Which light-sensitive chemicals are used to coat the film within an extra-oral x-ray film cassette?

The use of light-sensitive chemicals in extra-oral x-ray film is primarily associated with silver bromide salts. These salts are critical in the photographic process as they respond to light exposure by forming a latent image, which is then developed into a visible image through a series of chemical reactions in the darkroom.

Silver bromide is particularly effective because it has a high sensitivity to both direct and scattered radiation, enabling the film to capture detailed images of teeth and bone structures. When exposed to x-rays, these salts undergo a chemical change, allowing for high-quality imaging that can be processed later.

Other options do not serve this function. Lead, for example, is commonly used for radiation shielding but does not have any light-sensitive properties. Mercury is toxic and not used in photographic processes. Rare earth chemicals may have some role in enhancing image quality or sensitivity in certain imaging technologies but are not specifically used to coat x-ray film. Silver bromide salts remain the standard choice for extra-oral x-ray film, making this option the most accurate and relevant in the context of dental radiography.