To numb = 麻酔する
To treat = 治療する
Pain = 痛み
It hurts / It’s painful = 痛い
It hurts where they numbed it = 麻酔したところが痛い
There’s pain in the area they treated = 治療したところに痛みがある
The area they treated is painful = 治療したところが痛い
ちなみに 「虫歯」は cavity ですよ!
“They treated my cavities and the area where they numbed it is painful!”