A laboratory investigation of orthodontic elastomeric chains.

The dimensions and force/extension characteristics of 13 commercially available orthodontic chain elastomeric materials are reported. The relationship between force and extension was not linear over the range investigated and there were two definite transition points in the curves. Over the first linear part of the curve the two-loop specimens had stiffness values from 0.9 to 1.6 N/mm. Stiffness fell as the number of loops increased so that four-loop chains produced 0.6-1.1 N/mm. One hundred per cent extension produced forces in the 4-5 N range for most specimens. It is suggested that an extension of between 50 and 70 per cent would provide the most satisfactory orthodontic force.