How can you differentiate the zygoma from the maxillary sinus in a maxillary posterior PA radiograph?

The maxillary sinus is a three-sided pyramid shape, which is a crucial characteristic that differentiates it from the zygoma on a maxillary posterior periapical (PA) radiograph. The structure of the maxillary sinus features an open base that aligns with the maxillary alveolar ridge, while the apex points superiorly toward the infraorbital rim. This anatomical shape allows clinicians to identify it easily on a radiograph.

In contrast, the zygoma, or cheekbone, has a more complex structure and does not exhibit the same three-sided pyramidal geometry. The maxillary sinus, being an air-filled cavity, clearly outlines its distinct borders as it shows up radiolucent against the surrounding bony structures. Recognizing the maxillary sinus's shape helps in diagnosing issues in nearby structures and understanding the patient's dental and maxillofacial health.