Kidney and Bladder Stones
Most ranchers feel malocclusion is largely genetic, with some cases of trauma, extreme malnutrition and poor care becoming more frequent with pet owners.
My reason for believing it is largely genetic is that of two chins with the same poor care, one may malocclude due to the poor care, but the other survives. Maybe it wouldn't have done so with better care... but overall it was a genetically weaker animal.
Chins can also malocclude from trauma to the jaw if they are dropped and the jaw is knocked out of socket or they hit their front teeth. This will often cause the front teeth to have problems, not the molars like you would normally see in a maloccluding chin. With the violet above, the owner detected bumps in the jaw line earlier. The front teeth splitting is an odd occurrence in addition to the molars protruding from the bottom of the jaw line.
This chin was so far advanced that there is a hole in its lower jaw where the root has caused an abcess, ruptured, and left the jaw bone and root exposed. A chin's teeth grow so fast that this can happen in less than a month. The old term "Chinchilla Slobbers" came from the wetness of the lower jaw.