That's a good question. We can actually do implants in an emergency situation, but we also do immediate implants in a non-emergency situation.
The advantage of non-emergencies is that there is time to slowly plan and make the temporary crowns in the lab.
But in the real emergency scenario where there is no time for the lab to fabricate the crowns then the dentist will have to fabricate the temporary crowns in the clinic on the day of surgery.
For example, if you were involved in a road traffic accident this morning, just saying, and you lost your front teeth this morning, I would put you in the afternoon to put immediate implants and I might fashion the immediate temporary teeth free-hand.
So that when you wake up you will see the teeth and after the surgery is done, perhaps a week later, I will swap out these temporary teeth for a more refined version that looks nicer.