Understanding that it's a lose-lose, and that poor yelp reviews are tough... Most people respect a professional response to a scathing review on yelp. If your practice has ten excellent reviews, one guy who's angry, and your response:
"Mr. Smith, you were informed that the crown would only be successful if you came to your procedure within two months, and you ignored our calls, emails, and cards for over a year. We're very sorry the crown no longer fit, but we can always cast a new one."
Your prospective customers should get that.
I completely agree with this.
If I go on Yelp, I expect to see the most polarized customers providing responses to businesses. And I'll take the time to read the owner's response as well to the complainers.
But don't be a ####. Just last week I was looking for a granite contractor and someone had left him a negative review that hadn't even done business with them, just gone through the quote process and wasn't happy with his prices.
The owner responded, but he used words like selfish, immature, ignorant. The review itself I had taken with a grain of salt, but his response completely ruled him out as a contractor for me.