A Clear Perspective on Partial Denture Technology

While the need still exists for metal frameworks in certain cases, other options include nylon-based flexible partials, thermoplastic partials, and CAD/CAM partials. What if, however, a material existed that visibly disappeared in the mouth, only exposing the natural look of quality denture teeth and acrylic, while providing excellent function and unsurpassed natural esthetics for the patient? ClearMet from Keystone Industries meets those standards, providing the patient with a high-quality esthetic and functional result.

ClearMet is a clear thermoplastic resin specifically designed for durability and biocompatibility. The material is intended for use in an injection molding process. Unlike conventional metal partials, ClearMet frameworks are ultra-transparent. Patients can enjoy a lightweight partial without a metal taste or undesirable metal clasps showing on their teeth. No one will ever be able to see that a partial denture restoration is being worn.

The ClearMet framework can be fabricated easily by utilizing the FlexPress™ Automated Digital Injection System (Myerson, myersontooth.com).

First, the undercuts were blocked out for the correct path of insertion and spacing wax was added on the saddle areas so there was room for acrylic to flow in the ridge areas, and then the model was duplicated. No special gypsum is necessary for processing ClearMet.

The framework was waxed with clasps, rests, and major and minor connectors (Figure 1). Next, sprues were applied to the framework, and the model and waxup were invested into the bottom half of an injection flask using Type III stone. The author used two sprues in this case. A channel access sprue was added in the slotted section of the flask (Figure 2). Petroleum jelly was applied to all gypsum areas, the top half of the flask was screwed down, and the stone was vibrated into the top section of the flask (Figure 3 and Figure 4).

After the gypsum set, the case was ready to be boiled out. The bolts were unscrewed and immersed into boiling water for 5 minutes. At this point, the FlexPress Automated Digital Injection System was turned on. The injection system was programmed for a medium-sized tube with the recommended temperature of 542°F. Melt time was 19 minutes with a hold time of 2 minutes. After the case was boiled out, one coat of Keystone Industries’ Diamond D Ultra Sep was applied to all gypsum areas. The separator was allowed to dry, and then the flask was closed and bolts were screwed into it.

While the FlexPress was heating up, the author took the ClearMet tube and cut an X into the top solid section of the tube with a disc. Next, the medium-sized tube was placed in a toaster oven for 30 minutes. The temperature of the toaster oven was approximately 175-200°F. The heating of the tube removes any moisture that the ClearMet material may have absorbed.

When the alarm sounded on the FlexPress, the ClearMet tube was ready to be placed into the injection unit. The tube was lubricated with a release agent and placed into the FlexPress (Figure 5). Next, the flask was placed onto the FlexPress, the flask strap was secured, the bolts were tightened (Figure 6), and the “Start” button was pushed on the FlexPress. The machine heated up the medium-sized tube and injected the ClearMet material after 19 minutes. After the injection process was completed, the flask was cooled and the ClearMet partial was de-vested (Figure 7).

Once the ClearMet frame had been injected and de-vested, it was ready to be finished. No special tools are needed for this; carbide burs work well. The burs were used to fit the frame and reduce bulk while shaping clasps to the appropriate contour. Next, holes were drilled with a No. 2 round bur to create retention for the acrylic.

If the dentist has asked for a framework try-in, the frame can be polished at this point with a polishing buff and pumice, and then high shined at low speed with a soft buff and high shine compound. An excellent choice for polishing ClearMet is the Hatho Thermopol Set and the Hatho Acrypol Polishing Kit, available from Keystone Industries. After the ClearMet framework was polished and cleaned, a thin coat of Palaseal® (Heraeus Kulzer, heraeus-kulzer.com) was applied. It was then light cured for 3 minutes (Figure 8 and Figure 9).

Note the beautiful translucency on the ClearMet framework. The snap fit engages the undercuts of the patient’s natural dentition. The ClearMet framework takes on the natural shade of the patient’s gingival and tooth shade. Additionally, no shrinkage or expansion occurs with this material, ensuring an intimate, accurate fit time after time. Note the excellent adaptation to the model on Figure 10.

Special equipment is not necessary for setting teeth and processing the acrylic. In this case, the author used VITAPLAN PLUS® denture teeth (VITA North America, vitanorthamerica.com) and Diamond D Heat Cured acrylic from Keystone Industries (Figure 11 and Figure 12).

The combination of the ClearMet partial material, VITA teeth, and Diamond D acrylic produced a high-end cosmetic partial that will provide the patient with beautiful esthetics and function for years to come. ClearMet surely gives the patient, dentist, and technician a clear perspective on partial denture technology.

Dennis Urban, CDT, is the Director of Removable Technology at Jason J. Kim Dental Aesthetics in Port Washington, New York.

Disclaimer: The statements and opinions contained in the preceding material are not of the editors, publisher, or the Editorial Board of Inside Dental Technology.

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