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A hole in the gum behind the last molar has three common causes: an erupting wisdom tooth, a healing extraction socket, and a periodontal pocket. We sort them with one question at our Woburn office, which is whether a tooth was ever removed from that spot. The answer points to the cause, which decides what happens next.
The hole in the gum behind your last molar is an opening around a wisdom tooth, an empty tooth socket, or a deepened gap between the molar and the gum.
Your tongue finds the spot first. The back corner of the mouth is dark and hard to see, so the table below works from what you can feel and what you already know about that tooth.
Rows one and two describe healing or growth. Row three describes gum disease, and row four describes an infection that needs care today.
A small hole in the gums behind a back tooth is normal in two situations: while a wisdom tooth is coming in, and while an extraction site is healing.
Wisdom teeth are the last teeth to arrive, usually between the ages of 17 and 21. A wisdom tooth comes through gradually. Part of the crown breaks the surface first, and until the rest follows, the gum around it can look and feel like a hole.
Normal still deserves a look. The American Dental Association points out that a partly erupted tooth gives bacteria a place to enter the gums, which can lead to infection, pain, and a stiff or swollen jaw. Mention the spot at a routine dental exam so someone tracks it.
A hole falls outside normal when your wisdom teeth came out years ago, or when you are well past your early twenties and the spot is new. Holes that form in other parts of the mouth have a different list of causes, covered in our guide to a hole in the gums.
Food keeps getting stuck in the hole behind your molar because a flap of gum called an operculum covers part of the wisdom tooth and leaves a space underneath.
The flap behaves like a shirt pocket. Crumbs drop in easily and stay there until someone turns the pocket out. A toothbrush slides over the top of the flap and never reaches what sits below.
Trapped food and bacteria irritate the gum around the tooth. Dentists call that inflammation pericoronitis. The mild form brings an ache that comes and goes, bad breath, and a bad taste at the back of the mouth.
Recommended:
Toothpicks, fingernails, and the corner of a floss pick are the tools people reach for to dig the food out. Sharp objects cut the gum, and injured gum swells. Rinsing is the home step. Cleaning under the flap is a job for a dentist with the right instruments and a clear view.
Swelling around a wisdom tooth follows its own schedule, and we cover how long gum swelling takes to go down in a separate post.
A hole behind a molar needs a dentist quickly when pus, fever, or swelling shows up with it.
Cleveland Clinic notes that an untreated infection around a wisdom tooth can form an abscess and spread.
Red flags:
Trouble breathing or swallowing is a reason for emergency care, and the dental visit comes second.
A pimple-like bump on the gum that drains is a different finding with its own causes, explained in our post on a gum boil.
A dentist finds the cause of a hole behind a molar with a close look, a gum measurement, and an X-ray.
The look comes first. At Nova Dental, intraoral cameras and a Panorex X-ray do most of the work. The camera puts the back of your mouth on a screen, so you see the flap, the socket, or the gap for yourself.
The measurement comes next. A thin probe slides between the molar and the gum and reads the depth in millimeters.
The Panorex shows the whole jaw in one image, including a wisdom tooth still sitting under the gum. That single picture tells us whether the tooth has room to finish coming in or is stuck at an angle.
Dr. Talar Guldalian trained in prosthodontics at UCSF, and she walks every patient through the images on screen.
A hole you can feel but cannot see is hard to judge from home.
An exam shows which of the three causes you have and what, if anything, needs doing.
Nova Dental is independently owned, so no one here has a treatment quota to fill.
A hole that appeared after a wisdom tooth extraction is the empty socket, and seeing it there is expected.
A blood clot fills the socket first. The clot protects the bone underneath while the gum closes over the site.
Dry socket is the complication to know about. Mayo Clinic describes dry socket as a clot that never forms, comes out, or dissolves too early, and the pain typically begins 1 to 3 days after the tooth removal.
Signs of dry socket:
Call the dentist or oral surgeon who removed the tooth right away if those signs appear.
Food in a healing socket is common and unpleasant. Follow the rinsing instructions you were sent home with, and keep fingers, toothpicks, and your tongue out of the site. Drinks matter too, and we explain when coffee is safe after wisdom teeth removal.
A hole behind the last molar with no wisdom tooth and no recent extraction points to a periodontal pocket.
Gums fit around each tooth like a collar. A healthy collar leaves a shallow space, and the National Institute of Dental and Craniofacial Research puts the usual depth at 1 to 3 millimeters. Deeper readings can be a sign of periodontal disease.
The back surface of the last molar is a hard place to reach with a brush and floss. Plaque that stays there irritates the gum, and the gum can pull away from the tooth. Bleeding when you brush and breath that stays bad are the usual companions.
Treatment starts with scaling and root planing, a deep cleaning of the affected tooth below the gumline. Early gum disease often reverses with daily brushing and flossing. Advanced cases can need surgery.
"No wisdom tooth" sometimes turns out to mean "no wisdom tooth I can see." An X-ray settles the question.
A hole in the gum behind a molar closes on its own when it is a healing socket or a wisdom tooth that finishes coming in, and a periodontal pocket needs treatment to improve.
An erupting wisdom tooth with enough room fills its own opening once the crown is fully through. Irritation around a tooth that is still coming in can be temporary, and a dentist may choose to watch it.
A flap that keeps flaring gets treated in steps:
With treatment, pericoronitis usually clears within a week or two.
Dr. Guldalian will tell you whether the tooth can stay and arrange its removal when it cannot.
Sockets and treated gums both need time, and our post on how long gums take to heal covers what to expect.
A hole behind your molar that traps food or keeps swelling has a cause, and an exam is how you find it.
Tell us when you first felt the spot and whether a tooth was ever removed there.
Nova Dental is at 304 Cambridge Road, Suite 340, Woburn, MA 01801, serving Winchester, Woburn, Lexington, and Arlington. Call (781) 369-5722.
How long does pericoronitis last?
Pericoronitis lasts a few days in mild cases and several weeks in severe ones, according to Cleveland Clinic. With treatment from a dentist, the inflammation usually clears within a week or two. A gum flap that stays in place keeps trapping food and bacteria, so a dentist should check any flare-up that returns.
Can I use mouthwash on a hole behind my molar?
An alcohol-free antibacterial mouthwash, used twice a day, is part of the home care Cleveland Clinic lists for an inflamed gum flap, along with warm salt water rinses three to four times a day. Mouthwash keeps the surface cleaner. Rinsing cannot remove what is packed under the flap or inside a deep gum pocket.
Does every wisdom tooth with a gum flap need to be removed?
A wisdom tooth with a gum flap does not always need to be removed. The American Dental Association says the decision is made patient by patient, based on pain, infection, decay, gum disease, and damage to neighboring teeth. Wisdom teeth that stay still need daily flossing and regular checkups so changes get caught early.
Why does the hole behind my molar smell or taste bad?
A bad smell or taste from the hole behind a molar comes from food and bacteria trapped under the gum flap or inside the opening. Cleveland Clinic lists bad breath and a bad taste among the signs of ongoing pericoronitis. Pus adds a stronger taste and is a reason to call a dentist promptly.
Could a hole behind a molar be oral cancer?
A hole behind a molar has the three common causes described above. The National Institute of Dental and Craniofacial Research advises seeing a dentist or doctor about a sore, lump, thick patch, white or red patch, or numbness in the mouth that lasts more than two weeks. Appearance alone cannot rule anything out.