Worn chipped or cracked teeth
Wear of teeth is often assumed to be "normal" wear and tear with age. When the jaw is at rest the teeth are supposed to be slightly apart. This space of about 1/8 inch between the upper and lower teeth is called "freeway space". The only time the teeth actually touch is during swallowing, that occurs about 2000 to 3000 times a day. The lower jaw which is loose, needs to be stabilized by bringing the teeth together to allow for swallow. When chewing foods, no matter how fast we chew, the teeth don't actually touch each other. The muscles know precisely when to open just before the teeth touch. This is why if you run into a piece of bone or sand in your food, it startles you. With the soft foods we consume in our society, there is no real need for teeth to wear.
The only real reason for severe tooth wear is due to para-function. Para-function is putting teeth against teeth to clench or grind. The amount of force one develops in this clenching during sleep - especially during the Rapid Eye Movement (REM) part of the sleep cycle is many times higher than the highest voluntary clench.
This para-functional habit of clenching and grinding the teeth is due to an disharmony between the position where the teeth come together best for chewing (Habitual occlusion) and the position where the two jaws are related to each other when all the muscles of the jaws and posturing muscles of the head and neck are at their relaxed, unstrained position (Neuro Muscular occlusion). It is as though the lower jaw is trying to grind away anything in its path from Habitual occlusion and the Neuro Muscular occlusion.
If the worn or chipped teeth are restored with crowns or other restorations without regard to this underlying cause..then the same thing will happen to the new restorations as well..worn or chipped restorations! If the restorations are made with metal to make them, as a solution to this problem, then the forces of the muscle will destroy the bone that is holding the teeth in the jaws over time. This leads to receded gums, loose or lost teeth.