hi ...
well i think this is not a factual essay rite ?
normally essays with only one words or i would like to call them free writing for i dunno what reason
as long as ur essay has a word that can be relate to silence that it can be counted
the thing about this essay is that u can write freely and cannot be judged on facts
there may be just a sentence that contains the word "silence" and the marker cannot say ur wrong
but sometimes there are those stereotype teachers who think that the essay should contain more fact

so my opinion just to be on the safe side
put a little "silence" here and there and you should be good i guess ...