The interplay between toothbrush stiffness and charcoal-containing dentifrice on the development of enamel topography changes

Background: This study aimed to investigate the in vitro effect of a charcoal-containing dentifrice with different toothbrush stiffness on enamel. Methods: Four main groups were applied: distilled water, conventional fluoridated toothpaste (Colgate^® Total^® 12 Clean Mint Toothpaste), charcoal toothpaste (Colgate^® Total^® Charcoal Toothpaste) and whitening toothpaste (Colgate Total^® Advanced Whitening Toothpaste). Three subgroups for each toothpaste were further included according to the toothbrush bristles’ stiffness (soft, medium, and hard). Enamel specimens were subjected to 1,250 and 2,500 cycles of brushing using toothbrushing simulation machine. The average surface roughness change (ΔRa) in nanometer (nm) was measured to estimate the changes following the brushing simulation model. Two-way ANOVA and Tukey tests analyzed the data. Results: The type of toothpaste and the bristles’ stiffness were determinant factors in increasing the ΔRa value (P = < 0.05). Generally, charcoal and whitening toothpastes with medium and hard bristles yielded higher ΔRa than fluoridated toothpaste and smooth bristles. Following 1,250 cycles of brushing simulation, charcoal toothpaste did not increase the enamel roughness compared to the controls. However, in prolonged brushing via 2,500 cycles of brushing simulation, using bristles with soft stiffness revealed that charcoal toothpaste was associated with increased surface roughness (55.86 ± 41.18 nm), which was statistically significant (P = 0.024) compared to the negative control. Using bristles with medium stiffness showed that the whitening (68.23 ± 48.58 nm) and charcoal (73.62 ± 34.66 nm) toothpastes significantly (P = < 0.05) increased the enamel roughness compared to the conventional toothpaste (36.53 ± 22.56 nm). There was no significant difference among the groups when brushes with hard bristles were used, as all the groups revealed increased enamel roughness. Conclusion: The use of charcoal and whitening toothpastes increased enamel roughness, particularly with long-term use. The effect of bristle stiffness on enamel roughness was found to vary depending on the type of toothpaste used.