This is not how it typically works... Normally, the old fangs fall out first, usually lost in prey but can sometimes be found in their cage or water bowl. I have a little
collection of fangs...The snake pictured with double-fangs is an aberration as far as I know...can't say if all 4 can actually inject venom at the same time or not,
but they appear to all be solidly attached, so maybe so?
When a normal rattlesnake sheds their fangs, they aren't without them for long...maybe a few days at most, as the new ones come down from the roof of their mouth.
Too bad we poor humans can't just shed our old teeth & get nice new replacements, eh? Especially with the high cost of dentistry, not to mention the discomfort.