I recommend Waterpik.

I have been using a Waterpik for a while because I heard it is good for dental health. Since I started using it, I have noticed a significant reduction in tartar whenever I go to the dentist for a scaling. You fill it with water, and it uses water pressure to remove debris between your teeth. It also has a massage mode, so you can massage your gums. The water pressure can be adjusted in stages, so you can set it to the level that suits you best.