Please tell me, could get a finger under the tooth filling.?

Redo it!: If you can get a finger under the tooth filling, you either have a 1)an overhang at the margin, of which you must trim back to establish good gingival health, or 2) a gap at the margin or open margin, of which you must redo the filling or recurrent decay will happen after a while.

Fingernail ??: If the edge of the filling is not even with the tooth or if the tooth has worn underneath it then you might get a fingernail under the edge. Usually this happens at the gumline. See your Dentist to get this checked -- it might be decay at the edge (margin). Good Luck.

Return to yr dentist: If the discomfort still continues, it may indicate a further problems. You will need to return to your dentist and have the filling reshaped or replaced.