A study published in the March 2019 edition of Pain: The Journal of the International Association for the Study of Pain has made some remarkable discoveries that could shine a brighter light on temporomandibular joint disorder and why it affects more women than men. Temporomandibular joint disorder is a painful medical condition that occurs when the temporomandibular joint gets out of alignment. It can cause everything from a popping and clicking jaw to tinnitus, teeth grinding (or bruxism), headaches, upper-body aches and even the inability to open or close the mouth. The article studied 999 cases and a control group of 2,031 persons without temporomandibular joint disorder from a previously conducted study, the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) study. Researchers examined case data for patients to better understand if there is a genetic component contributing to who gets temporomandibular joint disorder and who does not. The study yielded some surprising answers. “They found that there definitely is some gender-based reasoning why more women suffer from temporomandibular joint disorder than men,” says Wexford, Pennsylvania, neuromuscular orthodontic practitioner Dr. Alexandra George. George specializes in treating patients with temporomandibular joint disorder and says the condition is much more common in women. George is right: Statistically speaking, an estimated 90 percent of temporomandibular joint disorder sufferers are women in their childbearing years – a phenomena that has left many scratching their heads. “There have been many theories as to why women are so much more frequently affected by temporomandibular joint disorder,” says George. “Everything from women just report it more to women lead more stressful lives. These could still all be contributing factors.” But there could be something else at play, too. According to the Pain study, some men may have a genetic predisposition to high pain tolerance and may simply not notice they have temporomandibular joint disorder in the first place. Researchers were able to locate what they call a single nucleotide polymorphism, located on chromosome 3 in men with temporomandibular joint disorder. The men were found to have what is known as a trait locus with decreased expression on a muscle near their temporomandibular joint. This is known as a MRAS expression, and it affects the resiliency to chronic pain in men. Thus, the more men who have this MRAS expression, the fewer who would notice the pain associated with temporomandibular joint disorder. It’s fascinating science that answers a long-held mystery – and a breakthrough in temporomandibular joint disorder research to boot.