From Bright Local:
- Going from a 3-star rating to a 5-star rating gets a business 25% more clicks from Google Local Pack
- Having a 5-star rating earns a business 39% more clicks from Google Local than having a 1-star rating
- 56% of consumers select a business if it has positive ratings/reviews displayed in Google Local Pack
- Star Ratings displayed in Local Pack results generate higher CTR than organic search results
- A positive reputation can boost search ranking, drive more clicks and build trust am
The linked article is worth reading. The research is for general Google business searches and is not dental specific. Never the less I expect dental results would be very similar.
Even with a good personal referral if a potential new patient Googles your name and encounters poor ratings I believe he/she will look elsewhere. A poor rating for a dental office is anything less than 4. On the other hand you do not need to be a perfect 5. I believe anything 4.8 or better is great. BTW that potential new patient will be Googling you just to get a phone number.
You do not need hundreds of ratings. If you have five or more and add a new one every few months that is golden. The easiest way to do that is to simply ask your happy patients to post a review.