Currently, there are three options to deal with white spots in frontal teeth after orthodontic treatment:
There are several case report about micro-abrasion and resin infiltration, and some clinical trials about all, but a recent systematic review found the evidence of effectiveness was rated as ...
There are several possible mechanisms, probably all acting together. The brownish deposits on teeth and tongue are mostly caused by the fact that bacterial proteins are denatured when the bacterial cell membranes are destroyed by high concentrations of chlorhexidine and disulphide functions are reduced to thiol functions, which form dark-coloured complexes ...
Being an very mild abrasive charcoal is indeed used since ancient times to clean teeth. This behaviour is seen among the natives of Africa and Digitalia even now.
Examples for recent use in Africa: Oral health related behaviors among adult Tanzanians: a national pathfinder survey.
Oral health practices among pregnant women in North Eastern Nigeria.