Thermoforming Clear Plastic Appliances

Before proceeding with the thermoforming technique, inspect the quality of the cast. It is best to correct any idiosyncrasies now. Start with the undercuts and incisal edges. The undercuts should not be so overly severe that the plastic would seep into the space. If this is the case, use acrylic or blockout compound to fill in the excessive space. Never use wax, it will melt under the thermoformer. Likewise, if the undercuts are a bit swollen, they can be accentuated by scraping the cast. However, if the gingiva is excessively swollen, it may be bet to use a conventional appliance until the swelling recedes.

Before discussing the thermoforming technique, it is important to realize that these appliances can be made on any machine including pressure machines. GAC highly recommends the Essix vacuum machine. Not only are these machines compact and inexpensive, but need only be plugged in. No compressed air is necessary. Unlike some vacuum machines, the Essix machine has been specifically designed to allow optimal suction beneath the cast. To further enhance the suction, vacuum maximizers are available to adjust the vacuum depending on the size of the cast.

Although there are more than two types of plastic, our most popular for constructing basic retainers are Essix A^® and Essix C+^®.

Essix A is crystal clear, FDA allowed and available in many thicknesses. Depending on the thickness of the Essix A being thermoformed and the type of machine being used, heating times will vary. Despite the heating time, Essix A plastic will sag 1/2" in a vacuum machine when it is ready to be thermoformed.

Essix C+ plastic is known for its durability. A bruxer will not grind through it. But despite its strength, Essix C+ is quite flexible – perfect for full arch retainers. Essix C+ has contact clarity, is FDA allowed and available in .040" thickness. Essix C+ plastic heats differently than the Essix A plastic. It will rise toward the heating element then return to a somewhat flat position when it is ready to be thermoformed. Do not make the mistake of letting Essix C+ sag 1/2" like the Essix A – it will be too thin.

Make sure the cast is dry before thermoforming plastic over it.

Because Essix C+ plastic takes longer to cool, immediately use the accentuator to push the plastic into the undercuts. Then spray the entire cast with Essix freeze spray. This serves two purposes: To end the thermoforming process (and subsequent thinning) and to eliminate the lingual lift that occurred sometimes in the early development of Essix C^® plastic.

Continue to let the vacuum run for approximately 30 seconds. When first learning the vacuum-forming technique – it is helpful to inspect the underside of the plastic encased cast to know if the thermoform was a good one or not.

Removing the cast from the plastic is not difficult. In order to preserve the cast, in case of remakes, following our guidelines will help.

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