I don't think that struggling with the supplements is a bad thing. You should take it seriously as some schools depend on it heavily. Take for example U Minn. which has the longest supplement ever. 3 questions longer than a PS. So, i would say don't over think the responses as some people has stated. These shouldn't just be a repeat of what you said, but you should also be honest with them. One school i think it was NYU asked what is one thing that you would change or do differently in undergrad? So, it does take some thought.
Lastly, i can't remember which school said this, but i read what they asked for their supplement and in it is said that not all adcomms will read all your application. Some will read some parts and others will read other parts. So you might think "well i wrote about my who in my family is a dentist, so i won't write about it again" but if the question asks something along the lines of what made you want dentistry, i think its ok to re-mention something you put in your app.
I hope this helps, and trust me, I did put a good amount of time in the supplements. spending a few extra hours is better than rushing it and looking bad infront of the adcomms.
