Why Does an Infected Back Tooth Sometimes Cause Pain in the Tooth Directly Above or Below It?

If you have ever experienced a dull, throbbing ache in your upper teeth only to be told by a dentist that the problem actually lies in a lower tooth — or vice versa — you are certainly not alone. This can feel confusing, even a little alarming, and it is one of the more common reasons people turn to the internet to understand what is happening inside their mouth.

Referred dental pain from tooth infection is a well-recognised phenomenon in clinical dentistry, and understanding it can help explain why diagnosing the true source of toothache is not always as straightforward as it may seem.

This article explores why an infected back tooth can generate pain that appears to come from the tooth directly above or below it, what is happening beneath the surface, and why early professional assessment matters. If you are currently experiencing unexplained dental pain, this article aims to provide clear, accurate information — while encouraging you to seek personalised advice from a qualified dental professional.

At a Glance

Referred dental pain from tooth infection occurs because the nerves supplying upper and lower back teeth travel closely together along shared nerve pathways. When one tooth becomes infected, pain signals can be misread by the brain, creating the sensation of discomfort in the opposing tooth rather than the actual source.

Understanding Referred Dental Pain From Tooth Infection

Referred pain is not unique to dentistry — it is a well-established neurological concept seen across many areas of medicine. In the context of dental infections, it describes a situation where the brain perceives pain as coming from a location that is different from the actual source.

The back teeth — the premolars and molars — are served by branches of the trigeminal nerve, which is the main sensory nerve of the face and mouth. The upper and lower branches of this nerve (the maxillary and mandibular divisions) run in close proximity to one another, particularly in the posterior region of the mouth.

When a back tooth becomes infected, the resulting inflammation can irritate the surrounding nerve fibres. Because the brain processes pain signals along shared or adjacent nerve pathways, it can sometimes misinterpret the source of that signal. The result is a sensation of pain that appears to arise in the tooth directly opposing the infected one — either directly above or below it.

This is why a patient might point to an upper molar as the problem tooth, when clinical investigation reveals the infection is actually in the lower molar beneath it. It is a genuinely common occurrence and something that experienced clinicians are well trained to identify.

The Role of Tooth Anatomy in Spreading Discomfort

To understand why dental infections can produce such confusing pain patterns, it helps to consider the internal structure of a tooth.

Each tooth contains a soft inner chamber known as the dental pulp, which houses blood vessels, connective tissue, and nerve fibres. When bacteria breach the outer layers of a tooth — whether through decay, a crack, or damage to existing dental work — they can penetrate the pulp and cause an infection known as pulpitis. If left untreated, this can progress to a periapical abscess, where infection spreads to the tissue at the tip of the tooth's root.

As the infection develops and pressure builds within the surrounding bone and tissue, the inflammatory response intensifies. This pressure can radiate outward along the nerve pathways described above, contributing to the misleading pain patterns that make dental diagnosis a process requiring careful clinical assessment rather than patient self-diagnosis.

This is also why the pain from a dental infection often feels worse when biting down, lying flat, or applying warmth — all of which can increase pressure within the affected area.

Common Symptoms That May Accompany Referred Dental Pain

Referred dental pain from a tooth infection is rarely an isolated symptom. It is usually accompanied by a range of other signs that, taken together, can help a dental professional identify the true source of the problem.

Symptoms that may be associated with an infected back tooth include:

• Persistent or throbbing pain that may worsen at night or when lying down
• Sensitivity to hot or cold temperatures that lingers after the stimulus is removed
• Pain on biting or chewing, particularly concentrated around one area
• Swelling in the gum, jaw, or face near the affected tooth
• A bad taste in the mouth, which may indicate that an abscess has partially drained
• General feelings of being unwell, in cases where infection has become more significant

It is worth noting that in some cases, a significantly infected tooth may cause very little pain initially — particularly if the pulp has become necrotic (the nerve tissue has died). This can make self-assessment unreliable, which is why professional evaluation remains important whenever symptoms arise.

Why Diagnosing the Correct Tooth Can Be Challenging

For both patients and clinicians, identifying the correct source of dental pain can require careful investigation. This is not a reflection of diagnostic failure — it is simply the nature of how referred pain operates within the nervous system.

A thorough clinical assessment will typically involve:

• A detailed patient history, including when pain began, what makes it better or worse, and whether there have been any recent dental procedures or injuries
• Clinical examination of the affected area, including visual inspection and gentle probing
• Percussion testing, where the dentist taps individual teeth to assess sensitivity and pain response
• Thermal sensitivity tests, to evaluate the vitality of the pulp
• Dental radiographs (X-rays), which can reveal infection at the root tip, bone loss, or other structural changes not visible to the naked eye

Occasionally, a dentist may refer a patient for more advanced imaging if the source remains unclear. This methodical approach is what distinguishes professional diagnosis from attempting to self-identify the problem based on where pain is felt.

If you are experiencing ongoing dental discomfort, the team at MD Dental London can carry out a thorough assessment to help identify the source of your symptoms.

The Connection Between Back Tooth Infections and the Sinuses

There is a further anatomical consideration worth highlighting specifically in relation to the upper back teeth. The roots of the upper molars and premolars sit in close proximity to — and in some individuals may even extend into — the maxillary sinuses, which are the air-filled cavities located on either side of the nose.

When an upper back tooth becomes infected, the resulting inflammation can sometimes cause sinus-related symptoms such as facial pressure, a feeling of fullness above the cheekbone, or what feels like a one-sided sinus headache. Conversely, genuine sinus infections or congestion can occasionally produce sensations that mimic toothache in the upper back teeth.

This sinus-tooth relationship adds another layer to the diagnostic complexity of referred dental pain, and it is one reason why a full clinical assessment — rather than self-treatment — is advisable when back tooth pain is accompanied by facial pressure or congestion.

When You Should Seek Professional Dental Assessment

There are certain situations in which professional dental evaluation should not be delayed. The following symptoms, particularly when persistent or worsening, warrant prompt attention from a qualified dental professional:

• Pain that lasts more than a day or two and does not improve
• Swelling of the face, jaw, or gums — particularly if swelling is spreading
• Difficulty opening the mouth or swallowing
• Fever or general malaise alongside dental pain
• Spontaneous pain that wakes you at night
• Visible changes to the gum around a tooth, such as a raised lump or spot

Dental infections, if not appropriately managed, have the potential to spread beyond the tooth and surrounding tissues. Seeking timely professional care helps ensure that any underlying issue is identified and addressed appropriately.

You can read more about dental pain and emergency dental care on the MD Dental website for further guidance on when to seek urgent help.

Prevention and Oral Health Advice for Back Teeth

The back teeth are particularly susceptible to infection because of their anatomy and function. Their complex, multi-cusped surfaces are more difficult to clean thoroughly, and their role in heavy chewing means they endure significant mechanical stress over time.

Here are some practical steps that may help reduce the risk of back tooth infections:

• Brush twice daily using a fluoride toothpaste, paying careful attention to the back teeth and ensuring bristles reach the gum line
• Clean between your teeth daily using floss, interdental brushes, or a water flosser — areas between the back teeth are common sites for undetected decay
• Attend regular dental check-ups, which allow early identification of decay, cracks, or early signs of infection before symptoms develop
• Consider dental sealants if recommended by your dentist — these thin protective coatings can be applied to the chewing surfaces of back teeth to reduce the risk of decay
• Limit sugary and acidic food and drink, which contribute to enamel erosion and decay over time
• Address teeth grinding (bruxism) — if you clench or grind your teeth, speak to your dentist about whether a night guard may be appropriate, as grinding can crack or weaken back teeth

For advice on maintaining your overall dental health, the oral health guidance available at MD Dental covers a wide range of topics relevant to London patients.

Key Points to Remember

• Referred dental pain from tooth infection is a recognised neurological phenomenon and is not unusual
• The upper and lower back teeth share closely connected nerve pathways, making it possible for pain to appear in the tooth opposite the infected one
• Dental infection develops within the pulp of the tooth and can spread to surrounding bone and tissue if not treated
• Self-diagnosing the source of dental pain is unreliable — professional clinical assessment is necessary to identify the true cause
• Symptoms such as swelling, persistent pain, or fever alongside toothache warrant prompt dental attention
• Regular dental check-ups, thorough cleaning of back teeth, and timely treatment of decay are key preventive measures

Frequently Asked Questions

Conclusion

Understanding why a dental infection in one back tooth can cause pain in the tooth directly above or below it helps to explain why toothache is not always as simple to self-diagnose as it might initially seem. Referred dental pain from tooth infection is a genuinely common clinical occurrence, rooted in the shared nerve pathways that supply the upper and lower back teeth.

If you are experiencing unexplained dental pain — particularly in the back of your mouth — it is always advisable to seek professional dental guidance rather than attempting to identify the source yourself. The symptoms associated with dental infection can vary considerably between individuals, and what may feel like discomfort in one tooth may in fact originate elsewhere.

Good oral hygiene, regular dental check-ups, and prompt attention to any new or changing dental symptoms are the most reliable ways to protect your dental health over the long term.

Dental symptoms and treatment options should always be assessed individually during a clinical examination.