Two options I'd recommend as your priority - and then two different exercises you can try now: a jaw exercise to help relax and strengthen the jaw, strengthening the muscles at an open position vs. how clenching will strengthen them at a grinding position, and a mouth strengthening exercise.

First of two is lower cost, however if you can afford it you may as well go for the higher cost option which will have much higher potent healing potential.

Re: PRP & stem cell treatments

I'd recommend PRP (platelet rich plasma) injections as low cost option for your jaw including the clenching muscles. PRP is healing property concentrate from your blood and is highly anti-inflammatory. That alone could help break the cycle of clenching, and perhaps heal some damage and reduce strains in the muscles.

The more expensive version is using your own stem cells that can potentially heal/regenerate the tissues fully. You'd be prescribed opiates for a number of days and need liquid, soft diet for a few days too. Stem cell treatment would literally be the best experiment you could try. That you mentioned jaw injury makes me feel like it's likely the best route, but if you can't afford the ~$7000 - $9000+ USD + travel and stay costs for stem cell treatment, PRP is usually closer to $1000 but from my own experience only heals maybe the top 20% of pain at a source and not the deeper pains - perhaps a good litmus test where if you feel improvement but not enough then you'd know that stem cells would heal further.

There would be enough stem cells to treat more than your jaw as well, and would be best to also have your neck looked at and treated. Different doctors/clinics have different requirements before treatment such as seeing an MRI of the areas to be treated or where they may only use ultrasound to check and guide them.

I've had my jaw treated multiple times - had a lot of pain from a dislocated jaw, and also a bicycle collision. My jaw pain is arguably 90%+ lower than it used to be. I've had a lot in my body treated, I have a complex pain situation - old injuries that are amplified by central sensitization I developed - so healing even small injuries helps reduce the pain a lot.

There are two places I've gone for treatment multiple times: a doctor in San Francisco, California, who uses adipose/fat derived stem cells (think mini liposuction), and a clinic near Denver, Colorado, that use bone marrow aspirate (drill into hip bone on both sides of Iliac crest to then suck out the marrow); then there's processing they do with it, along with drawing blood to mix the stem cells with PRP to support the healing. You may find a doctor or clinic closer to you, otherwise I'd trust recommending you to them if you'd like their details; I have no incentive for referring them to you, you could tell them I did or not, or hopefully find another place that seems reputable enough to you - I'm just wanting to help people.

Re: Jaw strengthening exercise

As I said the purpose of this jaw exercise is to help strengthen the muscles at an open position, which also helps relax the muscles through the resistance part of the exercise that acts to stretch them.

It's quite simple: 1) Open your mouth enough so your teeth aren't touching (your lips never need to separate) - you'll find what range of open is comfortable as you do the strengthening-stretching. 2) Place the fingers of both hands on your chin - thumbs underneath, other fingers in front with pinkies next to each other just touching above the last joint, with your elbows relaxed down. 3) Start by applying slight pressure diagonally towards the jaw joints which will engage your hands slightly preparing to the hold to begin. 4) It doesn't matter which order you start in: as you gently pull your jaw downward with your fingers, resist by engaging your jaw to keep your jaw from ...

This can stretch out really tight muscles and may cause things like a headache. It will also help stretch fascia as well that if tightened over time will contribute to problems.

Re: Mouth strengthening via oil pulling

Oil pulling will strengthen your tongue and the holistic musculature of your mouth, as well has help stretch it. You can use any type of consumable oil (though you don't want to swallow it) like coconut oil, however sunflower oil is more often recommended in certain holistic health circles as sunflowers can absorb radiation - whether that translates to oil pulling radiation from the body, I'm unaware if there's any research showing that. The mechanism for using oil over say water is that it's viscous - and the goal is to keep moving the oil around as fast as you can for tbe duration: pushing and pulling, swishing through teeth forward and back, and sides of the mouth through the teeth, using suction or pressure with the action of the tongue. Try to do it for 2 minutes when you begin, do it daily to quickly strengthen. Your tongue and other mouth muscles will get tired but you'll feel a difference and how it gets easier each day you do it. Use a tablespoon of oil, though if not enough resistance than add more oil - if too much resistance/difficulty, use less; mouth size varies. Oil pulling is good for your teeth and gums too. Spit the oil out into the toilet, it's often suggested then to rinse your mouth, swishing around like you were, with highly diluted hydrogen peroxide for 5 seconds or so - and can spit that out in sink.