ANCHORAGE / ELASTIC MATERIALS / THE PRODUCTION OF ORTHODONTIC FORCE

anchorage

resistance to unwanted tooth movement

examples of anchorage

palate

other teeth

TADS — screwed into the jaws

head or neck — extra-oral anchorage

anchorage value

roughly equivalent to its root surface area

example of anchorage situations

reciprocal tooth movement

reinforced anchorage

stationary anchorage

cortical & skeletal anchorage

reciprocal tooth movement

2 equal anchorage value teeth or groups of teeth (units) are moved against each other and move the SAME AMOUNT towards or away from each other

reinforced anchorage

adding additional teeth to a unit to distribute the force over a greater area and slowing the movement of the anchor unit

stationary anchorage

can be obtained by pitting bodily movement of one group of teeth against tipping of another

implants under cortical & skeletal anchorage

implants for anchorage TADS

implants for anchorage bone plates

implants for anchorage palatal implants

basic properties of elastic materials

stress

strain

strength

stiffness

range

deflection

elastic limit

proportional limit

yield strength

ultimate tensile strength

springback

resilience

formability

austenite

martensite

deformation

stress

internal distributon of load

strain

internal distortion produced by the load

strength

ability to withstand an applied force without breaking

stiffness

resistance to deformation under an applied force

range

the distance that the wire will bend elastically before permanent deformation occurs

deflection

amount of deformation that happens to the material when force is applied

elastic limit

the point at which any permanent deformation is first observed

proportional limit

can still go back to its original form

the highest point where stress & strain still have a linear relationship

yield strength

when the wire reach this point, the wire will not return to its original shape

ultimate tensile strength

maximum load the wire can sustain

between yield point & point of arbitrary clinical loading

the range the wire can still stretch but it will no longer go back to its original form

beyond point of arbitrary clinical loading

the failure point

meaning the wire will break

springback

the ability of the wire to go through large deflections without being permanently deformed

resilience

energy storage capacity of the wire

formability

amount of permanent deformation that a wire can withstand before failing

austenite

FCC structure

forms at high temperatures

softer and is non-magnetic

martensite

BCT structure

hard & brittle and is magnetic

forms at low temperatures through rapid cooling

deformation

the change in shape or length of the orthodontic wire or appliance as a response to the applied force

hooke’s law

the linear relationship that the stress & strain have

the stress and strain up until proportional limit still is parallel

formula of hooke’s law

F=−k⋅ΔL

3 chains of wires

round

square

rectangular

size of round wires

0.012 - 0.014 - 0.016

size of square wires

0.016 × 0.016

size of rectangular wires

0.025

0.017

0.028

4 properties of an ideal wire

high range

low stiffness

high strength

high formability

— weldable / solderable & reasonable cost

orthodontic archwire materials

beta-titanium

nickel-titanium

stainless-steel wires

chromium-cobalt alloy

precious metals

used in the first half of the 20th century

ex:

gold

platinum

palladium

stainless-steel wires

18% chromium – 8% nickel

better strength and springiness with equivalent corrosion resistance

are offered in a range of partially annealed states, in which yield strength is progressively enhanced at the cost of formability

chromium-cobalt alloy

40% Cobalt – 20% Chromium

can be supplied in a softer and more formable state

wires can be hardened by heat treatment after being shaped (heat treatment)

nickel-titanium

55% nickel – 45% titanium

memory wires

austenitic martensitic

have an exceptional ability to deliver light force over a large range of activation

beta-titanium

79% titanium – 11% molybdenum

offers a highly desirable combination of strength and springiness, reasonably good formability

brackets

small orthodontic attachments (metal or ceramic) secured to a tooth for fastening an arch wire

anatomy of brackets

base

wings

horizontal slot

horizontal slot

this is where the wire is positioned

base

this is where the wings are attached

where attaching orthodontics cement are attached

vertical scribe

a vertical line found between the 2 tie-wing to help position the bracket the same as the long axis of the tooth

identifying mark

these colors are always found on the distogingival wing

edgewise

made in 1925

conventional edgewise

single or double tie-wings

most commonly used orthodontic appliance

0.022 x 0.028

slot size of edgewise

1st order

in & out bends

facial, lingual & rotational — the movement that will be achieved

2nd order

tip bends

mesial & distal — the movement that will be achieved

3rd order

this is where torque will be applied

tipping but looking from the side (mesial & distal)

pre-adjusted edgewise appliance

aka: contemporary / straightwire appliance

the 3 order bends are incorporated in the bracket — tip & the torque of the bracket is already present

prescription bracket

refers to the specific design and angulation built into an orthodontic bracket

this determines how the bracket positions and moves teeth when combined with orthodontic wires

major bracket systems

tip-edge

edgewise

begg system

self-ligating system

straightwire appliance

edgewise

bracket base & bracket slot are always at a 90° angle

straightwire appliance

first prescription bracket

begg system

round wires

“pins” for retention

tip-edge

combination of straight-twire system and BEGG system

self-ligating system

straightwire

lock is built in the bracket

class 1 elastics

intra-arch

horizontal elastics

used in closing spaces

attached to the canine towards the mx 1st or 2nd molar

class 2 elastics

inter-arch

for class 2 cases

attached from right quadrant maxi #13 towards mandi #46

class 3 elastics

for class 3 cases

inter-arch