Describe how radiopacity is measured. How low a percentage can a cements radiopacity be before it becomes non-radiopaque?
Radiopacity is measured by taking an X-ray of a dental product alongside aluminum and then comparing the X-ray absorbing power (optical density) of both X-rays. If the X-ray absorbing power for the dental product is the same as that for aluminum, then the radiopacity of the dental product is 100% of aluminum. If the X-ray absorbing power for the dental product is 2 times as strong as that for aluminum, then the radiopacity of the dental product is 200% of aluminum. Dentin has a radiopacity of 100% of aluminum and enamel has a radiopacity slightly less than 200% of aluminum. To be called radiopaque, the radiopacity of the cement must be equal to or greater than that of dentin (≥ 100%). Generally, a cement with a radiopacity of less than 100% of aluminum is called radiolucent (or not radiopaque).
