Do I need to replace a temporary filling after a root canal done through a permanent crown porcelain banded to metal)

Yes, you definitely want to replace the temporary filling with a permanent filling. It is important that the inside of this tooth remains sealed. If your crown fits well and does not have any decay around the edges, there is no need to replace it. Filling this root canal access hole would likely cost $175-$250, a new crown would be closer to the $1100-$1500 range.

All temporary fillings must be replaced to prevent leakage and possible reinfection or contamination of the completed root canal.

Hi:If there is no damage to the crown, and the fit of the crown is good, you should change the temporary filling to a permanent filling immediately.  Any bacterial leakage can have bad effect on the recent root canal.Best,Dr. Maddahi