As a rule make sure the chew toy is larger in size than the distance between your dogs back molars when measuring across the jaw. (goughnuts.com)
And now I have a cracked back molar (sorry, you don't get a picture of that) but it also isn't causing any pain so that's a HUGE relief. (howtomakealife.com)
As you and your dog get more comfortable, work toward reaching the upper back molars. (doghealth.com)