MECHANICAL CONCEPTS IN ORTHODONTICS Flashcards
load on an object causing it to move in direction of application
FORCE
→ Newtowns
→ grams or ounces
FORCE
balance point of a free body where all mass of an object is concentrated
CENTER OF GRAVITY OR MASS
point on the body where a single force (at this point) results in translation
CENTER OF RESISTANCE
pint through which an applied force must pass for an object (tooth) to move linearly without rotation
CENTER OF RESISTANCE
1-2 mm apical to the bifurcation along the long axis of the tooth
Multirooted Tooth
1⁄3 to 1⁄2 of the length of the root from the crest of the alveolar bone along the long axis of the tooth
Monorooted Tooth
point about which the object circles around a certain point
CENTER OF ROTATIO
T/f
CENTER OF ROTATION controlled with couple and force
T
used to create bodily movement
CENTER OF ROTATION
CENTER OF ROTATION location:
o at the center of resistance
o apical to it
o at the root apex
o infinity
product of force times the perpendicular distance from point of force application and center of resistance (Cres)
MOMENT
longer roots have center of resistance more ____ located
apically
unit of MOMENT
: gm-mm
force will tend to translate and rotate around the object around Cres
MOMENT
tendency for a force to produce rotation or tipping of a tooth
tendency to tilt or rotate
MOMENT
ortho tooth movement is not applied on the center of the rotation of the tooth but it is delivered through the crown
MOMENT OF THE FORCE (𝑀𝑓)
T/f
MOMENT OF THE FORCE (𝑀𝑓), not pure linear movement but some rotational movement (moment of the force) will be present
two equal, opposite, noncollinear but parallel forces separated at a distance
COUPLE
two forces equal in magnitude but opposite in direction and parallel to each other
COUPLE
T/f
overcome the moment WILL force applied to the crown
T
T/f
decrease the magnitude of the moment → apply force closer to the center of resistance
T
T/f
in orthodontics:
o impractical to apply the force directly to the root
o similar effect could be achieved by constructing a rigid attachment that projected upward from the crown
T
T/f
ROTATION requires a couple
T
Movement of tooth around its own center of resistance
Rotation
T/f
forces passing through the center of resistance do not produce a moment, because the distance to the center of resistance is zero; hence, the tooth does not rotate
T
A _____ archwire fitting into a rectangular
bracket slot on the tooth is most widely used because the entire force system can be produced with a single wire
rectangular
T/f
in orthodontics, equivalent force systems produce the same effect if the force system was placed at the center of resistance or at the crown (bracket/tube)
T
US wire dimensions: thousandths of an ____
European wire dimensions: in ____
inch
millimeters
COMMON TOOTH MOVEMENTS
Translation
Tipping (Uncontrolled)
Tipping (Controlled)
Torque
10 - 20 gms
35- 60 gms
50 - 100 gms
100- 150 gms
• Crown and root apex moves in the same distance and the same horizontal direction
• requires the most
orthodontics force to achieve
Translation
tooth moves in the same amount in the same direction
force through the center of resistance or through the whole alveolar bone surface
one area of tension and one area of pressure
TRANSLATION (BODILY MOVEMENT)
Movement of crown but root apex position is maintained
•Crot at root apex
Controlled Tipping
Root apex and crown move in opposite directions
•Crot below Cres (near each other)
Uncontrolled Tipping
• displacement of the tooth from the socket in the direction of eruption
• Only areas of tension
Extrusion
•movement into the socket along the long axis of the tooth
•difficult to accomplish
Intrusion
force is applied at the bracket and an even larger couple is applied to prevent tipping of the crown caused by the force
ROOT MOVEMENT (TORQUE)
