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"What causes one's jaw to pop?"
Ever since I was a kid, my jaw pops when I chew. Is this a sign of something serious? I always just assumed it was like cracking knuckles or my neck.
You're right, it is the phenomena causing your jaw to pop as is causing your knuckles to pop. the popping noise is related to the anatomy of a joint and to the physical properties of the gases dissolved inside the fluid within a joint. the joint in your jaw, like the majority of joints within your body, is a synovial joint.
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the anatomy of a synovial joint is as follows: at the articulation of two bones (a joint) there is a small amount of lubricating fluid (synovial fluid) that is contained within a joint capsule. when you chew, you are stretching the joint capsule around the synovial joint in you jaw known as the temporomandibular joint, or the TMJ. as your stretch the joint capsule, you increase the volume within the joint. by the inverse relationship between pressure and volume (i.e. when you increase the volume of a container, you decrease the pressure within that container), as you increase the volume of the joint, you decrease the pressure within the joint fluid, which lowers the partial pressures of the gases dissolved in that fluid which causes them to bubble out of the solution of fluid (this is based on the physical properties of any gas dissolved in a fluid, think of opening the cap on a bottle of Coke, which lowers the pressure of the Coke inside the bottle and bubbling ensues). the main gas dissolved in your body fluids is nitrogen, so as you lower the pressure of the synovial fluid, nitrogen bubbles out and bursts--creating the familiar 'popping' sound. so why does your TMJ seem to pop more than those around you? this is probably related to the laxity if the capsule surrounding your joint, i.e. it takes less movement of your jaw to stretch the capsule to the point that the nitrogen bubbles out of the synovial fluid and pops. this is related to the strain put on your TMJ on a daily basis, generally the more strain the more you distort the anatomy of the joint capsule and the more susceptible it becomes to 'popping'. main strains on the TMJ are teeth grinding at night and malocclusion of the jaw when chewing. if the popping becomes associated with pain, then there is acute inflammation in the joint which is known as TMJ syndrome. this is normally treated with over the counter anti-inflammatory meds (advil, ibuprofen) as well as a night guard for your teeth and minimizing unnecessary strain on the jaw, i.e. stop chewing gum or eating very chewy meats or other foods. hope this helps!
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