I brush and clean my chi's teeth every night before bed.
I also use one of these, you need to keep his/ her mouth pointing down, and the pressure is easy to control since you pump it with your thumb.
I try to keep him from swallowing when I rinse, and then follow again with a between the teeth squirt. It all takes some getting use to for you and the chi.
The powered water floss things can not be as controlled as these.