This is something you can use to counteract the possible discomfort you might feel when you're at the dentist. Start by remembering a time or situation you really loved, enjoyed, etc. Maybe a moment in time when you felt invincible… you’ve had those… and then choose an action such as squeezing your fist, and while you think about that great time, squeeze your fist (or whatever you choose) and do that a few times.
With a few repetitions you’ll be able to create a conditioned response that gives you those feelings when you squeeze your fist in the same way on the day of your test. Obviously it’s important you always match the single action to the same desired response.