 Dental restorations (fillings, crowns) may appear lighter or darker, depending on the density of the material.The dosage of X-ray radiation received by a dental patient is typically small (around 0.150 mSv for a full mouth series, according to the American Dental Association website), equivalent to a few days' worth of background environmental radiation exposure, or similar to the dose received during a cross-country airplane flight (concentrated into one short burst aimed at a small area).Incidental exposure is further reduced by the use of a lead shield, lead apron, sometimes with a lead thyroid collar.