Influence of mouthwashes on the physical properties of orthodontic acrylic resin

Aim: The aim of this study was to evaluate the influence of acrylic resin immersion in different mouthwashes on hardness, roughness and color. Methods: Specimens of an orthodontic selfcured acrylic resin (Orto Clas®) were produced and immersed in five mouthwashes: Plax® Classic (Colgate®); Plax® alcohol-free (Colgate®); Listerine® (Johnson & Johnson®); Periogard® (Colgate®) and Periogard® alcohol-free (Colgate®). Nine different immersion times were studied: 1, 2, 4, 6, 8, 10, 12, 24 h and 7 days, totalizing 45 groups. The specimens were evaluated before and after immersion by Knoop microhardness (n=5), roughness in Ra parameter (n=5), and colorimetric analysis, CIElab (n=3). Results: All mouthwashes softened the acrylic resins after 7 days of immersion. PlaxÒ alcohol-free showed no statistically significant difference of softening between the immersion times. Listerine® showed softening after immersion at all times. Plax® alcohol-free and Listerine® showed significantly increased values of roughness after 12 h of immersion (p<0.05). Listerine® presented a significant increase in color variation after 12 h of immersion. Conclusions: Immersion in mouthwashes could influence acrylic resin hardness, roughness and color.