I never used Greenies per se, but I have used the Nylabone green puppy chew things. Bruno liked them, but we are not getting any more. Ever. I am happy he never had a problem, but I would much rather give RMBs, brush his teeth, and give antlers, hooves, and bully sticks/ears/tracheae/natural and digestible stuff for dental health.
My friend, however, used to use Greenies every day with no problems. She also used bully sticks, but she wanted a long-lasting chew, and eventually they failed, so she stopped getting them. She is now on DentaStiX for her 2 dogs, but thankfully she is stopping soon. Her next trial will be water additive for fresher breath and with a joint supplement. Hopefully that works better. She will be using Tropiclean. Any thoughts on that?
