Persons who are to undergo panoramic radiography usually are required to remove any earrings, jewellery, hair pins, glasses, dentures or orthodontic appliances.[4] If these articles are not removed, they may create artifacts on the image (especially if they contain metal) and reduce its usefulness. There is also a need for the person to stay absolutely still during the 18 or so second cycle it takes for the machine to expose the film. For this reason, radiographers often explain to the person beforehand how the machine will move.[4]