Korean J Orthod.  1999 Oct;29(5):511-519.

Factors affecting force system of orthodontic loop spring

• Choy KC
• Kim KH
• Park YC

Abstract

The shape of orthodontic retraction spring was varied and force system of each case was obtained using numerical analysis and verified with spring tester. The factors for obtaining biomechanically efficient spring under anatomic limitation were suggested as follows. 1. M/F ratio increases and L/D rate decreases as loop height increases. 2. M/F ratio increases and L/D rate decreases as incorporating more wire above bending moment area. 3. M/F ratio decreases and L/D rate decrease as incorporating more wire above bending moment area. 4. M/F ratio can not be greater than spring height no matter how much wire is incorporated at the apex of the loop. 5. Additional moment is necessary to obtain enough M/F ratio for translation under anatomical limitation. 6. Additional moment should be incorporated at every part of the spring because M/F ratio and L/D rate decreases as horizontal spring length increases. 7. Material, cross section, and shape of the spring influence L/D rate, whereas M/F ratio is influenced by the shape of the spring independent from material and cross section.

Keyword

biomechanics; L/D rate; M/F ratio; retraction spring