Natural radioactivity in zirconia-based dental ceramics.

摘要

Zirconia-based ceramics are being increasingly used in dental prosthetics in substitution of metal cores,which are known to induce local toxic reactions and delayed allergic responses in the oral tissues. Some concernshave been however raised about the use of zirconia, since it is known that unpurified zirconia materials maycontain non negligible levels of natural radionuclides of the U/Th series. Combined measurements of alpha andgamma spectrometry as well as beta dosimetry were conducted on zirconia samples used for dental applications.Samples were available in form of powder and/or solid blocks. The results showed that the beta dose rate inzirconia ceramics was on average only slightly higher than the levels measured in natural teeth, and generallylower than the values measured in feldspatic and glass ceramics. These materials are indeed known to deliver abeta dose significantly higher than that measured from natural teeth, due to the relatively high levels of ~(40)K(between 2 and 3 kBq·kg~(-1)). The content of radionuclides of the U/Th series in the zirconia sample was estimatedto be lower than 15 Bq·kg~(-1), i.e. doubtlessly below the exclusion level of 1 kBq·kg~(-1) recommended by IAEA in theSafety Standard Series. Beta dosimetry measurements, however, gave indications of possible inhomogeneousclusters of radioactivity, which might give rise to local doses above the background.