'Maybe agree with the dentist that he can start to drill without LA, but if DS feels any pain he can have an injection after all and wait for it to take effect before going on?'
Janh, exactly what I would say too. I don;t nderstand why LA wasn't offered, it would certainly help the dentist, as if your ds feels anything he will be jumping around!
Tell your ds & the dentist that he will raise his hand if he feels anything & that's when to give the LA.