What force used to push dented ping pong ball back to original shape?

The force that pushes a dented ping pong ball back to its original shape is the elastic force. This force arises from the material's ability to deform and then return to its original form when an external pressure is removed. When the ball is dented, the internal structure of the material compresses, and once the compressive force is released, the elastic properties of the material cause it to revert to its initial shape.