Minimal Forces in Tooth Movement

Sam Weinstein

The popularity and efficiency of light forces (that is, forces of small magnitude) in orthodontics suggest an analysis of the minimal forces produced by certain areas of the oral musculature and their influence on tooth position.
The stiffness factor, or elastic index, of the cheek can give useful information on the resting force of this tissue against the buccal surface of the tooth.
A group of children had a mean stiffness factor of 0.8 Gm./mm. and a mean resting force of 4.89 Gm. in the premolar region.
Muscle forces of such low values as 1.68 Gm. above the resting force, if acting over a sufficient time, are capable of moving teeth.
Both resting force and stiffness of the cheek mass increase with age.
Both the amount of tooth movement and the rate of movement associated with such low force values are significantly smaller in young adults than in the adolescent group.
There seems to be a genetic factor implicit in both the resting force and the stiffness of cheek musculature in males.
When a tooth is moved by low-magnitude forces and the force is then removed, the rate of the initial displacement is significantly less than the reverse rate of return.
Masticatory forces produce a buccal tipping tendency on the lower premolar and contribute to this tooth's position of equilibrium.