Orthopantomography, often referred to as an OPG X-ray, is a common diagnostic imaging technique used in dentistry. This specialized X-ray scan provides a comprehensive, wide view of the lower face, including all teeth, the jawbone, and the temporomandibular joints. It provides dental professionals a broad perspective of oral and maxillofacial structures, aiding in diagnosis and treatment planning.
What is an OPG X-ray?
An OPG X-ray, also known as a panoramic dental X-ray, captures a broad, two-dimensional view of the entire mouth. Unlike smaller intraoral X-rays that focus on a few teeth, an OPG machine rotates around the patient’s head. This movement images all teeth in both the upper and lower jaws, the surrounding bone structures, and the temporomandibular joints (TMJ) that connect the jaw to the skull.
The technology projects a narrow beam of X-rays through the patient’s head onto a digital sensor or film. As the X-ray source and sensor rotate synchronously around the patient, they create a continuous image of the dental arches and associated structures. This method produces a flattened, panoramic representation of the curved dental anatomy, making it possible to visualize the entire dentition and jawbones in a single exposure.
Why an OPG X-ray is Performed
Dental professionals commonly perform OPG X-rays for various diagnostic purposes. One frequent application involves assessing the development and precise position of wisdom teeth, especially when impacted or erupting abnormally. The panoramic view helps determine if these teeth need to be removed or if they pose a risk to adjacent structures.
The OPG is also valuable for detecting impacted or congenitally missing teeth. It allows for a thorough evaluation of the jawbone’s structure and density, which is particularly useful in cases of suspected jaw fractures or bone loss due to periodontal disease. Furthermore, it aids in diagnosing disorders of the temporomandibular joint.
Screening for the presence of cysts, tumors, or infections within the jawbone is another important reason for performing an OPG. Beyond diagnostics, OPGs are routinely used for treatment planning, guiding decisions for orthodontic treatment, designing dental implants by assessing bone quantity and quality, and planning for the placement of dentures or other prosthetic devices.
The OPG X-ray Procedure
Undergoing an OPG X-ray is a procedure that takes place outside the patient’s mouth. Patients typically stand or sit in a specific position, with their chin resting on a small shelf on the OPG machine. A bite-block, a small mouthpiece, is then placed between their front teeth, which helps align the jaws and separate the dental arches for a clearer image.
Once positioned, the patient is instructed to remain still for the scan, which usually lasts about 10 to 20 seconds. During this time, a rotating arm of the machine, containing both the X-ray source and the digital sensor or film, moves in a semicircular path around the patient’s head. This synchronized movement captures the panoramic view of the oral structures.
To ensure patient safety, a lead apron is typically placed over the patient’s chest and abdomen to shield them from radiation exposure. The extraoral nature of the OPG means there is no discomfort from film or sensors placed inside the mouth. The entire process, from positioning to image acquisition, is quick and comfortable.
Understanding OPG X-ray Images
Interpreting OPG X-ray images is complex due to the unique way these panoramic views are generated. The inherent curvature of the dental arches means the image undergoes varying degrees of magnification and distortion. Structures closer to the X-ray source or further from the focal trough, an imaginary curved plane where structures are clearly imaged, may appear magnified or compressed, affecting their perceived size and shape across the image.
A common feature of OPG images is the presence of “ghost images,” which are faint, blurred shadows of dense objects located outside the focal trough. These occur when the X-ray beam passes through a dense structure, such as an earlobe, the spinal column, or metallic jewelry, twice. The ghost image typically appears on the opposite side of the true structure, higher up, and more diffused.
“Double images” also appear for structures located in the midline of the patient, which are struck by the X-ray beam twice as the machine rotates. Examples include the hard palate, the hyoid bone (a U-shaped bone in the neck), and parts of the cervical spine. These structures appear as two distinct, superimposed images.
Patient positioning errors are a frequent cause of image artifacts. If the patient’s chin is positioned too high, the occlusal plane (the biting surface of the teeth) may appear flattened or inverted, and the condyles of the TMJ might be cut off the top of the image. Conversely, if the chin is too low, the occlusal plane forms an exaggerated curve, and the anterior teeth can appear blurred and narrowed.
Twisting the patient’s head during the scan can result in one side of the image appearing magnified and blurred, while the opposite side looks smaller and sharper. If the patient’s tongue is not pressed firmly against the roof of the mouth, a dark, radiolucent shadow can appear over the apices (root tips) of the maxillary teeth. If the patient slumps or leans forward, a ghost image of the spinal column can overlap and obscure the anterior teeth. Skilled interpretation by dental professionals is necessary to accurately diagnose conditions from OPG X-rays.