Evolution has rendered wisdom teeth, also called third molars, unnecessary in humans. If trapped in the gums, impacted wisdom teeth may lead to dental problems such as pain, infection or misalignment of other teeth. Ten million wisdom teeth are extracted from approximately 5 million people in the United States each year.

Causes

Once, wisdom teeth were useful parts of the human anatomy. The theories about why they are no longer important vary. One theory is that wisdom teeth may have been bigger and due to the invention of tools, may have shrunk during human evolution.

"It's always been presumed that sometime in early Homo, we started using more advanced tools," lead study author Alistair Evans, an evolutionary biologist at Monash University in Melbourne, Australia, told Live Science. "Tool use meant we didn't need as big teeth and jaws as earlier hominins. This may then have increased evolutionary pressure to spend less energy developing teeth, making our teeth smaller." [Food for Thought: Human Teeth Likely Shrank Due to Tool Use]

Now that these teeth are no longer needed, they can cause problems. Wisdom teeth are the last to erupt and typically do so between ages 17 and 25. According to the American Dental Association (ADA), they may grow sideways, emerge only partially or remain completely trapped under gum and bone.

Symptoms & diagnosis

Wisdom teeth either produces no symptoms or causes these problems:

PainTooth decayCystsSwollen, red, tender or bleeding gumsSwelling around the jawGum infectionDamage to other teethBad breathAn unpleasant taste in the mouth near the affected areaFood to be trapped behind the toothHeadache or jaw acheOccasional difficulty opening the mouthOccasional swollen lymph nodes in the neckTo diagnose impacted wisdom teeth, dentists look for swollen gums or signs of infection such as tenderness, redness and drainage, according to the National Institutes of Health (NIH). They also inquire about symptoms and regular oral cleaning habits. A diagnosis can be confirmed only with dental X-rays, which may also indicate damage to other teeth or the jawbone.

X-rays are needed because they show the exact positions of the wisdom teeth, and help surgeons decide the best strategy for removal, said Lee Carrasco, an associate professor of oral and maxillofacial surgery at the University of Pennsylvania in Philadelphia.

Surgical options

Some impacted wisdom teeth don't require removal, but symptomatic cases usually need surgical extraction by a dentist or an oral surgeon in an outpatient setting. Local or general anesthesia may be used, depending on the severity of the condition. First, an incision in the gums is made and any bone blocking the impacted tooth is removed before the tooth itself, according to the Mayo Clinic. Afterward, the incision is stitched shut and the empty tooth socket is packed with gauze.

If the tooth is too large to extract in one piece, or if it's coming in at an angle, the surgeon cuts the tooth into smaller pieces with a drill. "It's less traumatic for the patient to take the tooth out in pieces," Carrasco told Live Science. "The goal is that we make them as comfortable as possible."

Surgery may be delayed if a wisdom tooth is already infected, in which case a dentist would likely prescribe antibiotics and wait a week to 10 days before proceeding.

After surgery

Patients are sent home with instructions for diet modifications and other measures to help manage the expected postsurgical pain and swelling. Complications are unusual, but may include:

Infection of the tooth or gums due to bacteria or trapped foodSinus damage near upper wisdom teethDry tooth socket or bone exposureWeakened lower jawboneNerve damage to the lower lip, chin or tonguePatients who develop any postsurgical complications should contact their doctors immediately.

Complications are rare, but dry socket typically has the highest prevalence, occurring in about 5 to 10 percent of patients, Carrasco said. After the surgeon removes a molar, the body forms a clot to stop the bleeding. The clot initially has the texture of pudding, but it forms a scab within a few days.

"That sometimes doesn't happen," Carrasco said. "The clot sometimes washes away, leaving bare bone."

Dry sockets often lead to pain and inflammation, and doctors treat it with a sedative dressing. "Almost always, over a period of the next few days, it starts to feel better," Carrasco said.

The anesthesia may also cause some people to feel nauseous, he added. "Everyone has some seepage or oozing within the first 24 to 48 hours," he added.

But after eating soft foods for a few days, people are typically ready to eat regular foods again.

Patients can also take prescription painkillers following surgery. Carrasco encouraged people with leftover medication to return the pills to a pharmacist or dispose of them in another safe way. Parents who monitor their medicine cabinet and their children's medications can help stop painkiller addiction, he said.

Risk on non-removal

Because bone is more flexible in people under 30, wisdom tooth removal may be simpler before then, according to the NIH. Some impacted wisdom teeth never need removal if they don't cause dental problems.

Impacted teeth that are not removed may lead to serious complications, including:

Cyst development around the tooth that may gouge the jawbone and damage adjacent teethInfection of the tooth or gumsChronic mouth discomfortMisalignment of teethPlaque caught between teeth and gumsThis article is for informational purposes only, and is not meant to offer medical advice.

Additional reporting by Alina Bradford, Live Science Contributor

Additional resources

Mayo Clinic: Impacted Wisdom TeethADA: Wisdom Teeth VideoADA: About Wisdom Teeth Removal