What tests or X-rays are used to locate a dental abscess? 

To identify the presence and exact location of a dental abscess, a dentist will carry out a series of clinical examinations and use imaging technologies. These methods are necessary to determine whether the infection is located within the tooth structure, at the root tip, or within the gum tissues. Professional evaluation is required because symptoms of an abscess can occasionally mimic other oral health conditions or systemic issues. 

What We’ll Discuss in This Article 

• The role of periapical and bitewing X-rays in identifying bone loss. 

• Clinical vitality tests used to assess the health of the dental pulp. 

• Physical examination methods including percussion and palpation testing. 

• How periodontal probing identifies abscesses within the gum pockets. 

• The process of tracing sinus tracts to find the source of infection. 

• The use of advanced 3D imaging for complex diagnostic cases. 

• How dentists use a combination of tests to form a final diagnosis. 

The Role of Dental X-rays in Locating an Abscess 

Dental X-rays are the primary imaging tool used to identify the location of an abscess within the jawbone or at the tip of a tooth root. When an infection reaches the end of a tooth root, it begins to destroy the surrounding bone tissue as pus accumulates. On a standard 2D X-ray, this bone loss appears as a dark, circular shadow known as a radiolucency. This shadow allows the dentist to pinpoint exactly which root is infected, which is particularly useful in multi-rooted teeth like molars. Clinical guidance from NICE indicates that radiographs are an essential component of the diagnostic process to confirm the presence of a periapical infection. 

There are several types of X-rays used depending on the suspected location of the infection. A periapical X-ray provides a detailed view of the entire tooth, from the crown down to the very end of the root and the surrounding bone. This is the most common view used to find a periapical abscess. Bitewing X-rays, which show the crowns of the upper and lower teeth together, are helpful for identifying deep cavities between teeth that may be the original cause of an infection. In some cases, an Orthopantomogram (OPG) might be taken to provide a panoramic view of the entire jaw, allowing the dentist to see the relationship between multiple teeth and the sinuses. UK Government health resources provide guidance on the use of diagnostic radiation and the necessity of keeping patient exposure to the lowest level possible. 

Clinical Vitality Testing and Nerve Assessment 

Vitality testing is a clinical procedure used to determine if the nerve inside a tooth is still alive and responsive to stimuli. A tooth that has developed an abscess at the root tip typically has a dead (necrotic) nerve, meaning it will no longer react to temperature changes or electrical impulses. To test this, a dentist may use a thermal test by applying a very cold stimulus, often referred to as “endo-ice,” to the surface of the tooth. A healthy tooth will feel a sharp, cold sensation that disappears almost immediately, while an abscessed tooth with a dead nerve will often feel nothing at all. 

Another method is the Electric Pulp Test (EPT). This involves a small device that delivers a tiny, gradually increasing electrical current to the tooth. The patient holds a ground wire and signals the moment they feel a tingling sensation. If a tooth requires a much higher current than the surrounding healthy teeth to elicit a response, or if it does not respond even at the highest setting, it strongly suggests that the pulp is necrotic and an abscess is likely present. These tests are essential for confirming that the pain is coming from the internal part of the tooth rather than the surrounding gum tissue. 

Physical Examination: Percussion and Palpation 

Physical examination techniques such as percussion and palpation allow a dentist to identify exactly which tooth is responsible for the infection through direct contact. Percussion involves the dentist gently tapping on the chewing surface or the side of the tooth with the handle of a dental mirror. A tooth with an abscess at the root is usually very sensitive to this tapping because the infection has inflamed the periodontal ligament that holds the tooth in the bone. If a patient feels a sharp or localized pain during this test, it helps the dentist isolate the problem tooth from its neighbours. 

Palpation is the process of using the fingers to feel the gums and the bone around the teeth. The dentist will feel for any areas that are soft, swollen, or particularly tender. In many cases, an abscess will cause the bone over the root tip to feel thin or “springy,” or there may be a visible lump on the gum. By pressing gently on these areas, the dentist can determine if the infection is localized or if it has begun to spread into the soft tissues of the cheek or the floor of the mouth. The NHS provides information on how a dentist will check for signs of a dental abscess by looking at your teeth and gums for redness or swelling. 

Periodontal Probing for Gum-Based Abscesses 

Periodontal probing is used to locate abscesses that have formed within the gum pockets rather than inside the tooth itself. A periodontal abscess, which is often caused by gum disease, starts on the outside of the tooth root. To diagnose this, the dentist uses a specialized instrument called a periodontal probe, which has millimetre markings on it. The probe is gently slid into the space between the tooth and the gum to measure the depth of the “pocket.” A healthy pocket is usually between one and three millimetres deep. 

If the probe identifies a very deep pocket, particularly one that releases pus or blood when measured, it indicates a localized infection in the gum. This test is vital for distinguishing between a tooth-based (periapical) abscess and a gum-based (periodontal) abscess, as the treatments for these two conditions are very different. A periapical abscess requires treatment of the internal tooth canal, while a periodontal abscess requires deep cleaning and drainage of the gum pocket. 

Tracing Sinus Tracts and Fistulas 

Tracing a sinus tract involves using a flexible material to follow the path of draining pus back to its source. Sometimes, an abscess creates a small tunnel through the bone and gum to allow pus to drain into the mouth. This exit point often looks like a small pimple on the gum, known as a fistula or sinus tract. Because the path of the tunnel can be winding, the exit point may not be directly next to the infected tooth. 

To find the true source, the dentist may gently insert a thin, flexible piece of material called gutta-percha into the opening of the tract. They then take an X-ray with the material in place. Because the gutta-percha is visible on the X-ray, it acts as a pointer, leading the dentist directly to the root of the tooth where the infection originated. This is a highly accurate way to ensure that the correct tooth is treated, especially in areas where several teeth have large fillings or crowns. 

Diagnostic Tool	What it Locates	How it Works
Periapical X-ray	Bone loss at the root tip.	Shows dark shadows in the jawbone.
Thermal Test	Dead or dying tooth nerve.	Measures response to extreme cold.
Percussion Test	The specific tooth causing pain.	Tapping to check for ligament inflammation.
Periodontal Probe	Deep pockets in the gums.	Measuring the gap between tooth and gum.
Sinus Tract Trace	The origin of draining pus.	Following a path with a visible marker.

Advanced 3D Imaging: CBCT Scans 

Advanced 3D imaging such as Cone Beam Computed Tomography (CBCT) is sometimes required for complex cases where standard 2D X-rays do not provide enough detail. While traditional X-rays are excellent for most cases, they only show a flat view of a 3D object. This means that an infection located on the front or back of a root might be hidden by the tooth itself. A CBCT scan provides a three-dimensional view of the teeth and jawbone, allowing the dentist to see the abscess from every angle. 

This technology is particularly useful for identifying infections in teeth with unusual root anatomy, finding hidden cracks that do not show up on standard film, or assessing how close an abscess is to the maxillary sinus or major nerves. In the UK, CBCT is typically used when traditional diagnostic methods have been inconclusive or when a patient has persistent pain after a previous treatment has failed. This level of detail ensures a higher degree of accuracy in identifying the source of an infection before surgery or root canal treatment is started. 

Conclusion 

Locating a dental abscess involves a combination of visual inspection, physical testing, and radiographic imaging to ensure an accurate diagnosis. X-rays are the most frequent tool used to see the effects of infection on the bone, while vitality and percussion tests help confirm which specific tooth is affected. Using these clinical methods, a dentist can determine the best course of action to resolve the infection and prevent it from spreading. If you experience severe, sudden, or worsening symptoms, call 999 immediately. 

Authority Snapshot (E-E-A-T) 

This clinical education article explains the diagnostic procedures used by dental professionals to identify oral infections for public education. The content is developed by a professional medical writing team and reviewed for accuracy by Dr. Stefan Petrov, a UK-trained physician with extensive experience in general medicine and emergency care. All information and guidance are strictly aligned with the standards established by the NHS and NICE regarding dental diagnostics.