Over time teeth will wear down, but acids in the diet (e.g. from fruit juices and carbonated drinks), stomach acid (from reflux or vomiting), and grinding your teeth at night will speed up the amount of wear.
Finding out the cause of the wear is the most important factor so that it can be prevented.
Prevention and monitoring the problem is usually all that is needed but in severe cases the teeth may need to be built up with fillings or crowns.
If grinding the teeth in your sleep is the cause of the problem we would recommend that you wear a night guard (which is like a gum shield) to protect the teeth. Most people notice they are grinding their teeth if a sleeping partner wakes upon hearing it in the night, or in the morning you have a stiff jaw or aching muscles around the jaw joint.