I just bought an oral care kit for my dog that includes a toothbrush, finger brush, and brushing gel. The brush has a three-sided design (look up TropiClean toothbrush to see what I mean), which seems a bit tricky to use. I didn't want to overwhelm him on the first go, so I really just let him lick the toothpaste off the brush and did some light brushing in the front. My biggest concern is how to get is back teeth though. Any advice?