Hello & welcome,
If you are noticing hard chalky substance on teeth surface above the gums & that it never comes off, then definitely that is calculus formed on teeth.
Calculus formation occurs most commonly on the lower anterior teeth as those are directly in contact with saliva.
& food debris accumulates on teeth surface which if not cleaned for prolonged period, leads to precipitation of calcium from saliva over this plaque or food debris.
As calcium deposition goes on, the surface of the debris becomes hard & finally it gets chalky look.
It is so hard, that you cant remove it even with forceful brushing.
Visit your dentist
as soon as possible & get your teeth cleaned (scaling) thoroughly. You may require two or three sittings of the scaling if dentist thinks single sitting may not suffice.
Black dot on molar is just the start of decay in same tooth. Dentist will fill with any proper restorative material.
Use soft tooth brush after you undergo scaling & polishing by your dentist.
Hard & forceful Brushing is to be avoided .
Brush your teeth by holding your brush horizontally with bristles resting on teeth. Back & forth movement is then done followed by up & down movement with just a little pressure.
You can use mouthwash for shorter period so as to avoid staining your teeth & oral mucosa