When we clench or grind our teeth, especially over along period of time (such as during sleep), we overuse the muscles in our face. Just like any other muscles, if they are not allowed to rest/recover, you can expect sore muscles and injuries to occur. The main difference between going to the gym and clenching/grinding, is the fact these actions can be involuntary and habitual (and you will take time off from the gym to recover).
With patients who suffer majorly with TMD, they clench/grind their teeth most nights and their masseter muscles (used to clench) and the Lateral Pterygoid muscles (which move the jaw side to side) are not given time to recover, which can cause a whole host of symptoms as listed above.
One of the most common symptoms with grinders is a popping sound as they open their mouths. This happens because the Lateral Pterygoid becomes tighter (wound up) from excessive use, and when you open your mouth it pulls the articular disk (which sits at the end of the condyle – jaw bone) down. The articular disk is a thin bit of cartilage which has a purpose of sitting between the jawbones for smooth movement. So by treating the grinding as the root cause, it will allow the Lateral Pterygoid muscle to relax, allowing for a smooth movement again when you open your mouth.
With clenching, it is the masseter muscles that you use. Also known as the muscles of mastication (chewing muscles). Just like any other muscle, if you overuse them they can become more defined. As a result, if you bite together and feel your cheek muscles, you may notice they seem rather enlarged.
Now how the symptoms effect you is the bit that can be a bit vague, and we really don’t know why some people suffer more than others (it can often be a combination of factors).
When we clench/grind, overusing the muscles can cause pain to radiate to other areas in the body. Which is why clenching can cause upper back/neck pain or headaches. In some cases, you may be a clencher/grinder and you don’t experience any other symptoms. And in other cases, you experience a wide range of symptoms which causes extreme discomfort and stops you from enjoying your life as much as you should.