Never found great dentist during our time in Küsnacht ZH. It's worth traveling a few more train stops to get exactly what you need for your child IMHO.
Some kids just need special care (sensitive mouths, limited jaw range, fear of dentists, allergies to medicines, unusual oral bacteria or susceptible to infections, etc.) Best one by far I found and surprisingly reasonable was Dr Til Mutzbauer right off of Paradeplatz in Zürich http://www.zahnarzt-zuerich.com/seiten/de/c.htm
Don't be put off by website. Dr. Mutzbauer speaks great English, is both dentist and medical doctor (anaesthesiology), has great in-mouth instrument dexterity (how come so few mention this?), and deals with children all the time.
He treated our child who needed special care (incl. fillings, wisdom teeth, etc.) - really super experience if one can have such a thing with a dentist.