There are a multitude of websites that provide dentist reviews, including Healthgrades.com, Yelp.com and Dental-ratings.net. Note that most websites of this type are user generated, meaning that one disgruntled patient can potentially overshadow five content ones who elected not to write a review.
It is also possible for dentists to secure a favored position on these websites, either by hiring people to write favorable reviews or through a cash payment to the website itself. Therefore, these reviews can be biased in either direction. Due to the sheer number of dental providers, these sites all have filters for both geographic location and specialties.