Influence of a bleaching agent on surface and mechanical properties of orthodontic thermoplastic retainer materials : An in vitro study.

Objective: To investigate the effect of a tooth whitening agent on surface roughness, surface hardness, and force delivery properties of polyethylene terephthalate glycol (PETG) thermoplastic retainer materials of two different thicknesses.

Methods: PETG sheets (1 mm and 1.5 mm) were thermoformed over a 30 × 60 × 10 mm rectangular stone model. Surface hardness, surface roughness, and results of a three-point bending test were evaluated before and after treatment (5 h daily for 14 days) with a 15% carbamide peroxide home bleaching agent. Data were analyzed using an independent sample t‑test.

Results: Exposure of PETG specimens to the bleaching agent for 14 days significantly reduced surface hardness and increased surface roughness of samples of both thicknesses. The magnitude of force at different deflection points decreased significantly in the 1.5 mm thickness specimens treated with the bleaching agent, but no significant change was observed in the specimens with 1 mm thickness.

Conclusion: Use of a home bleaching agent could have adverse effects on surface roughness and hardness of PETG materials leading to reduced survival time of thermoplastic orthodontic retainers.