My vet sells Greenies in his OFFICE!! 

 Don't get me wrong, I love my vet, I just think the people who market these disgusting things do a great job marketing them to vets as a dental device.  They have cute little displays and probably all kinds of research proving the chews help remove tarter, etc. 
 I just copied your post and put this at the top:
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Dr. Bowen,  
The more I read about Greenies, the more unhappy I get about the fact that you sell them in your office.  I hope you read this and think about perhaps getting rid of this dangerous chew toy. 
I also hope I have not offended you.  I would just hate for you to have to operate on a dog whose owner had gotten a greenie from your office.
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I sure hope he reads it with an open mind.  I would feel soooo good about walking in there and seeing all the Greenies GONE!!! 

  And if it works, I own you a BIG thank you!!