The Effects of Cigarette Smoking on the Shade of CAD/CAM Restorations

Introduction: Digital dentistry has led to an inevitable shift in the paradigm of dental materials used for indirect restorations. There is a lack of information about the properties of these materials, such as color stainability, in the literature. Exposure to different agents can lead to staining of the external film of materials, leading to esthetic variability between restorative materials. Cigarette smoke has been shown to stain dental materials that are commonly used today. Purpose: The purpose of this study is to investigate the color stainability of CAD Lithium Disilicate (Ivoclar Vivadent e.max), monolithic CAD zirconia, as well as CAD acrylate polymer PMMA (Telio) when exposed to cigarette smoke. The null hypothesis states that the ∆E values before and after exposure to smoke and ageing will not differ within the following isolated groups as well as between the different surface finishes of the same material groups: a. Lithium disilicate (e.max) glazed b. Lithium disilicate (e.max) polished c. Zirconia glazed d. Zirconia polished e. Telio PMMA Materials and Methods: Materials preparation In this study, 100 discs (each 2mm thick) were prepared of 5 different CAD/CAM surface-finish (lithium disilicate glazed, lithium disilicate polished, zirconia glazed, zirconia polished and acrylate polymer). Each material produced 20 discs. The materials were glazed and polished according to the manufacturer’s recommendations. The experimental diagram is described in Figure 1. Color Measurement The baseline color measurement was performed using a spectroradiometer, and the spectral data was converted to CIELAB values. The specimens were divided into 2 groups: control and experiment. The experiment samples were subjected to conditions simulating cigarette smoking, similar to what a restoration would be exposed to in an oral environment of a person smoking cigarettes. The control specimens were stored in saliva-resembling conditions. After the exposure, color measurement were performed in the same way as baseline color measurement and color change (∆E) was calculated before and after the intervention using the L*a*b values to quantitatively analyze the shade difference of each treatment group. Results: For the color change seen in the experimental samples between baseline and after smoking, mean ΔE values ranged from 12.8 to 19.2. The highest mean ΔE value was seen in the e.max (polished) sample with a value of 19.2 +/- 4.8. These experimental values can be compared against the corresponding control samples, which had mean ΔE values ranging from 1.3 - 5.0. All samples exposed to cigarette smoke resulted in a higher mean color change compared to corresponding samples subjected to ageing only. The brushing of the specimens led to the removal of excess gross smoke residue that remained on the surfaces. In measuring the color change between the post-smoking measurements and the post-brushing measurements, mean ΔE values ranged from 13.7 to 20.3. These experimental values can be compared against the corresponding control samples, which had mean ΔE values ranging from 0.7 to 2.9. The final color change data that was quantitatively analyzed was the overall color change from the baseline measurements to the post-brushing measurements. These mean ΔE values ranged from 2.5 to 9.6. The polished zirconia sample demonstrated the largest mean ΔE value, 9.6 +/- 1.8, while the glazed e.max samples had the smallest overall color change, with mean ΔE values of 2.5 +/- 0.4. These experimental values can be compared against the corresponding control samples, which had mean ΔE values ranging from 0.7 to 4.3. Based on our study, cigarette smoke exposure led to greater mean color change for all samples, independent of surface finish, compared to corresponding control samples exposed only to ageing solution. Discussion and Conclusion: The following conclusions were drawn from the results of our studies: I. When exposed to cigarette smoke, the CAD/CAM available materials of lithium disilicate, zirconia, and Telio are all susceptible to staining. II. The polished finish of e.max lithium disilicate does not lead to increased stainability when compared to the glazed surface of e.max lithium disilicate. III. The polished finish of zirconia does not lead to an increased stainability when compared to the glazed surface of zirconia. IV. After exposure to cigarette smoke, all restoration materials tested that are brushed with a toothbrush exhibit a decrease in staining.