There have been incidents of choking with the greenies that glencorgi is talking about. Duncan and Chloe get them minimum. I got them an Easy Brush, which is a vinyl apparatus that has little brushes on both sides on each end. Put a little doggie toothpaste on it, work it into the brushes and give it to them to chew on for about 5 minutes. Saves me a lot of fighting with Duncan, but Chloe just licks the paste off. I see me paying for dental work for her in the future. Here's the website:
Easy Brush - The Chew-It-Yourself Toothbrush for Dogs