I can't vote, because I don't use any of them. (I'd say, "I have an appointment tomorrow for 3 o'clock.")
Force yourself. Imagine you were in London with crippling toothache.
I THINK IT IS FUTURE TENSE THAT WAS THIS IS CORRECT
"I will see the dentist tomorrow at 3"
I would say "I'm seeing the dentist tomorrow at 3". But I could use any of the top two options aswell.
I think the right answer is "I'm seeing the dentist at 3 tomorrow" if you have called the dentist; if you have the intention to go to the dentist at 3, but you haven't called yet you say "I'm going to see the dentist at 3"(but in that case you don't have an appointment).
And, as we normally make appointments to see a dentist, the first of your choices is more likely.
I`ll see the dentist - determination