Abstract
During the 20th century, metal alloys have assumed an important role as restorative materials. Among existing examples, cobalt–chromium (Co–Cr) alloys increasingly began to be used in medicine and especially in dentistry. Their success is mainly due to their mechanical properties such as stiffness, strength and corrosion resistance, thus allowing a high biocompatibility. There are quite meaningful data on the corrosion and toxicity of Co–Cr alloys for their use in restorative materials such as dental prostheses. Toxicological studies following Co and Cr exposures in the oral cavity are more difficult to conduct because there are many different situations leading to the release of metal ions and wear particles. Furthermore, the links between exposure and the appearance of local or systemic toxicity are not automatic. Since 2017, the European Union (EU) regulatory framework for Co–Cr alloys has been undergoing profound changes. A new EU Medical Devices Regulation (MDR) (2017/745) will be applied in May 2021 with the need to consider that Co metal is a new carcinogenic, mutagenic and toxic to reproduction (CMR) substance. On 18 February 2020, the 14th Adaptation to Technical Progress (ATP14) to the Classification, Labelling and Packaging (CLP) regulation was published, including the harmonised classification for Co metal as a CMR 1B substance. In this context, the use of Co might be forbidden if the medical devices are invasive and as soon as they include more than 0.1% (m/m) Co. This review provides a specific overview on Co–Cr dental alloys in terms of metal ions and wear particles release, toxicological risks, and the actual and new EU regulatory framework.
Highlights
During the 20th century, the history of dentistry has intimately been linked with metal alloys and those using cobalt (Co, CAS no. 7440-48-4, EC/List no. 231-158-0) and chromium (Cr, CAS no.Crystals 2020, 10, 1151; doi:10.3390/cryst10121151 www.mdpi.com/journal/crystals7440-47-3, EC/List no. 231-157-5) hold an important place
In 1907, the first Co–Cr alloys were designed as Co–Cr–W and Co–Cr–Mo alloys (W = tungsten and Mo = molybdenum) [1] and in the 1930s they began to be used for the preparation of removable partial denture (RPD) frameworks [2]
To identify and quantify metal ion release generated from Co–Cr alloys, different methods and techniques can be used to determine the corrosion rate linked with the release of metal ions and their biocompatibility [17,35,36,37,38,39,40]
Summary
During the 20th century, the history of dentistry has intimately been linked with metal alloys and those using cobalt (Co, CAS no. 7440-48-4, EC/List no. 231-158-0) and chromium Si: silicium; Mn: manganese; C: carbon; N: nitrogen; Ti: titanium; S: sulfur; Cu: copper; Nb: niobium; Ta: tantalum These two metals have their own characteristics and are, found in trace amounts in the human body where they are important for regulating biochemical functions as previously described. Once Co and Cr are artificially implanted in the human body via the use of medical devices, metal ions and wear particles release from these alloys can cause toxicity [10]. Europe has developed a regulatory package [14] to protect all players involved in alloys, whether they are metal producers, manufacturers of alloys and medical devices, healthcare professionals and patients This regulatory package will evolve with advances and scientific knowledge. In 2020, an important event affected the regulation of Co–Cr alloys because Co was listed as a CMR (carcinogenic, mutagenic and toxic for reproduction) substance. The legislative changes bring the need to propose new alternatives to Co–Cr dental alloys
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