Chemical Analysis of Charcoal Dentifrices and Their Abrasivity In Vitro

Objectives: The use of charcoal dentifrices has become increasingly popular in recent years. Manufacturers claim these products to have low abrasivity and to be non-toxic (charcoal prepared from coconuts). However, few studies have been carried out investigating these claims. Little is also known regarding their composition. This study aimed to investigate the composition and abrasivity of two commercially available charcoal toothpastes.
Methods: The charcoal dentifrices NAO (NAO Cosmetics, Fyllingsdalen, Norway) and COCO (Skin Technologies, Bergen, Norway) were investigated.

Suspensions of the charcoal dentifrices in toluene and in a mixture of methanol and toluene (1:7) were prepared and sonicated for 4 hours at 40^oC. Following filtration, solvent exchange, solid-phase extraction and concentration, the resulting extracts were analyzed using gas chromatography-mass spectrometry.

The abrasivity of the charcoal dentifrices on human molar dentin was investigated according to ISO 11609 – Dentifrices, and compared to a fluoride-containing whitening dentifrice (Colgate Max White, Lysaker, Norway) and distilled water as controls (n=6 molars in each group). A stylus profilometer (Mitutoyo, Neuss, Germany) was used to measure the roughness (Ra, µm) of the dentin surface after abrasion compared to baseline measurements. The roughness values were converted into relative dentin abrasivity values (RDA) according to ISO 11609.
Statistical analyses (One-way ANOVA) were performed with GraphPad Prism 7.01 (La Jolla, CA, USA).
Results: Regarding potential hazards, NAO contained naphthalene (possibly carcinogenic to humans, IARC 2B) and benzophenone (UV absorber, allergen), while COCO contained benzophenone.

The dentin surface roughness was higher after brushing with NAO and COCO, compared to controls. Both charcoal dentifrices gave higher RDA values (NAO: 130 and COCO: 108) compared to Max White (70) and distilled water (7).
Conclusions: The two charcoal dentifrices investigated contained compounds that may be hazardous to the patient, and their abrasivity was higher compared to the fluoride-containing dentifrice.