Oroantral fistula: an opening left between the mouth and the sinus after an extraction

The maxillary sinus is an air-filled space inside the cheek, on either side of the nose. Its floor lies just above the roots of the upper premolars and molars. In some people there are a few millimetres of bone between the roots and the sinus; in others, the tip of the root projects into the sinus. If a tooth was removed years ago, or the person has been without teeth for a long time, the sinus can expand downwards and the bone in between becomes even thinner. In this situation, removing the tooth or taking out a root can leave a window into the sinus at the bottom of the socket.

This happens more often than people think. In a multicentre study following 1,057 upper wisdom tooth operations at four universities in Germany, the sinus was opened in 13 per cent of procedures. The rate was 24 per cent for fully impacted teeth, 10 per cent for partly impacted teeth and 5 per cent for fully erupted teeth; 83 per cent of the openings were smaller than 3 millimetres. In a study in Zurich examining 1,562 upper wisdom teeth, an opening between the mouth and the sinus was seen in 2.4 per cent, and the risk rose with age and with root fracture. In a series of 98 patients in Ankara, the tooth most often responsible was the upper second molar, followed by the first molar.

The difference between a fresh opening and a fistula has to do with time. As long as the hole stays open, the tissue lining the inside of the mouth grows inwards from the edges and lines the inner surface of the channel. The literature reports that this lining starts when the opening has lasted at least 48–72 hours, and that an established fistula channel forms in 7–8 days on average. Once the inside of the channel is lined, the clot finds nowhere to hold on, and the chance of closing on its own falls markedly. This is why the same hole that could be closed with a simple stitch on the first day may need tissue-shifting surgery, called a flap, two weeks later.

The symptoms trace the route from the mouth to the sinus and from the sinus to the nose. Those listed in Indian and German surgical reviews are: liquid coming out of the nose when drinking water or soup, being unable to drink through a straw or puff out your cheeks, the voice changing so that it sounds nasal, a whistling sound when speaking, discharge from one side of the nose, a bad or salty taste in the mouth, air escaping into the mouth when blowing your nose, and pain at the extraction site. They do not all have to be present; a very small opening may only be noticed when blowing your nose. We have described liquid coming out of the nose when drinking on a separate page, in terms of what you should do in the first few days; the focus here is the opening itself, the options for closing it and its effect on an implant plan.

Whether it will close is decided above all by its width, and the thresholds in the literature are close to each other but not the same. One review states that if there is no infection in the sinus, openings smaller than 2 millimetres can heal on their own with a clot, while a diameter over 4 millimetres, a socket deeper than 5 millimetres or tissue damage at the gum margin put this chance at risk. In a systematic review from 2025, openings under 5 millimetres were closed with materials that stop bleeding, and those above with surgery. The German review states that a fistula that has not healed within 3 weeks needs surgery, and that bone grafting is considered for defects over 10 millimetres. Measuring it is the dentist's job, not the patient's.

The price of waiting is paid in the sinus. As long as the opening remains, bacteria from the mouth pass directly into the sinus. A surgical review reports that with large unclosed openings, sinusitis developed in about half of patients within 48 hours and in nine out of ten within 2 weeks; Güven's series of 98 patients also reports that sinus infection could be seen with fistulas of every size and duration, and that the most prominent cause of chronicity was intervening sinusitis. Once the sinus is inflamed, the job is no longer just closing a single hole: first the sinus has to be cleared, and if needed an ear, nose and throat (ENT) specialist has to carry out endoscopic sinus surgery through the nose.

Timing also affects success. The introduction of a 2024 network meta-analysis reports that, according to the literature, success in closing the opening is 90–95 per cent when treatment starts within the first 24–48 hours, while success in the secondary closure of established fistulas can fall to as low as 67 per cent. The same study, comparing nine randomised studies, found that closure with the buccal fat pad gave better results in terms of closure and recurrence than cheek and palatal flaps; the authors also note the limitations of the study. An older systematic review, on the other hand, states that there is no randomised study testing whether the opening should be closed or not, and that the choice of technique is for now left to the surgeon's preference.

The implant side is the often-overlooked aspect of this topic. A fistula sometimes arises not from an extraction but from implant surgery: a tear in the membrane during a sinus lift, an implant that has slipped into the sinus or an infected graft can leave an opening. In an Israeli series examining implants displaced into the sinus, 11 of 24 patients had chronic sinusitis, and in 5 patients the fistula was also closed from the mouth side while the implant was removed through the nose. In the other direction, closures done with bone are reported to make a later implant and sinus lift in the area easier. In other words, a fistula is a heading that needs to be discussed at the start of an implant plan.

The first list gives signs suggesting that the opening is small and fresh, with a high chance of closing on its own or with a simple procedure. If an item in the second list applies to you, the opening may have become a channel or the sinus may be infected; do not wait.

The sequence starts with the most urgent possibility, then proceeds according to the size of the opening and the condition of the sinus.

1. 1

   First, a spreading infection is ruled out

   If there is swelling around the eye, a change in vision, difficulty swallowing or breathing, or facial swelling growing quickly with a high fever, the assessment is done at A&E; call 112. If these signs are not present, it is enough to contact the dentist who removed the tooth or an oral surgeon the same day.

2. 2

   Examination and the nose-blowing test

   The dentist asks you to blow gently with your nostrils pinched shut and looks to see whether air or bubbles come out of the socket. This is called the Valsalva test. A case reported from the Netherlands shows that a natural channel behind the front teeth can mislead this test; this is why the test is interpreted together with an X-ray. Because probing the socket hard can enlarge a small opening, the dentist does this carefully.

3. 3

   Imaging

   A panoramic X-ray can show a break in the sinus floor; cone beam computed tomography (CBCT), on the other hand, shows in three dimensions any thickening of the lining inside the sinus, a displaced root fragment and the width of the bone defect. Imaging publications stress that the diagnosis still needs to be confirmed by examination.

4. 4

   Protecting the clot with a small, fresh opening

   With small openings, a material that stops bleeding can be placed in the socket and stitched. Then come the pressure rules: one review prohibits blowing your nose and sneezing with your mouth closed for 2 weeks, and recommends keeping your mouth open when sneezing and coughing and avoiding straws and smoking. The dentist decides whether antibiotics and decongestant nasal drops are needed.

5. 5

   If the sinus is infected, the sinus comes first

   A closure done while sinusitis is present may not hold. This is why medication and rinsing of the sinus are tried first; for chronic sinusitis that does not improve, an ENT specialist may carry out endoscopic sinus surgery through the nose. A 2025 review reports that combining this surgery with closure from inside the mouth gave high success in patients with sinusitis.

6. 6

   Surgical closure

   With a fistula that has become a channel, the lined inner surface of the channel is first removed, then the hole is covered without tension using well-nourished tissue: a flap shifted from the cheek, a flap rotated from the palate or the fat tissue inside the cheek. For wide bone defects, bone or a membrane is also added. The technique is decided by the location and width of the opening and whether an implant is being considered in the future.

7. 7

   Checking healing and the implant plan

   Closure is confirmed at check-up examinations and, if needed, with repeat imaging. If an implant is being considered in the area in the future, surgery is not planned until it has been seen that the sinus is clean and the closure has healed soundly.

There is no single right technique. The choice is decided by the width and location of the opening, the condition of the sinus and whether an implant or denture will be made in the area later.

The following are wrong decisions commonly seen in this situation, and what they cost. We set them out so that you can ask the right questions whichever dentist you see.

Timings vary with the size of the opening, the condition of the sinus and the technique. The course below is the usual one described in the literature; the instructions your surgeon gives take priority.

1. The first few days

   There may be swelling and a mild nosebleed. Soft foods and liquids are taken on the side that was not operated on. Not blowing your nose, sneezing with your mouth open and not using straws or smoking are the basic rules of this period.

2. The first 2 weeks

   One review states that the pressure restrictions last 2 weeks. The antibiotics and nasal drops your dentist gives you are used during this period; the stitches are assessed at the check-up.

3. The first month

   At the check-up examination, it is checked whether liquid comes out of the nose and whether any opening remains in the socket. If a cheek flap was used, the cheek groove may still be shallow during this period.

4. 1–2 months

   The cheek groove returns to its former state within 4–8 weeks in most patients, but can stay permanently shallow in some. During this period, the fit of a removable denture can be reassessed.

5. The implant plan

   If an implant or sinus lift is being considered in the area, the timing depends on the closure healing soundly and on a CBCT scan showing that the sinus is clean. Your surgeon decides the exact timing.

We do not give figures here, because the scope varies a great deal with when the opening was noticed and the condition of the sinus. The items that determine the scope:

When it was noticed

An opening noticed during the extraction or on the first day is often closed with a simple procedure in the same session; an established fistula needs a separate operation.

The condition of the sinus

If there is sinusitis, medication and, if needed, endoscopic sinus surgery by an ENT specialist are added to the scope.

Closure technique

Using a soft tissue flap, the buccal fat pad, or bone and a membrane changes the length of the procedure and the materials.

Imaging

A cone beam CT scan is often requested to show the width of the defect and the condition of the sinus.

Dental treatment to be done later

If an implant or denture will be made in the area, discussing the plan together with the closure can reduce the need for extra procedures later.