D9940 is an occlusal guard this procedure will require a brief narrative to prove medical necessity. It is a removable dental appliance and is designed to minimize the effects of bruxism and other occlusal factors.
D7880 is an orthotic device which also requires a brief narrative to prove medical necessity, however this device is used for treatment in TMJ disorders and includes splints.
You may not bill D0470 in addition to these codes as the impression is considered inclusive of the initial procedure.