Effects of various cleaning agents on polypropylene and copolyester thermoplastic orthodontic retainer materials

This study aimed to evaluate and compare the effects of four cleaning agents on the flexural modulus and light transmittance properties of polypropylene and copolyester thermoplastic retainer materials after long-term exposure.

A total of 120 pieces of standardized copolyester and polypropylene retainer materials were tested after being thermoformed. They were divided equally into six subgroups: as-received, artificial saliva, chlorhexidine, alcohol-based and alcohol-free mouthwashes, and Retainer Brite®. The pieces were subjected to a cleaning process involving 15 minute immersion three times weekly for 3 months. The flexural modulus and light transmittance were then measured for all specimens with three point bending tests and spectrophotometry, respectively. One-way ANOVA and independent samples t-test were applied to compare the means, and Tukey's post hoc test was used in cases of significant differences. The threshold for significance was 0.05.

For each retainer type, the statistical results revealed that the flexural modulus values of the copolyester retainer material significantly differed from those of polypropylene material under chlorhexidine mouthwash, alcohol-based mouthwash, and Retainer Brite® conditions. Copolyester and polypropylene showed significant differences in light transmittance under all conditions. No significant difference in flexural modulus values was observed among conditions, whereas significant differences in light transmittance were observed between alcohol-based mouthwash and the other conditions for copolyester material.

According to our results, any cleaning agent can be safely used for both materials without affecting the elastic modulus. However, alcohol-based mouthwash decreases the light transmittance of copolyester retainer material.