Flora
I'm not very clear from your post why you don't want to have the local anaesthetic with adrenaline in it. You say "...and was bad as it contained adrenaline which was bad if you have had nerve blocks like me."

I don't know what sort of nerve blocks you previously had or where they were inserted which makes you think you can't have a normal dental anaesthetic injection. Maybe it would help people advise you if you could clarify what the previous treatment/problems were you had with the normal local anaesthetics containing adrenaline. It might also help us understand why the dentist is concerned to have the local hospital facilities available.

Adrenaline is added to dental local anaesthetic in order to prolong the action of the anaesthetic. It does this by causing only very localised vasoconstriction - this holds the dental anaesthetic in the local area better and for longer and it also helps to prevent bleeding.

Local dental anaesthetics containing adrenaline are not suitable for diabetics and people with certain other health conditions.

Such limited evidence and guidance there is for patients with CRPS undergoing dental treatment would recommend plenty of local anaesthetic applied to suitably block the possibility of any pain to make sure that any pain is fully blocked for as long as possible to make sure the treatment is not felt. Yes, it is possible for an injection to cause a spread of CRPS but having dental work done involving drilling into the teeth close to the nerves in the teeth is a bigger risk for trauma and pain which is more likely to cause a subsequent CRPS risk. You have had dental injections previously without any spread of your CRPS so I would have thought on balance, long acting and extensive local anaesthetic would be the best way to proceed before your next dental drilling and treatment.

There's no evidence that Vitamin c will prevent spread of CRPS symptoms in the dental circumstances you are asking about but it won't do you any harm.