Is fluoride necessary to have good teeth?

Yes. Fluoride tooth paste and Fluoride in the water help prevent cavities.
Important. Do you have to have it, actually no but if you don't you must be critical with you diet and be perfect with your brushing and flossing, this is not an easy task so really Fluoride for any person is beneficial to aid in decay prevention and you should use it. I would never recommend not having Fluoride but concentration and delivery are important. It is best topical such as paste and rinse.