As a materials engineer researching dental materials, I am currently investigating the effects of radiopacifier additives on dental cements. I am seeking guidance from an expert in this field, and I believe you may be able to assist me based on your profile. Specifically, I would like to know how to measure the radiopacity (in mm AL) of dental cement samples using a radiography machine, and what role a step wedge plays in digital x-ray images. Any help you can provide would be greatly appreciated. Thank you and best regards.