I have tried both methods, but I prefer to use the inset mouth method, so that the side head pieces have a cut in them to insert the, roughly, diamond shaped inside mouth piece. I didn't explain that very well. Here is a picture of my latest open mouth miniature. He is approximately 4inches (10cm) tall.
Thanks for the input, Gail.
I have thought about adding a "ear-shaped" piece onto the chin but having given the tiny fur length this wouldn't work well, I think. I was then thinking about your method but didn't know if it would work out on a small bear, it definitely sounds very fiddly - but I'll try it out!