Long-term Effects of Cleaning Methods on Properties of Vivera and ACE Clear Retainer Materials

Hypothesis: In the long term, Vivera® and Essix® ACE are not significantly different in transmittance, surface roughness, and flexural modulus among 7 cleaning methods. Objective: Clear retainers have increased in popularity due to their esthetic nature. However, few studies have focused on long-term maintenance of these retainers. This study evaluated the long-term effects of 7 different cleaning methods on light transmittance, flexural modulus, and surface roughness of Vivera® material. Methods: Vivera® retainer (Align® Technology) specimens (n=10,2x0.5x0.04in) were exposed to 7 different cleaning methods: Invisalign® cleaning crystals, Polident®, Listerine®, 2.5% vinegar, 0.6% sodium hypochlorite, 3% hydrogen peroxide, and toothbrushing with distilled water twice a week for 6 months. Before treatment and after 6 months, light transmittance, flexural modulus, and surface roughness of specimens were quantified. Qualitative assessment of random specimens from each method was performed at 6 months using a scanning electron microscope. Mean difference comparisons were done using the independent student t-test and ANOVA (P<0.05). Results: A decrease in transmittance of specimens was found with all cleaning methods compared to baseline, with toothbrushing causing the greatest decrease for Vivera® and Listerine® causing the greatest decrease for ACE. Surface roughness was unaffected by the cleaning methods except NaOCl eliciting a difference in Vivera and Listerine with ACE. Quantitative analysis with SEM however showed negligible difference. Vinegar and toothbrushing showed an increase in flexural modulus in Vivera®, however when compared to each other, showed no difference. All methods increased modulus for ACE except for Invisalign Crystals. Hydrogen peroxide caused the greatest decrease in flexibility of ACE. Conclusions: Over the long-term there is a gradual decrease in transmittance of clear retainers with certain solutions creating less translucency. Surface roughness and flexibility are generally unaffected in the long term but may be affected by oxiders. Funding: Align® Technology