Dental Sinus Infection: Causes, Symptoms and Treatment

A persistent sinus problem that does not respond to antihistamines or decongestants may not be coming from your nose at all. In some cases, the source is a tooth.

This article explains how dental sinus infections develop, how to recognise the symptoms, and what treatment looks like by the team at Bellevue Hill Dental.

What Is A Dental Sinus Infection?

A dental sinus infection, clinically known as maxillary sinusitis of endodontic origin (MSEO), happens when bacteria from a decayed or infected upper tooth migrate into the maxillary sinus. The maxillary sinuses are the large air-filled cavities behind your cheekbones, and they sit just above the roots of your upper back teeth.

Because the roots of upper premolars and molars are in close proximity (sometimes physically touching), the sinus cavity, which is an infection that starts in a tooth can travel directly upward through the sinus floor. Once bacteria reach the sinus lining, inflammation follows, triggering the typical symptoms of sinusitis.

Importantly, a dental sinus infection usually affects only one side of the face. This is one of the ways to distinguish it from a common cold or seasonal allergies, which typically affect both sinuses equally.

Dental Sinusitis Vs Regular Sinusitis — Key Differences

Feature	Dental sinus infection	Regular sinusitis (viral/allergic)
Side affected	Usually one side only	Often both sides
Primary symptom	Toothache + sinus pressure	Congestion + facial pressure
Mucus appearance	Thick, yellow or green, one nostril	Both nostrils, watery to thick
Response to decongestants	Minimal or temporary	Usually helps
Duration	Persists until dental cause treated	Typically resolves in 7–14 days
Trigger	Tooth decay, abscess, failed root canal	Virus, allergen, bacteria

What Causes A Dental Sinus Infection?

Any condition that allows bacteria from a tooth to reach the sinus lining can cause dental sinus infection. The most common causes may include:

• Tooth decay that has progressed to the pulp (inner nerve) of an upper molar or premolar
• A dental abscess, which is a pocket of infection at the root tip
• A failed, cracked, or incompletely treated root canal
• Advanced gum disease (periodontitis) affecting upper back teeth
• A wisdom tooth that is impacted or partially erupted near the sinus
• Trauma to an upper tooth that results in a dead (necrotic) nerve

The maxillary sinuses are most commonly involved because the roots of the upper second premolars and first and second molars extend closest to or into the sinus floor.

The condition may cause years of recurring sinus problems if the dental origin is missed. Many patients are treated repeatedly for general sinusitis before a dentist identifies the tooth as the source.

Dental Sinus Infection Symptoms

Symptoms overlap with regular sinusitis, which is why dental sinus infections are frequently misdiagnosed. The key is the one-sided pattern and the presence of dental pain.

Common symptoms

• One-sided facial pain or pressure — particularly under the cheekbone or around the eye on one side
• Thick, discoloured mucus from one nostril — yellow, green, or brown in colour
• A persistent bad taste or bad breath that does not improve with brushing
• Toothache in the upper back teeth — often a dull ache that worsens when chewing
• Congestion or a blocked nose, typically on one side
• Post-nasal drip — mucus running down the back of the throat, which can cause a cough or sore throat
• Headache or sinus pressure that worsens when you bend your head forward

Less obvious symptoms that patients often miss

• Sensitivity in upper teeth to temperature (hot or cold foods)
• A foul smell in the nose without an obvious cold or flu
• Swelling or tenderness along the cheekbone on one side
• Earache or a feeling of pressure in the ear (referred pain)
• Fatigue, especially if the infection has been present for weeks

Can a tooth infection cause a sinus infection?

Yes. A study published in 2023 found that up to 40% of cases of maxillary sinusitis in otherwise healthy adults have a dental origin.

The mechanism is straightforward: when bacteria from an infected tooth reach the sinus lining, they trigger an immune response. The sinus lining swells, drainage is blocked, and mucus accumulates, producing the classic symptoms of sinusitis.

The key difference is that antibiotics alone will not resolve a dental sinus infection. Until the infected tooth is treated, the bacteria have a persistent source and the sinus problem will keep returning.

Can Sinus Infection Cause Tooth Pain In Lower Teeth?

Sinus pressure can cause referred pain in upper teeth (not lower), because the roots of upper molars sit close to the maxillary sinus floor. When the sinus lining becomes inflamed, it can press on the nerve endings near these tooth roots, causing a generalised ache across several upper teeth, even if none of them is infected. This can make it difficult to pinpoint which tooth is causing the problem without dental X-rays or a CBCT scan.

Lower tooth pain is generally not related to sinus infections and should be assessed independently.

Tooth Root In The Sinus Cavity: What This Means

In some patients, the root tip of an upper molar actually extends into or through the floor of the maxillary sinus. This is a normal anatomical variation. It doesn’t cause problems on its own.

However, if that tooth becomes infected, the proximity means bacteria can reach the sinus almost immediately. It also means that extracting such a tooth requires care to avoid creating an oro-antral communication (a small opening between the mouth and the sinus), which would need to be surgically closed.

Your dentist will identify this from dental X-rays or a CBCT (cone beam CT) scan before proceeding with any treatment. At Bellevue Hill Dental, we assess this carefully before recommending extraction or root canal therapy for upper back teeth.

Dental Sinus Infection Treatment

Effective treatment addresses the dental cause first. Treating only the sinus with nasal sprays, antibiotics, or surgery without fixing the infected tooth will not resolve the problem.

Step 1 — Treat the tooth

• Root canal therapy: Removes infected pulp and bacteria from inside the tooth, sealing the canal to prevent reinfection. This is usually the preferred option when the tooth can be saved.
• Tooth extraction: Recommended when the tooth is too damaged to save. The dentist will take care to protect the sinus during extraction and will monitor for oro-antral communication.

Step 2 — Manage the sinus infection

• Antibiotics — typically amoxicillin or augmentin, prescribed for 7–14 days in cases where the sinus infection is established. Note: Antibiotics alone will not resolve the condition if the dental cause remains.
• Decongestants — nasal sprays or oral decongestants to reduce sinus pressure and improve drainage
• Saline nasal rinses — daily use helps clear mucus and soothe inflamed tissue
• Pain relief — anti-inflammatories such as ibuprofen to manage pressure and discomfort

Step 3 — Follow-up assessment

Your dentist will usually review you 4–6 weeks after treatment to confirm the sinus has resolved. If symptoms persist despite successful dental treatment, referral to an ENT (ear, nose and throat) specialist may be recommended to rule out any residual sinus disease.

Do antibiotics clear a dental sinus infection on their own? Usually not. Antibiotics may temporarily reduce symptoms, but because the source remains active, the infection tends to return. Definitive treatment requires addressing the dental cause.  If you’ve had multiple courses of antibiotics for sinusitis without lasting improvement, ask your GP for a referral to a dentist for dental assessment.

How Long Does A Dental Sinus Infection Last?

Without treatment of the underlying dental cause, symptoms can persist for months or even years, returning in cycles as bacteria continue to irritate the sinus lining.

Once the tooth is treated (typically through root canal therapy or extraction), most patients notice significant improvement within 2–4 weeks. Full sinus recovery, including clearance of residual mucus and return of normal drainage, generally takes 4–8 weeks, depending on how long the infection was present.

Sinus Infection Vs Tooth Infection — How To Tell The Difference

This is one of the most common questions patients ask when they have both facial pressure and tooth pain. In practice, the distinction matters because the treatment is different.

Clue	Points to dental cause	Points to sinus cause
Pain location	Aches in one specific tooth	Vague ache across several upper teeth
Pain trigger	Worsens with hot, cold, or biting	Worsens when bending forward
Mucus pattern	One-sided, persistent, discoloured	Both sides, often clears with decongestants
Dental history	Recent decay, extraction, or root canal	No recent dental issues
Duration	Present for weeks without improvement	Linked to cold or allergy season
Response to antibiotics	Minimal or temporary	Often improves with treatment

The most reliable way to distinguish them is a dental examination combined with X-rays. A CBCT scan gives the clearest view of the relationship between tooth roots and the sinus floor.

How To Prevent Dental Sinus Infections

The best prevention is straightforward dental hygiene combined with regular check-ups that catch tooth decay before it reaches the nerve.

• Book a dental check-up every 6 months. This allows early detection of tooth decay before it becomes an abscess
• Address the toothache promptly. Pain in an upper back tooth that persists beyond a day or two warrants a dental assessment, not just pain relief
• Don’t delay treatment for a cracked or broken upper molar. Cracks allow bacteria to enter the pulp and travel toward the sinus
• Maintain good dental hygiene. Brushing twice daily with fluoride toothpaste and flossing daily to prevent the decay that leads to pulp infection
• If you’ve had root canal treatment on an upper molar, attend your review appointments. Failed or leaking root canals are a known cause of MSEO

Frequently asked questions

Can a tooth infection spread to the sinuses?

Yes. Bacteria from an infected upper molar or premolar can travel through the thin bone separating the tooth root from the maxillary sinus. This is particularly common when the infection has progressed to an abscess at the root tip.

Can a bad tooth cause mucus in the throat?

Yes. A dental sinus infection can cause post-nasal drip, which is excess mucus that drains from the maxillary sinus down the back of the throat. Patients often describe a persistent phlegmy feeling or a mild cough that doesn’t respond to cold and flu remedies.

Can a tooth infection cause congestion or a runny nose?

It can. Inflammation in the maxillary sinus from a dental infection often causes one-sided nasal congestion. The side affected usually corresponds to the side where the infected tooth is located. If your congestion is one-sided and persistent, see a dentist.

Will a dental sinus infection go away on its own?

It is unlikely to resolve without treatment. While symptoms may fluctuate, the underlying bacterial infection will persist as long as the dental source remains. When it is left untreated, the infection can spread to adjacent teeth, the surrounding bone, or, in rare cases, to deeper structures. Early treatment leads to better outcomes.

Can a sinus infection cause tooth pain in the lower jaw?

Sinus infections typically cause referred pain only in the upper teeth, not the lower jaw. Lower jaw pain has other dental causes, such as decay, cracked teeth, TMJ dysfunction, or gum disease, and should be assessed separately.

How is a dental sinus infection diagnosed?

Diagnosis involves a clinical dental examination, dental X-rays to assess root condition, and often a CBCT scan to visualise the relationship between tooth roots and the sinus. Your dentist may also refer you for a CT scan or ENT consultation if the picture is unclear.