## 6 Discussion  
The MDR will involve significant modifications in the field of CMF implants, which have become nowadays indispensable devices to perform accurate patient-specific reconstructions of the facial skeleton. However, with the previous legislation it was hard to establish whether CMF implants underwent all the necessary evaluations to confirm their safety for patients. For this paper, mechanical, clinical, and material engineers mutually shared their knowledge with surgeons to suggest a sequence of analyses and tests that should be implemented for each aspect of the implant connected to hazard, including for instance the risk of rupture, cracking, particle release, deformation, biological damage. Our idea is that surgeons should become acquainted with concepts related to the fabrication of the implant and should understand the key principles of mechanical defects related to 3D metal printing and how they originate, not only to perform a rudimental assessment of the implants they plan to use, but also to be more participative in studies involving the development of new devices. Current literature provides evidence that surgeons are progressively more interested in designing their own implants, or, at least, in taking active part in the process of developing novel devices for surgeries. In our opinion, the surgeon must strictly supervise and actively participate in the design of the implant, while engineers are supportive for technical aspects. In a multidisciplinary team, surgeons have the deeper anatomical knowledge and are aware of possibilities offered by surgical access that might limit the positioning of an implant, a factor the engineer hardly considers while evaluating a raw skeletal model. On the other hand, engineers have a deeper knowledge of CAD packages and are able to perform structural calculations and coupling design. The MDR impacts on the reclassification of several devices, as certain CMF devices are subject to a step forward to a higher class. For instance, partial or total articular prostheses have been included in class III [1]. As mentioned, the number of companies providing CMF implants underwent an exponential growth in the last years, leading to a variety of devices, that might show consistent differences among each other. Moving a device to a higher risk class might result in a substantial increase in costs and conspicuous delays for the recertification process. This may discourage manufacturers from continuing to sell some of their devices, considering that many of them might not be compliant with the MDR after the class shift [34]. On the other side, customized CMF implants have become unrenounceable in modern CMF surgery, considering the significant reduction in surgical times and improvement in accuracy they allow to obtain, thereby representing a limitation for several medical centers across Europe. We foresee that several centers will cautiously stop the implantation of devices that have not yet been approved as compliant with the MDR. This initial step might pose several challenges especially to small-scale companies, which will be forced to withstand the burden of costs and expertise required to satisfy conditions imposed by the new regulation. In the meantime, it is advisable that surgeons address their requests to manufacturers able to provide their implants in compliance with the MDR. In parallel, manufacturers will be required to implement all possible solutions to lower the risk of accidents, and this is especially true for high-risk class devices. The Annex I of the MDR explicitly reports that \"_manufactures shall establish, implement, document and maintain a risk management system_\" [34], but the regulation does not establish a predefined sequence of tests the prosthesis should undergo before surgical implantation. Intuitively, lack of standardization is intrinsically present in the concept of custom-made devices, therefore each device is completely different and might exhibit peculiarities in its biomechanical features as well as throughout the production process.