Why would anybody crown baby teeth. That is insane.
And why would any parent in that situation do anything but grab the kid and run out the door while dialing 911, for Christ's sake? Not that I'm by an means excusing the dentist who afaic (at first glance and without giving it any professional consideration) should be charged with negligent homicide at the very least, but still...
And treatment, including fillings, sure, but
crowns? The peculiar combination of dental-related genes I managed to inherit (some from both sides) can only be described as "Satan's handiwork itself" and I've had more dental work done than I care to recall starting in my mid teens (plus what seemed like an innocuous few fillings in "baby teeth" but which were in retrospect probably harbingers of doom..) Over that time, my parents (at first) and I both asked a lot of questions, and I've done my own research, so I'm familiar with most of what can/might be done and the reasons for it. And I've never even heard of such a thing.
But even if it
is ever warranted in particularly bizarre circumstances, it's certainly not something I"d allow to be done to a child in my care without thorough discussion beforehand (plus 2nd and/or 3rd opinions), never mind on a spur-of-the-moment, "oh-lookie-what-we-just-found" basis... I mean, it's not like exploratory surgery where you can't be sure what you'll find before you go in, decay that serious would show up like (really bright) neon lights on X-rays, not to mention most likely causing a kid that young to scream bloody murder when it was poked with pretty much any dental instrument...