Cobalt–Chromium Dental Alloys: Metal Exposures, Toxicological Risks, CMR Classification, and EU Regulatory Framework

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.

Framework Materials for Full-Arch Implant-Supported Rehabilitations: A Systematic Review of Clinical Studies

“…The biocompatibility of non-noble metal alloys has been questioned. According to a recent systematic review, it is well known that metals can go into corrosion, and consequently induce local and systemic effects, or hypersensitivity reactions can appear [48].…”

Experimental Study Regarding the Behavior at Different pH of Two Types of Co-Cr Alloys Used for Prosthetic Restorations

“…Co-Cr alloys are frequently utilized for dental restorations, and the corrosion resistance ensures the reduction of complications in the component part of the oro-facial system. They are sufficiently chemically inert, so they are relevant in diminishing irritations, allergic reactions, and general immune system resistance [ 5 , 29 ]. However, because the oral environment can be aggressive due to pH variation, chloride and fluoride ions can decrease the corrosion resistance [ 30 ].…”

“…Cobalt-chromium (Co-Cr) alloys are among the widely utilized alloys in dentistry and are alternatives to other types of dental alloys used to manufacture fixed prosthetic restorations [ 4 , 5 ]. The castability, the metallic luster, and the corrosion resistance of the dental alloys are important factors for the biocompatibility and feasibility of dental prosthetic restorations [ 6 ].…”

A Comparative Electrochemical and Morphological Investigation on the Behavior of NiCr and CoCr Dental Alloys at Various Temperatures

“…Toxicological risks of the cobalt-chromium alloys used in dentistry are a part of new EU Medical Devices Regulation (MDR) (2017/745) which will be applied in May 2021 [26]. With the new regulation, Co metal will be considered carcinogenic, mutagenic, and a substance toxic to reproduction [27]. The novelty of the present work is related to the investigation of temperature effect on corrosion and ion release of reprocessed NiCr and CoCr dental alloys.…”