Quoting Mj's Crazy Mama♥:" I started brushing my son's teeth when he started teething (3 months) with this tooth brush I found that ... [snip!] ... and brushes his teeth constantly (only twice a day with kid's tooth paste) with a $5 vibrating tooth brush at wal-mart lol"
I was just going to recommend the rubber tip that goes on your finger too! My mom found it at walmart, she got one for the dog. The next time I go to walmart, I'll be picking one up for my 4 month old. I'm going to refrigerate it before I use it each time because he is starting to teeth. I figure it will be a nice relief along with using his teething rings.