Comparison of force degradation and color change of esthetic elastomeric chains

Objective: this study compared the force degradation and color change of esthetic elastomeric chains of four commercial brands. Materials and methods: the study analyzed 10 medium-force esthetic elastomeric chains with 6 links of Morelli, Orthometric, Eurodonto and 3M brands from sealed packages within the expiration date. The elastics were stretched twice their length, according to the manufacturer's recommendations, and were immersed in artificial saliva at 37°C. The forces were measured with an orthodontic dynamometer at onset and at intervals of 1, 7, 14, 21 and 30 days after immersion. The force degradation was evaluated calculating the percentage of force lost in relation to the initial force in each time interval, for each group tested separately and also between them. The color change was evaluated by visual analysis scale by observation of photographs of chain elastics before and after study completion by 31 examiners. The ANOVA test of repeated measures was applied considering 2 factors, time and groups, and the Tukey test was used for analysis of multiple comparisons. A significance value of 0.05% was adopted for the analyses. Results: the elastics showed great force degradation. After 7 days the groups presented degradation around 50% of the initial force. In the evaluation between groups, the elastics showed significantly different mean forces. When assessing color change, the scores assigned by examiners evidenced less color changes for elastics of Eurodonto brand. Conclusion: regardless of the commercial brand, transparent elastomeric chains show significant force degradation values after 1 day. The scores assigned to color change evidenced that all commercial brands showed staining, with the best results for Eurodonto elastics.


Introduction
In recent decades, there has been a greater demand from adult patients in orthodontic clinics. This likely occurred due to greater dissemination and also due to the standpoint of prevention of modern dentistry, increased longevity, greater access to information, advances in orthodontics and psychosocial variations (Tweng et al., 2012;Zhang et al., 2008;Mandall et al., 2006). Even though the esthetic reasons are sufficient to justify this increase in the demand for treatment by adults, which directly results in better self-image of the patient, the esthetic and psychological benefits are more valued than the functional and oral health benefits (Aldrees et al., 2015;Cavalcante et al., 2013).
Within this context, to meet this greater demand from patients with great esthetic needs, the orthodontic appliances and accessories have been improved. Ceramic and self-ligating brackets, aligners and esthetic elastics have been marketed in large scale. Regarding the orthodontic elastics, the elastomeric chains are one of the most important accessories in orthodontic treatment, being mainly used for closure of spaces between teeth (Alexandre et al., 2008;Baty et al., 1994).
An ideal elastic chain should release smooth and continuous forces to obtain greater control over tooth movements, besides presenting adequate characteristics for oral use and providing the desirable tooth movement (Santos et al., 2009;Loriato et al., 2006;Cabrera et al., 2003). Despite the widespread utilization of these accessories, there are some disadvantages related to their use. One of the characteristics inherent to elastics is the force degradation, which is reduced over time, decreasing the tooth movement and consequently increasing the treatment time (Fernandes et al., 2011;Moris et al., 2009;Loriato et al., 2006;Cabrera et al., 2003;Henriques et al., 2003;. Other factors also influence both the clinical performance of these materials and changes in their color, such as extended exposure to water, enzymes, diet and temperature variation (Oliveira et al., 2011;Martins et al., 2006;Von Fraunhofer et al. 1992;DeGenova et al., 1985).
Knowledge of the changes in mechanical properties of elastomeric chains is of great interest, since they will remain for a long period in the oral cavity and, during this interval, should continue to deliver a clinically adequate force. Thus, the present study aimed to evaluate the initial force and its degradation, as well as the staining of esthetic elastomeric chains of four commercial brands.
In the Figure 1 it is possible to visualize the packages of each brands of esthetic elastic chains that were evaluated in the present research. Each group consisted of 10 segments of 6 links of elastomeric chains extended twice their length, which corresponds to 30 mm, maintained by simple devices with two metal tips to secure the elastics, simulating the continuous use of elastics by the patients. Then, the force was measured using a Zeusan precision orthodontic dynamometer (São Paulo, SP) and recorded on a Microsoft® Excel spreadsheet. After that, these devices securing the elastics were immersed in artificial saliva. The containers were kept in an oven at 37°C, simulating the oral environment. After the periods of 1, 7, 14, 21 and 30 days, the forces were again measured and recorded. The Figure 2 shows the device that was used to keep de elastsic chains stretched for the requested period. Observe that all elastic had the same amount of stretch.
Also, before study onset and after the 30-day period, when the elastics were discarded, photographs were taken using a mobile device (cell phone), on a white background, of 3 randomly selected samples of each commercial brand to observe color changes (Figure 3). This color change was assessed subjectively by 31 examiners who evaluated the photographs using a visual analogue scale (VAS) in the Mentímeter remote interactive presentation software. The examiners marked the degree of color change of rubber bands for each group on a scale from 1 to 10. This scale consisted of a 10-cm horizontal line, with number one at the left end representing no color change and the right end (10) indicating the greatest degree of color change of rubber bands. The brand of elastomeric chains was kept confidential to avoid any influence on the final decision of examiners. Research, Society and Development, v. 10, n. 4, e54310414307, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i4.14307 5 In the Figure 3, despite some difference among brands, it is interest to note that all elastic chains had some color degradation after the evaluation period.

Statistical analysis
Data from the collected information were organized in a table in Excel format (Microsoft Office Excel, Redmond, WA, USA), submitted to the SigmaPlot software (SigmaPlot, San Jose, CA, USA) version 13.0 and analyzed in relation to the normal distribution (Shapiro-Wilk test). Data were evaluated by the Analysis of Variance (ANOVA) test for two factors, time and groups. The Tukey test was used for analyses of multiple comparisons. A significance level of 5% was adopted for the analyses. The study power was evaluated and for comparisons between groups, intervals, and groups vs. intervals, considering an alpha value of 1.0.

Resultss
After completion of the 30-day period of elastomeric chains immersed in artificial saliva in an oven simulating the oral cavity, it was observed that no elastic was ruptured. Table 1 presents the forces measured for each brand at different time intervals. It is observed that the brand whose elastomeric chains showed the greatest initial force was Eurodonto (384g), followed by Morelli (334g), Orthometric (282g) and 3M (247g). At completion of 30 days, the Eurodonto and Morelli elastics showed the highest residual force (144.5g), followed by elastomeric chains of the brands Orthometric (110g) and 3M (105g). Tabela 1. Evaluated mean force (grams) and standard deviation for each elastic chain brand group for observed period of time. Graph 2 presents the mean color degradation of elastomeric chains after the 30-day period. This graph evidences, by the mean scores assigned by examiners on the VAS, that 3M elastics presented the greatest change (8.1), followed by Morelli (6.1) and Orthometric elastics (5.6). Eurodonto elastomeric chains showed the lowest color degradation (5).

Period/Brand
Graph 2. Color change of the different elastics evaluated after the 30-day period.

Discussion
Knowledge on changes in the mechanical properties of elastomeric chains has great interest for orthodontists, since these accessories will remain for a long time in the oral cavity and, during this period, they continue to deliver a clinically adequate force (Alexandre et al., 2008;Baty et al., 1994). Due to the large number of commercial brands with different prices in the market, the use of one brand or another should primarily be based on the characteristics of mechanical efficiency associated with the best esthetic performance during the interval between sessions (Santos et al., 2009).
This study compared the amount of force dissipated by esthetic elastomeric chains from four different commercial brands and the force degradation over time, besides the color change of these elastomers. According to the literature, elastomeric chains tested in a wet environment experience greater force degradation over time compared to testing in a dry environment (Ferriter et al., 1990;Huget et al., 1990;Ash & Nikolai, 1978), and are also influenced by the temperature of the medium, whose increase worsens the reduction of generated load (Wang et al., 2007;Stevenson & Kusy, 1994). Thus, this study employed an environment as close as possible to the oral cavity. For thar purpose, the elastomeric chains were immersed in artificial saliva stored at 37°C in an oven, simulating its continuous use by the patients.
The results were analyzed and revealed a gradual decrease in forces released by elastomeric chains throughout the study. However, the greatest degradation occurred after the first day. After this period, the magnitude of force degradation was smaller and maintained a pattern for all groups during the study. Similar findings were also observed in other studies (Alexandre et al., 2008;Baty et al., 1994;Huget et al., 1990;Ash & Nikolai, 1978) that observed that the greatest reduction in the amount of load generated by elastomeric chains occurred in the first hour of testing, 30% in the average. For this reason, it is recommended to apply an initial force greater than desired for a given orthodontic movement, aiming to compensate for this force reduction during the continuous use of elastics (Fernandes et al., 2011;Moris et al., 2009;Loriato et al., 2006;Cabrera et al., 2003;Henriques et al., 2003;Bishara & Andreassen, 1970 When observing the residual force obtained in the different time intervals, it was observed that Morelli elastics showed the greatest amount of residual force (43.26%) at completion of 30 days (Graph 1), dissipating 334g in the average at the onset of evaluation (Table 1). This result differs from that obtained in a study conducted in 2008 (Alexandre et al., 2008).
In that study, the authors found that Morelli elastomeric chains released an initial force of approximately 200g, with a residual force of 29% after 30 days. However, it should be mentioned that such study evaluated gray elastomeric chains, different from our study that compared esthetic elastomeric chains.
This study also aimed to compare the color change of elastomeric chains at completion of 30 days, a period when elastomeric chains are usually changed following the orthodontic treatment protocol. Thus, it is also fundamental to assess whether the color change of elastics compromises their esthetics, since esthetic accessories are increasingly asked by patients who wish to be treated with the most imperceptible devices as possible (Aldrees et al., 2015;Cavalcante et al., 2013).
Thus, after the study period (30 days) when elastomeric chains were removed from the support immersed in saliva, 3 samples of each brand were randomly selected and photographed together with 3 intact samples from the packages. These photographs of elastomeric chains before and after the study were evaluated by 31 examiners, who assessed subjectively using a visual analogue scale to verify the color change.
Based on the evaluation of images of the 4 groups of elastomeric chains, it is evident that only exposure to artificial saliva for 30 days already caused changes in color. The 3M elastomeric chains showed the greatest degradation of their original color. This result agrees with different studies that, comparing the color stability of esthetic elastomeric chains of different brands, reported that 3M elastics presented the greatest changes (Aldrees et al., 2015;Cavalcante et al., 2013).
Considering the present findings and from a clinical standpoint, it can be concluded that, regardless of the brand, esthetic elastomeric chains present significant force dissipation after 24 hours, without significant difference between brands.
However, all clear esthetic elastomeric chains are susceptible to significant color changes in the oral environment, which may bother more demanding patients in relation to the appliance esthetics. Considering that esthetic brackets have a high cost in relation to metallic brackets, and assuming that patients who accept to pay this extra cost are concerned with the appearance of the appliance, the accessories must also be carefully chosen to meet this esthetic demand. In this sense, 3M elastics had worse performance, and at least in vitro these results suggest the indication of other brands. Also, dental professionals must be aware of the restrictions and guidelines to be provided to the patient to avoid some types of food that can stain and change the color of clear elastomeric chains (Cavalcante et al., 2013;Loriato et al., 2006;Martins et al., 2006;Henriques et al., 2003).

Conclusion
All elastics showed force degradation over time, regardless of the brand.
After 1 day, all brands showed force degradation around 40% of their initial force.
The color change occurred for all elastics and was similar between them, except for 3M elastics, which showed greater change in relation to the other brands tested.