Additive manufacturing can be used to create faster, more flexible, and more cost-effective development and production methods. Direct metal laser sintering (DMLS) is an additive manufacturing technique that uses that uses a laser to sinter fine metal powder and build up the product layer by layer to create a solid structure. This method can be used to create products with extremely complex geometries.

Figs. 1a and b – Using Direct Metal Laser Sintering additive manufacturing technology, digital scanner data can be used from multiple patients (top) to manufacture a variety of individually customized dental restorations (bottom) for dental labs. (Credit: Argen)
Companies are using direct metal laser sintering to create a range of medical products, including patient-specific orthopedic implants such as artificial knee joints, acetabular cups for hips, prosthetic arm joints, and finger implants, as well as many dental applications. The metals used in medical applications include stainless steel, titanium, and cobalt chrome.

Case Study

When Paul Cascone, senior vice president of research and development at Argen, speaks to a potential dental lab customer, he always leads with the benefits of digital technology. “I tell them it can broaden their offerings, eliminate inventory, cut waste, and significantly boost their productivity,” he says. Those advantages can be powerfully persuasive for the laboratories who are listening.

Staying at the cutting edge of dental methodology is crucial for Argen, the largest dental-alloy manufacturer in the world. Founded 50 years ago in South Africa and now based in southern California, the company sells some 600 different dentistry products in more than 100 countries worldwide. Their reputation has been built, in large part, on supplying dental laboratories with the highest-quality precious-metal alloys for the fabrication of restorations such as crowns, copings, and bridges.

For years, the manufacture of dental prostheses has been based on the lost-wax method, which has roots in 5,000-year-old casting techniques. In this approach, dentists rely on a molded impression of the damaged tooth (or teeth), a careful sequence of production steps, and painstaking hand finishing– with high remake rates. But during the last decade, digital tools and technology have been cutting time and cost from workflows, enabling the dental lab business model to evolve towards greater efficiency and precision.

Digital Dentistry Practices

The transition to digital begins with the impression. Where a physical mold of a patient’s teeth serves as the starting point for a lost-wax casting, the digital equivalent is an image of the teeth taken in the mouth with an intraoral scanner (although scans can also be made from physical impressions). The resulting computer-aided design (CAD) 3D model can be used to create a restoration in several ways.

Fig. 2 – A four-unit bridge (foreground) additively manufactured with selective laser melting (background) using a DMLS system. (Credit: Argen)
One path is via a computer-controlled milling machine (CAD/CAM dentistry). In this subtractive manufacturing approach, the digital file of the model guides the cutting of either a solid ceramic or composite-resin block into a prosthesis matching the shape of the teeth. While fast and often completed in a single office visit, this technique doesn’t create restorations that fit as precisely as those made using the traditional lost-wax method. The same CAD model can also be used to generate a mold from which the restoration is cast, but this takes longer than milling.

A more precise and efficient digital-based path is called selective laser melting (SLM). In this additive manufacturing (AM) process, which utilizes direct metal laser sintering technology, the CAD model guides production that adds on layers of material, rather than cutting it off and throwing it away (as with milling). The automated sintering process starts with the system depositing a thin layer of metal powder onto a build platform. A laser, guided by the CAD model, then traces a cross-sectional outline of each patient-specific dental unit, melting and hardening the material into a 20-micron-thick layer. This cycle repeats, adding on layers one at a time, until the restoration is fully formed. (See Figures 1a and b)

The benefits of AM technology for laboratory customers are many: Steps in the traditional workflow can be skipped; virtually any geometry can be created; waste is reduced; the resulting restorations are accurate and as durable as those made with lost-wax casting; and, while fine detail can be captured in both the subtractive and additive processes up to certain limits, there is no added cost with AM for sculpting more complex tooth geometries. (See Figure 2)

Going with the DMLS Flow

“We were one of the first US companies in the dental industry to use DMLS technology,” Cascone says. That was in 2007, and the system Argen purchased, after considering other AM processes, was an EOSINT M 270 from EOS. Up until that time, according to Cascone, digital STL files were only being used to mill all-ceramic restorations. “We wanted to use the available CAD data to meet the need for strong, precise-fitting porcelain-on-metal restorations,” he notes. “Our new DMLS system gave us the flexibility to manufacture the metal base.”

In the US, several types of metals—nobles, high nobles, and base alloys—are used widely by dental labs and dentists. While base materials predominate, Argen (with a history of dealing in precious metals) wanted to offer digitally produced precious- metal products to the domestic market. So they decided to develop their own noble alloy (containing 25 percent palladium) suitable for laser sintering. Of importance in their research efforts were characteristics such as biocompatibility, porcelain compatibility, thermal properties, mechanical strength, and corrosion/tarnish resistance. Thousands of possible metal combinations were evaluated, followed by field testing of the best candidates. The result: Argen is now supplying labs with more than 100,000 restorations yearly from its proprietary noble alloy.

With a first success in hand, the company decided to undertake another development project to meet the marketplace’s broad spectrum of needs. This effort involved an even more durable high-noble alloy (made with 40 percent gold and at least 20 percent of another precious metal such as platinum or palladium).

“Now we offer nobles, high nobles, and base alloys in the digital workflow, and we can make bridges of different sizes from all three classes of metals. What’s next for R&D is a high palladium noble alloy plus a unique composite made from a gold-platinum-palladium alloy combined with almost pure gold, which gives the restoration both great aesthetics and high strength. We’re also gearing up to produce partial dentures and plan on dedicating an entire system to that product alone.”

While industrial 3D printing has increased product offerings, it is also boosting productivity. Unlike traditional casting, where units are made one at a time, AM can produce a variety of unique, custom restorations in a single run: the batch size is limited only by the dimensions of the manufacturing chamber; and associated software is used to optimize placement of multiple parts.

The system’s software also automatically labels each patient’s unit and generates supports on the models prior to manufacturing. These hollow supports allow for easy removal from the build plate once the run is complete and, during finishing, they are eliminated along with excess material from each restoration. The unit is then shipped to the lab customer for bonding with ceramic. Slight cosmetic refinements can be done in the dentist’s chair. The additive manufacturing operation is straightforward, quality is high, tolerances are constant, and the process is reproducible.

Catching the Digital Current

In some countries, DMLS technology has almost completely replaced traditional casting techniques. In the US, dentists are increasingly requesting products that force labs to get involved with digital workflows. But those labs still have a choice about how fast and fully to embrace digitalization.

If they are thinking about all-ceramic units, they can either invest in a scanner and milling machine, or they can just purchase the scanner and outsource the rest. “Lab size and work volume may dictate their decision,” says Cascone, “but we advise them to at least purchase a scanner and get started.”

If the goal is porcelain-on-metal restorations, there is a different set of considerations. “In the past, we provided the purest raw metals to our lab customers and they manufactured the entire unit,” Cascone says. “Now with our selective laser melting services, we supply them with metals in an ‘advanced form’ that allows them to skip the old waxing and casting steps. They can now concentrate on the important aesthetic and functional aspects of applying the ceramic. This represents a change in their business model, but they’re really excited about the change.”

For the dental laboratory, taking the digital path can be a game changer. In a small lab, a scanner can help them expand their product offering. In a large production lab, the whole scale of the operation can be transformed. “A skilled technician using traditional hand operations can make about 20 units in a day,” Cascone explains. “If you take that same person and train them to use a scanner and software, output accelerates to 80 units a day. That’s why labs are switching.”

This article was written by Chris Hardee, a science and technology writer based in New Hampshire, on behalf of EOS of North America, Inc., Novi, Michigan. For more information, Click Here " target="_blank" rel="noopener noreferrer">http://info.hotims.com/49750-163.