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Purpose: To investigate the composition and conformity with the stated declaration for alloys used for dental crowns among Norwegian and overseas laboratories.
Materials and Methods: Tooth 16 of a patient given his informed consent was prepared for single porcelain fused to metal crown. An impression of the upper jaw including the prepared tooth, antagonist impression and a bite registration was performed. This was used to make an epoxy model for production of identical impressions that were distributed to dental clinics (n¼23) covering the whole of Norway. The dentist distributed the received impressions and the bite registration to their commonly used laboratory (some in Norway and some overseas) (n¼38). The dental laboratory was not informed that the crown would be used for research purposes. The dentist sent the produced crown with the all enclosed information to NIOM for examination. This examination consisted of registration whether a Declaration of Conformity was enclosed or not, analysis of the chemical composition and if the alloys contained toxic elements (Ni, Cd, Be, Pb) above the limit values specified in ISO 22674:2016. These analyses were performed at Sheffield Analytical Services (UK).
Results: Analyses of the alloy part of the crowns did not match to the stated composition for 14% of the Norwegian and 8% of the overseas works. However, the composition was not stated for a third of the crowns. The Declaration of Conformity was missing for 29% of the Norwegian and for all of the imported work. Concerning toxic elements, 18% of the works appeared to contain Pb above the permitted limit (0,02wt %) according to ISO 22674:2016.
Conclusion: The study revealed major deficiencies for both Norwegian and overseas made crowns regarding conformity between composition and the stated declaration.

Reference:
A comparison of Norwegian and overseas made dental metallic crowns
Syverud M, E. K, Mulic A, Valen H. 
Biomaterial Investigations in Dentistry 2019, Vol. 6, No. S1, 19.