Investigation of force decay in aesthetic, fibre-reinforced composite orthodontic archwires

Summary Background/Objectives: Because polymer-based materials typically exhibit viscoelastic properties, the objective was to determine if commercially available, aesthetic, fibre-reinforced composite archwires maintain continuous forces without undergoing force decay when deflected continuously. Materials/Methods: Quasi force decay was evaluated by comparing three-point bending profiles of nickel-titanium (NiTi) and fibre-reinforced composite archwires (BioMers) prior to and after 30 days of continuous deflection of either 1 or 2mm. Paired t-tests or non-parametric signed rank tests were used to statistically compare pre- and post-deflection bending forces. A control group consisting of wires not subject to the 30-day constant deflection was tested to check whether the initial testing altered the second three-point bend test. Results: Significant (P < 0.01) differences in the pre- and post-deflection deactivation force delivery were most evident in the composite 2mm deflection group and all of the NiTi groups. The composite 2mm deflection group failed to deliver consistent forces as the majority of the wires experienced crazing during the 30-day deflection period. The decrease in force delivery in the NiTi groups may be attributed to the small standard deviations. Conclusions: The composite 1mm deflection group demonstrated that fibre-reinforced composite archwires are able to deliver a consistent force after 30 days of deflection. However, the clinical applicability of these fibre-reinforced composite archwires may be limited as they are unable to sustain deflections of 2mm without experiencing crazing and loss of force delivery. Limitations: Clinical efficacy of the aesthetic, fibre-reinforced composite orthodontic archwires remains to be observed.