I will change the title for you so it gets more attention
I dont like the sound of what I have read and the one thing you didnt tell us, or I am blind, is Lewis age. This is quite important being the number of times he has been sedated.
I thing your first vet did not do a good job and I now know how important this is cos have a cat who has a serious brain infwection which it is suspected was caused by an infection entering his blood stream during a dental.
Its sad that the second vet has not really been of much help and I hope you have insurance.
My next option would be to get one of the vets to refer you to a dental specialist to try and get to the bottom of this properly, you dont say where you live but there are a number of full blown vet hospitals round the country.