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Pour Isn’t Poor Anymore
The use of pour acrylics is making a comeback
By Arian Deutsch, CDT
Pour acrylics have seemingly had a bad reputation for some years. However, recently, the use of pour technique acrylics in Europe and in North America has resurfaced. Due to improvements in color stability, resistance to breakage, and lower shrinkage rates throughout curing, pour acrylics can be an efficient and reliable solution in modern prosthetics technology.
Add to this the improvements in acrylic casting ancillary products such as the modern flask design, a variety of unique investment materials, and sophisticated pressure vessels, and technicians have a practical alternative to other processing materials and methods.
In this article, the acrylic casting process will be explored using NATURE-CRYL® Pour Acrylic (GC America, gcamerica.com), Castdon flask (Dreve, dentamid.dreve.de), Anaxdent clear silicone (Anaxdent, anaxdent.com), and Polymax 5 Heat/Pressure Curing Unit (Dreve).
After the wax try-in has been approved for processing (Figure 1), the maxillary wax-up is sealed to the master cast, placed in the base plate of the Castdon flask, and held in place by the magnetic element incorporated into the model and the metallic base plate of the flask. The top transparent portion of the flask is now locked into the base plate portion of the Castdon flask (Figure 2 through Figure 4), using the two incorporated clamps.
The bottom section of the flask has a magnet and another unique feature, an integrated reservoir designed to hold artificial teeth for steam cleaning while the base plate is in place (Figure 5). The transparent top and locked-in baseplate are now joined with the bottom element of the flask. Clear silicone (Anaxdent) is poured into the flask after vacuum mixing, and the entire flask is placed in the Polymax 5 Unit without water, and set to “2 bar” for approximately 20 minutes (Figure 6).
The flask is removed, and the clear silicone is free of any porosities (Figure 7). The flask is disassembled, and the wax-up and master cast are removed with compressed air (Figure 8). Sprue accesses are now cut from the recessed sprue wells to the wax-up using the sprue tool (Figure 9).
The artificial teeth are removed from the wax-up, steam cleaned, and placed back into the clear silicone matrix (Figure 10). NATURE-CRYL Pour is available in the same large variety of shades as all of the NATURE-CRYL family of acrylics that provide for a range of options for tissue characterization. Two additional colors of NATURE-CRYL Pour Acrylic, shades No. 34 light and No. 35 light reddish pink, are sifted for removal of fibers and modified with pigments until the desired shades are achieved. The two shades are injected by hand into the clear silicone mold, and placed strategically so that they can be blended into each other for a smooth transition from blanched tissues, which are less vascular, into the more vascular mucosal areas (Figure 11).
To blend the colors, the technician feathers the first color, No. 34, outward toward the more vascular area from the cervical areas, using a Kolinsky brush. By doing this, the thickness is controlled and gradually diminished toward the transition zone. In addition, thin cuts into the edges of the transition zone with a thin blunt instrument are made. The second color, modified No. 35, is injected into the cuts and transition area, and manipulated by pulling the color toward the transition area with the Kolinsky brush. Once a smooth transition is achieved without any stark color contrasts, the surface of the acrylic is kept slightly moist with NATURE-CRYL Pour liquid via the Kolinsky brush to avoid any “frosting” of the acrylic.
The master model is cleansed of all wax, and one coat of COE-SEP™ (GC America) separator is brushed onto the surfaces to be processed. Water is run over the surface to carefully remove any excess separator from the master model, and the model is allowed to cool.
Once the master model is cooled, it is returned to the clear silicone matrix, and the Castdon flask is assembled. NATURE-CRYL Pour Acrylic original shade is mixed according to the manufacturer’s instructions and poured into the sprue well until the other two-sprue accesses show that the internal cavity is full of acrylic. The flask is rocked gently, allowing trapped air to escape. The flask is then left to bench set until the excess acrylic in the sprue wells appears dry.
The flask is then carefully placed into the Polymax 5 unit, and the water level should be just below the top of the flask (Figure 12). The temperature is set to 55° C, and the master dial is set to 25 minutes. The lid is closed, and the master dial is pressed to start the process cycle.
Once the process is complete, the Castdon flask is removed from the Polymax 5 Unit and allowed to bench cool for 15 minutes. The master model with processed prosthesis is carefully removed (Figure 13).
Another great option is to utilize the same clear silicone matrix and a duplicate model to pour a clear duplicate prosthesis for use as a surgical stent using NATURE-CRYL Pour Clear. In this case, a duplicate model is steam cleaned and coated with COE-SEP separator (Figure 14) and, once cooled, is seated into the clear silicone matrix. The Castdon flask is reassembled, and NATURE-CRYL Pour Clear is mixed according to the manufacturers instructions and poured into the flask. The same gentle rocking technique is used to express any trapped air, and the flask is returned for curing in the Polymax 5 unit.
Arian Deutsch, CDT, is the owner of Deutsch Dental Arts in Surprise, AZ.
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Disclaimer: The statements and opinions contained in the preceding material are not of the editors, publisher, or the Editorial Board of Inside Dental Technology.