Open up the image you want to work on, press Command-1 (PC: Control-1) or double-click the Zoom Tool to bring the image to 100%. Select the upper left corner of the Color Picker (the whitest white). Then select the Brush Tool B and adjust the Hardness to anywhere between 0-20%, and make the Size just a little smaller than the width of the tooth you are working on (we made the Size larger on the front teeth and smaller on the back teeth). Adjust the Opacity to 18%.
Open up your original photo file that you wish to apply the zoom to and create two duplicate layers of your Background layer. You do this by dragging your Background layer to the Create A New Layer icon at the bottom of the Layers palette or simply press Command-J (PC: Control-J) twice. Then, hide the top layer (Layer 1 copy) by clicking on the Eye icon next to it. Then, you want to rename the middle Layer (Layer 1) to Zoom.
To create the zoom blur effect, select the middle layer (Zoom). Then go