The use of photocurable 3D resins for printing medical, dental and orthodontic materials with stereolithography or inkjet printers is a practice that is becoming popular in the lasts decades. There is ample evidence that "certified" 3D resins have been marketed for years as if they were medical devices. This has allowed printers and medical device manufacturers to use these 3D resin certifications instead of certifying their products and facilities.
The certifications of resins as if they were medical devices do not make sense, since they are photoreactive liquid resins that depending on with which equipment are printed and processed can polymerize to a greater or lesser extent, leaving a greater or lesser percentage of uncured monomers, and other leachables and extractables, which can cause health problems to end users.
"Certifications must be obtained for 3D printed medical devices, which include the facilities and production system, by manufacturers of medical devices. 3D resins need to be compliant but not certified since certification applies to medical devices, not to their raw materials" by 3Dresyns
The use of the certification of raw materials that do not undergo physical or chemical modifications during the production of medical devices facilitates the certification of medical devices, such as in the milling of metal implants, or of plastic discs to make dentures, crowns and bridges, where the manufacturer of these dental appliances shapes the material with milling, without inducing or causing any change in the composition of the material.
On the other hand, the use of the "certification" of raw materials that undergo physical and chemical modifications during the production of medical devices confuses and supplants the legally b required certification of medical devices, such as all medical, dental and orthodontic applications that use photocurable 3D resins with stereolithography or inkjet printers, since 3D resins undergo compositional changes when polymerizing, passing from liquid to solid during printing.
The degree of curing of the resin depends on many factors, such as the design and composition of the resin, its tuning to the printer, the type of printer and its technical specifications, such as its wavelength, power, uniformity of light power in the printing area, design, size, design orientation of the printed material, the cleaning process, the type of solvent used, its composition, properties, biocompatibility, cleaning time, cleaning temperature, extraction capacity of residual monomers and other contaminants, the specifications of the light post-processing unit, wavelength, power, post-processing equipment and its specifications, time and temperature, type and method of light post-processing, with air or with inert atmosphere, or by immersion, as well as the final cleansing process, type of solvents used, cleansing method, temperature, time, etc.
The certification of a resin does not make sense without taking into account the aforementioned variables since the certification is applicable to a manufacturing process and its final result, the resulting medical, dental or orthodontic device.
The certification of photoreactive raw materials and their CE marking as if they were biomedical devices leads to confusion and uncertainty since it is encouraging manufacturers of medical, dental and orthodontic devices to use the certifications of their 3D resin suppliers, instead of certifying their own production facilities and their own produced medical, dental and orthodontic products.
Instead of certified, 3D resins must be compliants and meet the quality and safety requirements for their intended medical application to facilitate the medical device certification by the manufacturers of medical, dental and orthodontic devices.
There are countless publications of resins certified as biocompatible that have been found to be toxic. Examples:
- Assessing and Reducing the Toxicity of 3D-Printed Parts
- Dental resins used in 3D printing technologies release ovo-toxic leachates
- Biocompatibility of Photopolymers in 3D Printing
- Assessment of biocompatibility of 3D printed photopolymers using zebrafish embryo toxicity assays
These findings prove the importance of certifying medical devices rather than their raw materials to hold medical device manufacturers accountable for products manufactured in their facilities.
3D printed medical devices fall within the scope of specific EU product legislation, such as the EU Medical Device Regulation MDR 2017/745. Therefore, manufacturers of medical devices must ensure that their 3D printed products meet the requirements of the applicable EU legislation, carry out the necessary conformity assessment procedures, compose a technical file, draft the EU declaration of conformity and affix the CE marking, before placing them on the EU market.
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