To allow light to reach the interior of a dense maple, remove 1 leaf from each pair, once they’ve hardened off. Back-budding should result from the added light. Water use will slow down a bit too, so keep an eye on watering.
Before:
Top half done:
Finished:
Much more light can get into the tree now. Some light pruning was done in denser areas, and more will be necessary in the spring.
Wolf's Birding and Bonsai Blog 