Objective

For all leading brands, evaluate force decay, dimensional change and permanent deformation of molded elastomeric ligatures in a simulated oral environment.

Methodology

Initial wall thickness, inside diameter, outside diameter, and force levels of each ligature were measured. Three of four test groups of ligatures were stretched over stainless steel dowels with a circumference approximating that of a large orthodontic twin bracket. Test group one was kept at room temperature and humidity for 28 days and test groups two to four in synthetic saliva baths at 37°C, pH 6.84. The residual forces and dimensional changes were measured. Force levels were tested at 28 days for test group two and at 24 hours, 7 days, 14 days, and 28 days for test group three. The fourth test group of unstretched samples was measured to evaluate dimensional changes due solely to moisture absorption at 28 days.

Results

Elastomeric ligatures deform permanently when stretched, and within just 24 hours exhibit force loss of up to 68%.

Permanent Deformation of Elastomeric Ligatures

Permanent Deformation of Elastomeric Ligatures

Conclusion

The rapid force loss and permanent deformation of these products may preclude their use for rotational and torque corrections.