If my dentist accidentally injected the articaine into a blood vessel(intravascular injection), what dose would cause severe toxic symptoms of local anaesthesia?

More than you were given! and more than we are alloed to give at one time. There is always a chance that anesthetic could be injected into a blood vessel, it wastes the anesthetic and can rarely cause a reaction. We have a strict policy of asperating when we are administering shots so that this mistake is not made.

Dr Davantzis and another doctor agreed

Chance of injecting anesthetic directly into a blood vessel is limited by standard of care aspiration technique. If it did happen the anesthetic would be quickly carried away, not deposited in the appropriate area, and therefore would not provide effective "numbing." Also the amount of anesthetic provided is nowhere Also, the amount of local anesthetic utilized is well below toxic levels.