Hyrax 3D Printing: Cobalt Chrome Alloy in Orthodontic Practice

3d print model for hyrax rapid palatel expansion device

A hyrax in cobalt chrome is a temporary oral appliance that helps widen the upper jaw, a treatment known as rapid maxillary expansion (RME). The name is derived from HYgienic RApid eXpander, and due to its shape, it is sometimes referred to as a spider or butterfly expander. A hyrax is used for narrow upper jaws, crossbites, crowding, and sometimes to improve airway space. This rapid palatal expansion is often made from a cobalt chrome. Since every mouth is unique, a hyrax must always be custom-made. 3D printing is ideally suited for this purpose.

Hyrax rapid palatal expander in a child, used to increase the width of the upper jaw. Photo: wikimedia.org – Ian Furst CC BY-SA 4.0

3D Printing in Dental Practice

3D printing for dental applications has existed for several decades. Its use is now commonplace, yet it continues to experience strong growth in modern dental practice. Recent studies and clinical experience have shown that metal-printed hyrax appliances offer numerous advantages. According to the scientific article Three-dimensional metal printed orthodontic laboratory appliances, the greatest benefit is personalization:

Each design can be perfectly tailored to the patient.

Other key advantages include:

Less laboratory waste, as resin-based models are non-recyclable;
Higher accuracy;
Better standardization;
Improved patient comfort;
Fewer orthodontic appointments, as separators are no longer needed;
Ability to create advanced or complex structures, such as integrating additional components.

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3D Printing a Cobalt Chrome Hyrax

Before a Cobalt Chrome hyrax can be printed, an intraoral scan of the upper jaw must first be taken. Then, a 3D digital design of the appliance is created on a computer. The hyrax is printed using selective laser melting (SLM) or similar powder bed fusion techniques, in which metal powder is fused layer by layer with a laser. After printing, the appliance undergoes post-processing, including sandblasting and (electro)polishing, to ensure it is safe and comfortable for placement in the mouth.

3D model for printing a Hyrax rapid palatal expansion device

Key Properties of Cobalt Chrome Alloy (Co-Cr)

Cobalt Chrome is considered a high-performance alloy and is widely used in dental instruments. Other suitable metals include titanium and nickel. A typical Co-Cr alloy contains 55-65% chromium, 20-30% cobalt, and often 3-6% molybdenum. Depending on the specific requirements, small amounts of nickel, manganese, carbon, iron, and/or tungsten are added.

A cobalt-chromium alloy is hard, wear-resistant, and lightweight. It is also corrosion-resistant and biocompatible. It is less expensive than precious metals used in dentistry, such as gold, palladium, and platinum. Therefore, it is no surprise that Co-Cr has been used for decades in dental applications. It is a proven material.

Other Dental and Medical Applications of Cobalt Chrome

Cobalt Chrome alloys are among the most widely used metals in dental and medical technology, not just for hyrax appliances. They are used for partial and full dentures, crowns and bridges, implant components. Thanks to their strength and biocompatibility, Co-Cr alloys are also used in orthopaedic implants, such as hip and knee prostheses, which must withstand long-term wear. Surgical instruments and medical devices are also commonly manufactured from Co-Cr.

Industrial Applications of Cobalt Chrome

In addition to the properties mentioned above, Cobalt Chrome alloys are also resistant to extreme heat (well above 1000 °C), like tungsten alloy. Therefore, they are commonly found in demanding industrial applications, including turbine and aircraft components, cutting tools, chemical and petrochemical equipment, precision instruments, and 3D-printed high-tech parts.

Conclusion

The combination of digital orthodontics, computer-aided design, and 3D printing in Cobalt Chrome provides orthodontists with a precise, reliable, and efficient way to fabricate hyrax expanders. With high stability, excellent fit, and perfect personalization, the 3D-printed hyrax is rapidly becoming the new standard in rapid maxillary expansion.

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