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While pressed restorations are designed to save time and labor, the techniques involved aren’t instantaneous or completely deplete of necessary skill sets. “Right now, the most complicated step in pressing is the waxing,” said Verano.
Like the steps required for metal casting, pressing incorporates the lost-wax technique comprised of waxing, spruing, investing, and burning out. The form is pressed and divested, then ready for basic layering or a stain-and-glaze finish.
Even the relatively uncomplicated waxing (compared with layering porcelain) can be simplified, with steps removed, simultaneously speeding the process while ensuring a more-consistent result through automation.
“There are ways to make it more efficient so you literally don’t have to hand wax to a whole case,” said Laingchild.
“Pressing allows you to be more esthetic, but it also allows you to be more productive.”
– Trevor Laingchild, RDT | |
On the low-tech side, pre-formed wax patterns, such as ProWax veneers and occlusion from XPdent and Redi-Form wax facings and occlusal surfaces from KerrLab allow the waxing technician to place the prefabricated full-contour wax form in place. Also, occlusal molds like Bredent Gnathoflex molds from XPdent and Biofit occlusal morphology molds from Jensen act as cookie cutters to stamp the anatomy of tooth surfaces onto an unformed wax shape (see Peter Pizzi’s “Pressing conversion” on page 30 for an example).
“As far as speed,” said Verano, “It really helps because you have the bulk of your occlusal anatomy there. You just need to add wax to the buccal, proximal, and lingual surfaces and contour the emergence profile.”
Suitable for lower-volume production, both of these methods are designed to help streamline and speed the conventional hand waxing procedures for both pressing and casting cases and make them more consistent. But computer-based systems are poised to move pressing into high gear.
Waxing is the area where CAD/CAM technologies have the most influence in pressable restorations. Several similar, yet distinct, methods are available now for large-scale production that also allow for the precision and consistency of digital design and the automation of machine-based production.
Sirona’s inLab and Dentsply’s Cercon CAD/CAM systems can be used to design and mill wax/resin blocks for pressing single cases, while CAD/CAM machines from Digital Dental Lab, CAD BLU, and Wieland mill forms from larger wax/resin disks that can accommodate multiple cases. For very high-volume caseloads, technologies such as stereolithography (3D printing) or digital light processing of wax (similar to laser sintering of metal copings) can be utilized to produce up to 200 units per processing run.
| | Versatility
From single to multiple units, from frame-supported to all-ceramic, labs are pushing forward with pressables.
Percentage of labs providing on a regular basis...
All-ceramic pressed crowns, 46.8% All-ceramic pressed bridges, 23.1%
Press-to-metal crowns, 14.1% Press-to-metal zirconia crowns, 11.5%
Press-to-metal bridges, 10.3%
Press-to-metal zirconia bridges, 6.4%
Press-to-Captek crowns, 3.8%
Source: DLP April 2008 Cosmetic Indirect Restoration Survey. | | | |
With any of these systems, hand waxing is completely eliminated, replaced by digital design on the computer screen. The technician designs the digital waxup on a virtual model, generated by scanning a poured model or physical impression or by transferring data from a digital impression taken at chairside. The computer mouse replaces the traditional waxing tools to define margins, create anatomy, set pontics, and place sprues. Of course, being a computerized system, many of the steps can be set up to be performed automatically, with operator adjustments as needed.
Daxton Grubb, President of R-Dent Dental Lab near Memphis, started using the Envisiontec Perfactory DDP rapid prototyping machine in combination with the Dental Wings digital scanner (both available through Zahn Dental) to design and print wax forms for use in casting his PFM copings and full-occlusion metal cases. He’s looking to incorporate the system soon into growing his pressing business by minimizing the reliance for labor-intensive hand waxing.
“That’s one of the beauties of CAD/CAM,” said Grubb about the support afforded by the wax printer and accompanying design software. “Finding good technicians is so hard. Using this technology, you really don’t have to know anatomy when you’re designing bridges other than placing a pontic. It would help, of course, but the software will tell you where to place the pontics. It also places the sprues for me.”
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