A look behind the scenes of the development of a 3D printer: From the idea to the printed part

The dental 3D printer was one of the biggest topics at the IDS 2019. Lively discussions took place about the precision and speed of these machines and the advantages and disadvantages of 3D printing in the dental laboratory industry. Read the first part in a series of articles to find out about the background and benefits of 3D printing and the current status of this technology in the dental laboratory.

Tobias Specht, MDT, Director GBU Labside Digital, and Jörg Ebert, Senior Research Associate at Ivoclar Vivadent, talk about these topics in the following interview.

Mr Specht, what is the status of 3D printers in today’s dental laboratories? What are the benefits of 3D printing?

Tobias Specht: This technology is relatively new in our field. Even though it may seem as if a large number of dental laboratories have undergone digital transformation, this is not really the case.

Nevertheless, we have noticed a significant increase in the use of intraoral scanners in dental practices in recent years. As a result, dental laboratories are receiving a growing number of digital files, which require them to have access to CAD software in order to work with them. Therefore, it is highly beneficial for small laboratories in particular to start using digital technologies so that they can continue to work with their dentists and stay competitive.

Many laboratories that have introduced digital workflows no longer send their CAD designs to be milled externally, because they can do it themselves in-house. However, not all dental parts are suitable for milling due to their shape. Models are a case in point. Nevertheless, as a result of recent advances in 3D printing, laboratories will be able to produce all types of parts in the future.

This webinar covers everything from the scanning of the intraoral situation to the virtual design and 3D printing of dental models.

How would you position 3D printing compared to milling? What are the benefits of 3D printing for dental laboratories?

Tobias Specht: Using a milling machine in your laboratory does not prevent you from owning a 3D printer. It is a great supplement to a milling machine. The two devices combine the best of both worlds.

As previously mentioned some objects are easier to print than mill due to their specific shape and structure. Furthermore, printing can be more economical in terms of the material used than the milling process. For example, when bite trays are milled, a relatively large amount of PMMA material has to be removed to create the final product. When a tray is printed, for example, only the amount of material needed to produce the tray and the supporting structures is used.

If you find that your milling machines are being used to full capacity for producing zirconia and cobalt-chromium crowns and bridges and there is hardly any time to mill models, trays and wax, it is worth investing the possibility of purchasing a relatively affordable printer instead of another milling device in order to free up machine capacity.

In addition, printers are often more efficient in terms of time compared with milling units. For example, all crowns have to be milled separately. However, the printing process allows as many parts to be produced simultaneously as the size of the build platform permits. The construction process in Digital Light Processing (DLP) is not restricted by the number of parts, but merely by their height.

Mr Ebert, Mr Specht just mentioned the topic of Digital Light Processing. Could you please give us a brief description of the technologies used in 3D printing and when they were developed?

Jörg Ebert: The invention of 3D printing is attributed to Dr Hideo Kodama who applied for a patent for a rapid prototyping device in 1980.

3D printing entered the dental industry in the course of the digitalization process and the development of suitable software solutions that fulfil specific indications and new methods When you are selecting a manufacturing technique, you have to consider the following three questions:

• What type of material and properties are needed with respect to the requirements of medical devices?
• What level of precision, surface finish or esthetics do I require?
• How productive should or would I like to be?

Metal frameworks are usually produced using selective laser melting  (SLM). The size and cost of the equipment for this process is usually tailored to the needs of manufacturing centres. However, the more affordable option is to use the lost wax process. The first printers were used to print wax structures, which were built up one layer at a time. Nevertheless, this process was very time-consuming, taking several hours to produce a single restoration.

Stereolithography has the longest development history attributed to the extensive work of Dr Kodama. This technique was refined in various stages, which resulted in the developed of laser-based stereolithography (SLA) and digital light processing (DLP). Today, it represents the most sophisticated additive manufacturing technique, producing high-precision results with polymers.

Digital dentistry and dental technology: The dental world in transition

At IDS 2019, Ivoclar Vivadent presented a 3D printer which will be available in the near future. On what type of technology is the printer based?

Jörg Ebert: The PrograPrint PR5 is a DLP-based stereolithography printer. DLP is short for Digital Light Processing. This technology offers decisive advantages compared with laser-based stereolithography: for example, increased speed because each built-up layer is light cured in one exposure. In the development of our printer we have gone one step further and we have optimally combined digital data with the available physical hardware and the chemical properties of the given materials.

Could you please explain this in more detail?

Jörg Ebert: You will most probably have noticed that you can intensify the brightness of a torch at the centre of the light source in relation to its circumference. Furthermore, you can adjust the torch to emit the same amount of light throughout the lens, but it will not be as bright. In the same vein, we have had to focus our efforts: Precise and rapid polymerization demands the following requirements: even and maximum brightness – in addition to a razor-sharp image. However, experience has shown that in most cases, it is not actually necessary to have this maximum amount of light throughout the entire field of illumination during the build process. As a result, we have devised a new technique. It calculates an even and layer-specific maximum light output. This strategy ensures that each layer is printed in the best possible quality. At the same time, consistent precision is guaranteed – irrespective of whether the part is located at the centre or on the periphery of the build platform. By adjusting our materials to the build area resolution of only 49 µm and optimizing the scaling factor to the shrinkage compensation factor as well as other factors, we have achieved an average deviation of < 20 µm and a standard deviation of < 50 µm.

The system takes into consideration cleaning and post-curing processes, which are important for the precision of the results. If the post processing step is not properly coordinated, the precision and fit of the printed part could be negatively influenced.

What made you choose this form of printing over other technologies?

Jörg Ebert: After carefully analyzing all the available options, our decision fell on stereolithography because of its exceptional precision and speed compared with other technologies of its kind.

Since our objective was to develop an integrated system, it was important for us to base our work on a mature technology.

Furthermore, we wanted to offer our customers the additional benefit of being able to use an advanced LED post processing device. It is matched to the ProArt Print materials as well as the Ivoclar Vivadent composite resins. It goes without saying that our expertise in the field of light-curing materials gave us an additional edge in our development efforts.