Hi Guest!

D8680 - orthodontic retention (removal of appliances, construction and placement of retainer(s))

The code listed above does not have a direct crosscode - so you can either bill the "D" code (dental code) on the medical claim (many insurers these days will process "D" codes when they are medically necessary services), or you can use the CPT code below and include a narrative report describing the procedure:
41899 - Unlisted procedure, dentoalveolar structures


Hope this helps!