Black spot near the gum line..i had teeth cleaning made by a dentist 2 days back and he said that my teeth don't have any cavities but today i find a b?

Probably a bruise: A dark spot on the gum appearing shortly after dental work may be due to an "bruise" of the gum. A spontaneous dark area on the gum, or a dark spot after dental work which does not go away within a few weeks should be investigated by a doctor. RARELY, melanoma or other cancers can appear this way.

Review: Could be oversight or nothing at all. Return to Dentist and ask him/her to take another look.

See your dentist: Visit your dentist for re-evaluation to check the "Black spot". Could be only a simple stain or gigngival cavity. Hope it helps.

Could be blood in: the gum. Give it a few days if not going eway call your dentist.