Wire-composite Bond Strength of Bonded Retainers with Wire Surface Treatments

Objective: Bonded orthodontic retainers made of wires embedded in composite resin are commonly used in dentistry to secure orthodontically treated teeth. These retainers are usually prescribed for long-term use, and can be prone to bond failure at the wire-composite interface, resulting in relapse. The purpose of this study was to determine the effects of various wire surface treatments on the wire-composite bond strength in lingual bonded retainers. Methods: Three-inch lengths of 0.0175in co-axial stainless steel orthodontic wire were embedded in composite resin attached to 0.75x1.5in pieces of supporting plastic. Prior to embedment, wires were subjected to the following: 90-degree bend, microetching, silane treatment, metal primer treatment. Microetched and 90-degree bended wires also were given the silane and metal primer treatments. Following these procedures, the wires were bonded into a 2mm length of Transbond XL composite and soaked in water for 12 hours. The wires were subjected to tension in an Instron test machine until the wire was fully dislodged from the composite resin. Differences in dislodgement forces among groups were determined using t-tests. Results: Tests demonstrated that wires with a 90-degree bend required a much greater force (37.5±3.5lb) to break the wire-composite bond than control specimens (9.2±1.0lb) and wires with other surface treatments. Wires treated with a metal primer also required greater force (15.1±1.5lb) to break the attachment than the control wires, microetched wires, and wires treated with silane bond enhancer. Conclusion: These results indicate that co-axial stainless steel orthodontic wires treated with a 90-degree bend or a metal primer significantly increase attachment in lingual bonded retainers, with the 90-degree bend offering the greatest retention. These surface treatments may reduce the incidence of failure at the wire-composite interface, thus increasing the longevity of lingual retainers.