Our 172 has two screws missing from under the wing where
it connects to the fuselage above passenger door.

The size of those screws are quite big. My question is whether
they are important to the stuctural integrity of the wing ? They
may have come off during flight due to the vibrations. But it
is still some hours before the next 100 hours.

Are those screws important for holding the wing to the fuselage ?
or are they only there to cover the holes, and there are some
other bigger screws/nuts inside the wing that are doing the real
work ?

A speedy reply will be appreciated.

P S