Any new appliance comes with care instructions. A lot of these instructions relate to the material the appliance is made of, and it's the same with an orthodontic appliance, like your new Invisalign trays. There are certain things that your trays should not be exposed to, and heat is at the top of the list.
Your transparent Invisalign trays are made of a thermoplastic polymer. This makes them reactive to heat—which they need to be during the manufacturing process. This is how the trays can be molded to perfectly fit your bite. Thermoplastic softens when exposed to heat (and this is when it's molded into its predetermined shape), and hardens when it cools, while still retaining a small amount of elasticity, depending on the thickness of the thermoplastic product. Thermoplastic polymers are capable of repeating this process.
If your Invisalign aligner trays are exposed to excessive heat, they will soften and warp, changing their shape. These changes will be small but can have an effect on your treatment. You must never place your Invisalign in the vicinity of a heat source while they're out of your mouth. This can include all forms of household heaters (radiators, fireplaces, and so on). Depending on weather conditions in your area, it may be necessary to avoid leaving your aligners in direct sunlight. Your trays are not dishwasher safe, and if they happened to be left in a clothes pocket during a washing and drying cycle, it's a safe enough bet that they've become warped.
Warped trays are inefficient trays. The warping destroys the precise outlines of the internal curves of the trays. Your teeth are being moved to match the outline of the tray's internal curve, and when this outline has been altered by warping, then the tray is of little use. It may even damage your teeth. If one of your trays becomes warped, contact your orthodontist.
Your orthodontist will advise you on the best way forward, but chances are you'll be told to skip ahead to the next aligner tray in your series. This will create some unexpected pressure on your teeth because they've skipped the phase of alignment that the warped tray was unable to deliver. This means that the next tray will feel extra tight, and maybe even a little uncomfortable. You'll quickly get used to it, and it can be a reminder not to expose your trays to heat.
Your Invisalign trays can put up with a lot of things, but they don't like heat. Be careful with your trays when around a heat source.
For more info about Invisalign, contact a local company.