Inter proximal reduction, how many millimeters can we safely remove from each side of the tooth? (photo)

Hello, I have an adult fused tooth that formed with my lateral in front. Resulting in a large tooth I then added composite to the other front tooth for symmetry. I am unhappy with the look so I'm beginning orthodontic treatment to open space for missing lateral and to widen the other. As I begin to slenderize my front teeth my question is how many millimeters can we safely remove from each side of the tooth?