Try to day dream of something nice while you are in the chair having your mouth worked on.
Also have you taken any painkillers yet, if you can ask your parents for something like Ibuprofen. This might not stop the pain totally but it may take the edge off it.
_________________
Health is a state of physical, mental and social wellbeing and not merely the absence of disease or infirmity

I am not a jigsaw, I am a free man !
Diagnosed under the DSM5 rules with autism spectrum disorder, under DSM4 psychologist said would have been AS (299.80) but I suspect that I am somewhere between 299.80 and 299.00 (Autism) under DSM4.