Part 1: 3D printing using the laser sintering process
Something that was still difficult to imagine a few years ago has today – often under the label Industry 4.0 – become reality: additive manufacturing. Hardly a day passes which does not include reports of new, even cheaper printers and exciting new applications – from the manufacture of toys to the printing of complex geometries made of sugar icing for the restaurant trade.
The additive or generative processes in dental technology deriving from rapid prototyping can already be classed almost as old hat. This is because the principle of 3D printing has already been in use for many years, e.g. in the form of the digital metal laser sintering (DMLS) of metal alloys. Today, applications include, in particular, the low-cost production of restorations in materials such as cobalt-chrome, titanium, burn-out wax and gold alloys. This has been followed in recent years by the increased manufacture of precise dental working models, based on the increasing spread of intraoral impression taking.
Fig.1: Dentale Restaurationen auf Bauplatte (Quelle: EOS GmbH)
At INFINIDENT Solutions, the fields of application for this – no longer particularly new – technology go far beyond the manufacture of crowns and bridges. For example, partial frameworks, bar attachments, retention nets and bondable tertiary constructions are now being realised. What is also new is equipment for orthodontics and, from October, implant structures made in hybrid processes.
We spoke to Mr Thomas Hack, Managing Partner at INFINIDENT Solutions GmbH, about the advantages and possible uses of digital metal laser sintering (DMLS) for non-precious metal frames for dental laboratories and practice labs. In the following articles, we intend to look at the special technical features of this technology in detail as well as other additive production processes. It is sure to be fascinating!
Fig.2: Thomas Hack explaining the pros and cons of additive manufacturing (Source: INFINIDENT Solutions)
Mr Hack, what does dental 3D printing refer to?
Put very simply, 3D printing involves an additive or generative layering process. This initially means disassembling the three-dimensional data of a construction file (usually STL) into a multitude of layers. These are then used additively to produce the desired geometry layer by layer using a laser. This new technology offers important advantages.
Fig.3: General functional principle of laser-sintering (Quelle: EOS GmbH)
What are these advantages?
One important advantage compared to subtractive procedures is the geometrical freedom in the implementation of a CAD construction. Using a 3D printing process, complex structures and the associated non-millable areas can be reproduced with absolute accuracy. For example, the interdental spaces in a bridge can be reproduced down to the tiniest detail, although even the smallest milling tools of a 5-axis CNC machine can only "freely work" the desired form to a limited degree. Even extreme dental designs are not subject to any limitations in terms of construction height.
Another factor: alongside the costs for tool and machine wear, the subject of material loss is an often disregarded cost factor. A standard CoCr blank 12 mm in height and 985 mm in diameter weighs about 770 g. Normally, 30 non-precious metal units can on average be milled per blank. Depending on the situation, a CoCr unit weighs between 2 and 5 g. As a result, in a subtractive process only 10-20% can be achieved as actual output. The remaining 80-90% represents material loss ("chip removal"). With such a proportion, this can hardly be described as a really efficient production solution.
What can be expected in terms of the materials for the laser sintering of dental components?
At INFINIDENT, we have been intensely occupied with the subject of the additive production of dental restorations since 2006. We have relied ever since on the systems of EOS GmbH (Electro Optical Systems), Krailing (Germany), with whom we jointly developed the process back then.
The material used, EOS CobaltChrome SP2 or EOS CobaltChrome RPD, consists of cobalt-chrome (CoCr) particles with a maximum grain size of <55 µm. The CoCr powder used is classified as a class IIa medical product and possesses a CE marking. The materials involved are highly standardised ones, whose properties guarantee homogeneous melting using a laser thanks to the optimised grain size distribution of the powder.
In general, material development for additive manufacturing is far from a plug-and-play affair, but requires accurate testing and adjustment on the basis of numerous additional parameters in order to achieve the final desired result. We cooperate closely with the manufacturer to ensure ongoing technological development.
Does additive manufacturing compete with the milling of non-precious metals?
Not at all. A distinction has to be made here according to indication. If we are talking about the production of crown and bridge frames, additive manufacturing represents an appropriate and, above all, affordable supplement to our service in the area of simultaneous 5-axis milling. But if a dental technician wants to have a so-called full-cast crown (with anatomical formation) produced, which they have designed with great attention to detail in their CAD software, we would always advise them to choose the milled version. Additive manufacturing is at a slight disadvantage here for design reasons compared to "milling out of a block".
And what about new areas of application?
That is a completely different story. Let us take the subject of model casting as an example. When one realistically considers the machining time required, tool costs (milling tools), and material and personnel costs, the milling of a digitally designed model casting prosthesis does not strike us as economically viable. By contrast, additive manufacturing by a specialist provider is at an advantage here thanks to the possibility of producing many parts at once in one construction process. At the same time, the materials consumed are actually used in the structure and holding elements. The final advantage is once again the geometrical freedom of 3D printing, whereas subtractive processes often quickly come up against their limits in terms of adjustment angle.
Fig.4: Build plate for partial frameworks (Quelle: EOS GmbH)
What conclusion can be drawn?
We ensure the competitiveness of our customers in dental technology through the further development of additive manufacturing at INFINIDENT to include new fields of application. This secures access to otherwise very expensive process technology at attractive prices. As a result, laser sintering is accessible to every dental technician and offers attractive approaches for processing customer orders.
Thank you very much for the informative discussion. We are already looking forward to the next part, focusing on the technical framework for additive manufacturing!