When should a mouth sore that is not healing be examined, and what will the dentist do?

Why two weeks is the dividing line

Most mouth sores are ordinary. A canker sore, a spot where you bit your cheek, a burn from hot food, or a place where a denture or a sharp edge of a tooth has been rubbing usually heals on its own within about two weeks, although some take longer. That healing pattern is what makes the two-week mark useful: a sore that is still there after two weeks is behaving differently from the common, self-limiting kind, and an examination is the only way to find out why.

This does not mean a slow sore is probably serious. Most sores that are checked turn out to be benign. The reason dentists and physicians use the two-week threshold is that oral cancer can begin as a small sore, lump, or red or white patch that does not hurt and does not heal, and it is treated more successfully when it is found early. A painless sore that lingers is exactly the kind that is easy to ignore, which is why the calendar, not the pain level, should decide when you call.

If you have not seen a dentist in a long while, the guide Haven't seen a dentist in years? What to tell the office before you arrive explains how to describe your situation so the first visit is useful.

Common causes and how they usually behave

The table below summarizes the features that are typical of each cause. It is a guide to the conversation, not a way to diagnose yourself: several of these can look alike, and a dentist or physician may need to look, feel, and sometimes test the tissue to tell them apart.

Two things stand out from the table. First, pain is not a reliable guide: canker sores hurt but are not cancerous, while an early cancer may not hurt at all. Second, several causes involve white patches, and only an examination, sometimes with a biopsy, separates a fungal patch from lichen planus, leukoplakia, or something more serious.

What the examination involves

A visit for a mouth sore is a focused examination rather than a full cleaning. If you are due for a routine visit anyway, the guide A dental cleaning and a dental exam do different jobs: what each one checks explains how the two differ. For a sore, expect the following.

• A history. When you first noticed it, whether it hurts, whether it has changed in size or color, whether you have had sores like it before, whether anything rubs against it, and whether a medicine was started around the same time. Your dentist will also ask about tobacco in any form, vaping, and how much alcohol you drink, because these change how a sore is interpreted. The guide Why your dentist asks about medications before looking at your teeth explains why the medication list matters here.
• Looking and feeling. The lips, cheeks, tongue (including underneath and along the sides), floor of the mouth, roof of the mouth, gums and throat are inspected, and the tissues and the neck are felt for lumps, firmness or tenderness. The surrounding teeth are checked for sharp edges, broken fillings, or an appliance that may be causing the sore.
• Measuring and recording. The size, location, color and texture are noted so a change can be recognized at the next visit.

Removing the cause and rechecking

When a sore sits against an obvious irritant, the first step is usually to remove the irritant: smoothing a sharp edge, adjusting a denture or appliance, or repairing a broken filling. The sore is then rechecked after a short interval. A sore caused by rubbing usually improves once the rubbing stops. One that does not change after the cause is removed deserves further investigation, because the irritant may not have been the explanation after all.

When a biopsy or referral may be advised

If a sore, patch or lump has no clear cause, has not healed in about two weeks, or looks suspicious on examination, your dentist may recommend a biopsy, in which a small sample of tissue is removed and sent to a pathologist, a doctor who examines tissue under a microscope, or may refer you to an oral surgeon, an oral medicine specialist, or a physician for that step. Ask the office whether a biopsy would be performed there or by referral, and how long results usually take. A biopsy is the test that usually gives a definite answer; an examination alone, however careful, can only estimate.

What raises the urgency

Any sore past two weeks should be examined. Some features make the examination more pressing, or change how it is interpreted.

• Tobacco and vaping. Tobacco in any form, including cigarettes, cigars, pipes, chewing tobacco and snuff, raises the risk of oral cancer. Combining tobacco with alcohol raises it further than either alone. Tell your dentist if you vape, so it can be weighed with the rest of your history.
• Heavy alcohol use. Heavy drinking is a risk factor on its own.
• HPV. The human papillomavirus is linked to cancers at the back of the throat and base of the tongue, which are hard to see and may show up as a lump in the neck, a persistent sore throat, or trouble swallowing rather than a visible sore.
• Sun exposure for lip sores. A sore or crust on the lip that does not heal, especially in someone with years of outdoor sun exposure, should be checked, because lip cancer is linked to sun.
• Age. Oral cancer occurs most often in people over 40, although it can occur at any age, and younger people with a persistent sore still need an examination.
• The sore itself. Numbness in the lip, tongue or chin, a sore that bleeds easily, a lump that is growing or feels firm, difficulty swallowing or moving the tongue, or a change in speech all move the visit up the priority list. Tell the office about these when you call so the appointment can be arranged appropriately.

None of these features means a sore is cancer. They are reasons not to wait out a third or fourth week hoping it resolves.

When to go to emergency care instead

A mouth sore is rarely an emergency, but some situations are. Go to the nearest emergency department or call 911, rather than using the appointment request form, if you have:

• difficulty breathing or swallowing;
• swelling of the face, mouth or neck that is spreading quickly;
• fever together with facial swelling;
• bleeding from the mouth that you cannot control with steady pressure;
• a serious injury to the mouth or jaw.

The guide Facial Swelling With Tooth Pain: When Emergency Medical Care Comes First explains these warning signs in more detail. A sore that hurts but has none of these features can wait for a dental appointment; a sore with any of them cannot.

The next step: describe the sore when you request an appointment

When you use the appointment request form or call during office hours, say that you are asking about a mouth sore and give the basics: where it is, how long it has been there, whether it hurts, whether it has changed, and whether you use tobacco or vape. That lets the team arrange the right kind of visit. A request is not a confirmed appointment; the team follows up to set the time.

Bring your sore tracker, any photographs you have taken, your current medication list, and the names of any medicines started in the past two months. If you wear a denture, retainer or night guard, bring it, because the fit may be part of the explanation. And if the sore heals before the appointment, keep the visit if you can: a sore that came and went may still be worth describing, and the examination also covers areas you cannot see yourself.