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Technology Spotlight: Laser-Sintered Crown Copings

Technology Spotlight: Laser-Sintered Crown Copings
Joe Hattouni, CDT, General Manager of Fixed Prosthodontics
Duy Lam, Manager of Fixed Prosthodontics

by Joe Hattouni, CDT, General Manager of Fixed Prosthodontics;

and Duy Lam, Manager of Fixed Prosthodontics

The monolithic crown has revolutionized dentistry by harnessing CAD/CAM technology to produce esthetic, highly accurate and exceptionally durable restorations. For the production of porcelain fused to metal crowns, however, traditional crown fabrication methods have persisted. Now, with the advent of laser sintering, the advantages of CAD/CAM can be leveraged for the benefit of doctors who prefer PFMs over monolithic ceramic crowns.

A laser beam is focused onto a tray containing metal powder, which is melted layer by layer until the crown coping designed by the CAD software is produced.

Laser sintering to create metal frameworks is an additive manufacturing process that is analogous to the resin-printing devices that have now become familiar to dentists for printing models. This unique method of creating precisely fitting copings is now being used in the fabrication of Obsidian® Fused to Metal restorations (Glidewell Laboratories; Newport Beach, Calif.). A laser beam is focused onto a tray containing metal powder, which is melted layer by layer until the crown coping designed by the CAD software is produced. This process results in a more accurate restoration and avoids the errors that can occur as a result of material expansion and contraction during the traditional waxing and casting procedures used to create PFM copings.

With the advent of laser sintering, the advantages of CAD/CAM can be leveraged for the benefit of doctors who prefer PFMs over monolithic ceramic crowns.

The Process

From the final impression, a master cast is created and scanned, generating a virtual model of the prepared tooth or implant site. A technician utilizes customized CAD software to design the restoration on the virtual model. Both the coping and the crown pattern are produced in the digital design, as the crown pattern will eventually be 3-D printed in wax and used to heat-press Obsidian lithium silicate to the coping. Each individual crown coping design is then selected by the technician, readied for laser sintering, and added to the batch (Figs. 1a, 1b).

This process results in a more accurate restoration and avoids the errors that can occur as a result of material expansion and contraction during the traditional waxing and casting procedures.

The digital data is transferred to the Mlab laser-sintering machine (Concept Laser Inc.; Grapevine, Texas), which is essentially a 3-D metal printer (Fig. 2). The technician then selects the transmitted file using the machine software (Fig. 3). The metal powder from which the copings are fabricated is loaded into the tray (Fig. 4). After activating the machine, high-power laser beams strike the powder, fusing together tiny particles of metal. As the laser-sintering process progresses, each metal coping is built up layer by layer, producing an exact replica of the 3-D computer-aided design.

Once the laser-sintering process is complete, excess powder is cleared away and the base plate and metal copings are removed from the machine (Fig. 5). The lab technician cuts away the sprues that connect the individual crown copings to the base plate (Figs. 6a, 6b). Then, the metal surfaces of the crown copings are finished and prepared for the heat-press process used to create the final Obsidian Fused to Metal restoration.

Obsidian® Fused to Metal

To create the restoration, an Obsidian lithium silicate ingot is heat-pressed into a digitally fabricated mold and fused to the metal coping. The result is a precisely fitting, esthetic restoration that, due to the durability of Obsidian lithium silicate, is over four times stronger than traditional PFMs (Figs. 7a, 7b). Because of this unique combination of strength and lifelike translucency, Obsidian Fused to Metal is well-suited for both the posterior and anterior regions of the mouth.

Clinical dentistry by Anamaria Muresan, DMD, ME, CDT

Figures 7a, 7b: After heat-pressing Obsidian lithium silicate over the metal framework, characterization can be added if desired. For the case shown, a 3-unit bridge was delivered with a precise fit due to the accuracy of the laser-sintering fabrication process. The new restoration is more lifelike and over four times stronger than this patient’s preexisting PFM bridge, which had fractured on the lingual aspect of tooth #30.

Because of this unique combination of strength and lifelike translucency, Obsidian Pressed to Metal is well-suited for both the posterior and anterior regions of the mouth.

Chairside Magazine: Volume 11, Issue 4

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