Dear Doctor: I had trouble opening my mouth wide when I was getting my teeth cleaned, and the hygienist said it could be TMJ. But my sister, who is a chiropractor, says she thinks it’s a muscle spasm. What is TMJ, anyway?

Dear Reader: TMJ refers to the temporomandibular joint, which connects the jaw to the skull. We each have two, one on each side of the jaw. These are the structures that allow us to open and close our jaw, move it from side to side and back to front. The temporomandibular joint, which is a sliding hinge joint, is a complex and delicate mechanism. It gets almost nonstop use as we speak, chew, yawn, smile and swallow. For some people, the joint continues to get a workout throughout the sleep cycle as they clench their jaws or grind their teeth.

When the joint stops working properly, it’s known as a temporomandibular disorder, or TMD. However, this type of malfunction has widely come to be referred to simply as TMJ.

Symptoms of a TMJ disorder can range from quite mild, such as an occasional clicking sound while chewing, to severe enough to interfere with eating or speaking. Someone having problems with this joint may experience tenderness or pain within the joint itself, in or around the ear, or in other areas of the face. The joint may make crackling or popping sounds when in motion, and it can lock, making it difficult, or even impossible, to fully open or close the mouth. Malfunction in the joint can cause tinnitus, which is a ringing sound in the ear, or other noise that isn’t caused by an outside stimulus.

Your sister’s suggestion that your range-of-motion problem is related to the muscles in the jaw refers to a condition known as trismus. It’s sometimes called lockjaw, which brings to mind the muscle contractions associated with tetanus. However, these days, trismus refers to any muscle spasm within the temporomandibular joint that limits range of motion. It occurs when the muscles we use in chewing contract and don’t release.

When someone can’t open his or her mouth wider than 1.3 inches, they are considered to have trismus. It can be caused by damage or injury to the jaw, and it can also arise as a result of TMD. Symptoms include the reduced range of motion you experienced, pain or cramping in the jaw that occurs with or without movement, and pain or difficulty when exerting pressure, as when eating.

Whether or not your jaw problem is due to TMD or trismus, we urge you to see your doctor or a TMD specialist for diagnosis. This will include a medical history, including information about recent dental procedures or physical injuries, an exam to rule out structural or other abnormalities, and measurements of how wide you can open your mouth. Depending on what is found, additional imaging studies may be requested. Treatment of TMD and trismus can include resting the jaw with a soft food diet, medications for pain, muscle relaxers, exercises to gently stretch the jaw, behavioral therapy and devices to prevent nighttime clenching. In rare cases, surgery may be required.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My hair has been thin since I was young, and now that I’m growing older, it’s getting worse. Why is that happening? Is there anything I can add to my diet to make my hair thicker and healthier, or is thinner hair inevitable with aging?

Dear Reader: Among the many changes we can expect to see in our bodies as we grow older are gradual differences in the appearance of our hair. In addition to going gray and, for some people, growing bald, this includes changes to hair’s thickness and texture. Aging hair typically grows more slowly and becomes more sparsely distributed. The strands themselves become more brittle, dull and thinner than they had been in the past. They become more fragile, as well, which can lead to increased splitting and breakage. Since the state of our hair contributes to our overall appearance, as well as to our sense of self, it’s understandable that these changes might be unwelcome.

A single strand of hair is composed of three separate layers of a hard protein called keratin. In younger adults, it has a life span of two to seven years -- or more -- and grows about one-half inch per month. Due, in part, to hormonal changes as we age, hair falls out more quickly in older adults and is replaced with finer hair that grows more slowly. Some hair follicles go completely dormant. Genetic, environmental and behavioral factors can also play a role in these changes and vary greatly from person to person. The good news is that, although you can’t completely turn back the clock to youthful hair, there are steps you can take to navigate these changes.

You asked about diet, and you’re correct that it can make a difference. The cells in hair follicles have a high rate of turnover, so maintaining a balanced diet is important. Some studies have suggested that supplementation of biotin, one of the B family of vitamins, can contribute to healthier hair. However, the National Institutes of Health reports there is insufficient data to back up these claims. Added biotin in the diet can interfere with important medical test results, including those used to diagnose heart problems, and can interact with some medications. Better to focus on getting adequate protein in your diet and eating from a wide range of fresh fruits and vegetables for vitamins and minerals.

Because hair becomes more fragile as we age, you’ll want to examine your styling routine, including the use of hair dryers and curling irons. Although it’s tempting to use hair sprays to build up volume, the alcohols they contain can contribute to drying. Try to find a good hydrating shampoo and conditioner to help your hair stay strong and flexible.

Certain medications, including some that control blood pressure and manage blood cholesterol, can contribute to thinning. Your doctor can let you know if this is the case and help find a solution. Some women opt for medications that promote hair growth, such as Rogaine or Propecia. Again, whether or not to go this route is a discussion you should have with your health care provider.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I am 53 and have diabetes. I live in California and can get the COVID-19 vaccination soon. What side effects can I expect? There are so many stories floating around, and knowing what to believe is hard.

Dear Reader: It’s true there’s a lot of confusion and, sadly, misinformation about the coronavirus vaccine. We’ve been answering specific questions in recent columns, and we are happy to share the bigger picture with you and the rest of our readers.

At this time, three vaccines have received emergency authorization from the U.S. Food and Drug Administration. They are manufactured by Pfizer, Moderna and, most recently, Johnson & Johnson. Clinical trials found all three vaccines to be effective in preventing symptomatic COVID-19. The Pfizer and Moderna vaccines require two doses, with the second dose administered three or more weeks after the first. The exact interval depends on which vaccine you receive; you get directions about how and when to get your second dose at the time you receive your first. Johnson & Johnson’s is a single-dose vaccine.

Potential side effects from the coronavirus vaccine can range from mild to severe. Anaphylaxis, which is a life-threatening allergic reaction, has received a lot of attention. However, this response to the vaccine is exceedingly rare. According to the latest figures from the Centers for Disease Control and Prevention, which tracks a wide range of data related to the vaccine, we are currently seeing about 2.5 episodes of anaphylaxis for every million doses of COVID-19 vaccine doses administered.

The vaccine itself is delivered via a very thin needle. Many people say they don’t even feel the injection. After you receive the vaccine, you will be directed to a designated area to wait during the CDC-mandated 15-minute period before leaving the site. People at risk of an allergic reaction, which is determined via a pre-vaccination questionnaire, are asked to wait for at least 30 minutes. Each vaccine site is required to have on hand the medication, equipment and trained medical personnel needed to address potential serious allergic reactions.

The most common side effect of the vaccine is temporary soreness and swelling at the injection site. This can begin anywhere from a few minutes to a few hours after the injection. Additional reactions can include fever, chills, headache, muscle aches, nausea and fatigue. These arise because the vaccine delivers a fragment of the coronavirus’s genetic code to stimulate the immune system to recognize it as a foreign invader and mount a response. You can reduce potential discomfort at the injection site by exercising your arm prior to getting the vaccine, and by applying a cool, wet cloth to the injection site.

Some people have a stronger response to the second shot of the two-dose vaccines. If that’s the case, over-the-counter meds such as aspirin, acetaminophen or ibuprofen can help manage post-vaccination symptoms. But don’t take these meds ahead of time to prevent side effects, as it’s not yet known if they affect the vaccine’s efficacy. If symptoms don’t go away after a few days, or if they grow worse, be sure to see your health care provider.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)