Hi Carole Nelson!

I actually don't show that F9940 is a valid code. My best guess here would be that it was intended to be D9940, which was actually recently deleted from the coding system, replaced with the following 3 codes:
D9944 occlusal guard – hard appliance, full arch
D9945 occlusal guard – soft appliance, full arch
D9946 occlusal guard – hard appliance, partial arch

Having said that, with Medicare, there is language in Medicare policy that indicates that appliances being used to treat temporomandibular joint disorders (TMJD) should be coded D7880 (occlusal orthotic device, by report). We do typically see Medicare deny claims for appliances being used to TMJD. As the doctor mentioned, most private/commercial medical insurers do deem intra-oral appliances for the treatment of TMJD medical in nature, but we do typically see the response from Medicare that they consider it dental in nature, therefor a statutorily non-covered service.

With that in mind, you may consider going ahead and sending it along to your secondary to see if they may offer some coverage, instead of appealing the denial from Medicare.

Hope this helps!