Remember that all but the very newest composites expanded thermally,more
than amalgams did on oxidization.  The resins just start to decay before the
fractures appear.  The alloy keeps trying to reseal through oxidation.

    I have routinely seen these radiating out from amalgams of various
signs with absolutely no other signs of parafunction.  Not saying that
just because I can't see it means it ain't there--but considering the
well-known setting expansion of amalgam, together with differences in
coefficients of thermal expansion between tooth structure and
restorative materials, I think it might be overdoing it to say that
"all" cracks should be considered the result of parafunction.

Steve

Your dentist should be able to tell if these are surface crazing lines, or
deep fracture lines.

These are all the result of "parafunctional" activity.  That means activity
which is not associated with normal function of the organism.  In this case,
we are discussing forceful clenching with isometric grinding (grinding
forces without actually moving the teeth across each other).  Most often
this a sleeping occurance which the patient can not detect they are doing
until a dentist points out the damage.

I found some cracks on the edge of my back teeth and searched on
internet. I think they might be so-called "craze lines".  Because I
don't have pain on these teeth.

How can I tell the difference between crack and craze lines? How do
these crack lines form? Does loss of one tooth produce too much
pressure hence crack lines on other teeth?