Which term describes the item placed in the patient's mouth before exposure to ionising radiation?

The term that accurately describes the item placed in the patient's mouth before exposure to ionising radiation is "film packet." A film packet typically contains the X-ray film itself, which is sensitive to radiation, and other materials that help to shield the film from unnecessary exposure, thereby ensuring high-quality imaging.

The film packet is designed to be easy to handle and position within the patient's mouth to capture the necessary images of teeth and surrounding structures effectively. It is critical in the process of dental X-ray imaging, as it protects the film from light and ensures that the radiation passes through the oral structures to create a clear and precise image.

In contrast, while "film" and "X-ray film" refer to the actual photographic material capable of recording the images, they do not encompass the entire packaged unit that is placed within the mouth. "Radiograph" refers to the image produced after the film has been exposed to radiation and developed, rather than the item placed in the mouth before exposure. Therefore, "film packet" is the most accurate term in this context.