Lecture 8 Flashcards
What is it called when a load is applied to an object that will tend to move it to a different position in space?
force
point at which resistance to movement can be concentrated for math analysis.
Center of Resistance
*For an object in free space, the center of resistance is in the same as the center of mass
Where is the center of resistance when a tooth root is embedded in bone?
half way between the root apex and the crest of the alveolar bone
A measure of the tendency of a force to rotate an object around some piont
moment
what is a moment generated by?
a force acting at a distance to the center of the resistance
what is a couple?
two forces equal in magnitude and in opposite directions
*create spinning object
what is the center of rotation?
point where the rotation actually occurs
where is the center of resistance for a tooth?
approximately at midpoint of the embedded portion of the root
*technically at 6 tenths
where is the moment arm?
the perpendicular distance from the point of force application to the center of resistance
using a lingually directed force and a buccally directed force on the crown of a tooth is an example of what?
a couple
using an ortho bracket to place a couple force on the crown of a tooth is an example of what?
a couple
if the moment arm is small, the force must be _____
large to generate the necessary Mc
what determines the type of tooth movement?
ratio between the moment produced by the force applied and the counterbalancing moment produced by the couple
what determines where the center of the rotation will be on the tooth?
the moment couple ratios
what happens when there is no couple?
the tooth rotations around the center of resistance
*creates pure tipping movement
what is it called when the moment-to-force ratio increases and the center of rotation is displaced further and further apically, away from the center of resistance?
controlled tipping
loss of alveolar bone height moves the center of resistance closer to the apex or incisal edge?
closer to the apex
what is force times distance?
magnitude of tipping moment from force
what happens when the center of resistance moves apically?
the tipping moment produced by the force (Mf) increases because the moment arm is longer
what is required if root movement in someone with alveolar bone loss is the goal?
a fixed appliance
*almost impossible with braces or clear aligners
where is heavy pressure felt when moving teeth?
apex and crest of alveolar bone
*ZERO pressure at center of resistance
what is the optimal force to create rotational movement?
35-60 grams
a Hawley retainer with finger spring is capable of moving a tooth by which type of movement?
tipping
how does a hawley retainer work?
finger spring places a single force at a distance from the center of resistance…causing tipping at center of resistance
*what direction of incisal movement
what is it called when the PDL space is loaded uniformly from alveolar crest to apex?
translation
- rectangular diagram
- twice as much force needed compared to tipping
optimal force for translation?
70-120 grams
*twice as much force needed compared to tipping
what kind of tooth movement occurs when a force is concentrated over a small area at the apex?
Intrusion
what is the optimal force for intrusion?
10-20 grams
*very light!
optimal pressure for extrusion?
35-60 grams
what 2 things would an ideal spring do?
1-maintain the same amount of force regardless of distance
2-would be the most ideal force system for ortho tooth movement
*but real springs’ force decays as tooth moves away
What is a continuous force in ortho?
forces that are maintained between activations, even though force declines
what are interrupted forces?
forces drop to zero between activations
what are intermittent forces?
forces that fall to zero when a removable appliance is taken out, but resumes when its is reinserted.
*these forces also decay as tooth movement occurs
On a typical force deflection curve, what does the slope of the linear portion represent?
the wire stiffness
on a force-deflection curve, what does the range on the x axis represent?
permanent deformation
How do you calculate strength on a force-deflection curve?
range x stiffness
what is the proportional limit on a force-deflection curve?
the point where force on the wire is proportional to its deflection
what is spring-back?
The position the wire will return to after it’s deflected
what is the failure point on a force-deflection curve?
point where the wire breaks
the major elastic properties of an ortho wire are affected by what 2 things?
1-length
2-cross section of wire
4 points about stainless steal wires
1-strong
2-stiff
3-formable
routinely used for years
3 points about chromium alloys wires
hint: compare to stainless steel
1-softer than stainless steal
2-more formable (because softer)
3-can be heat treated to make it harder
4 things about Ni-Ti alloy wires
1-very useful in initial ortho
2-light force over large range
3-shape memory and superelasticity
4-poor formability
3 things about beta-titanium wires
1-great strength/springiness combo
2-good formability
3-between SS and NiTi
what are the 2 bracket slot size dimensions?
1- .022 in (.55mm)
2- .018 in (.45mm)
each bracket has what 3 things prescribed?
1-torque
2-angulation
3-offset
what is a Begg bracket?
narrow slot for loose fitted wire. Held with locking pin
what is an edgewise appliance system?
most common. rectangular archwire
*gets teeth in the ball park
in the edgewise straight wire theory, what is the labio-lingual direction?
- lingual max incisors and canines should be level
- buccal mand incisors and canines should be level
What is indirect bonding of brackets?
fabrication of a splint on a model which contains the brackets
5 advantages to indirect bracket bonding
1-place brackets all at once 2-reduct chair time 3-more precise location 4- control thickness of resin 5-can be delegated to staff
2 disadvantages to indirect bracket bonding
1-technique sensitive
2-Clean up of excess bond can be difficult
3 advantages to direct bracket bonding
1-don’t have to make a splint2
2-don’t have errors on splint placement
3-easy excess bond cleanup
2 disadvantages to direct bonding
1-longer chair time
2-some brackets difficult to place
class 1 elastics
vertical direction, no ant. post. forces
class 2 elastics
Anterior maxillary teeth to posterior mandibular teeth
class 3 elastics
lingual of maxillary teeth to buccal of mand teeth
what is anchorage?
resistance to unwanted tooth movement
what is traction?
used to create space
*headgear to distalize tooth
T/F reciprocal effects though the dental arches must be analyzed, evaluated, and controlled?
true
T/F a major part of tx planning is maximizing desired movement and minimizing undesirable movement
True
What is the goal of anchorage?
concentrate movement on desired tooth, while keeping pressure off PDL of anchored tooth
how do you determine anchorage value?
roughly the root surface area
example of reciprocal tooth movement?
pulling 8 and 9 together to close diastema.
equal force on each tooth
what is reinforced anchorage?
adding additional teeth to the unit ti distribute force over larger root surface area
what are the 4 possible places for skeletal anchorage?
1-palate
2-head or neck
3-cortical anchorage
4-temporary anchorage (implants)
What is the shortest space of time ortho appliances can be reactivated?
3 week intervals
how much time does undermining resorption requrie?
7-14 days
*longer for PDL
average bone loss during ortho
less than .5mm
*rarely exceeds 1mm
T/F biologic width changes when a tooth in intruded or extruded with ortho?
false, it stays the same
T/F there in increased mobility in ortho patients?
true
- thickened ligament
- will go away when force does
T/F all patients will feel pain when ortho force is applied
False
- pain my last 2-4 days
- some say to chew gum
T/F ortho can cause pulpitis
true
*may contribute to pain
Ortho has more to do with pulp or PDL?
PLD
*endo teeth can be treated normally
category 1 root resorption
slight blunting
cat. 2 root resorption
moderate resorption, up to 1/4 root length
cat. 3 root reorption
sever resorption, greater than 1/4 root length
over ____% max incisors and over ________ of al teeth show some loss of root length form ortho
90, half
*length is clinically insignificant
what percent of ortho patients will have moderate to severe root resorption?
3% adolescence, 4% adults
what 2 things have studies indicated might cause root resorption?
1-hyalinization
2-sterile necrosis
What is worse for root resorption, continuous or intermittent forces?
continuous
T/F root resorption continues after ortho tx
false
*unless you continually use a retainer
what are the 4 variables to root resorption?
1-pre-tx resorption is visable
2-duration of ortho tx
3-premolar extraction cases
4-family history of root resorption
T/F genetic screening in the future may help id px who are predisposed to resorption?
True
Generally speaking, does more force=more root resorption?
yes
many adverse effects of ortho are caused by what?
poor patient compliance
what 4 things must ortho pxs do to cair for teeth and gums?
1-proper brushing and flossing
2-reduce sugar
3-quickly report any loose brackets
4-dental visits every 3-6 months
what 3 other things must an ortho px do to be considered compliant?
1-wear headgear and/or elastics
2-stop tongue and finger habits
3-keep appointments
Proseal is an example of a fluoride releasing sealant that is placed around brackets to prevent decay. Does it work?
NO! Prophylactic sealing did not significantly reduce decalcification
