Biomechanics Flashcards
Define mechanics
The branch of physics that is concerned with the analysis of the action of forces on matter or material systems
Define biomechanics
- Application of mechanical principles on living organisms
- Includes research and analysis of the mechanics of living organisms and the application of engineering principles to and from biological systems
Define wire
Metallic strand stretched by tensile forces
Active use of orthodontic wires? (2)
- Archwires
- Coils or springs
Passive use of orthodontic wires? (3)
- Retention: adams clasp, ball clasp, arrowhead clasp
- Stabilization: labial wire spring (labial bow)
- Ligatures
What is an archwire?
Metallic strand shaped according to a diagram that reproduces ideal dental arch
form
What is Hooke’s law?
The displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions the object returns to its original shape and size upon removal of the load
What are the physical properties described in biomechanics? (6)
- Hooke’s law
- Springiness
- Stiffness
- Resilience
- Formability
- Range
Formula for Hooke’s law?
K=stress/strain
K- elastic modulus/young’s modulus
stress = force
strain = deflection
What is hooke’s law measured in?
Megapascals (MPa)
Formula for force?
F=K*Deflection
What happens if force is greater than deflection?
stiffness
What happens if deflection is greater than force?
Springiness
Define stiffness
The extent to which it resists deformation in response to an applied force
Define springiness (2)
- aka elasticity
- Property of materials which return to their original shape after they are deformed.
Define resilience
Energy storage capacity of the wire, which is a combination of strength and springiness
Define formability
Amount of permanent deformation that a wire can withstand before failing
Define deflection
If the wire is deflected beyond its yield strength, it will not return to its original
shape, but clinically useful springback will occur unless the failure point is reached.
Define range
Distance that the wire will bend elastically before permanent deformation occurs
Biocompatibility properties of an ideal wire? (3)
- Corrosion resistant
- Dental plaque
- Environmental stability
What are the types of forces? (3)
- Tensile (traction and compression)
- Torsion
- Bending
How can you classify wires? (3)
- cross-sectional shape
- size (cross sectional diameter)
- alloys
What are the cross-sectional wire shapes? (5)
- Round
- Multistrand
- Square
- Rectangular
- Others: Semicircular, oval
Convert mm to inches
multiply by 4 and divide by 100
Convert inches to mm
multiply by 100 divide by 4
What are the types of wire alloys? (4)
- Gold and precious metal
- Stainless steel
- Cobalt Chromium alloy
- Titanium alloys
What is the composition of stainless steel alloy wire? (4)
- iron and carbon alloy
- 18% chromium
- 8% nickel
Stainless steel martensitic? (3)
Body centered cubic
- stronger and more resistant
- instruments
Stainless steel austenitic A-300? (5)
Face centered cubic
- Springiness (Depends on diameter)
- formability
- good properties
- most used
Advantages of stainless steel wires? (6)
- Formability
- Reasonable degree of stiffness/springiness
- Low cost
- Low superficial friction
- Can be soldered and welded
- Corrosion resistant
Disadvantages of stainless steel wires? (4)
- High Young’s modulus
- Intense deactivation curve
- Nickel release
- Difficult clinical management
What is the composition of cobalt chromium alloy wires?
- 40% Co
- 20% Cr
- 15 % Ni
- Iron
- Mo (Molybdenum)
What is another name for cobalt chromium alloy wires?
Elgiloy
Cobalt chromium alloy wires are ______ stiff than stainless steel
less
Which wire type has the greatest formability?
cobalt chromium alloy wires
How many different grades with different properties do cobalt chromium alloy wires have?
4
Which cobalt chromium alloy wire can be soldered?
Blue eligiloy
How much are cobalt chromium alloy wires used?
little use
What are the different generations of titanium alloy wires? (4)
- Nitinol or M - NiTi
- Beta Titanium. TMA (Titanium Molybdenum alloy)
- A – NiTi
- Copper NiTi
What is NiTi composed of?
- 54% titanium
- 44% Nickel
What is the structure of NiTi? (3)
Two criystallographic structures
• Austenitic. Cubic crystal. Stable. “High temperatures”
• Martensitic. Monoclinic crystal,, hexagonal. Unstable. Low temp.
Austenitic of Ni Ti?
- Cubic crystal.
- Stable.
- “High temperatures”
Martensitic of Ni Ti?
- Monoclinic crystal
- Hexagonal
- Unstable
- Low temp
Phase transitions of NiTi in response to… ? (2)
- reasonable temperature
changes - applied force
NiTi elasticity? (2)
- Superelasticity
- Thermoelasticity
NiTi memory?
Shape
NiTi hookes law? (2)
Non-elastic force-defelction curve
don´t obey Hooke’s law
What happens when there is a phase transition from austenitic to martensitic? (5)
changes crystal’s structure, volume, shape and
properties WITHOUT atomic strain
How do wires change from austenitic to martensitic? (2)
In response to applied forces or cooling
How do wires change from martensitic to austenitic?
Martensitic phase is unstable so it returns to austenitic structure with the ideal dental arch form
What is shape memory?
Ability of the material to “remember” its original shape after being plastically deformed while in the martensitic form
What is superelasticity or pseudoelasticity?
Elastic (reversible) response to an applied stress, caused by a phase transformation between the austenitic and martensitic phases of a
crystal (fails Hooke’s law)
What is thermoelasticity?
Great “elastic” deflection that reverts in response to temperature changes
Look at slide 51/61
and figure out what its for
M-NiTi general characteristics? (5)
- Stabilized martensitic form
- No phase transition effects
- Great shape memory
- Much more springiness than stainless steel
- No formability
TMA general characterisitcs? (4)
- Titanium-molybdenum alloy
- Nickel free
- Formability-elasticity
(More springiness than stainless steel
Less formability than stainless steel) - Little use: Springs of some appliances (pendulum)
A-NiTi characterisitcs? (4)
- Not stabilized
- Phase transition in response to applied force
- Superelasticity
- Light, continuous, predictable forces
Copper NiTi (5)
- Thermoelasticity
- Copper allows control of transition temperature.
- From austenitic form to martensitic by cooling, without atomic strain.
- Rising temperature makes the wire return to austenite and ideal arch form.
- Austenite transition temperatures: 27, 35 y 40ºC
Deactivtation graphs
slide 56/57
Clinical characterisitcs of A-NiTi, Niti-Cu? (5)
- Light, continuous, constant, predictable forces
- Easy clinical management
- Shorter chair time
- More time between appointments
- Easy to get out of control. Iatrogenic
Formability of the types of titanium wires in order? (5)
- 1º Cr -Co
- 2º Acero
- 3º TMA
- 4º M- NiTi
- 5º A-NiTi
Springiness of the types of titanium wires in order? (5)
- 1º NiTi - Cu
- A-NiTi
- 2º M-NiTi
- 3ºTMA
- 4º Cr -Co
- 5º Acero
Effects of length and diameter on elastic properties?
The force needed to deflect a wire (stiffness) is directly proportional to the fourth power of diameter and inversely proportional to the third power of length
Formula for stiffness?
Stiffness = d^4
or
Stiffness = 1/(L^3)
Formula for springiness
Springiness = 1/(d^4) Springiness = L^3
Round wire? (2)
- Initial stages of treatment
- Crown alignment and leveling
Multistrand wire? (2)
- Initial stages of treatment
- Crown alignment and leveling
Square wire?
Harder to bend because there is more volume
Rectangular wire? (5)
- Used in final stages of orthodontic treatment
- Causes very small teeth movements
- ex. changes in inclination of roots
- Torque control
- Radicular movements
Rounded wire size 0.008-0.012
Ligatures (fragility)
Rounded wire size 0.012-0.020
Archs (springiness)
Rounded wire size 0.020-0.045
Auxiliary appliances (formability)
Rounded wire size 0.045-0.060
Intra/extra oral appliances (stiffness)
Multistrand wire size 0.015-0.021
Archs
Square wire size 0.016-0.018 x 0.016-0.018
Archs
Rectangular wire size 0.016-0.018 x 0.022
Archs - Bracket slot (0.018”)
Rectangular wire size 0.017-0.022 x 0.025
Archs - Bracket slot (0.018”)
