Why do cracks go with loose teeth?

Periodontics & Bite: Cracks are formed from trauma. It can be from an accident or biting forces. Loose teeth are from lack of bone support (periodontal). I don't know if i understand the question exactly, because teeth can get loose without a crack and cracked teeth do not have to be loose. But which came first, the crack or the mobility? That is for your dentist to determine.

Im sorry I don't: Quite understand your question. Teeth can develop cracks for numerous reasons - malalignment of teeth, types of foods eaten, occupational, from accidents, from decay, ... Etc. Loose teeth can be the result of an accident, gum disease, bone loss ... Sometimes, the two go together.

Structural failure: For the same reason cracks go through wood, stone, plastic and glass. Or any other solid. Common cause of tooth cracks are amalgam silver-mercury fillings or acute trauma like getting hit in the teeth or biting on something hard quickly (olive pit).