink)

intertubular dentin

Collagen-rich dentin associate with proteins along and between the collagen fibrils (organic content 12%)

Hydroxyapatite crystallites of 2-5 pm and 60 nm long (inorganic content: 88%)

Hardness: near DEJ - 0.49 to 0.52 GPa and near pulp 0.12 to 0.18 GPa (becomes softer)

• less inorganic content closer to pulp

• more inorganic content closer to DEJ

is there more or less inorganic content closer to pulp?

less inorganic content closer to pulp

is there more or less inorganic content closer to DEJ?

more inorganic content closer to DEJ