Bonded Orthodontic Retainers: A Comparison of Initial Bond Strength of Different Wire-and-Composite Combinations

Objectives: The aim of this in-vitro study was to evaluate initial bond strength in Newton (N) of two types of wires (Ortho-Flextech (TM) chain and Penta-One (TM) Coaxial wire 0.0215") bonded with three lingual retainer composites (FlowTain (TM), Light Cure Retainer (TM) and Transbond (TM) LR). Materials and Methods: One hundred and eighty sound, extracted human premolars were randomly divided into six equal groups. One of the two types of lingual retainer wires was bonded with one of the three types of the composite material in each group. Initial bond strength was measured using an Instron universal testing machine. We also evaluated the failure characteristics after failure at maximum load using an optical microscope. Results: Our findings demonstrated that the Coaxial/Transbond (TM) LR group was statistically significantly stronger than the other combinations. Statistically, 0.0215" Coaxial wire provided significantly stronger bond strength than Ortho-Flextech (TM) chain, and when the three composite systems were compared, Transbond (TM) LR revealed significantly higher bond strength than the others. However, Transbond (TM) LR left significantly more resin on the enamel surface after bond failure. Conclusion: Significant differences exist between different combinations of wires and lingual retainer composites; however, all the wire-and-composite combinations we tested possess sufficient bond strength for clinical application.