Background: In Korea, the adoption of dental panoramic radiography devices is steadily growing, and diagnostic reference level (DRL) continues to increase in parallel with this phenomenon relative to that in other countries. Moreover, radiation dose is a risk factor for public health; however, to our knowledge, no study has investigated the cause of this rise in DRL. This study therefore sought to discern why the proposed DRL is high by measuring the use status and the dose area product (DAP) of panoramic devices. Materials and Methods: DAP was measured under standard adult exposure conditions to 41 panoramic devices in use at dental clinics in Incheon, and the differences between the groups were analyzed by stratifying them into below-the-DRL group and exceeding-the-DRL group. Results: Ultimately, the most significant cause of the increase in DRL in dental panoramic radiography was that patients were irradiated by the system in a high-definition mode using high tube voltage or were subjected to long exposure time. Conclusions: To protect public health from excessive radiation dose, dentists or radiologists must attempt to use the lowest possible radiation dose according to the “as low as reasonably achievable” principle while ensuring that sufficient image quality is attained for diagnostic and treatment purposes. In addition, the Korea Disease Control and Prevention Agency needs to revise the current DRL, which is a third quartile value of the measured dose distribution, to an appropriate value by referring to the opinions of expert groups.