| Sumario: | Background & Objective: Fixed retainer success is reported to increase with passive adaptation of the retainer wire to the tooth surface, reducing saliva contamination during bonding. Flexible wires minimize bond failures by reducing stress concentration inside the bonding compound; therefore, the ideal fixed orthodontic retainer should be passive and semi-rigid. This in-vitro study aimed to evaluate the deflection load of different orthodontic fixed lingual retainers, and evaluate the bending properties of a chain type stainless steel fixed retainer comparing it with the other types. Materials & Methods: Five types of fixed bonded lingual retainers were flat metallic wire (FMW), round metallic wire (RMW), braided chain wire (BCW), and Fiber-reinforced composite with spot (SF) and full (FF) techniques were used to be tested. A three-point bending test was done at 0.1, 0.2, and 0.3 mm, and maximum deflection with an acrylic Frasaco mandibular model. These forces were measured using a Universal Instron testing machine. Results: The FF retainer showed significantly higher load deflection values than other retainer types at 0.1, 0.2, and 0.3 mm and at the maximum load deflection. On the other hand, there were no significant differences between the remaining types of fixed retainers, except for the significant differences between FMW and RMW, SF groups at 0.2 and 0.3 mm. Conclusion: The FMW retainer showed the lowest load deflection values, the BCW retainer would be an e xcellent choice for retaining tooth positionas it had an intermediate load deflection values compared with other retainer types; and the FF retainer had the largest values of load deflection.
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