Biomechanics In Orthodontics Flashcards
What are Newton’s three laws of motion?
1) a body at rest remains at rest, and a body in motion continues to move in a straight line with constant speed unless and until an external unbalanced force acts upon it
2) The rate of change of momentum of a body is directly proportional to the impressed force and takes place in the direction which the force acts
3) whenever A exerts a force on B, B simultaneously exerts a force of the same magnitude and in the opposite direction on A. This can be stated simply as: “for every action, there is an equal and opposite reaction”
What is a vector in physics?
A concept characterized by a magnitude and a direction.
Force is a vector quantity defined as the rate of change of the momentum of the body that would be induced by that force acting alone.
Since momentum is a vector, the force has a direction associated with it
What is the difference between a vector and a scalar?
A vector has both magnitude and direction
A scalar only has magnitude
Orthodontic forces are describe by their ___, ___, and ___. The direction of the force is defined by the line of action and the sense (arrowhead). The magnitude of the force is detected by the length of the line using an arbitrary scale.
Magnitude
Point of application
Direction
Any force applied to a tooth can be broken up into its vertical and horizontal components using the ___ as the horizontal reference of an orthogonal coordinate system.
Occlusal plane
The center of resistance (or centroid) of a physical object coincides with its center of mass if….
If the object has uniform density, or if the objects shape and density are symmetric
In orthodontics, the center of resistance of a tooth is a point in the tooth at which a force application results in ___ movement
Translational
The center of resistance remains constant and is located about __-___ of the root length from the CEJ in a normally sized tooth and normal periodontium
1/3rd - 1/4th
What is the center of rotation in orthodontics?
Is it constant like the center of resistance?
The center of rotation of a tooth is the point around which the tooth rotates.
Unlike the center of resistance, the center of rotation is NOT constant and is determined by the type of movement that the tooth is undergoing. For example, in translational tooth movement, the center of rotation is located at an infinite distance from the center of resistance
What is controlled tipping?
Occurs when the net force on a tooth results in a center of rotation that is near the apex of the tooth.
This results in the crown moving in the direction of the force, but the root ripe moving minimally. Orthodontic treatment requires this type of tooth movement in many instances
What is the unit of moment of the force?
Nm (Newton meter)
Given the distance and force, you can calculate the moment of force placed on a tooth in three planes of space.
What is static equilibrium?
A rigid body is in equilibrium when the external forces acting on it form a system of forces and moments whose sum is equivalent to zero. an object in mechanical equilibrium is neither undergoing linear nor rotational acceleration; however, it could be translating or rotating at a constant velocity
How does the law of equilibrium apply to orthodontic appliances?
Application of force on one part of a system leads to an equal and opposite force on another part of the system. For example, extraoral appliances deliver active forces intraorally, while the reactive forces are extraoral. Another example is the intermaxillary elastics where the active and reactive forces are in the opposite arches. Similarly, the consolidation of spaces in interarch mechanics results in static equilibrium
What is a one-couple orthodontic force system?
A one-couple orthodontic force system results with an orthodontic appliance that has two points of action in the system, each with the capability to deliver a force, but only one of which generates a couple.
What is a two-couple orthodontic force system?
An orthodontic appliance that has two points of action in the system with capability deliver force at both points that result in separate couples at each of these sites is a two-couple orthodontic force.
