Polished splints direct from the 3D printer

Jeroen Klijnsma

Wed. 27. March 2024

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As a certified dental technician, I have worked in, managed and owned several laboratories around the world. This has exposed me to many different analogue, digital and crossover techniques. Even though digital technology has been widely available in our industry for over two decades, the uptake and trust in this technology are still fairly low compared with analogue methods. Even if digital technology is available in a clinic or laboratory, the knowledge of it is often limited. Knowing the benefits and limitations and especially how to operate the technology as efficiently as possible are key.

Fig. 1: The new UltraGLOSS resin tray (Asiga).

I am personally a huge fan of additive manufacturing (3D printing) and the possibilities this technology offers. The high accuracy, low entry costs and minimal amount of geometric limitations in our manufacturing processes make 3D printers our best equipment in this modern world. In our fully digital dental laboratory, we have eliminated traditional plasterwork, negating the need for investment in a plaster room. 3D printing has taken over and allowed us to create the highest quality dental models and dental appliances every single time.

If we look at the hardware of affordable 3D-printing systems, there have been few jaw-dropping innovations. Recent years have been dominated by innovations in 3D-printing resins. Consider biocompatible resins and especially hybrid resins for denture bases. Hybrid resins, which are biocompatible US Food and Drug Administration Class II medical devices, now allow us to print long-term (permanent) approved restorations. In recent years, how we manufacture night guards and splints has evolved dramatically. However, the tedious labour of manual adjustments or manual polishing is still required.

When Asiga asked me to try a new type of resin tray that would eliminate or minimise manual post-processing, I was initially sceptical. How could just a different tray make such a difference? After printing my first splint with this new tray, I knew it was a game-changer and one of the best new products on the market. Let me introduce you to the new UltraGLOSS resin tray (Fig. 1). The outcome of printing with this tray is a smoother finish of the printed object. A trick is to increase the number of layers, making the individual layer height smaller and thus resulting in fewer visible layers. The magic of the tray does the rest. We print using our MAX UV printer (Asiga), but UltraGLOSS trays are also available for its big brother, the PRO 4K series. In the following paragraphs, I will explain our processes of manufacturing splints.

Data recording

In order to digitally design a night guard or splint, we need to have a digital recording of the oral cavity, specifically of both arches and a bite registration. This can be done in one of three ways:

taking a traditional impression, including pouring a plaster model and then scanning the model with a desktop scanner;
taking a traditional impression and directly scanning that impression with a desktop scanner; or
taking a digital impression using an intra-oral scanner.

In this case, an as-yet-unreleased intra-oral scanner was used (Fig. 2). A spacer or leaf gauge is used to record an open bite in centric relation independent of tooth contact. In this position, the mandible is restricted purely to rotary movement. From this unstrained, physiological position, the patient can make vertical, lateral or protrusive movements. We only accept scans with an open occlusion, as virtual opening (static or dynamic) of the bite might result in incorrect interpretation of patient’s condylar or occlusal guidance and bite.

Fig. 2: Intra-oral scan on the screen.

Fig. 3: Design of the splint using the Splint Studio CAD program (3Shape).

Fig. 4: During the design of the splint, if we add material to the palatal gingival margins, we avoid any local pressure and increase the comfort when the splint is worn.

Fig. 5: All splints designed in our laboratory have canine extensions for additional retention and to help avoid tipping during articulation.

Order form set-up

After receiving the scans, we start designing the splint using the Splint Studio CAD program (3Shape). In our order form (Fig. 3), we select it as a digital impression and select the upper jaw. Next, we select the option to design a splint and the material we would like to use. We print our splints with KeySplint Soft (Keystone Industries). After we have set up the order form, we import the intra-oral scans and open Splint Studio.

CAD

Once Splint Studio is open, we confirm the given bite and select the path of insertion. Here, we can also add or remove space in the block-out stage to determine whether the splint needs to engage more or less. By adding material to the palatal gingival margins, we avoid any local pressure and increase the comfort when the splint is worn (Fig. 4).

The most common designs in our laboratory are Michigan or flat-plane splints. However, all of them have canine extensions for additional retention and to help avoid tipping during articulation (Fig. 5).

Fig. 6: View and position of the splint to be printed (Asiga Composer).

Fig. 7: Close-up view and position of the splint to be printed (Asiga Composer).

Fig. 8: Printed splint.

Printing set-up

There are many ways we can set up splints, but the goal is to minimise or even eliminate polishing after post-processing. A splint-nesting position close to horizontal can result in inaccurate prints, depending on the printer, and requires more manual post-processing. We put in a huge effort to design the perfect splint and placing supporting pins on the occlusal surface would undo much of our work as well require more manual post-processing.

Orientating the splint near vertically has the benefits of the splint being self-supporting, of a smaller surface area and therefore less pulling force, and of a smaller chance of visible printed layers on the occlusal surface. For positioning the splint vertically, we have two options: placing either the anterior or the posterior area towards the build platform (Fig. 6). Each has their own benefits, and the choice depends upon what suits you best and whether you prefer to perform a final polish.

The advantage of printing with the posterior downwards is that we do not need supporting pins and therefore no manual finishing is required, except for the area touching the build platform. A disadvantage can be that we need two areas to print successfully, going from both posterior areas towards the anterior area (Fig. 7).

Most of our clients prefer a highly polished appliance, so we print mainly with the anterior area downwards to minimise the risk of a failed print. We see the main benefit in the massive time reduction in our polishing processes. Our team is now spending less than half the time polishing than they did before, as the splints come out much smoother and shinier.

Printing time

When printing in a vertical position, we can fit more splints on a build platform, but it increases the printing time. The printing time is also increased by printing with an UltraGLOSS tray at 50 μm to achieve the best smooth surface. However, based on our time management in our manufacturing processes, we recommend starting printing splints at the end of the day.

They will be finished during the night and ready to take out of the printer in the morning. Manufacture during the night and if anything goes wrong or there is an urgent case, you can print that during the day. This advice would be the same if you were performing subtractive manufacturing with a milling machine with a material loader or changer.

Washing

After printing (Fig. 8), we remove any excess material by washing it in isopropyl alcohol. We clean our splints in an ultrasonic cleaner and have a pre-wash and post-wash container filled with alcohol. These containers are widely available. We use individual cleaning solutions for each material, so we do not have any cross-contamination or lose our biocompatibility classification. Because we use an ultrasonic cleaner and not a stirring cleaner, the splints do not slam and rub against the cleaning containers and therefore the surfaces are not damaged and the splints retain their transparency.

Fig. 9a: Post-processed splint.

Fig. 9b: Splint on the model.

Fig. 9c: Occlusal view of the splint.

Light polymerisation

After carefully cleaning and drying the splint, we give it a final light polymerisation. We have different light polymerisation units that are all validated for use with KeySplint Soft. However, we have had better results with those with which we are able to remove the oxygen and thereby avoid an oxygen inhibition layer. We have achieved the best results with our Otoflash G171-6 (NK-Optik; with nitrogen connection) and our Straumann/Rapid Shape vacuum polymerisation unit (Fig. 9).

Polishing

To achieve a highly polished splint, we remove the supporting pins using a Scotch-Brite wheel (3M) and then use pumice on a lathe to smooth the splint where required. We finalise the splint by giving it a high-shine buff and a proper steam clean (Fig. 10). I do have to emphasise that, the more we work with the UltraGLOSS tray and learn how to optimise the post-processing, we foresee that manual polishing will soon be something of the past.

I have been asked whether UltraGLOSS will work with every material. Technically, the answer is yes. We can print everything with these wonderful trays. However, you have to ask yourself whether printing a model or custom tray at 50 μm would be of any real added value. In contrast, printing denture bases with such a level of detail would be of tremendous benefit, as there will be less manual finishing. Therefore, I am a firm believer that the UltraGLOSS printing technique is an absolute winner and we all benefit, regardless of how we would like our products to be finished.