Orthodontic Biomechanics Flashcards

A force applied at a distance from the center of resistance of a tooth produces which type of movement?

Answer: Tipping combined with rotation

A single force offset from the center of resistance creates a moment, causing tipping (rotation) plus translation.

The center of resistance of a single-rooted tooth is generally located at what position along the root?

Answer: About 33–40% of the root length from the alveolar crest

For a single-rooted tooth, the center of resistance lies roughly one-third to two-fifths down the root from the alveolar crest.

What is the moment-to-force (M/F) ratio approximately required to produce pure translation (bodily movement) of a tooth?

Answer: 10:1

An M/F ratio of about 10:1 counteracts tipping and produces bodily (translational) tooth movement.

Increasing the M/F ratio beyond that needed for translation results in which movement?

Answer: Root movement (torque)

M/F ratios higher than ~10:1 (near 12:1) move the root more than the crown, producing root torque.

A couple is defined as:

Answer: Two equal and opposite non-collinear forces producing pure rotation

A couple consists of two equal, opposite, parallel forces that create pure rotation without net translation.

Which factor most directly determines the magnitude of the moment created by a force on a tooth?

Answer: Force magnitude times perpendicular distance to the center of resistance

Moment equals force multiplied by the perpendicular distance between the force line and the center of resistance.

Optimal orthodontic force for tooth movement is best described as:

Answer: Light continuous force that does not exceed capillary blood pressure

Light, continuous forces that avoid occluding the periodontal capillary blood supply produce efficient, safe movement.