I have a great dentist here in Plymouth that rivals any US dentist for cleanliness, effectiveness and efficiency.
Meavy Way Dental Practice
01752 773412
45 Crownhill Road, Plymouth, PL5 3AL
It's closer than Boston and Zurich!

I am sure you can find a good one in London though. Ask around and in particular people with nice teeth. It's what we did and have a great place as a result. Just remember that you might need two appointments. One with the dentist to check things out and if you need a scaling or something more in depth you might be sent later to the Hygenist. We always book the Hygenist a week or two later as he is very popular and hard to get to see.
Luckily we just needed a quick polish and clean this time. We go every six months. Cost is about £35 for the dentist. You can go NHS (free at point of delivery) if you can find one in your area.