Chromatic analysis of orthodontic resin bonding agents exposed to different antiseptic mouthrinses

ABSTRACT Objective: To assess the color of different orthodontic resin bonding agents exposed to three antiseptic mouthrinses for a prolonged time interval (10-year aging simulation). Methods: 160 specimens were distributed into four groups, according to the orthodontic resin bond agent (Concise, Transbond XT, Transbond Plus Color Change, and Natural Ortho). Each group was exposed to different antiseptic mouthrinses: alcohol-based (Listerine®), alcohol-free (Oral-B®), chlorhexidine (Periogard®) and distilled water as the control. Specimens were submitted to two cycles of staining and artificial aging. Color was evaluated by means of a digital spectrophotometer at the beginning of the experiment and after every cycle. The system used to assess color changes was the CIE L*a*b*. Data was analyzed using the ANOVA and Tukey post-hoc test. Results: After simulation of 10 years of aging, Transbond XT and Natural Ortho composites presented no statistically significant differences in ∆E when exposed to different mouthrinses. The Concise composite specimens exposed to alcohol-free mouthrinse presented a significant difference when compared with specimens from the same group exposed to other antiseptic mouthrinses. Transbond Plus Color Change specimens exposed to chlorhexidine mouthrinse and to alcohol-containing mouthrinse presented a significant difference when compared with the specimens from the group exposed to water and alcohol-free antiseptic. Conclusion: All orthodontic resin bonding agents tested presented clinically perceptible color changes when exposed to at least one of the mouthrinses, except for the Natural Ortho composite. The Concise composite exposed to the alcohol-free solution was the resin that presented the highest color change values.


INTRODUCTION
The constant evolution of techniques, materials and concepts in Dentistry demands that dentists keep up to date with these innovations. This is especially important with regard to new trends in esthetics, considering factors that include tooth color, shape and alignment, as well as facial expressions and gingival appearance. 1 A more demanding orthodontic patient is also generally concerned with a possible tooth color change during and after treatment. Depending on the frequency and period of exposure to agents that affect color, some environmental factors may cause changes in esthetics during treatment. 2 The main purpose of using antiseptic mouthrinses is to control the development and progression of periodontal disease and caries. However, their frequent use may lead to adverse effects on teeth and oral tissues, 3,4,5 including chromatic changes. As a result, several studies have analyzed the color stability of dental materials exposed to alcohol-containing, alcohol-free and chlorhexidine antiseptic mouthrinses. 3,[5][6][7][8] Alcohol and chlorhexidine have unique characteristics that have contributed to their addition to mouthrinse solutions and both have antiseptic properties. Alcohol helps the breakdown or dissolution of active principles and preserves the components of the formula. Chlorhexidine is capable of denaturing Moreira AD, Ferreira JB, Mattos CT, Marquezan M, Araújo MTS, Sant'Anna EF Chromatic analysis of orthodontic resin bonding agents exposed to different antiseptic mouthrinses 5 the components of biofilm. Among their disadvantages and side effects, alcohol may be responsible for lesions in oral tissues and softening of resin composites; 9,10 and chlorhexidine may be associated with changes in sensitivity, superficial peeling of the oral mucosa, calculus formation and change in color of the tongue and teeth, resulting from the precipitation of dietary pigments. 4,11 The lack of color stability of orthodontic resin bonding agents is a main source of tooth darkening or staining. Acid conditioning on dental enamel performed before the procedure of bonding orthodontic fixed appliances to the teeth results in an increase in microporosities on their surface. When these microporosities are filled with resin, tags (resin extension within the dental enamel) are created, and the depth and thickness of these tags is highly variable, with their mean size ranging from 11.8 µm to 18.9 µm. Many tags may reach a depth of 89 µm to 100 µm 12 . These tags are intended to provide retention between the orthodontic bonding agent and the tooth, and they may remain in the dental enamel permanently. Nevertheless, the aging process in addition to pigments present in a person's diet, and chemical products used in the oral cavity may alter the color of these composites, leading to poor esthetics. 13 Moreira AD, Ferreira JB, Mattos CT, Marquezan M, Araújo MTS, Sant'Anna EF Chromatic analysis of orthodontic resin bonding agents exposed to different antiseptic mouthrinses 6 Additionally, it is commonplace for a certain amount of excess resin bonding agent flash to remain on the bracket edges; between the bracket and the enamel, during bracket bonding. 14 Armstrong et al. 14 observed that even the addition of a color change feature in the bonding agent does not guarantee a reduction in the amount of excessive resin bonding agent accumulating around orthodontic brackets. Therefore, the color change in these excessive orthodontic bonding agents could be esthetically important during orthodontic treatment, particularly in the anterior teeth.
Thus, the aim of this study was to perform an in vitro chromatic analysis of orthodontic resin bonding agents exposed to different antiseptic mouthrinses for a prolonged time interval.

MATERIAL AND METHODS
In this study, 160 5mm-diameter and 2mm-high disc-shaped specimens were made from four different orthodontic resin bonding agents and divided into four groups, according to the orthodontic resin. All specimens obtained were immersed in distilled water at a temperature of 37 o C for 24 hours, in order to ensure complete polymerization. The Commission Internationale de L'Eclairage (CIE L*a*b*) 15,16 defined a system of color reading, where L* represents the luminosity axis (from black to white). The chroma is described by two variables: a* and b*; a* represents the green-red axis (-a = green; +a = red), and b* represents the blue-yellow axis (-b = blue; +b = yellow). Thus, the calculation of total color change (∆E*ab) was possible by using the following formula: The values of L*, b* and ∆E* were compared. 16 The results obtained were analyzed using the Kolmogorov-Smirnov normality test. Analysis of variance (ANOVA) and the Tukey post-hoc tests were used to identify differences between groups in each period. The paired-samples t-test was used to identify differences related to mouthrinses in each group between time intervals, compared to distilled water.

RESULTS
All four resins showed some color change when immersed in any of the tested solutions, however, the resins presented different behavior when exposed to the individual solutions.
Considering ∆E values, Concise resin showed a more significant   Moreira AD, Ferreira JB, Mattos CT, Marquezan M, Araújo MTS, Sant'Anna EF Chromatic analysis of orthodontic resin bonding agents exposed to different antiseptic mouthrinses Plus Color Change specimens exposed to the Listerine ® solution and to Periogard ® showed statistically significant difference between the initial and final L values.. The comparison between initial and final L values found for the Natural Ortho specimens showed a statistically significant difference when exposed to the Listerine ® solution ( Table 2).
Moreira AD, Ferreira JB, Mattos CT, Marquezan M, Araújo MTS, Sant'Anna EF Chromatic analysis of orthodontic resin bonding agents exposed to different antiseptic mouthrinses 11 Comparison between the initial and final b* values of the Concise specimens showed a statistically significant difference for all the mouthrinses studied, except for Oral-B ® solu-

tion. Transbond XT, Transbond Plus Color Change and Natural
Ortho specimens showed a statistically significant difference between the initial and final b* values when immersed in any of the mouthrinses studied and distilled water (Table 3).

DISCUSSION
Visual color perception is essentially a subjective matter, which may be physiologically and psychologically influenced, and may be different for each researcher willing to assess color changes. Some of the factors that may influence visual color assessment and contribute to this subjectivity are: the distance between the object and the observer, the color of the light used for illumination, the metamerism phenomenon, fatigue and aging of the object, and even the emotional state of the observer. 17 In this context, the use of a spectrophotometer eliminates the errors of subjective color assessment.
The ∆E values are frequently used to assess color change Transbond Plus Color Change specimens, however, only presented ∆E values (3.86) that characterized a clinically perceptible color change when they were exposed to the Periogard ® solution. Natural Ortho specimens presented no visually perceptible color changes, according to the threshold of ∆E considered in this study (3.3). 18,19 Luminosity is the most important factor in determining color, as colors with low luminosity values appear to be darker.
The assessment of L* values allowed the analysis of whether the studied resin bonding agents became lighter or darker.
When the L* values rose, this meant that the luminosity increased, and the object became lighter. When the L* values decreased, this meant that there was a reduction in the luminosity and the object became darker. Changes in the L* values are the most significant parameter in color change, as the human eye may detect these changes more easily than changes in other parameters, such as the a* and b* values.
Any change in L* values below 2.0 is not clinically visible. 21 All bonding agents assessed in this study became darker or showed no difference in luminosity after the two cycles of staining and artificial aging, when immersed in distilled water and when they were exposed to different mouthrinses. The only exception was the Transbond Plus Color Change specimens exposed to the Oral-B ® solution, which showed a discrete increase in luminosity that was not statistically significant. Color Change) presented a clinically perceptible color change when exposed to the chlorhexidine solution Periogard ® .
According to Eliades et al, 13 one of the sources of exogenous discoloration of polymeric materials may be the superficial absorption of color pigmentation from colored mouthrinses, even though the discoloration of these materials may originate from a wide array of exogenous or endogenous sources.
The effect of antiseptic solutions on composite color change may be material-dependent and the resin susceptibility to staining may be attributed to its matrix. Some authors have shown that the type of material played a significant role in resistance to staining. 3 Likewise, in this study, different types of orthodontic resin bonding agents showed different behaviors when exposed to antiseptic mouthrinses and submitted to two cycles of artificial aging and staining.
Clinicians should thus be aware of the properties of the orthodontic resin bonding agents they use, in order to indicate a more compatible mouthrinse that affects it the least. Remnants of orthodontic resin bonding agents around metal orthodontic brackets, which become stained, may impair esthetics during orthodontic treatment. In addition, this staining may become even more evident in the remaining orthodontic resin bonding agents located around translucent esthetic brackets. After orthodontic treatment and bracket debonding, resin tags remain on enamel surface, so the esthetic appearance and color stability of the resin continue to be cause for concern.
Therefore, to enable clinicians to maintain esthetics during and after orthodontic treatment, it is essential for them to know which orthodontic resin bonding agents are more likely to be stained with certain mouthrinses.
The results of this study showed that antiseptic mouthrinses may cause chromatic changes in orthodontic resin bonding agents. However, in general, the specific presence of alcohol or chlorhexidine in these solutions did not seem to trigger these color changes.
In vivo studies are necessary to observe the effect of antiseptic mouthrinses on orthodontic resin bonding agents under clinical conditions, as some factors such as saliva, biofilm and diet may not be adequately reproduced in vitro and may influence the physical and esthetic properties of resins.