Can very small cavity or hole on smooth occult surface of mollar be remineralized, that is not black in colour & very tiny? no pain or sensitivity.if it can't be remineralized then will excellent oral hygiene arrest it & prevent further progression?

Your are seeing only the surface enamel. If you can see the hole with your naked eye, there are literally tens of thousands of bacterial cells within its confines. And once bacteria reach the underlying dentin they rapidly hollow-out the inside of the tooth. No, cannot bee remineralized. No, oral hygiene procedures will not result in resolution. See Dentist, get it fixed before it spreads.

Asked and answered. See a dentist to determine if what you see is a carious lesion that needs restoration. Lack of pain has no bearing on treatment necessity. Only slightly demineralized enamel can be reversed with appropriate medicaments.