Optimization of the Mechanical Performance of Titanium for Biomedical Applications by Advanced, High-Gain SPD Technology

Fatigue properties of UFG Ti grade 2 dental implant vs. conventionally tested smooth specimens

Complicated geometry in combination with surface treatment strongly deteriorates fatigue resistance of metallic dental implants. Mechanical properties of pure Ti grade 2, usually used for dental implant production, were shown to be significantly improved due to intensive grain refinement via Conform SPD. The increase of the tensile strength properties was accompanied by a significant increase in the fatigue resistance and fatigue endurance limit. However, the SLA treatment usually used for the implants' surface roughening, resulted in the fatigue properties and endurance limit decrease, while this effect was more pronounced for the ultrafine-grained comparing to the coarse-grained material when tested under tensile-tensile loading mode. The testing of the implants is usually provided under the bending mode. Even though different testing condition for the conventional specimens tests and implants testing was adopted, a numerical study revealed their comparable fatigue properties. The fatigue limit determined for the implants was 105% higher than the one for coarse-grained and only by 4 % lower than the one for ultrafine-grained Ti grade 2. Based on the obtained results, conventional specimens testing can be used for the prediction of the fatigue limit of the implants.

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

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.