Are Greenies enough to keep my dog's teeth clean without brushing?

Both help fight tartar formation on your dog's teeth. Both do a fairly good job of slowing the process down, however neither brushing or Greenies treats will eliminate or remove the tartar that has already built up on a dog's teeth. In an ideal world you would be brushing Bella's teeth daily and giving her dental chews (like greenies). The downside of brushing is really just the time it takes and getting your dog comfortable with the act of tooth brushing. The downsides of greenies and similar treats is that some dogs just don't chew on them enough to get the effect of the tartar control and instead swallow big chunks in their enthusiasm at getting a treat. Additionally if weight control becomes an issue as Bella gets older, extra treats mean extra calories. You're in a great position with Bella being so young to start getting her used to regular tooth brushing while she is still teething and may enjoy the act of brushing on her teeth and gums as her adult teeth come in. I recommend using a commercial toothpaste that is labeled pet safe (can be found at a local pet store, online, and many veterinarians have samples for patients to try) and a toothbrush that is appropriate for your dogs mouth (Bella will probably need a small brush since she is a little dog). Ask your vet if they have any instructional information for how to slowly introduce brushing into your routine. Also with dental chews always make sure you follow the charts and give the right size treat for your size dog (my 6.5 chihuahua once ate a Greenie that was for a much larger dog and did get a little loose stool for about a day... lesson learned). I hope this was helpful!