Hi, thanks for writing to HCM.
This is just to educate you that plates and screws that are applied for fractures
act only as "internal splints" (supports) till the bone unites naturally. Generally, the bony union period for mandible and maxilla
will be around 12 weeks.
As it has been more than 3 years, I feel there should not be any problem and you can participate in martial arts training without any issues.
Hope this helps