Esthetic RPDs Made Easier with Zirlux Acetal
Material blends with tissue and provides ample flexibility
Kris Schermerhorn, CDT
Achieving esthetic outcomes that satisfy patients is one of the most significant challenges facing the dental team today. As the technology and materials available have evolved, so too have patient expectations. This challenge can be particularly daunting when fabricating removable partial dentures (RPDs). With an appliance that replaces so many teeth, function can be created more easily if esthetics are a lesser consideration, but if both are priorities, then Zirlux Acetal from Zahn Dental (zahndental.com) helps significantly.
Acetal (polyoxymethylene) is a 99.9% pure, highly crystalline millable thermoplastic. What makes this copolymer special is that the material is flexible when thin, but becomes more rigid as it becomes thicker, making it ideal for fabricating a variety of tooth-retained removable appliances. Furthermore, the material absorbs virtually no water, delivering long-lasting performance and making it less likely to develop stains or odors.
Think of acetal like a much-improved PMMA, but it is both stronger and more flexible than PMMA, and it can be used in a variety of unique indications. For instance, acetal allows laboratories to make thinner, more flexible appliances, and it can engage natural undercuts in teeth for maximum retention and patient comfort.
Acetal has been successfully used in dentistry worldwide for decades in injectable form. Now this super-material comes in millable form: Acetal mills cleanly and quickly (dry or wet), so a laboratory can take advantage of unused capacity in its CAM machines. With the high predictability a digital workflow provides, a laboratory can count on acetal to give dentists and their patients esthetic, excellent-fitting, durable removable appliances at a great value.
With these advantages, acetal can power new, highly profitable growth in a laboratory's removables department. Today's dentists are increasingly prescribing metal-free, removable partial dentures; with Zirlux Acetal, a laboratory can now offer a digitally produced, tooth-borne framework. The laboratory can also offer dentists thinner, more hygienic, virtually unbreakable acetal bite splints. Smile-enhancing, patient-retrievable acetal anterior bridges provide patients with an affordable alternative to other permanent treatment options such as veneers or orthodontia. It can also lead them to choose those other options at some time in the future. Best of all, acetal is a great material for minimally invasive dentistry. This can certainly increase patient acceptance of recommended treatment plans.
Most laboratories already have everything needed to begin using acetal. Both 3Shape and exocad now provide CAD solutions that support all of the indications for which acetal resin can be used. This results in reduced cost, reduced labor, improved consistency and accuracy, and shortened manufacturing cycles. Acetal is milled dry or wet, and it can be processed in any dental mill that accepts a 98.5-mm disc. Either a Mono or PMMA milling strategy can be used. Acetal cuts very easily, resulting in minimal tool wear, and it can also be easily polished to a beautiful luster due to its density.
A female patient presented with missing dentition for teeth Nos. 4, 5, 8, 9, 10, 12, 13, and 14 in the maxillary arch, and Nos. 19, 21, 28, 29, and 30 in the mandibular arch. For both functional and esthetic reasons, the dentist and the patient decided on a treatment plan involving removable appliances.
The laboratory technician discussed the case with the dentist, who indicated that he wanted appliances that would have exceptional esthetics along with adequate stability. The ability to reline in the future was another important consideration that was discussed.
The team decided to use Zirlux Acetal for the appliances. The material's ability to blend in with the tissue, along with its flexibility, allows the clasp to be placed more toward the cervical and away from the smile zone for most patients.
The dentist took the initial impressions and sent them to the laboratory. Models were poured and then scanned into CAD software, and the partial frameworks were designed digitally. The frameworks were then milled using an S2 mill from vhf (vhf.com) and sent to the dentist for try-in. The pink clasps blended with the gingiva (Figure 1), and due to the material's flexibility, the clasps were able to be placed highly enough on the tooth that they did not show when the patient smiled (Figure 2). The material fit nicely around the lingual aspects of the teeth and to the palate (Figure 3 and Figure 4).
Myerson DB Plus teeth (Myerson LLC; myersontooth.com) were processed traditionally and set in wax, just as they would have for a metal framework. The only concern was when flaming the wax to smooth it. (It is important to be careful around the acetal material, as it could warp or even catch fire.) Once the teeth were set, the frameworks were delivered to the dentist for another try-in (Figure 5 through Fig 9).
Once the try-in was confirmed as successful, there was nothing significantly different required for the fabrication of the final prosthesis. The great thing about Zirlux Acetal frameworks is that they can be integrated into a laboratory easily; just be careful with the heat and the flame. The frameworks are designed to be thicker, but like metal frames, large tissue stops on the frame keep it stable during the drying and packing or injection of the acrylic.
In this case, the final appliances were delivered to the patient and everything went well. The dentist was initially worried about flexing and movement of the free-end extension on the maxillary and mandibular arches, so the frameworks were thickened and designed to minimize that factor. Once the final appliances were placed in the mouth, both the dentist and the patient were very pleased.
Acetal materials have been used in dentistry for more than 30 years. During that time, the material was melted and injected. That worked fine, but it did have drawbacks. The material exhibited a large amount of shrinkage as it cooled, and that was difficult to manage. The digital workflow and milling of the material allows for more consistent design as well avoiding shrinkage in the process. The fact that Zirlux Acetal is available in tooth color as well as pink provides exceptional variety and options for the dentist and the laboratory. With the help of this material, a process that once was daunting can now be much easier.
Disclaimer: The statements and opinions contained in the preceding material are not of the editors, publisher, or the Editorial Board of Inside Dental Technology.
About the Author
Kris Schermerhorn, CDT, is the Owner of Northern Virginia Dental Lab in Triangle, Virginia.