| dc.description.abstract | Aims: To evaluate the force required to promote failure of fixed orthodontic retainers with different adhesive (composite) coverage; and to assess the presence and extent of force propagation with two different fixed orthodontic retainer wires. Methods: Retainer wires each of 15cm length was bonded on acrylic blocks with different adhesive surface diameters of 2mm, 3mm, 4mm, and 5mm. Two types of retainer wires were used namely, Ortho-FlexTechTM and Ortho-Care PerformTM coaxial (0.0175”). The prepared samples (n=160) were subjected to tensile pull-out test and the debonding force recorded. Fixed retainers using two different wires and 4-mm adhesive diameter were bonded on acrylic bases resembling the labial segment of a maxillary dental arch (n=72). The retainers were loaded in an occluso-apical direction until first sign of failure while being video-recorded. Individual frames of the video recordings were extracted every 0.2 second. Two video frames, each representing the start of load application and just before first sign of failure were compared, and their differences highlighted using an image comparison website. A force propagation scoring index was developed and used to quantify the extent of force propagation along a retainer wire when loaded. Results: An adhesive surface diameter of 4mm required the highest debonding force for both retainer wires with significant differences in comparison to 2mm (P=<0.001; 95% CI: 8.69, 21.69) and 3mm (P=0.026; 95% CI: 0.60, 13.59). The extent of force propagation was significantly increased in the Ortho-Care PerformTM coaxial wire. A greater degree of deformation was observed for Ortho-FlexTechTM prior to failure. Conclusion: On the basis of this laboratory-based assessment, consideration should be given to fabrication of fixed retainers using adhesive (composite) coverage of up to 4mm on each tooth. Force appears to be propagated more readily with Ortho-Care PerformTM than with a flexible chain alternative. This may risk stress accumulation at the terminal ends of the retainer wire with the potential for associated unwanted tooth movement. | en_US |
