Its ability to withstand multiple cycles of dry-heat sterilization made PEEK a natural choice when Dentronix, a Coltene/Whaledent subsidiary, was designing its new "High Heat" dental bite stick. Strength and other characteristics also played into the material's hand. And because processing the material takes some experience, Dentronix went to Performance Plastics Ltd. to mold the parts.
In answer to questions from MPW, Joe Simmons, sales engineer at Performance Plastics (Cincinnati, OH), said Dentronix did not have the proper molding equipment to mold PEEK. "I am not sure exactly what the shortcomings were with the molding machine, but there were also shortcomings in their auxiliary equipment to get the mold to the proper temperature, and their hot runner system," he recalled. The OEM decided instead to find a contract molder to handle the work, to Performance Plastics' benefit.
So what equipment and hot runner systems does Performance Plastics use? Simmons won't say, honestly admitting his company won't "tell people the keys to running PEEK effectively, thereby creating additional competitors in our market space." He said about 3000 of the dental sticks will be molded annually. (Ed. Note: The keys to effectively molding PEEK were discussed in depth in our webinar on the subject; register for free here to view and hear that online report.)
A bite stick is an orthodontic instrument used to seat bands on a tooth. An orthodontist places a band on a patient's tooth and then positions the bite stick so that when the patient bites down on the top portion, a metal insert helps slide the band in place. "Impact strength is important because the bite stick is used to mechanically seat a band on a tooth," explained Mark Van Meter, an engineer at Coltene Whaledent. His company specified a polyether etherketone (PEEK) grade from supplier Victrex.
According to Van Meter, the most important requirement for the new design was the ability of the stick to withstand multiple cycles in a dry-heat sterilizer. Within the chamber, temperatures can reach up to 216°C (420°F). The PEEK polymer gives the sticks the ability to withstand at least 50 cycles in a dry-heat sterilizer with no loss of properties, or change in shape or color. The bite sticks also needed to withstand sterilization in an autoclave, as well as sterilization in solutions such as glutaraldehyde, peracetic acid and hydrogen peroxide.
PEEK rose above other materials, including polyphenylene sulfide (PPS), as having the best combination of material properties for this application, reports Dentronix. —Matt Defosse