For the past 10 years I've been lightly grinding my teeth. Previous partners have noticed it at night and my dentist has suggested a mouth guard in the past to help.
I hate the feel of a mouth guard so avoided the suggestion for years and also avoided trying to solve it. But in the past 3 years i accidentally discovered the root cause and have been using various methodologies that as a side effect have mostly got it to stop.
Root cause: Trauma. (this can be either mental and/or physical)
The body will attempt to protect you in different ways. Tension, clenching, stiffness, etc. These are short term strategies which can be useful. But if the trauma isn't worked out it can leave the sympathetic nervous system in a heightened state.
Toolbox: (I like this metaphor because it's never one "trick" to fix things)
* Therapy - Seems obvious in retrospect but i was very skeptical at first. I ended up seeing one who specialized in mindfulness & cognitive behavioral therapy (CBT). But you'll want to see what system works best for you
* Acupuncture
* Meditation practice
* Literally learning how to breathe (i would oddly hold my breath)
Using this toolbox has been a life-changer for various "bugs" in my life. Many i wrongly assumed were unfixable.
All of this has led me to feel calmer. Which has relaxed my body and helped with my posture. I can sleep better, and this lowered heightened state has largely removed my jaw clenching.
Find a way that works for you. But know that it's not a forever issue <3