I was impressed with how toothbrush manufacturers get the bristles into the heads. But I did not realize that those bristles, and the wire that binds them in place, is what leads them to be rejected by recycling centers. With no easy way to separate those components, toothbrushes are considered unrecyclable and sent to the landfill, even though the handle is entirely plastic.
What's the design fix for this? If the bristles were designed to not be permanently mounted, there's a chance they could come out in an end user's mouth, which could be disastrous.
Colgate-Palmolive's approach to the problem is one of compromise. Rather than redesign the bristles, they've accepted that not all of the toothbrush can easily be recycled, so they've minimized the unrecyclable part. Their new Keep toothbrush has an aluminum handle that you're meant to keep, as the name suggests, and use together with snap-on, disposable replacement heads made of plastic.
While this approach still has perfectly good plastic going into the trash, I can't see how else to reconcile the bristle problem.