Building a Better Product

In their literature-based review of additive manufacturing in dentistry, Javaid and Haleem¹ studied the current status and applications of 3D printing along with various technologies, benefits, and future scope. The study concludes that the significant benefits of these technologies include:

• faster, more accurate service;
• cost-effectiveness;
• ease of determining depth and width of teeth;
• easy fabrication of customized implants;
• reduced fabrication time;
• considerable inventory reduction of physical models (through digital storage);
• rapid production of custom designs; and
• accurate sizing for implants.

Several questions should be asked as a dental laboratory chooses printing materials: Which printing technology is best suited to the laboratory's workflow? Is it a closed or open-architecture system? What kinds of restorations can the laboratory print? How fast does the laboratory need to print models, restorations, digital dentures, etc?

Currently, 3D printing technologies utilized in dentistry include fused deposition modeling (FDM), stereolithography (SLA), selective laser sintering (SLS), and digital light processing (DLP). FDM is a more basic technology, while SLA offers highly detailed output and SLS is ideal for making products with excellent mechanical characteristics. FDM, SLA, and SLS all can use simple materials such as plastics (resins), metals, wax, and, soon, ceramics and glass. Ceramic printing is still in the development stage, mainly because post-processing requires eliminating the resin matrix while leaving the crystalline glass structure intact.

Most recent innovations in printing resins utilize DLP technology, which combines the latest technology of SLA with faster throughput, mainly due to a specially developed digital light projector that cures one complete layer at a time. Additionally, direct metal laser sintering (DMLS) now even makes it possible to print titanium.

As technology allows dental professionals to digitally design treatment plans and send information to 3D printers, a need also exists to question the quality of the printed restorations. The most widely used technologies, such as SLA and DLP, need to be challenged in terms of quality, speed, and cost. This area continues to be a hotbed of innovation, so new technologies undoubtedly will improve upon the advances of the past.

Determining what type of technology will be best for each laboratory can seem complicated. Remember to focus on your own needs, even if it is not the most popular choice. Oftentimes, the criteria depend on whether precision or speed/productivity are higher priorities, based on the types of work being done. For laboratories primarily printing models, stents, or provisionals, speed and production likely are major considerations because the output for those products typically does not need to be as fine or detailed as it would for implant-supported restorations or fixed cases. For fixed restorative work, using the most accurate printer and materials is critical. Fixed restorations typically require a precise output of 25 μm or less per layer; for orthodontic aligners, 50- to 100-μm layers are deemed acceptable. Some laboratories may choose to deploy multiple printers and assign the less accurate one to indications where precision is not a critical factor.

Some 3D printing systems are closed because their software, proprietary branded printers, and/or materials are validated internally; the manufacturer guarantees the outcomes produced with that system in accordance to its own parameters and specifications. However, open systems provide the laboratory with the ability to use more of the various materials in the increasingly competitive market, which can affect costs as well as output. Some manufacturers require proprietary materials for their own printers but also allow their materials to be compatible with other printers. Similarly, other manufacturers offer their own materials for their printers while also making those printers open to other materials that may be available at different price points or offer other advantages. Careful attention is necessary when using an open-system resin to ensure that it is used for the intended indications, and that the printer is properly calibrated to optimize the material's properties.

Most practices and dental laboratories that utilize 3D printing technology use it to print inlays, onlays, splints/night guards, models for aligners, temporary crowns, surgical guides, and restorative models; some are even printing full or partial denture bases. Regardless of the restoration being created, additive technology provides the benefit of speed; a crown can be printed easily in less than 30 minutes using the appropriate resins.

Several key characteristics and measurable specifications must be considered when comparing printable materials. Build time is always a factor, though it may be more of a priority for some applications than others. Meanwhile, shade accuracy is a higher priority for provisionals and dentures.

Like with many millable or analog materials, the durability and longevity of a printable material are important as well for certain indications. Some resins are very appropriate for digital dentures and provisionals because of their resilience and longevity, whereas fixed restorative model resins certainly require high accuracy but not as much longevity beyond their intended use.

Regardless of the indication, post-processing is extremely important for the laboratory. This includes the way the printed object (a model or restoration) is cleaned; whether the system requires the use of glycol, alcohol, or water wash after printing; and what the appropriate light range and wave frequency are for light-curing. These steps ensure that the output is fully cured and accurate, but the time and effort required to complete these steps can vary depending on the material and technology. Isotropic parts, for example, achieve peak mechanical properties during printing, require minimal supports, and can be post-processed in minutes, with no baking, polishing, or dyeing required.

Various materials—resins, metals, waxes, ceramics, etc—come with different speed expectations. Currently, DLP offers the fastest throughput for resin printing, with its build time based on the overall vertical print dimension rather than the mass or number of units. This means that a laboratory can print everything on the build plate in the same amount of time required to print a single appliance or model with the same vertical dimensions. SLA technology takes longer because a laser passes over the whole plate one layer at a time; similarly, SLM involves a laser passing over a bed of metallic powder. Build times for both of those technologies as well as FDM are based on the number of units being printed; one or two units can be printed relatively quickly, but printing an entire build plate can take significantly longer. Subsequently, DLP and similar technologies are becoming standard in dental laboratories that print in high volumes.

Increased precision in 3D printing entails printing thinner—and, thus, more—layers, which is why more accurate printing typically takes longer. Models that print at 50-μm accuracy will take longer than models that print at 100 μm per layer. Many new printers offer ways to manipulate the levels of accuracy in order to find the right balance between speed and precision for whatever product is being printed.

While factors such as price, resolution, software, and speed are key concerns for laboratories when choosing an additive manufacturing system, the print materials that will be used in that system are critical as they can be just as significant in determining both laboratory efficiency and output quality. As additive processes continue to evolve, dental professionals can be most excited for the introduction of new printable ceramic materials and other long-term options, as seen across the floor at the IDT International Digital Denture Symposium last September. 3D printing has already proven to be the future of the dental laboratory, so if you have not already, now is the time to start building a better product for for you.

1. Javaid M, Haleem A. Current status and applications of additive manufacturing in dentistry: A literature-based review. J Oral Biol Craniofac Res. 2019 Jul-Sep; 9(3): 179-185. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6482339/

Sander Polanco, MDT, is the owner of FMR Prosthetic Center in Staten Island, New York.