Nanomechanical properties, surface topography, and color stability of fiber-reinforced composite orthodontic retainers

The present study investigated the nanomechanical properties, surface topography, and color alterations of fiber-reinforced composite (FRC) orthodontic retainers. Two FRC orthodontic retainer materials (glass fiber reinforced (group 1) and polyethylene fiber reinforced (group 2)) were evaluated. Nanomechanical properties (nano-hardness and elastic modulus), surface roughness (Ra), and color stability of FRC retainers at baseline and after 2 years of simulated aging were evaluated. The data collected were analyzed using analyses of variance, followed by Tukey’s honestly significant difference test for post hoc comparisons at the significance level of p < 0.05. Group 1 specimens exhibited highest hardness (0.16 ± 0.06) and elastic modulus (2.68 ± 0.17) at baseline, and group 2 specimens showed lowest hardness (0.09 ± 0.16) and elastic modulus (2.19 ± 0.36) after aging. Significant difference in hardness and elastic modulus was observed between the groups at baseline and after aging (p < 0.05).The aged specimens demonstrated decreased hardness and elastic modulus values compared to baseline specimens, but the differences were not significant (p > 0.05). Group 2 specimens exhibited increased Ra at baseline (0.46 ± 0.79) and aging (0.84 ± 0.94), and the least Ra values were observed with group 1 specimens at baseline (0.31 ± 0.87) and aging (0.59 ± 0.65). There was a significant color alteration of the specimens from baseline to aging in both the groups (p < 0.05). However, group 1 specimens showed noticeable color change, and group 2 showed appreciable color change. Glass fiber-reinforced FRC orthodontic retainer exhibited superior properties compared to polyethylene fiber-reinforced FRC. Accelerated aging decreases surface hardness of the polymer matrix and increases Ra and discoloration of the FRC retainer materials.