First, contrary to popular belief, not every dropped helmet needs replacement. In fact, if it was dropped from a height of 4' or less and wasn't hard enough (i.e. thrown) to damage the EPS liner (and it takes a lot to damage those impact absorbing layers), then your helmet is likely just fine. You just need to contact Bell to see if a replacement shield is available for your model. Been there ... done that.... snipped ... I’ve worn a Bell Mag 9 which is a 3/4 helmet for past five years or so, fits me perfectly. Dropped it and broke off the flip down shield so I need another helmet. I had decided to get a full face helmet because I’ve got a couple other full-faced helmets I use for my dual sport bike and I figured I should get a full face to replace my Bell Mag 9.
Secondly, you might want to check out the 1981 Hurt Report which although very old now, still has some great data in it. Pages 91 and 432 are most relevant to your question/issue.
Lastly, you might want to check out the linky below. David Hough also publish something similar in his "Proficient Motorcycling -- The Ultimate Guide" book. Also "dated" but a great collection of articles on just about every aspect of riding including lots on riding safety .
Where's the most likely place your helmet will take a crash impact?
There are full faced, flip up and flip over helmets that are designed to give you lots and lots of peripheral vision. Anything much over 180* (the most I've read about is 190*) you can't physically take advantage of anyway (due to the limits of a human's peripheral sight). This is coming from someone who rode with jet (3/4) styled helmets for many years before making the "never go back" switch to a full face, flip-over helmet about 3 years ago.