Download On optimum orthodontic force theory as applied

On optimum orthodontic force theory as
applied to canine retraction
Robert
J. Nikolai,
Ph.D.*
St. Louis, MO.
T
he terms threshold, light, optimum, and heavy have become familiar
adjectives used to categorize the magnitudes of orthodontic
force, but their
meanings are not universally clear. Weinstein1 has reported that a 2-gram force
successfully displaced a premolar; this might be understood as being a threshold
value for the tipping of that tooth. Light and heavy forces are largely indicative
of the technique and appliances employ-ctl by the clinician in treating a case and
are actually more descriptive of the ranges of force magnitude rather than
specific force sizes. For a number of reasons, including variations in tooth size
and number of teeth affected by a given force, there can be no specific boundary
value between light and heavy force ranges. In the total range of orthodontic
force magnitudes, the very question of the exist,ence of optimum forces seems to
remain unresolved in the minds of many practitioners.
Introduction
The search for optimum force values in orthodontics was perhaps begun in
earnest by Scl~wartz.2 The theory of optimum forces was proposed by Storcy
and Smith,“, 4 and the advent of light-wire
appliance usage and light-force
mechanics is generally associated with their research and that of Bcgg.” In the
late 1950s and throughout
most of the sixties, there appeared writings of
prominent
orthodontic researchers which were supportive of the concept of
optimum forces.“-10 More recently, however, a number of clinical and experimental investigations have been reportctl in the literature in which the results
did not wholly agree with the optimum force theory and/or its corollaries (for
example, the differential force concept) as formulated to date.“-‘” These later
developments have motivated me to conduct a theoretical study in an atternpt to
contribute to the discussion from a somewhat different standpoint.
The optimum orthodontic force has been defined as that which produces a
*Professor,
290
Department
of
Orthodontics,
Saint
Louis
Univrrsity
Mrdic:~l
(“rnter.