Cigarette Smoke Combined with Staining Beverages Decrease Luminosity and Increase Pigmentation in Composite Resin Restorations

The color mismatch between dental esthetic materials and teeth is one of the primary reasons for replacement of composite resin restorations. Although previous studies have reported the staining effect of cigarette smoke on esthetic dental materials,¹ the literature has not established a relationship between smoking habits and restorative materials discoloration. Tobacco smoke is a complex mixture of almost 4000 different components and presents two distinct phases.² The volatile phase is composed of CO, CO₂, NO, H₂O, and other components, and the particulate phase mainly consists of tar.³ Approximately 0.2% of the tar composition is represented by brown pigments from tobacco leaves.² These brown pigments are considered to be the agent responsible for staining teeth and esthetic dental materials.

The joint effect of staining substances on the discoloration of dental restorative materials has been described previously in the literature.^4,5 It was stated that external conditions, such as the presence of chlorhexidine, can increase the staining effect of colored beverages, such as red wine, tea, and coffee on composite materials.⁵ Because the color of dental materials is greatly influenced by patient’s habits and considering that smoking is usually ass°Ciated with a great intake of coffee⁶ or alcoholic beverages (eg, red wine),⁷ the effect of the combination of such factors on the color of esthetic materials should be investigated.

A reduction in exogenous stains on composite resin materials is obtained by polishing, cleaning, and bleaching pr°Cedures.^4,8,9 Some authors described perceptible color change in stained esthetic materials after repolishing pr°Cedures, especially in terms of increasing luminosity and decreasing yellowish appearance.⁹ However, repolishing pr°Cedures can cause wear and may not return the color of the esthetic material to the shade presented before the exposure to environmental factors.

The purpose was to evaluate the effect of coffee and red wine solutions alone or combined with cigarette smoke on the color change of a composite resin before and after repolishing pr°Cedures. The hypotheses were that the exposure to staining agents changes the color parameters of the composite resin and these parameters return to baseline values after repolishing pr°Cedures.

A total of 60 specimens were made from a nanofilled composite resin  (Filtek™ Z350 Supreme, 3M ESPE, https://www.3mespe.com) . A Teflon® (DuPont™, https://www.dupont.com) mold with a central orifice of 9-mm diameter and 2-mm thickness was filled with a single increment of the composite. A Mylar strip was placed over the mold (OptiPlus, Gnatus), and specimens were light-cured for 20 s. The surface directly exposed to the visible light was polished using medium, fine, and ultra-fine aluminum oxide abrasive disks (Sof-Lex Pop-On™, 3M ESPE). Specimens were stored in artificial saliva for 24 hours 37°C, and then all°Cated into six groups (n = 10): 1) control (no colorant); 2) cigarette smoke (Hollywood Red KS, Souza Cruz S.A.); 3) coffee (Traditional Coffee Santa Clara, Eusébio); 4) coffee and cigarette smoke; 5) red wine (Aurora, Bento Gonçalves); and 6) red wine and cigarette smoke.

Groups 2, 4, and 6 were exposed to smoke from 20 cigarettes daily (10 cigarettes per 8 mins, twice daily) for 21 days. Cigarette exposure was conducted in a hermetically closed acrylic device. This apparatus contained two chambers connected by an orifice closed with a cigarette filter paper. Lighted cigarettes were placed in the first chamber, which received external ventilation. The air steam conducted the smoke from the first to the second chamber, where composite specimens were placed. To reach the second chamber, smoke had to penetrate the cigarette filter barrier. The second chamber had another orifice to release the air steam. This method is an adaptation of the one described by Le Mesurier et al.10

In groups 3, 4, 5, and 6, specimens were exposed to coffee or red wine solutions through 4 min of daily immersion in the respective solution (2 mins of immersion every 12 hours). After each 2-minute cycle of immersion, specimens were washed in running water and then stored in artificial saliva at 37°C. Repolishing was conducted after the 21-day period of exposure to the staining agents, using aluminum oxide disks with decreased abrasiveness as described earlier.

Color measurements were performed according to the Cie L*a*b* system. Color parameters, L* (luminosity), a* (green-red), b* (blue yellow), and ΔE (total color variation), were measured at three periods: at baseline, after 21 days of exposure to the staining agents, and after repolishing pr°Cedures. To perform the color readings, each specimen was repositioned in the Teflon mold. A white Teflon cover containing a central orifice was positioned over the mold to allow the placement of the tip of the spectrophotometer (VITA Easyshade® System 3D-Master, VIDENT, https://www.vident.com). Therefore, the distal end of the light guide from the spectrometer remained in contact with the specimen and in a fixed position, controlling the influence of external light and preventing the dissipation from the light of the spectrophotometer.

L*, b*, and DE* values were analyzed with split-plot analysis of variance (ANOVA); multiple pair-wise comparisons were performed with the Tukey post-h°C test. The dependent variable a* did not present a normal distribution and was analyzed with Kruskal-Wallis and Friedman tests. A  confidence level of 95% was considered in statistical analyses.

Statistically significant interactions between staining agents and periods were detected for L* and b* variables (P < .001). The ass°Ciation of red wine and cigarette smoke (group 6) resulted in significantly lower L* values. Red wine (group 5), coffee and cigarette smoke (group 4), and cigarette smoke (group 2) presented similar luminosity. Repolishing increased the luminosity, but L* values remained statistically lower than baseline. After repolishing, all groups demonstrated similar luminosity (Figure 1).

After staining, the combination of coffee and cigarette smoke (group 4) and red wine and cigarette smoke (group 6) produced a statistically greater yellowish effect. Cigarette smoke (group 2) and red wine (group 5) presented similar b* values, comparable to baseline. The control group presented decreased b* values. Repolishing significantly reduced the yellow appearance in stained groups; however, differences in b* values still were noted. Higher means were detected in groups 2 and 4, followed by groups 3 and 6, and finally by groups 5 and 1 (Figure 2).

Significant differences between staining agents and periods were also detected for a* variable (P < .05). Specimens from groups 2, 4, 5, and 6 presented a significant increase in red pigmentation after the staining period (> a*). Repolishing could not reduce the red after the exposure to staining agents; and groups 6, 2, and 4 presented similar and higher a* values than the other groups (Figure 3).

The total color variation (∆E*) presented a significant interaction between main factors (Table 1, P = .003). Higher ∆E was observed during the staining baseline period in specimens exposed to red wine and cigarette smoke (group 6), followed by coffee and cigarette smoke (group 4). The effect of isolated agents was higher for red wine (group 5), followed by cigarette smoke (group 2), and coffee (group 3). Repolishing reduced extrinsic stains in different extents. Nevertheless, the ∆E values resultant from the periods of repolishing – staining and repolishing – baseline indicated only significant differences for groups 1, 2, and 3. The color change of specimens immersed in artificial saliva was significant; however, the comparison between staining baseline and repolishing baseline was not.

The first hypothesis tested in the present study was accepted because color parameters of the composite resin changed after the exposure to the staining agents. Otherwise, the second hypothesis examined in this investigation was partially accepted because repolishing pr°Cedures reduced the staining but were not able to return some of the color parameters to baseline values.

In the past years, esthetic issues have become extremely important for clinicians and patients. In several clinical situations, the use of restorative materials is urged for providing not only health and function but also a highly esthetic outcome. In addition, there is a common concern regarding how long esthetic restorations can retain their color features in the oral environment, where they will be exposed frequently to more than one type of staining agent.^9-12
According to the findings, all groups presented color changes that could be visually detected because the ∆E* values were greater than 3.3.12 However, only specimens exposed to coffee and cigarette smoke, red wine, and red wine and cigarette smoke presented total color change significantly different from the control group. Although the control group presented the lowest total color variation (∆E* = 8.19) after 21 days of storage, this value is clinically significant. These findings concur with the ones of a previous study, which suggested an extrinsic staining mediated by saliva.5 The authors speculated the staining effect of saliva is probably caused by mucin, which is a component of the artificial saliva used in the present study.⁵

The combination of red wine and coffee with cigarette smoke provided considerable changes on the color parameters, indicating that cigarette smoke might intensify the effects of some staining solutions. Compared to the isolated action of the staining solutions, the combination with cigarette smoke significantly decreased the luminosity and increased the trend to yellow (> b*) and red (> *a) pigmentation of composite specimens.

The cigarette smoke alone increased the trend to red pigmentation and reduced the luminosity of composite resin specimens compared to coffee. A superior staining effect of cigarette smoke compared to coffee and black tea was previously reported.¹³ The brown pigmentation from tar seems to explain the change in color caused by cigarette smoke. This study used a brand of cigarette containing 10 mg of tar. Because the results obtained in this investigation are limited to this brand of cigarette/amount of tar, further research should be performed to verify if different contents of tar can produce other staining effects on esthetic restorative materials.

Specimens exposed to red wine presented a significant reduction in the luminosity and an increased trend to red pigmentation. The insignificant yellowish effect of red wine can be related to its dark red color. The literature explains that the chromogen effect results from its alcoholic content, which can damage the resin matrix,8,14 and from its acidic pH, which might increase the sorption and solubility of the composites.¹⁴ A previous investigation analyzed the in vitroadsorption of chromogens in the salivary pellicle.¹⁵ It was stated that the amount of pigments adsorbed increased over 10 times upon exposure to red wine. This effect was justified by the action of pigments referred to as anth°Cyanins, originating from the outer few layers of the grape skin. They represent complex polyphenolic materials, which can readily form complexes with proteins found in the mouth, causing discoloration of the tongue and teeth.¹⁵

Although repolishing promoted some increase in the luminosity and decrease in the yellowish pigmentation, such a pr°Cedure was not able to return all color parameters to baseline values. The trend to red pigmentation also changed after repolishing, but this effect was not uniform in all experimental groups. Another study9 indicated that repolishing can significantly reduce superficial staining without completely removing it. Similar findings could be shown in the present study when repolishing pr°Cedures removed the superficial staining in groups G4, G5, and G6, which were visually perceptible (∆E* > 7.60). However, the repolishing pr°Cedures did not effectively remove the superficial staining in these groups because the values of the total color variation found between repolishing and baseline periods significantly exceeded the clinical perceptibility and acceptability thresholds (∆E* > 8.34). The adequate performance of repolishing in some of the groups indicates that this pr°Cedure can be an alternative to partially removing the superficial stains. Nonetheless, alternatives for repolishing other than aluminum oxide discs of decreased abrasiveness should be further evaluated to establish a method with general effectiveness, that is, independent of the staining agent.
According to the limitations of the present in vitro investigation, it could be concluded that the staining agents tested can induce significant color change on the composite resin. In addition, the joint exposure to cigarette smoke and red wine provides an even higher pigmentation of the composite. Finally, repolishing pr°Cedures with aluminum oxide discs of decreased abrasiveness can be an alternative to reducing the staining from the composite despite their inability to completely remove the superficial pigmentation.

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