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Inside Dental Technology

Jul/Aug 2012, Volume 3, Issue 7
Published by AEGIS Communications


Additive Technology

A step ahead of the game.

By Jack Marrano, CDT

The reality of technology is more evident now than ever in dentistry, and its footprint is expanding at an accelerated pace. Dentistry can now benefit and apply technology that up until now has only been available in other industries. As research continues and the demand for digital dentistry increases, digital capabilities will rise. Selective laser melting (SLM) is a new technology that recently emerged on the dental stage, but it has been used across a broad platform of manufacturing industries because of its ability to create the most complex of CAD digital designs. From the fashion industry to robotics and now dentistry, laser-melting technology is being credited for creating the impossible (Figure 1).

An additive rapid manufacturing technology, laser melting is beneficial to dental manufacturing because the technology uses only the exact material needed to create a digital design. This eliminates the issue of material waste, unlike subtractive technologies such as CAM milling. Therefore, manufacturing a digital design now becomes extremely cost-effective (Figure 2). The fabrication process can meet the high standards for accuracy that the dental laboratory industry demands and also offers high tolerances for sub-standard preparations (Figure 3 through Figure 5). SLM is an extremely cost-effective solution for the digital fabrication of ceramic-to-metal substructures. Large and small laboratories alike can take advantage of this technology today.

Additive technology has been around for centuries, but in a much simpler form. The marriage of two forms to create a single object is an early example of additive technology. Modern-day examples are much more advanced in that a design is conceived digitally and produced through the aid of advanced machinery. Additive technology is front and center in manufacturing and complements digital design.

Modern additive technology is cost-effective, fast, and extremely accurate. One of the applications in dentistry for this technology is laser-melted substructures for ceramic-to-metal restorations (Figure 6). The conventional hand fabrication of these metal frameworks was previously labor-intensive and could be subject to possible inaccuracies in the fabrication process (Figure 7 and Figure 8). Now, through laser-melting technology and CAD digital design, a quick, extremely accurate, and cost-effective solution for fabricating ceramic-to-metal substructures can be achieved. Today, this is important for dental laboratories striving to gain a competitive edge in a tough economy—due to the ever-increasing cost of doing business and the current threat of work being exported overseas.

The ability of dental laboratories to access this technology through outsourcing partners provides the opportunity to offer semi-precious and base-metal customized metal substructures that are highly accurate without the need to invest in expensive capital equipment. Production centers such as Argen, Bego, Dentsply Comp-artis, Sirona infiniDent, and Custom Milling Center (CMC) offer laser-melted substructures. Currently, Argen is the only company offering semi-precious single copings (Figure 9). Many terms are used to refer to the commercially available systems that build parts in metal. The most common are “laser melting,” “selective-laser melting,” and “direct-metal deposition.” Other terms, such as “direct-metal laser sintering,” “electron-beam melting,” and “laser-engineered net shaping,” are specific to the company that offers the machine.1 The build process begins with a fine layer of powdered alloy being spread across the build platform. A laser projects onto the powdered alloy and melts the powder in its path based upon CAD design data. Once the laser has finished the first layer, another layer of powdered alloy is spread on top of the previous layer and melted. This cycle continues until the units are completely built up from the bottom to the top according to the CAD design data (Figure 10). The units, completely embedded in build alloy powder for support, are then retrieved from the build platform and the sprues are removed from the units. Laser melting results in a coping or framework that is very dense with a more homogeneous microstructure (Figure 11 and Figure 12).

Argen’s current alloy offerings are NobleCrown NF® (PdCoCr) (www.argen.com) and Argeloy NP Supreme (CoCr), both of which are nickel-free. Argeloy NP Supreme has a tensile strength of 1000 MPA, making it optimal for bridge frameworks. The NobleCrown NF alloy has a CTE of 14.4 to 14.8, while the Argeloy NP Supreme exhibits a CTE of 14.1 to 14.5. Indications for use include all semi-precious and base alloy single copings. Bridge substructures are only offered in CoCr at this time. The substructures are compatible with most leading ceramic layering and pressing systems.

Bego offers laser-melted copings and bridges in Wirobond®C+ chrome cobalt alloy (www.begousa.com). With a CTE of 14.0 to 14.2, the Wirobond metal substructures are compatible with most of the leading ceramic layering and pressing systems. The 24.7% chromium content alloy ensures corrosion resistance and a passivity layer for biocompatibility.

Sirona infiniDent production center (www.infinident.com) offers 3D rapid prototype metal-printed single copings and bridge frameworks for up to six units in its inCoris NP (www.sirona.com) chrome cobalt alloy. With a CTE of 14.2, the non-precious frameworks can be layered with all porcelains formulated for non-precious metal alloys.

Custom Milling Center (www.custom-milling.com) offers laser-melted, nickel-free chromium cobalt single copings and bridge frameworks for up to six units. The alloy exhibits a CTE of 14.4, making it compatible with most non-precious layering materials.

Dentsply’s Compartis® production center (compartisusa.dentsply.com) produces single copings and bridge frameworks for up to 14 units in non-precious chrome cobalt alloy. With a CTE of 14.3 to 14.6, the alloy substructures are compatible with most porcelain layering systems.

Dental laboratories are now able to digitally design and process a large volume of their individually customized everyday work. This technology seamlessly integrates into the dental laboratory workflow with no disruptions to current flow or standard protocols. With no high-cost initial expenditure or set-up and a minimal learning curve, this is a turnkey technology.

References

1. Wohlers T. Additive Manufacturing 101: Part IV. Time Compression. 2010;July/August.


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Image Gallery

Figure 1  A laser-melted, full-contour crown. The crown exhibits exceptional detail and accuracy.

Figure 1

Figure 2  A variety of ceramic-to-metal substructures manufactured in a single production cycle immediately after SLM fabrication.

Figure 2

Figure 3   The coping has been fabricated using SLM technology and sectioned immediately after the SLM fabrication process. The coping fit on the die with no internal adjustments needed. Note the retention cut in the preparation and the accuracy of t

Figure 3

Figure 4  A sub-standard preparation and the SLM coping.

Figure 4

Figure 5  The coping has been sectioned to show the accuracy of the unit. The SLM fabrication process has high tolerances for sub-standard preparations.

Figure 5

Figure 6  A SLM fabricated substructure for tooth No. 9 designed with a metal lingual. Note the crisp finish lines.

Figure 6

Figure 7  With SLM produced copings, there is no sprue to be removed versus the manual lost-wax casting fabrication method.

Figure 7

Figure 8  A coping fabricated with traditional methods exhibiting the possibility of inaccuracies. Note the presence of a large sprue, which must be removed—increasing finishing time.

Figure 8

Figure 9: A SLM fabricated coping designed with a metal occlusal.

Figure 9

Figure 10  The SLM process uses a 200-watt laser to fabricate copings and bridge frameworks.

Figure 10

Figure 11  SEM scan of an alloy that has been cast using traditional methods.

Figure 11

Figure 12  SEM scan of alloy of the same composition that has been fabricated through SLM technology.

Figure 12

Figure 13  A SLM coping showing the accuracy and tolerances for various preparation types.

Figure 13