Charcoal whitening agents and composite resin: investigating color change and surface roughness

Abstract

Background: This study aimed to investigate the effects of different charcoal-based whitening products on the color stability and surface roughness of resin composite, following coffee-induced staining and subsequent brushing with whitening products.

Methods: Fifty disc-shaped specimens of Harmonize nanohybrid composite resin were fabricated and divided into five groups (n = 10 per group): Control (untreated), Colgate Total (CT), Colgate Total + Charcoal Solution (CT + CS), Colgate Charcoal (CC), and Charcoal Powder (CP). The specimens were immersed in coffee for five days to simulate staining, followed by brushing with the respective whitening products. Color changes (ΔE₀₀) were evaluated using the CIEDE2000 formula, and surface roughness was measured with a non-contact profilometer. Color and roughness analyses were performed at three stages: baseline, post-staining and post-whitening. SEM (Scanning Electron Microscopy) analysis was conducted descriptively at the end of the study to observe surface morphology. Statistical analysis was conducted using one-way ANOVA and post-hoc Tukey tests (p ≤ 0.05).

Results: All experimental groups showed significant color changes after staining (ΔE_{00 - 1}>1.8, p ≤ 0.05). The CP group exhibited the highest color change after whitening (ΔE_{00 - 2} = 7.13 ± 1.38, p ≤ 0.05). Surface roughness increased significantly in the CT + CS (Ra = 0.57 ± 0.22 μm) and CP (Ra = 0.54 ± 0.20 μm) groups (p ≤ 0.05). No significant differences in surface roughness were observed in the regular toothpaste and charcoal toothpaste groups (p > 0.05). SEM analysis revealed pronounced surface irregularities, particularly with CP treatment.

Conclusion: Charcoal-based whitening products significantly affected color stability and surface roughness, with the CP group showing the greatest adverse effects. Regular and charcoal toothpastes had no significant impact on surface roughness, indicating a safer profile.

Keywords: Activated charcoal; Color stability; Resin composites; Surface roughness; Whitening products.

Fig. 1

A schematic drawing summarizing the study method (CT: Colgate Total, CS: Charcoal Solution, CC: Colgate Charcoal, CP: Charcoal Powder)

Fig. 2

Mean color change (ΔE₀₀) of resin composite samples after immersion in coffee solution (ΔE_00 − 1) and subsequent use of whitening products (ΔE_00 − 2) Different lowercase letters (a, b, c) above the bars represent statistically significant differences between experimental groups at the same time point (either ΔE_00 − 1 or ΔE_00 − 2) (p ≤ 0.05). Different lowercase letters (x, y) within the same group, comparing ΔE_00 − 1 and ΔE_00 − 2, indicate statistically significant differences between time points (before and after whitening) (p ≤ 0.05)

Fig. 3

Histogram showing the frequency distribution of color change (∆E₀₀) after staining (∆E_00 − 1) and subsequent whitening treatment (∆E_00 − 2). The control group exhibited minimal color change, while the “Charcoal Powder” group showed the greatest color change after whitening

Fig. 4

Changes in surface roughness parameters (R₀: baseline, R₁: after staining, R₂: after whitening) of resin composite samples across all groups. Different lowercase letters (a, b, c) above the columns indicate statistically significant differences between different groups at the same measurement stage (R₀, R₁, or R₂) (p ≤ 0.05). Different lowercase letters (x, y, z) within each group across the three time points represent statistically significant differences within the same group over time (p ≤ 0.05)

Fig. 5

Histogram illustrating the frequency distribution of surface roughness parameters (R₀, R₁, R₂) following staining and whitening procedures. The data indicate distinct variations in surface roughness across the treatment stages, with significant changes noted particularly in the R₂ measurements

Fig. 6

SEM images showing the surface morphology of resin composite samples after brushing with various whitening products. (a) Control, (b) Colgate Total, (c) Colgate Charcoal, (d) Colgate Total + Charcoal Solution, (e) Charcoal Powder