I cracked the two lower molars next to the back molars the same way... pork shoulder picnic chops had little pieces of bone in the meat. Don't buy em anymore.

Apparently, I am one of the lucky ones that have four roots in these and very lucky to have such large and deep roots. It was excruciating. Drill, inject, drill, inject... 8 times with some of them. $1800 a crack. But, Mexico is a fair drive from here.