# The Influence of Different Cleaning Protocols on the Surface Roughness of Orthodontic Retainers
## 4 Discussion  
Patients are advised to use a variety of cleaning procedures for retainers. Although antimicrobial activity is present in both over-the-counter (OCC) and applied-chemical orthodontic appliance cleaners (ACC), the effectiveness of these cleaners is not comparable due to heterogeneity in the study design, materials and methods, and evaluation methods used by current research data [28]. Therefore, the present study evaluated changes in surface roughness of polyethylene terephthalate glycol (PET-G) material exposed to mechanical and chemical cleaning methods. In this study, Ra was used as it is a common parameter in industry and therefore ensures the stability of the parameter, not being affected by any accidental stray spikes or scratches. Brushing is a mechanical cleaning method, while Corega tablets fall under chemical cleaning procedures. In our study, there was a statistically significant difference between baseline and final roughness values on the top side of all specimens that were exposed to the toothbrush, Corega + toothbrush, and toothbrush + toothpaste cleaning protocols. By contrast, in the Corega group, no statistically significant difference was found. The combination of brushing + Corega and brushing + toothpaste led to greater surface roughness values than brushing only. Thus, toothbrushing affected surface material. Corega tablets caused an increase in surface roughness, but this rise was not significant. Greater values of Ra can be explained by the chemical properties of the tablet's components. When sodium perforate comes into contact with water, it decomposes into hydrogen peroxide, sodium metaborate, and nascent oxygen [38; 39; 40]. It can be assumed that the active oxygen released by the hydrogen peroxide solution is the main reason for increased surface roughness. Furthermore, oxygen bubbles released from this oxygen-liberating solution are responsible for both mechanical and chemical cleaning/damage of the material [38; 40]. Another explanation for the changed surface roughness after exposure to dissolving Corega tablets is the absorption of water. PET-G material has a high water-absorption property [41; 42; 43]. Water penetrates polymer material; several physicochemical changes can occur and mechanical properties can be irreversibly degraded. All this can cause a change in the nanoroughness of the polymer material [43; 44]. Corega tablets in the study by [PERSON] et al. [43] also caused an increase in surface roughness of Biolon, but the results were statistically insignificant, which corresponds to our findings. The importance of brushing on the retainer clearance is described in the [PERSON] et al. study. They reported that brushing with toothpaste leads to 99.9% reduction of _Streptococcus mutans_[45]. However, we must keep in mind that brushing can scratch the surface of the retainer, resulting in an increased surface area that is conducive to bacterial colonization. Moreover, brushing may damage the cosmetic appearance of the retainer and reduce its longevity [45]. [PERSON] et al. [43] discovered that brushing affected the surface roughness of PET-G material more than chemical cleaning procedures, but their findings were statistically insignificant. Other studies, however, found that brushing has no effect on the surface roughness of polyurethane and copolyester retainer material [29; 30]. Brushing with distilled water was less effective than brushing with toothpaste in a study conducted by [PERSON] et al. [45]. Furthermore, there was no statistically significant difference between the control group and rinsing with sterile distilled water, indicating that it is ineffective at removing biofilm [45]. It is well-known that abrasive toothpastes can cause increased surface roughness of various restorative and thermoplastic materials [46; 47; 48]. In this study, whitening toothpastes affected the surface roughness of the PET-G material.