Oral mouthwashes could degrade acrylic resin used in orthodontic appliances such as braces - Brazilian Journal of Oral Sciences Vol.13 No.3

The latest issue of the Brazilian Journal of Oral Sciences includes "Influence of mouthwashes on the physical properties of orthodontic acrylic resin" by Collares et al. This article could be of particular interest to both people in the orthodontics industry and consumers of orthodontics products. Collares et al. say that mouthwash could help remove biofilm on removable orthodontic appliances such as wires, clasps and springs, as well as acrylic baseplates. But how does mouthwash affect the acrylic resin in these parts in the long-term? This is the question that Collares et al. aim to answer in their study.

Orto Clas brand acrylic resin was used in this experiment. It was self-cured according to the manufacturer's instructions. All samples used in the study were ensured to have a smooth and flat surface, without roughness or tested for microhardness. Five brands of mouthwash were tested: Plax Classic, Plax alcohol-free, Listerine Cool Mint, Periogard and Periogard alcohol free were used. The Knoop microhardness of each acrylic resin was measured using a hardness test in which a 15 gram load was used on each acrylic resin sample for 10 seconds. Afterward, they were immersed in the different mouthwashes for several different time periods. They were then washed with distilled water for 10 seconds each and dried with compressed air for one minute. The hardness test was performed again, and the measurements of the softening of acrylic resin were recorded as the percent difference between the final and initial Knoop hardness.

Roughness, colorimetric analysis, mouthwash pH and statistical analysis were also measured in the test. Among the results indicated, Collares et al. found that after 7 days, all the mouthwashes decreased the surface microhardness. Plax alcohol-free mouthwash was found to have no difference on acrylic resin that was immersed between 1 hour and 7 days. The results also suggest that acrylic resin immersed in Listerine showed decreased microhardness after all time periods. In terms of surface roughness, the results indicated that all mouthwashes increased surface roughness. However, acrylic resins immersed in Plax alcohol-free mouthwash and Listerine mouthwash showed significantly higher measurements of surface roughness after 12 hours than the other mouthwashes.

Collares et al. conclude that in order for biofilm to form on orthodontic appliances, a minimum measurement of 0.2mm of surface roughness has to occur on the appliances. Listerine and Plax alcohol-free were shown to increase surface roughness past this measurement. This roughness could cause discomfort in the patient and allow biofilm and microorganism colonization to occur. Collares et al. also note that acrylic resin immersed in Periogard had the highest softening values over time, potentially due to its alcohol base. The alcohol could be absorbed by the resin over time and change the structure of the polymer. It was also noted that Listerine caused high values of softening on acrylic resin over time. Collares et al. note that this could be because of the essential oils in Listerine that are said to help antibacterial activity. However, after 7 days of immersion in Listerine, acrylic resin was shown to have an increase in hardness and decrease in softening. Collares et al. suggest that this may be because of the ethanol in the Listerine.

The study concludes that hardness, colour and roughness affects the acrylic resin in orthodontic appliances, therefore it is important for orthodontists to notify their patients of these possible changes when establishing a hygiene care routine.

You can find more articles from this issue here.