Some of the tougher leaves may help - they need more chewing action so are more abrasive as they take longer to eat. My dental bunnies always seem to find flat shapes easier to manipulate in their mouths - especially if they are able to graze from the branches as well. I would suggest trying things such as short branches of willow, raspberry, bramble, strawberry, blackcurrant etc cut straight from the plant with leaves intact. They are readily available at the moment, especially if you know someone with an allotment or soft fruit bushes in their garden. They also make good dried forage for winter.
