We have occasionally heard from customers that they have trouble with thin parts when thermoforming Zendura sheets. In particular, some Zendura retainers come out very thin in front, and as a result are too flimsy to be useful. We hate it when our customers have problems, so here are the best practices to avoid overly-thin surfaces or wasted appliances when working with Zendura materials:
When the material is heated past its glass transition temperature during thermoforming, it starts to soften and the sheet will sag in the middle. The process of pressing the material over a tooth model further stretches and thins the material. This thinning is expected due to the inherent geometry of deforming a sheet over a shape.
Zendura material sheets are purposefully designed as thinner than many competing sheets to give patients a more comfortable mouth-feel, but over-stretching of the material is undesirable and can render the appliance unusable. Thus the aim is to keep thinning controlled in a reasonable range. Usually the key to doing this is not stretching the sheet further than is needed to cover the working surface of tooth model.
To avoid unnecessary thinning:
• Prior to thermoforming, bury the base of the tooth model with granules so that the model is properly held in place. If the tooth model has sharp and long anterior teeth, tilt down the front part of the tooth model so that the part of the model above the granules has the same height (no more than 1 inch) in back and front.
• If you do not use granules but rather prefer sitting the tooth model on the thermoforming plate, trim the base of the model to be no taller than 1.5 inches and with back to front at the same height.
The below picture shows a teeth model with a high base and the front teeth has a steep slope from top to bottom, this is likely to cause unnecessary material stretching.
The below picture shows a teeth model that is properly trimmed with a low and uniform base and can be used directly on the thermoforming base plate.
The below picture shows a teeth model that is properly buried in granules to avoid unnecessary stretching during the thermoforming process.