This article presents the current indications for the 3D printer in the laboratory routine. It addresses the increasing automation of 3D printing, shows various perspectives and highlights the importance of well thought out process chains consisting of printers, software, materials and post-processing. The article focuses on the Straumann® CARES® P30+ printer from the company Straumann (Basel, Switzerland).
3D printing has established itself in many dental laboratories within a relatively short period. 3D printers are now integrated in the daily workflow and have become part of the dental technology process chain. Despite that fact that dental 3D printing is still in the early stages of development – research and development is still required particularly in the area of materials – the potential is huge. The 3D printer is currently used in prosthetic dentistry mainly for producing models and accessories. In this context, 3D printing is not an end in itself, but a response to the changes in the sector and the working world. The automation of processes has become the focus of attention in many sectors, and is also a key issue in the dental laboratory. While "optimizing processes" seems a rather abstract concept that sounds like some meaningless business jargon, it is an important basis for a successful laboratory routine. Since dental technicians work in the field of medical devices, process must be coordinated in a such a way that a high quality standard can reliably be achieved. This is where modern 3D printing systems offer interesting possibilities. Printers, software, materials and post-processing are ideally coordinated. Work tasks are increasingly being handed over to the machine, giving dental technicians more scope for practicing their actual key skills.
Automation means increased productivity and efficiency, but also reliability within the process chain. Sources of error are reduced by dispensing with manual operations. But this does not mean that dental skills and manual abilities are replaced. Rather, the following principle applies: The more repetitive a task is, the greater its potential to be automated. Handing over "undemanding", repetitive operations to machines makes the work routine easier for the dental technician. But other, non-commercial, aspects should also be cited as benefits of automation, including customer and patient satisfaction, and therefore also the reputation of the dental laboratory. Taking the example of impression trays: Experience has shown that individually printed impression trays are welcomed by dentists since they offer uniform wall thicknesses and look like high-quality, industry-standard professional items. For dental technicians, the digital opportunities also mean dealing with and critically evaluating the various technologies. What is useful for the dental laboratory? The answer often depends on the individual circumstances. Just because the automation of a process seems useful from the technical standpoint definitely does not mean that it offers any economic added value for the dental laboratory. Or, to put it the other way round, it also means viewing processes not just from the economic standpoint. Taking the example of impression trays: A 3D printed impression tray is not necessarily cheaper than a conventionally produced version, but the other, non-monetary, advantages (easing the workload, quality) mean that 3D printing often becomes the technology of choice. As always, it is basically a matter of carefully weighing up the advantages and disadvantages, not just in relation to the actual technology (3D printing), but also in relation to the equipment and the 3D printing systems.
The quality criterion and 3D printers
Although 3D printing is an automated production process, manual operations are still often needed in the laboratory routine before the printed object is ready for use. Despite all the digitization, 3D printing still requires manual interventions. Such tasks are often laborious, time-consuming and have little to do with the key skills of dental technology (for example, removing the printed object from the build platform, cleaning the printed object). But despite all the euphoria surrounding 3D printing, the strict requirements relating to precision, reproducibility and the regulatory framework still need to be borne in mind. Against this backdrop, 3D printer manufacturers are constantly optimizing their operations, validating processes and materials and making their applications easier to use.
One example of a modern printer that facilitates increasing automation in the dental laboratory is the Straumann® CARES® P30+ ASM produced by the company Rapid Shape (Heimsheim) (Fig. 1). Like all printers in this series, the P30+ ASM unit is based on force-feedback technology. What sounds rather technical and theoretical manifests itself in everyday practical terms as fast print speeds and high precision. Using force-feedback technology, a measuring device monitors the process and provides real-time data for motion control. One advantage is that the separation process is both controlled and smooth, while the other movements for the mixing and replenishment of fresh printer material for the next infill layer are accelerated. The printer is integrated in a validated process chain consisting of
The new printer differs from the P30 model in just one tool: The printer has an integrated tray and blade (Figs. 2 and 3). This performs the ASM function (peel-off mechanism). The advantage of this function becomes apparent in the laboratory routine. The manual removal of the printed objects from the build platform is time-consuming and is certainly not one of the dental technician's favorite tasks. The ASM functions relieves the dental technician of this chore. When a print job ends, the blade automatically moves over the build platform and separates the printed object. The objects fall into the reservoir below, and the next print job can start, thereby prolonging the period of unattended operation of the printer. Later on, the dental technician removes the collected printed objects from the reservoir and starts the post-processing.
The ASM function is one more step towards the automation of dental technology operations in 3D printing. Combined with the automated cleaning and light-curing processes, this results in an almost fully automated workflow, saving time. It also dispenses with the often laborious and, thanks to the "greasy" resins, dirty chore in the manual procedure of removing the objects from the model platform.
Printing individual impression trays is part of the normal routine in many laboratories. This is another illustration of how quickly technologies (software, hardware, materials) develop and how user acceptance increases at the same time. Just a few years ago, criticism was being expressed about the indication of "trays" for the 3D printer. Nowadays, including in the author's laboratory, all trays and bite plates are produced with a 3D printer, and processes have been modified accordingly.
Basically, two questions should be considered when introducing new processes: 1. Is the new process cheaper? 2. Is the new process better? Printing impression trays is not necessarily cheaper, but the result is better. Good software applications are available for constructing trays and bite plates. Popular CAD programs (for example from 3Shape (Copenhagen, Denmark), Dental Wings (Berlin), Straumann® CARES® Visual, Exocad, (Darmstadt)) integrate corresponding options. Clever software solutions have also been developed as stand-alone applications, giving the dental technician numerous choices (for example SHERAeasy-base from Shera (Lemförde), or BISS Dental from Promadent (Nienhagen)).
The quality and "look and feel" of a printed tray are impressive. Particularly if a complex prosthetic restoration is being fabricated, the impression tray should also look like a high-quality product. This is readily achievable with 3D printing (Figs. 4 to 6). Advantages of the printed impression tray:
Figs. 4 to 6 Various 3D resins are available in the material portfolio for impression trays. Transparent material can be beneficial in implant impression-taking. Manual post-processing is reduced to a minimum.
Not always cheaper, but better: From the economic standpoint, printing the tray is not cheaper. But given that the dental laboratory already operates on the basis of a dataset, the digital fabrication of the tray is the logical conclusion. 3D printing is also the preferred option for many other indications, for example for bite plates and bite fork attachments used in connection with electronic bite registration (Figs. 7 and 8).
Model fabrication is a classic indication for the 3D printer. In addition to models for producing crowns and bridges on natural abutments with removable dies and implant models with laboratory analogs, models for digital orthodontics (aligners) are becoming increasingly relevant. As regards the data from the intraoral scanner, it is not a question of whether the digitally fabricated model is better or worse than the plaster model. 3D printing is the logical consequence, except in situations where no model is involved. As a rule, the dental technician needs a model (for producing components, for checking), and 3D printing is the process of choice here.
How do removable dies fit in the model? Particularly for models with removable dies (Geller models), many printers have problems with generating a reproducible fit for the dies. Two problematic factors appear to play a role here: on the one hand, the precision of the printer generally. On the other hand, the design software for the dies often limits their use. The challenge is to achieve a die geometry that is not too round for producing an exact fit of the die in the model. This is where the Straumann® CARES® P series printers offer a unique selling point. For such cases Rapid Shape and Straumann have developed a new die geometry for the CADCAM software Straumann® CARES® Visual. The removable dies have a special design with the key feature of elastic guide wings that allow for a tolerance of around 30 µm in relation to the dental component. Another element is a support for the Z axis that is optimized for 3D printing, with a deviation of +/- 25 µm. The three-wing elements with an identical spring effect automatically adjust the model in relation to the tooth center, even if the die geometry differs (Figs. 9 to 11). As soon as the die is inserted in the model, the elements deflect very slightly (Figs. 12 and 13).
Implant prosthetics
A good fit is a key requirement likewise for printed implant models. It must be possible to reposition laboratory analogs with differing geometries precisely (Fig. 14). If the printer parameters are set accordingly, precise, secure and reproducible results are possible. But: The parameters must be newly evaluated and adapted according to each laboratory analog and its shape. An example shown here is the classic Straumann laboratory analog with its elongated conical shape; the laboratory analog fits exactly in the model (Fig. 15). An alternative would be the Medentika laboratory analog, which has a completely different design. Here too, a high level of precision is possible with the right printer parameters (Fig. 16).
The ability to fabricate a model with a precise implant position prior to surgery opens up new possibilities for the dental laboratory. In a digital workflow, the provisional restoration (immediate solution) can be produced directly from the implant planning. For temporary crowns, the material P pro Crown & Bridge is available within the described printing system (Fig. 17).
Special aspects are the nature of the post-processing within the validated process chain and the innovative cleaning process. Directly after the printing operation, the objects (for example temporary crowns) are centrifuged (Fig. 18), thereby removing excess resin from the printed object. This type of cleaning is an alternative to the standard procedure with alcohol; alcohol can impair the long-term stability of a printer resin. Although cleaning in the centrifuge requires a bit more effort, it can have a positive effect on the material quality. This aspect should be borne in mind particularly for objects that remain in the mouth for a long time (for example temporary crowns) (Figs. 19 and 20). When used for the described indications, the 3D printer becomes a protagonist in implant prosthetics. If all the parameters are coordinated, the model, drill template and temporary crown can be printed before the surgical procedure (Fig. 21).
Outlook: Materials
As regards materials, a selection is offered for a wide variety of indications. The printer manufacturer works with verified material partners and provides industrially and technically checked parameters for their portfolio. The Development Department at Straumann also validates the materials, including for biocompatibility and sterilizability. Nine different materials for use in the relevant indications are currently available (Fig. 22). Since research in this area is very active, new indications are expected. One interesting development is a sediment-free resin for 3D printing (still in development) (Fig. 23). With traditional 3D printer resins, there is a risk that the sediments sink to the bottom of the material if the resins are not used for a long time. The resin separates out, potentially affecting the quality of printing. Straumann is currently working on plastics that are free of sediments. This idea comes from the industry, which works with very large tanks in which the material is stirred up only with difficulty. With sediment-free dental resins, this problem would also become a thing of the past in the lab routine and one more step towards the complete automation of 3D printing.
Now that 3D printing has become an established part of the laboratory routine, the focus turns to material development. Manufacturers are also seeking to make 3D printing a more pleasant and reproducible experience. This goal has been achieved with the 3D printer systems from Rapid Shape, with their increased automation, software applications and new materials. For a long time now, the focus has been on 3D printers not as soloists, but as part of the whole validated process chain of printers and post-processing, software and materials. This article has presented the latest popular indications for printing dental components and temporary restorations. In some areas of dental technology, conventional processes have become obsolete in the author's laboratory, for example in the fabrication of impression trays or bite plates. Additional applications for 3D printers are expected in future. In addition to the expanded range of materials, artificial intelligence (AI) will come to be used in printer systems and software, for example in order to optimize workflow management. For dental technicians this will mean greater automation of the 3D printing process and more time for performing their actual key tasks of dental technology. Modern printers offer a reliable and practical technology that can safely and conveniently be integrated in the laboratory routine.
