You're stating that the insurance downcoded the procedure based upon the evidence of the perio chart? It would depend on if you are in network or out of network with the insurance company as to how they process the difference when they downcode the procedure. If you are in network, it's likely that they process it as a write off. If you are out of network it will depend on the payor, but they may make the difference the patient responsibility. Chances are, the difference will be written off in most cases.