This document discusses the center of resistance and moment of force in orthodontics. It defines the center of resistance as the point through which a single force can be applied to a tooth to cause translation without rotation. The center of resistance is affected by the number of roots, amount of alveolar bone loss, and root resorption. Analytic studies show the center of resistance in single-rooted teeth with normal bone is 1/4 to 1/3 of the distance from the cementoenamel junction to the root apex. The moment of force is the tendency of a force to cause rotation, determined by multiplying the force magnitude by the perpendicular distance to the center of resistance. Understanding moment is important for effective appliance design

1. Presented By Dr. MUSTAFA HADDAD
MSD , MCU 1st Year , 1st Semester
Center of Resistance &
Moment

2. center of resistance.
- All objects have a center of mass.
- This is the point through which an applied
force must pass for a free object to move
linearly without any rotation,
- i.e., the center of mass is an object’s
“balance point.”

3. It is the point on the tooth when a single
force is passed through it, would bring about
its translation along the line of action of the
force
3

5. 5
• Factors affecting Centre of Resistance
1. Number of roots
2. Degree of Alveolar Bone loss
3. Degree of Root Resorption

7. analytic studies have determined that the
center of resistance for single rooted
teeth with normal alveolar bone levels is
about 1/4 to 1/3 the distance from the
cementenamel junction (CEJ) to the root
apex.

8. *as the orthodontic forces are delivered
through the tooth crown they will not
produce a pure linear movement ,, some
rotational movement will be present ,, those
rotational movements are called Moment of
the force .

9. *The moment of the force is the tendency for
a force to produce rotation.

10. *Its direction is found by following the line of
action around the center of resistance toward the
point of origin
*It is determined by multiplying the magnitude
of the force by the perpendicular distance of the
line of action to the center of resistance

11. * The importance of the moment of a force is often
not recognized in clinical orthodontics, but
awareness of it is needed to develop effective and
efficient appliance designs

13. Orthodontics Current Principles and
Techniques 5th ed. By THOMAS GRABER
Contemporary Orthodontics 4th & 5Th edition
by WILLIAM PROFITT