That's not what they usually use... but people have different reactions to novacaine, and different innervation; for dental work, there's a couple typical options for where nerves are and which nerves cover which teeth, some of which need more shots in more places.
For the GP, most likely the anesthetist put a note in the chart that they need more or different drugs to go under.
My lips and gums go numb but my teeth generally do not. I am sure it takes the edge off, but I can still feel it and it is still incredibly uncomfortable.
On the other hand, while having a tooth pulled and opting to be put under, the nurse and I were having a great laugh after because I was so awake. Apparently there are multiple drugs and whatever the first one was hit me so hard they only have me a half dose of another. It was enough though. They said count, I hit nine, and I woke up somewhere else. Exactly what I wanted considering local doesn't work.