Journal of Dental Research, Vol 73, 67-74, Copyright © 1994 by International & American Associations for Dental Research Online Journals
3-D force and moment analysis of repulsive magnetic appliances to correct dentofacial vertical excess
A. D. Vardimon, C. Bourauel, D. Drescher and G. P. Schmuth
Maurice and Gabriela Goldschleger School of Dental Medicine, Department of Orthodontics, Tel Aviv University, Israel.
Repulsive magnetic appliances can intrude posterior teeth, but create a
lateral shift of the mandible and also decrease in force as the mouth
opens. To model their optimal use, the 3-D spatial force/displacement (F/D)
and moment/displacement (M/D) diagrams of four magnetic repulsive
appliances in diverse overlapping arrangements were characterized and
compared. In this orthodontic measurement and simulation system, only the
medial eccentric magnetic arrangement, of the four compared, partially met
the criteria of an optimal repulsive force system, i.e., keeping a constant
intruding force and excluding shearing force. The moment analysis found
that eccentric arrangements, however, developed high Z-moment. Thus, a
perplexing point was reached where the force analysis favored medial
centric arrangement and the moment analysis favored centric arrangement.
When the gap between juxtaposed magnets increased over 2 mm, the repulsive
force declined and the attractive force was favorably eliminated. At gap
distances of 3 to 6 mm, the intrusive force was almost constant. These data
suggest that centric arrangement is indicated clinically when the gap is
minute and Muller prongs are used to prevent deleterious lateral shearing
forces.
