Using charcoal for oral hygiene purposes is no new trend. In fact, powdered charcoal was used as an ingredient for toothpastes as far back as ancient Greece.
A recent literature review examining the effectiveness and safety of charcoal and charcoal-based toothpaste has found insufficient clinical and laboratory data to prove the safety and success of charcoal and charcoal-based toothpastes. It is advised to be cautious when using charcoal and charcoal-based toothpastes with unproven claims of effectiveness and safety.
Among other concerns, charcoal has been recognised as a mineral abrasive to the teeth and gingivae. Inclusion in products may remove external stains from teeth due to its abrasiveness but in doing so will cause damage to these tissues and could increase caries (tooth decay) susceptibility owing to the potential loss of enamel.
Refrence: John K. Brooks, Nasir Bashirelahi, Mark A. Reynolds The Journal of the American Dental Association, Volume 148, Issue 11, November 2017, Pages 785