Abstract
Abstract
Objectives: Vacuum-formed retainers (VFRs) are commonly used for orthodontic retention. Some patients use their VFRs for tooth whitening, but the presence of whitening agents may potentially affect the biomechanical properties of VFRs. The aims of this study were: (1) To investigate the effect of tooth whitening (10% carbamide peroxide) on the biomechanical properties of VFRs, and (2) To evaluate the change in tooth colour when using VFRs as the whitening tray.
Methods: Using a split-mouth, randomised controlled trial design, thirty participants were randomly allocated to receive whitening of either the upper or the lower arch using 10% carbamide peroxide for two weeks. Biomechanical properties (hardness, tensile strength, and surface roughness) and tooth colour change were assessed two weeks after whitening was completed.
Results: Tensile strength of VFRs in the whitening arch (mean ± standard deviation = 40.93 ± 3.96 MPa) was significantly lower than that of the control arches (47.40 ± 5.03 MPa) (difference 6.47 MPa, 95% CI 4.51–8.42, p < 0.001). The hardness and internal roughness of VFRs in the whitening arch (VHN = 14.63 ± 2.29 N/mm2 and Ra = 1.33 ± 0.35 µm, respectively) were significantly greater than those of the control (VHN = 12.22 ± 1.86 N/mm2 and Ra = 0.96 ± 0.29 µm, respectively) (differences 2.41 N/mm2, 95% CI 1.56–3.25, p < 0.001 and 0.37 µm, 95% CI 0.23–0.51, p < 0.001, respectively). The whitening arch showed greater tooth colour change (ΔE = 6.00 ± 3.32) than the control (ΔE = 2.50 ± 1.70) (difference 3.49, 95% CI 2.43–4.56, p < 0.001) over the entire trial period.
Conclusions: Marked tooth colour change was achieved by whitening with VFRs as the whitening trays, but this changed the VFRs’ biomechanical properties, including a decrease in the tensile strength and increases in the hardness and internal roughness.