Stress retention refers to the propensity of a material to resist permanent deformation under an applied load. For the non-engineers; stress retention is a key property of an aligner (or most dental appliances) because virtually all plastic materials become weaker over time as they are pushed on. Specifically clear aligners may not provide enough force to move teeth when worn for a few days - especially at body temperature.

The Zendura material's robust, rigid polyurethane (PU) system (learn more about "What's so special about polyurethane?") was developed specifically for aligner applications and optimized to deliver the correct balance of key properties including strength, ductility, chemical resistance, clarity, and stress relaxation resistance.

Most of the other commercially available materials are made of polyester material using PETG as its base resin. Zendura A, by comparison, is made of a high-performing rigid engineering resin with superior stress retention and crack resistance properties. In addition to being tough and durable, this material performs exceptionally well in aligning patients’ teeth. Its other significant benefits include superior chemical stain resistance and clarity.

The all-new 3-layer construction of Zendura FLX brings an advanced 3rd-generation design to maximize tooth-moving force after days of wear while also reducing the force it takes to insert the appliance and the initial pressure on patient's teeth. This dynamic elasticity of Zendura FLX defines a new performance standard for clear aligner materials.

Cracking can occur when removing an appliance from a forming mold, or by a patient when in use. The mouth of a bruxing patient is a very hard environment for a dental appliance! Zendura, has a tough polymer backbone, and a reputation as the benchmark for crack resistance.  

Impact strength is one means to evaluate a plastic's toughness and crack-resistance. Zendura was evaluated for impact strength alongside other orthodontic products, and demonstrated superior performance. Zendura appliances have been used in retention and night guard applications for periods as long as three years - a tribute to its toughness.

See a video of Zendura retainer withstanding stress testing Here.

Dental appliances are frequently exposed to oils, coffee, staining agents in food and cleaning products such as toothpaste and mouth wash.  Such exposure can cause many plastics to yellow, stain and structurally deteriorate.  

To demonstrate the staining resistance of Zendura materials, we perform a standardized "mustard stain" test. Parts are immersed in mustard and placed in an oven at 37C for 24 hours. At the end of the mustard soak, Zendura A showed  little change in level of yellow color compared to competing orthodontic products. Zendura FLX demonstrates similar stain resistance

Temperature, humidity, the thermoforming equipment, and the technician can all impact the success of producing a quality appliance. 

Zendura was designed with a broad processing window to reduce the risk of a poor thermoforming experience. This includes a foil-barrier package to maintain the optimum moisture content. 

The in-office manufacturing of Zendura material using positive-pressure forming system is fast and seamless. You can turn over the manufacturing of Zendura within hours and know every single time the appliance will fit like a glove.

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