Defoliation is completely unnecessary with boxwood and can weaken the tree, although boxwood is pretty tough and can survive anyway.
It's also a lot of unnecessary work, as the petiole (leaf stalk on each leaf that connects to the branch) on boxwood is extremely small or virtually non-existent. If you prune the leaf off without cutting through the petiole, you may not stimulate the resting bud at the base of the petiole. If you trim too closely at the leaf/stem joint you could destroy the resting bud--there is VERY little room for error. The new leaves you're hoping to produce are those resting buds (along with a few in the branch itself) In other words, in removing old leaves, you could be removing 80 percent of the new leaves you're hoping to induce the plant to grow.
Internal ramification on box is easily done through detailed hard pruning on old shoots-not leaves. You cannot get ramification by trimming only the outside profile of the plant or by pinching new growth--only growth that has "hardened off" is capable of pushing new leaves.
Hard pruning older and old shoots (mostly anytime in spring and summer) will produce new growth back on the branch. You have to go through the plant branch-by-branch and select hardened twigs and tertiary branches to cut back. This can take several afternoons if it's a larger tree.