Underbite Surgery-Not Covered Completely by OHIP?

My son, 21 y/o, needs underbite surgery (Orthognathic surgery), procedure that is covered by ohip.

Oral surgeon explains there is an additional $7,000 (pre and post surgical planning) not covered by ohip.

Family income <25000/ year. Since ohip doesn’t cover completely this procedure, is there another gubernamental Institution that could help me pay this additional amount?

Thank you