After orthodontics treatment, feeling pain in lower jaw bone when mouth closed. Due to this cant keep my mouth closed, have to keep it open. Please help?

Straight Talk. A beautiful smile is meaningless if a patient cannot function normally. If the origin of the problem is a result of muscular hyperactivity, it is a good idea to have your bite digitally balanced by your orthodontia/dentist.
Contact DDS. If you are currently undergoing orthodontic treatment and your mouth feels sore from tightening, see your orthodontist. It is probably transient and can be handled with over the counter medication. If a particular tooth is hurting, see your general dentist for a definitive diagnosis. Though not common, teeth can become devitalized if moved too quickly, sometimes not recognized until years later.
Transient. Especially when braces 1st you will have some soreness. It will gradually diminish. Didn't your Orthodontic Specialist give you management instructions? Try soft high protein diet, 1-2 200mg ibuprofen every 4 hrs with food or 8oz liquids, rinse w 1 tsp salt in 8oz warm water 3-4x/day.
More info needed. did you finish orthodontic treatment,or you just started. During orthodontic treatment,jaw soaring and mild pain is expected and that can be taken care of with OTC pain meds. . do you go to your ortho maintainance visits ? Consult your treating doctor if pain persists.