DOI: 10.2478/aoj-2006-0011 ISSN: 2207-7480

An investigation of the forces used by clinicians to open spaces with coil springs

Gregor Steinbach, David Armstrong, Om P. Kharbanda, Peter Petocz, M. Ali Darendeliler
  • Orthodontics



To determine the forces applied by coil springs used to open spaces for blocked out lateral incisors, and to compare the actual forces used with clinicans’ concepts of an ‘ideal’ force.


Twelve postgraduate orthodontic students (7M, 5F) and 12 orthodontic tutors (9M, 3F) participated in this study. They were asked to state what they considered was an ideal orthodontic force, and then to cut appropriate lengths of stainless steel and nickel titanium open coil springs to open spaces for blocked out maxillary and mandibular permanent lateral incisors on a typodont set-up. The forces generated by the open coil springs were measured and compared to the stated ideal forces.


The mean ideal force was 76.75 g (Range: 25–200 g). The mean applied force was 314 g (Range: 21–519 g).

There were no significant differences in the forces used by the male and female postgraduates, but the male tutors used a significantly higher force than the male postgraduate students (p = 0.007) and the female tutors (p < 0.001). The female tutors used a significantly lower force than the female postgraduates (p = 0.024) and the male postgraduates (p = 0.003).

Higher forces were produced by the stainless steel coil springs in both arches (Maxillary arch: p = 0.007; Mandibular arch: p < 0.005).


The clinicians could not agree on an ideal force to open spaces for blocked out lateral incisors. There were substantial differences between the forces applied by the coil springs and the forces considered by the clinicians to be ideal. There were large differences in the forces used by the different groups of orthodontists.

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