**Core Concept:**

The question is about a patient with reduced mouth opening following road traffic accident (RTA) and panoramic X-ray taken using a fast intensifying screen (FIS). A panoramic X-ray is a dental radiograph that provides a broad view of the teeth, jaws, and surrounding structures. Fast intensifying screens (FIS) are used in dental radiography to enhance the image quality and reduce the radiation dose to the patient. They work by converting the X-ray emitted by the X-ray tube into visible light, which is then captured by a charge-coupled device (CCD) camera.

**Why the Correct Answer is Right:**

The correct answer (Option C) is "Fast intensifying screens are not used in dental radiography." This is incorrect because FIS are commonly used in dental radiography to improve image quality and reduce radiation dose. FIS work by converting X-ray photons into visible light, which is then captured by a CCD camera.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because FIS are indeed used in dental radiography, as mentioned above.
B. This option is incorrect because the correct use of FIS in dental radiography does not involve the X-ray tubes in this context. In a panoramic X-ray, FIS is used to enhance image quality, not to modify X-ray tubes.
D. This option is incorrect because FIS improves image quality and reduces radiation dose, not increase them. Their primary purpose is to enhance the image quality and minimize the radiation exposure to the patient.

**Clinical Pearls:**

1. Fast intensifying screens are essential tools in dental radiography, particularly in panoramic X-ray imaging, for improving image quality and reducing radiation exposure to the patient.
2. Improved image quality allows for more accurate diagnosis and treatment planning in dental medicine.
3. Always ensure to accurately understand the role of various imaging technologies, including FIS, in dental radiography to provide optimal care for your patients.