That's a pretty valid question...
the W/O is short for without... Inc is short for including...
So the GPA Inc +- would include the + or - in the letter grade ( A- , B+ etc. )
the GPA W/O simply does not account for these + or - ( so a B+ would just count as a B and a C+ would count as a C )
.....So for the W/O ... a B+ would equate to a 3.0 rather than a 3.33
Some dental schools prefer to use the +/- system and others prefer to use grades without +s and s.
I hope this somewhat helps!