Okay, marrow bones. I used to always give but had one very aggressive chewer. The vet showed me the actual cracks in her teeth! The other dogs were fine, btw. But every once in a while, shine a flashlight on the teeth and look for cracks. I check their teeth, but I never saw the cracks til she put actual light on them.
I was struck by the fact that your Bernese lived to be 20 years old! Wow! I know they have had concerns with cancer in the breed, and very few of them live that long. How wonderful for you that you got to have her for that long.