Mine largely just won’t open up and so it’s next to impossible to reach the inner sides of the teeth. I encourage eating things like apples in the hope there’s some beneficial effect.
My daughter does her own outsides then opens to let me do the inners-
That’s very lucky 😅…it’s what to do when they clench their teeth and/or run away that I’m trying to figure out.
It's a twice daily battle when I semi-pin him in my arms and brush for a bit, hoping for the best. No magic tips I'm afraid. They're a law unto themselves. Our daughter on the other hand, was proudly doing them thoroughly at 10 months old! Kids eh?!