Color stability of laboratory glass-fiber-reinforced plastics for esthetic orthodontic wires

OBJECTIVE: In our previous study, glass-fiber-reinforced plastics (GFRPs) made from polycarbonate and glass fibers were prepared for esthetic orthodontic wires using pultrusion. These laboratory GFRP wires are more transparent than the commercially available nickel-titanium wire; however, an investigation of the color stability of GFRP during orthodontic treatment is needed. Accordingly, in the present study, the color stability of GFRP was assessed using colorimetry. METHODS: Preparation of GFRP esthetic round wires (diameter: 0.45 mm [0.018 inch]) using pultrusion was described previously. Here, to investigate how the diameter of fiber reinforcement affects color stability, GFRPs were prepared by incorporating either 13-µm (GFRP-13) or 7-µm glass (GFRP-7) fibers. The color changes of GFRPs after 24 h, and following 1, 2, and 4 weeks of coffee immersion at 37℃, were measured by colorimetry. We evaluated the color stability of GFRPs by two evaluating units: the color difference (ΔE(*)) and National Bureau of Standards (NBS). RESULTS: After immersion, both GFRPs showed almost no visible color change. According to the colorimetry measurements, the ΔE(*) values of GFRP-13 and GFRP-7 were 0.73-1.16, and 0.62-1.10, respectively. In accordance with NBS units, both GFRPs showed "slight" color changes. As a result, there were no significant differences in the ΔE(*) values or NBS units for GFRP-13 or GFRP-7. Moreover, for both GFRPs, no significant differences were observed in any of the immersion periods. CONCLUSIONS: Our findings suggest that the GFRPs will maintain high color stability during orthodontic treatment, and are an attractive prospect as esthetic orthodontic wires.