#5 Arch wire, biomechanics, appliances Flashcards
T/F the thickness or diameter of the arch wire will change the force/deflection curve.
Truth
What’s the difference between the stress/strain curve and the force/deflection curve?
The stress/strain curve has plastic deformation until breaking point with no springbuck. The force/deflection curve has a springbuck range
The stiffness measured by an F/D curve is called _____ stiffness.
Extrinsic
The stiffness measured by an S/S curve is called _____ stiffness.
Intrinsic
What is spring back?
The ability to return to the original shape (clinically useful springbuck can be beyond the elastic limit)
What is range (concerning arch wires)?
The distance a wire can be bent elastically before permanent deformation occurs
What is formability?
It is the amount of permanent deformation a wire can withstand before failure
What is the effect of tying an arch wire tightly to the brackets?
It increases its strength, but decreases both springiness and range
What does adding loops to an arch wire do?
It increases length, which increases its range and springiness
What are the characteristics of NiTi wires?
Low stiffness, good strength, high range, but very poor formability
What kind of wire would you use for initial alignment?
Small size NiTi or stainless steel (but only stainless steel if formability of AW is needed)
What kind of wire would you use for leveling?
Relatively large size TMA or stainless steel archwire
For torquing, what kind of arch wire would you use?
Large size rectangular stainless steel or TMA (Titanium molybdenum Alloy)
What is the initial slope of the F/D or S/S curve?
It is the stiffness
For the purpose of finishing, which wire would you use?
stainless steel or TMA- the size can vary depending on the purpose
Springiness is defined as _______.
1/stiffness
What is the center of resistance?
It is the point at which resistance to movement can be concentrated for mathematical analysis.
For a free object the center of resistance is the center of gravity.
For a normal tooth, where is the center of resistance?
Well it’s not the center of gravity because the tooth is partially in bone, so the center of resistance is at about the midpoint of the embedded portion of the root- halfway between the apex and the alveolar crest
Does the center of resistance of a tooth vary with orthodontic force?
Nope
What happens to the center of resistance of the root resorbs slightly? What about alveolar bone loss?
Root resorption- center of resistance moves coronally
Alveolar bone loss- center of resistance moves apically
What is the resultant force?
It is the combination of two forces
What happens if the line of action of a force doesn’t pass through the center of resistance?
The force will cause the tooth to rotate. The potential for rotation is measured as the moment
The center of resistance is found where on a normal tooth?
Looking at the embedded portion of the tooth only, about the midpoint of that.
A moment is what?
The magnitude of a force measured in gram millimeters . It’s either clockwise or counterclockwise
What is an orthodontic couple?
two forces of equal magnitude, parallel and collinear in the opposite direction
What does a couple cause?
Pure rotation
What kind of movement does a single force that doesn’t pass through the center of resistance produce?
rotation and translation, unlike a couple, which causes purely rotational movement
What is the center of rotation?
It is the point around which an object is rotating
Is the center of rotation a fixed point? Is this the same case for the center of resistance?
Nope, it can changed based on where the force is hitting the tooth.
This is different than the center of resistance, which is fixed
What are the three types of orthodontic tooth movement?
Translation
Pure rotation
A combination of the two
What needs to happen to produce translation only?
The line of action of a single force needs to pass through the center of resistance
T/F, it is the line of action, rather than the point of attachment determines whether or not translation if produced?
True
If you’ve got a force not passing through the center of resistance, can you cancel that moment out in order to produce translation instead of rotation only?
Indeed you can. This would then be called a couple because you’d have to cancel the rotational force out
When the line of action of a single force doesn’t pass through the center or resistance, tipping results. What are the two components of a tipping movement?
Translation and rotation
For the following, where is the center of rotation? Translation: Uncontrolled tipping: Controlled tipping: Pure rotation (couple):
Translation: infinity
Uncontrolled tipping: slightly apical to the center of resistance
Controlled tipping: at the apex
Pure rotation (couple): at the center of resistance
When a simple* tipping force is applied to the crown of a single-rooted tooth, the center of rotation is usually located where?
- at the apex? - at the cervical line? - 5mm. beyond the apex? - one-third root length from the apex? - two-thirds root length from the apex?
1/3 the root length from the apex
How do you calculate a moment?
Calculate the force (IE 200 grams) and then measure the number of millimeters from the the line of action to the center of resistance (IE 10 mm) in a perpendicular manner. The moment would be 2000 gram millimeters.
What are some advantages of removable appliances? Disadvantages?
It’s removable and therefore can be more esthetic and more hygienic
Disadvantages- involves lab work, less precise, and you have to rely on the patient to actually wear them
What is a bionator?
It stimulates mandibular growth and controls tooth eruption
What is a twin block?
Stimulates mandibular growth
Frankle appliances are tissue born appliances.
Indeed it is. These are basically useless and not in use anymore
Face mask and reverse pull head gear is for what purpose?
It is for preadolescent (6-8 years old) patients with maxillary deficiency
What are bite planes?
IE for someone who has a really deep bite you’d put a bunch of acrylic where your incisors contact. This allows your molars and premolars to erupt some more to improve the deep/over bite
What kind of wires are necessary for producing torque?
Rectangular ones
1st order bend is in and out
2nd order bend is up and down
3rd order bend is torque- twisting the tooth
indeed, these are all correct
The downside of the standard edgewise technique (the old school method) is
lacks a prescription for each tooth
Class II patient uses class II rubber bands. Class III rubber bands for a class III patient
it makes sense
The open coil spring is for opening space
the open coil spring is where the coils aren’t touching, there are spaces between them
