To me, serrations are such a fascinating tool. They were independently evolved many times in many different animals. They concentrate force into smaller points (increasing the pressure = Force/Area) so that the thing being bitten would break or cut along the line of serrations. They also are great for "sawing" through things such as muscle. T. rex definitely made great use of this adaptation.
Topmost (greyscale) image from "Physical evidence of predatory behavior in Tyrannosaurus rex:"
Most of the pictures (color) in this collage are from two associated fragments of what I am certain was a T. rex tooth from the Hell Creek Fm., SD based on the size and shape of the serrations. The images with the scale markings have been scaled to match each other.
More on theropod serrations: "Developmental and evolutionary novelty in the serrated teeth of theropod dinosaurs:" https://www.nature.com/articles/srep12338