The number of x-ray photons produced during a dental radiographic exposure is determined by which factors?

• A. Milliamperage setting
• B. Exposure time
• C. Both milliamperage and exposure time
• D. Kilovoltage peak

Answer: (C)

Photon quantity in a dental X-ray exposure comes mainly from the flow of electrons to the target, which is set by the milliamperage and the exposure duration. The product of milliamperage and exposure time, called mAs, represents the total number of electrons reaching the target, and thus the total number of photons produced. If you raise either the current or the time (while holding the other constant), you increase the photon count accordingly.

Kilovoltage peak, on the other hand, mainly changes the energy of the photons—their penetrating power and the resulting image quality—not how many photons are produced. Higher kVp gives you more energetic photons, but it doesn’t substantially increase the number of photons generated.

So the best answer is that both milliamperage and exposure time determine the number of photons, through their product mAs.