What is this?

Switched to this set a few days ago. I just noticed this rectangular ridge that was not on my previous set before. Is this a manufacturing error? Before I ask my ortho, anyone know what this is?

Thanks!

Switched to this set a few days ago. I just noticed this rectangular ridge that was not on my previous set before. Is this a manufacturing error? Before I ask my ortho, anyone know what this is?

Thanks!