... but not yet for dental prostheses.
Article by Nadine Heilemann,
It is likely that 3D printing will play an important role in the process chains of future digital dental technology and medicine. But where are we today and what is technically possible?
There are a number of dental indications that are interesting for additive manufacturing. However, the euphoria and willingness to invest that we saw three to four years ago seems to have cooled down a bit. There has been some disillusionment with printed, polymer-based medical devices. The oral cavity is a "hostile" environment and places high demands on denture materials. In addition to fitting well, good biocompatibility, mechanics and longevity are conditions that 3D printed dental structures must meet.
Our assessment of the state of 3D printing technology:
Skepticism is appropriate
CoCr – an old hat
3D bite splints & Co.
3D Printing and Biocompatibility
Bite splints – milling still has advantages
A certain amount of skepticism is called for in the medical application of synthetic materials. In risk management and clinical evaluation, as is common for medical devices and their life cycle, the guideline is: the advantages must outweigh the disadvantages of the product. Poor biocompatibility should be considered unacceptable. With the new, upcoming MDR (Medical Device Regulations), documented risk assessment and market observation will also become a major issue for dental laboratories as manufacturers of patient-specific dental prostheses.
3D printing by Selective Laser Melting (SLM) from non-precious metals (CoCr) has become strongly established, especially for crown and bridge constructions. Alternatives made of printed polymer for the non-precious metal indications are not yet available. However, if one looks at the developments and tendencies of the international markets, the 'printed CoCr all-cast crown' is gradually being replaced by monolithic all-ceramics. Ceramics are convincing due to their better body compatibility and appearance, thus giving the patient a better and more valuable feeling of well-being. In Germany, the subsidy for non-precious metals in the health care system still plays a role in the final decision for a dental prosthesis material, which explains why the proportion of 'steel' in all indications, analog or digitally produced, is still relatively high at 20% (source: AG Keramik. Status Vollkeramik – jetzt im Praxisalltag, Wiesbaden 2019). In our DD Technology Centre we manufacture with our own SLM team on machines from Concept Laser. The material usage and costs are lower compared to a milled crown. If you have very high demands on the surfaces, a milled CoCr crown is better. In terms of body compatibility, we are not aware of any relevant differences between 3D powders, milled or cast non-precious metal.
The printing of models in dental technology is already "state of the art". Although the printed models are not considered medical devices, they are an important component in the digital production chain and achieve a better fit due to the innovative 3D printing technology. Printing therapy models – after the intra-oral scan – has now become an indispensable operation of Align Technology (World Class Orthodontics – Ortho Organizers® GmbH). The worldwide consumption of printing resin for 3D models is now so significantly high that interest has also been aroused by chemical companies and corporations outside the industry. Since competition is known to stimulate business, it can be assumed that the prices for the model resins will fall.
First of all, it should be mentioned that Exocad with its CAD software (DD Designer by Exocad) and the "Bite Splint" module has laid the foundation for the planning and design of bite splints for digital production. Quality, accuracy of fit and time efficiency offer advantages over the analog way. Compared to the milling of a splint, 3D printing requires less material and is likely to save time. So it not surprising that the first medical resins for indications with short-term use (MPG Medical Devices Act – Class I – uninterrupted use in the mouth limited to a maximum of 29 days) such as bite spoons, drilling templates and splints were printed. In the past, however, many users had negative experiences with the brittleness and likelihood of 3D-printed splints breaking.
Keeping the human organism safe from foreign substances and toxins through polymers should be guaranteed as far as possible. The sensitivity to toxins in everyday plastics, such as packaging is now very high among the population – and rightly so. It is therefore more important to critically review the photopolymerizing printing materials to be used in an oral environment. These are chemically complex products for which details in the process management are decisive for a biocompatible result. An indicator for assessing the medical quality and the risk of secretions is the examination of the solubility, which should ideally be as low as possible and at least meet the requirements (DIN EN 20795-1) for the intended indication. The material-damaging saliva absorption is also an optimization topic for 3D-printed objects, especially when it comes to long-term or permanent use.
A look into the future
At Dental Direkt we are convinced that 3D technology and printing materials will continue to evolve. In the future, both factors will be better coordinated for the manufacture of medical devices. However, since the longevity of the product in the oral cavity is important for many indications, the polymer milling blanks currently offer advantages for the patient in terms of biocompatibility.
Materials for permanent dentures are classified as risk class IIa products for continuous use in the mouth for more than 30 days. Printing resins for denture bases are also available in this risk class. Digital dentures are a future-oriented option and the worldwide demand for dentures is huge. But here too, it should be checked whether CAM milling blanks for the base are currently still the better alternative. Especially the affinity to the saliva absorption of the printed parts can be a problem for odour formation, susceptibility to breakage and deformation. Class IIa materials must be significantly improved in terms of brittleness and fracture susceptibility compared to first class I resins.
With the DD Bio Splint P HI we have developed a blank made of impact-resistant PMMA, which provides the patient with a comfortable elasticity and resistance for longevity. Although we have developed DD Bio Splint P HI especially for splint therapies in which the patient interrupts the wearing period by removing it, it meets all criteria for the higher MPG Class IIa. Due to the thermoplastic injection & embossing manufacturing process, in which medical, completely polymerized granules are heated up to the viscosity level and then injected into a mould under extreme pressure, the blanks and thus the splints achieve high strength and very good biocompatibility. As the polymerization of the medical PMMA granulate takes place under controlled, industrial conditions, the material has extremely low MMA values, is free of bisphenols and shows a very low water/saliva absorption (ISO 20795-1), which is close to "zero".
Explanation of the illustration:
The hype cycle represents the different phases of public awareness that new technology goes through when it is introduced. In terms of 3D printing, the following can be noted: The expectation that medical devices can be printed right out of the box that can compete with milled designs in terms of mechanics, biocompatibility and aesthetics is - for the time being - disappointing. However, 3D printing makes particular sense for the production of dental models, i.e. non-medical products.
Phase 1: „Technology Trigger”: The trigger is the introduction or announcement of new technology.
Phase 2: „Peak of Inflated Expectations”: The new technology generates a lot of attention and high expectations.
Phase 3: „Trough of Disillusionment”: Expectations are not met (printing of medical devices, e.g. bite splints), attention is waning.
Phase 4: „Slope of Enlightenment”: Despite decreased public attention, the technology is further developed and finds its application areas (non-medical devices, e.g. models).
Phase 5: „Plateau of Productivity”: The technology is recognized, establishes itself in the application areas and continues to mature.
Source: Edelhoff D., Güth J.-F., Trimpl J., Schweiger J., 3D-Druck in der Zahnheilkunde – zwischen Hype und Produktivitätssteigerung, in: BZB 9/2018, S. 46 - 55. The authors' assessment of the status of the individual applications based on a modification of the Gartner Hype Cycle with regard to the application of 3D printing in dentistry.
Head of Technology Center
»We have a huge hype in the industry for 3D printing. And I think we all agree that 3D printing is going to play a very important role in the dental industry of the future. But also for medical devices? Our biocompatible DD Bio Splint P HI PMMA material continues to score points, especially when it comes to milling bite splints.«