there's a door gasket that seals it not the metal part of the door so you might be able to stick your thumb in there as long as the seal on the door is closing tightly to the frame,when you open the door it should be on a 90 degree angle,before you had new hinges put on the door, most likely the door sagged lower to the floor and didn't close properly,if you think alot of heat is escaping you could have a bad door gasket.so open the door,look at it from the side,it should look like an L or at a 90 degree angle or even up a little,if it is the hinges aren't the problem if you think to much heat is escaping,call whoever did the work for you and have them check the door seal or gasket same thing.you didn't send the model number so i don't know what seal you need,go here and watch video should be similar and you can put your model number in to find correct part
http://www.appliancepartspros.com/whirlpool-gasket-oven-door-wpw10162384-ap6016005.html
hope this helps you out,if heat is coming out with door closed and you have new hinges this is most likely what's wrong