This International Standard specifies a test method for determining the radiopacity of a test material by comparison with a test specimen made from an aluminum standard. This test is designed to discriminate radiopacities at a clinically relevant level and is not intended to take into account factors affecting the precise inherent values of radiopacity such as background noise, x-ray beam power, grayscale correction, and image enhancement. It is recognized that such factors may alter the value of radiopacity, but not the relative ranking when compared to the standard thickness of an internal standard such as aluminum. This test can be carried out using conventional or digital sensor techniques from dental x-ray devices.