The temporomandibular joint (TMJ) – or what non-medical people call the jaw - is one of the most complex in the human body. It moves from side to side and up and down to enable us to speak and eat. Tension can occur in the jaw, and this is known as tightness.
You should visit your dentist for a diagnosis. Some causes are:
- Teeth grinding (aka bruxism)
- An improper bite due to a misalignment in the teeth or jaw
- A TMJ disorder
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Jaw tightness can range from mild to severe and be most painful when moving the jaw, such as when chewing or speaking,"
You can learn more in this article:
https://yourdentalhealthresource.com/what-causes-jaw-tightness/