Lots of micro cracks never enlarge to create any problems.
Some progress and become real cracks in the tooth structure.
Caught soon enough, these teeth can be restored with onlays
or crowns.

Delayed too long, and you can end up with a root canal or
extraction.

Keep wearing your NTI, get regular check ups, and relax.

I wouldn't rush to crown every tooth in your head (unless I
had to pay for my new boat <G>).

D

    Almost everyone of a certain age (myself included) has craze lines in
the enamel.  This can be in restored teeth and in non-restored teeth.
Some may represent true cracks that can progress (as when, for example,
a wide cavity is restored with a filling that would have better been
filled with an onlay or crowned).  Some I believe are from thermal
cycling (have a bite of ice cream, drink some hot coffee), and most of
these never go anywhere.
    My advice--wear your NTI, don't worry about the cracks.

Steve