Hi Black discolouration may be stains or deposits in the teeth or may be due to demineralization which causes initial caries....you need to go for complete clinical examination tonruke out the cause... If it is due to stains and deposits thn cleaning should be done....If it is any demineralized lesion them restoration should be done

Dental examination should begin, immediately when the first tooth begins to appear in the oral cavity. Roughly at 6months of age. Please see a local dentist every 6months To keep any dental concerns under check