The Mohs scale of substance hardness is a scientific qualitative ordinal scale which characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material.   You’ve all heard or read that a diamond is the ‘hardest’ substance on earth.  What does this mean exactly?  It means that on the mohs scale which runs from 1 to 10 a diamond is a 10.  The diamond can scratch every other substance and nothing can scratch it.  At the bottom of the scale is talc coming in at 1.  It can scratch nothing else.

Now where does the enamel of your tooth lie on the mohs scale?  it comes in around 5 on the scale and again, a lower number does not scratch a higher number.   Where does activated charcoal come in on the scale?  It rates at around a 2 meaning it cannot possibly scratch healthy tooth enamel.   Sodium Bicarbonate also has a light abrasive quality and comes in around a 2.5 on the scale.   Therefore, they are good for removing the soft material on the surface of the tooth without scratching it.