My Lionhead bunnies also occasionally chew on the bars despite free roaming most of the day and spending the rest of their time in an enclosure that consists of 3 playpens put together. I believe they have a natural tendency to test the boundaries of their environment. They don’t usually enjoy coming in and would rather free roam even if they have a large space to themselves. My males in particular tend to chew the bars when they see something on the outside they’re interested in, like one of the female bunnies going by. Anyway as long as he has enough free roaming time and adequate space when he’s in,  he should be okay and I wouldn’t worry about it.

Does your bunny chew constantly or just take “test bites” here and there? I agree that bunnies will naturally want to test boundaries and a little nibble on the bars just to make sure they are solid isn’t going to hurt anything.

One trick to help with bar chewing is to put a visual barrier up, like a towel or sheet clipped to the pen walls (or a piece of cardboard). For whatever reason this really seems to help. You can also clip grass mats to the bars as a toy.

Rabbits are apt to do silly wabbity things, like chew bars from the outside or from the inside of a cage that’s always open. Why they do this is still not fully understood by us mere humans. It could be that they just always want to take the shortest distance route to whatever target spot they’ve picked.

It is however best to try and stop them, for the very reason you give, they can hurt their teeth by chewing on metal bars. Even if chipped rabbit teeth grow out quickly, they can grow out wonky (all the teeth in the mouth don’t grow at the same rate), which can cause chewing problems down the line.

When my bun chewed at metal bars I wove apple and willow twigs through the bars to distract her from the metal. It worked great. I couldn’t block her view of her perceived target (it’s a gate that leads from the veranda out into the garden), but I would’ve probably gone with that option first if it’d been possible. Out of sight, out of mind really does seem to apply to rabbits.