While it's easy to find a wide variety of interesting fake costume teeth, getting them to look natural when you wear them is another story. To get a comfortable, secure fit, you need a set of teeth that are fitted to your own and kept in place with adhesive, neither of which you'll get with most basic costume teeth. However, with a simple alteration technique and the right adhesive, you can turn any set of costume teeth into something that will fit your own mouth comfortably and securely.
Place the plastic beads in a microwaveable container. Fill the container most of the rest of the way with water; leave about an inch of space at the top to avoid bubbling over. If there isn't more water than plastic, use a bigger container.
Heat the plastic beads in the microwave on “high” for 30 seconds at a time. Continue until the plastic has changed from opaque to completely clear; this means it has melted.
Pull the plastic from the hot water using a metal spoon. Let it cool for about 15 seconds before carefully handling it with wet hands. Knead the sculpt the plastic like clay, but leave the portion you're not currently working with in the hot water to keep it soft.
Fill the cavities in the top of your fake teeth with plastic. Mold the plastic into small pellets with your fingers for single teeth (like vampire fangs) or roll out into a snakelike-shape for a row of teeth. The plastic will be hardening quickly while you work with it; if it's starting to firm up as you work with it, put it back in the hot water and try again. Microwave again, as needed.
Wet your teeth, gums and lips with your tongue to prevent sticking (the plastic won't stick permanently, just enough to alter the shape of the finished product).
Press the teeth to your own teeth and press your teeth into the plastic to make a fitted impression. Wait for about 30 seconds, then pull the fake teeth away. Let the plastic continue to harden for at least another five minutes.
Secure the teeth in place using denture adhesive or costume teeth adhesive.