What's so Special About Polyurethane?

by Aaron Stewart October 25, 2018

A few of our customers have asked about what a "polyurethane resin" is, and why we chose it as the primary component of the Zendura material. If you're one to wonder about the micro-world of material science, and how polyurethane makes Zendura awesome, read on. If you are not so interested, we invite you to read our customer testimonials instead, to see how Zendura has pragmatically improved practices or businesses like yours.

A polyurethane (PU) is a molecule that includes many (poly) urethane segments. A urethane is a molecular structure, also called "carbamate," comprising nitrogen, carbon, hydrogen and two oxygen atoms. This molecular structure is very strong yet versatile. Depending on the chemical used to help form the link between these segments, the urethane segment may bond on two, three, or many more other urethane segments. This variety means the formulation of polyurethane can be tuned to serve a particular purpose by controlling that branching factor and link type.

In formulating Zendura, one of the major engineering efforts was to balance both polar and nonpolar molecules in these other segments, which segregate into microdomains of "hard" and "soft." While in distinct phases, these hard and soft materials are strongly chemically bonded together by the urethane links. By combining hard and soft materials, Zendura achieves both high strength (from the hard materials) and high toughness (from the soft materials)!

This natural strength of the urethane linkage, along with that branching flexibility, gives polyurethane the advantage over other commonly used resins such as polyethylene (PETG), polypropylene (PP) and copolyester, which are less capable in achieving the simultaneous toughness and strength.

For aligner applications, stress retention ensures that the aligner continuously moves the teeth (to its ideal position) under applied force without losing its exact shape. For retainer applications, toughness is important as the appliance stays in patients’ mouth for a much longer time (than aligners) and needs to hold the teeth in position while withstanding regular grinding, biting, and handling.

However polyurethane, like all materials, has limitations. Polyurethane is very sensitive to moisture during processing, has a higher melting point and is harder to shape than many other plastics, and requires an expensive base resin.
Managing these limitations was part of the challenge of engineering Zendura. It wasn't enough to design the material alone. Precise manufacturing, high-barrier packaging, and handling processes had to be developed as well. For the end-user, these limitations are why Zendura must be: shipped in moisture-barrier bags, handled quickly, and is best molded on a positive-pressure machine.

We feel the additional cost and effort spent molding Zendura is rewarded with the best orthodontic device performance available. We invite orthodontists, dentists, and dental/orthodontic labs everywhere to see for yourself by testing the material first hand.

Aaron Stewart
Aaron Stewart