Grinding teeth causes problems for teeth, jaw joints (tmj) and muscles in your head and neck. Damage occurs so gradually that it often is not noticed until teeth are very worn.
This question illustrates this type of slow but sure tooth damage but could be caused by a combination of factors.
Besides tooth fractures or cavities, there are two main causes of teeth getting smaller. One is mechanical wear also called abrasion and the other is erosion.
Abrasion is most often caused by grinding teeth.
Erosion can come from eating too many acidic foods.
Acid reflux and the eating disorder bulimia also cause tooth erosion.
Assuming that your teeth didn't fracture and that you don't have cavities, the cause of your teeth shrinking could be either, or a combination of erosion and abrasion.
Abrasion from grinding is more common than erosion.
After the first (and hardest) layer of tooth called enamel has been worn through, the next layer called dentin wears or erodes away faster. this is because dentin is not as hard as enamel.
It's interesting that you only have this problem on the left side.
Pay close attention to how you hold your teeth together while falling asleep at night. If your upper and lower teeth are touching, it is likely that you are grinding them in your sleep.
Ideally, your teeth should never touch but should stay slightly apart during the day and at night.
Many have the habit of grinding or clenching their teeth and need an appliance called a night guard to prevent damage to their teeth and jaws.
It would be good to have a dentist look at the pattern of wear on your teeth and help you determine the cause.
A close look at your health and diet will help you know if erosion is all or part of the cause.
This article on grinding teeth might be helpful.
A dentist can help you figure out what is making your teeth shrink and the best way to prevent further shrinkage.
Shrinking teeth will only get smaller and the smaller they get, the more difficult and involved restoring them will be.
Thanks for writing and good luck,