Dental X-rays routinely taken in a dental office often capture the lower portion of the maxillary sinuses, the largest of the paranasal sinuses. An X-ray is a two-dimensional image that uses radiation to create a picture of dense structures like teeth and bone. When a sinus infection, or sinusitis, is present, the inflammation causes visible changes to the sinus cavity. A dentist can observe these changes on the radiograph due to the close anatomical relationship between the upper teeth and the sinus floor.
The Anatomical Connection Between Teeth and Sinuses
The maxillary sinuses are situated just above the upper jawbone. The floor of the maxillary sinus lies in close proximity to the roots of the upper posterior teeth, specifically the molars and premolars. Often, only a thin layer of bone separates the tips of these tooth roots from the sinus lining.
In some cases, the roots of the upper molars may even protrude slightly into the sinus cavity, covered only by the delicate sinus membrane. This close relationship creates a direct pathway for infection to spread between the mouth and the sinus. An infection at the root tip of an upper back tooth can break through the thin bone and enter the sinus space, causing odontogenic sinusitis.
Identifying Sinus Issues on Common Dental X-rays
Certain types of dental X-rays are especially effective at capturing a clear view of the maxillary sinus. Periapical X-rays, which focus on an entire tooth from crown to root, often include the adjacent floor of the sinus. Panoramic X-rays, which provide a broad view of the entire upper and lower jaws, capture large sections of the maxillary sinuses on both sides of the face.
When a sinus infection is present, the X-ray image will show changes in the appearance of the sinus cavity. A healthy sinus is filled with air and appears dark on a radiograph. Inflammation of the sinus lining, or mucosa, causes it to swell and thicken, which appears as a cloudy, white, or gray band tracing the contours of the sinus walls. This is known as mucosal thickening, and a thickness greater than two millimeters is considered abnormal.
In sinusitis, the entire sinus cavity may appear cloudy or filled in, a finding called opacification. Opacification indicates that the air space has been replaced by fluid, pus, or swollen tissue. Occasionally, an air-fluid level may be visible, which appears as a distinct, horizontal line within the sinus. These radiographic signs, particularly unilateral opacification (cloudiness on only one side), are highly suggestive of a problem like sinusitis, often one originating from a nearby tooth.
Determining the Source and Clinical Follow-Up
The dentist’s observation of a sinus issue on an X-ray leads to determining the infection’s origin. The infection is classified as either odontogenic, meaning it started from a tooth, or non-odontogenic, meaning it originated from a nasal or systemic cause like a cold or allergy. Odontogenic sinusitis accounts for a notable percentage of chronic maxillary sinus cases.
Two-dimensional dental X-rays, such as periapical or panoramic images, have limitations because they overlap structures. This two-dimensional nature can make it difficult to clearly distinguish between a tooth infection and a primary sinus issue. Advanced three-dimensional imaging, such as a Cone-Beam Computed Tomography (CBCT) scan, offers a much clearer view. A CBCT provides detailed cross-sectional images that allow the dentist to precisely visualize the relationship between the tooth roots and the sinus floor to pinpoint the exact source of the infection.
If the dentist suspects the sinusitis is non-odontogenic, they will refer the patient to a primary care provider or an ear, nose, and throat (ENT) specialist. If the X-ray clearly shows dental pathology, such as an abscess near the sinus floor, the dentist will proceed with dental treatment. This may include a root canal or extraction of the infected tooth to eliminate the source of the odontogenic infection and allow the sinus to heal. Collaboration between the dentist and other specialists is necessary to ensure the correct diagnosis and treatment plan.