Trees should never be "topped." Removing the uppermost stem and branches of the tree will disfigure the tree, distort its growth and shape, pose a greater risk of sunscald to the inner portions of the tree and open a large wound that is prone to disease and insect problems.
Trees that are topped will respond by sprouting dense upright branches near the pruning cut. These are often referred to as "water sprouts." These branches are weakly attached to the branches and tend to break off easily. A topped tree may end up in a far more hazardous condition than with the original growth.