Objectives: To evaluate the long-term effects of seven different cleaning methods on light transmittance, surface roughness, and flexural modulus of a polyurethane retainer material. Materials and Methods: Polyurethane retainer specimens (Viverat, Align Technology Inc) (70 specimens, n ¼ 10 per method, 50.8 mm 3 12.7 mm 3 1.0 mm) were exposed to seven cleaning methods twice a week for 6 months. Before treatment and after 6 months, light transmittance, surface roughness, and flexural modulus of the specimens were quantified. Qualitative assessment of randomly selected specimens from each solution was performed at baseline and after 6 months using a scanning electron microscope. Statistical analyses were performed at the .05 significance level. Results: Of the three test variables, light transmittance through the specimens was the only one that changed significantly from baseline to 6 months for all cleaning solutions, with all of them causing a decrease. However, except for 0.6% sodium hypochlorite showing a change in surface roughness values and 2.5% vinegar and toothbrushing showing an increase in flexural modulus, none of the other four cleaning methods resulted in significant changes in surface roughness or flexural modulus values for the polyurethane specimens between baseline and after 6 months. Conclusions: Of the seven cleaning methods, Invisalignt cleaning crystals, Polidentt, and Listerinet showed the least amount of change in light transmittance values for the polyurethane specimens over 6 months, and they had no effect on surface roughness and flexural modulus values. (Angle Orthod. 2018;88:355-362.)

Objective: To evaluate light transmittance, surface roughness, and flexural modulus of copolyester retainer material after long-term exposure to different cleaning methods. Materials and Methods: Standardized copolyester retainer specimens (ACE) were subjected to seven chemical cleaning solutions for 6 months: Invisalign cleaning crystals, Retainer Brite, Polident, Listerine mouthwash, 2.5% acetic acid, 0.6% NaClO, and 3% H 2 O 2 . Seventy specimens (n ¼ 10 per method, 50.8 mm 3 12.7 mm 3 1.0 mm) were exposed to the different solutions twice a week for 2 minutes or according to manufacturer's instructions and stored in artificial saliva at 378C. Another group of specimens (n ¼ 10) was brushed with a standardized toothbrushing machine for 2 minutes twice a week. At baseline and 6 months, light transmittance, surface roughness and flexural modulus of the specimens were quantified using spectrophotometry, profilometry, and three-point bend testing, respectively. Qualitative assessment was performed using scanning electron microscopy (SEM). Statistical analyses were accomplished at a significance level of .05. Results: The results indicated that light transmittance through the specimens decreased significantly from baseline for all cleaning methods at 6 months. Flexural modulus of the specimens decreased significantly for all cleaning methods except Invisalign crystals and Retainer Brite (P . .05). The Listerine group demonstrated the worst light transmittance change while H 2 O 2 demonstrated the greatest change in flexural modulus of the specimens compared with other cleaning methods; however, no qualitative difference was observed using SEM analysis. Conclusions:The results suggest that different cleaning methods affect long-term physical properties of the ACE retainer material. At the present time, none of these cleaning methods is ideal for copolyester retainer material. (Angle Orthod. 2019;89:221-227.)

Objectives: To evaluate long-term light transmittance, surface roughness, and flexural modulus of polypropylene/ethylene copolymer retainer material after exposure to different cleaning methods. Materials and Methods: Standardized polypropylene/ethylene copolymer retainer specimens (n = 70, 50.8 mm × 12.7 mm × 1.0 mm) were subjected to seven chemical cleaning solutions: Invisalign cleaning crystals, Retainer Brite, Polident, Listerine mouthwash, 2.5% acetic acid, 0.6% NaClO, and 3% H2O2 for 6 months. The specimens were exposed to the different solutions twice a week for 15 minutes or according to manufacturer's instructions, then stored in artificial saliva at 37°C. Another group of specimens (n = 10) were brushed with a standardized toothbrushing machine for 2 minutes twice a week. At baseline and 6 months, light transmittance, surface roughness, and flexural modulus of the specimens were quantified using spectrophotometry, profilometry and three-point bend testing, respectively. Qualitative analysis was performed using a scanning electron microscope (SEM). Statistical analyses were performed at a significance level of .05. Results: The results showed that light transmittance decreased significantly from baseline for all cleaning methods at 6 months. For an individual method, no significant differences were observed between specimens at baseline and 6 months in surface roughness and flexural modulus. No discernible differences in surface features were observed on SEM images. Conclusions: The results indicate that different cleaning methods affect the long-term light transmittance of the studied polypropylene/ethylene copolymer retainer material. However, for an individual cleaning method, no significant differences were shown for surface roughness or flexural modulus values at 6-months compared to baseline.