Board Thread:Boruto Discussions/@comment-1452242-20170117195252/@comment-4912646-20170121170532

Hiruzen compared the balls to Dust Release after seeing them erase his shuriken, and Obito apparently wasn't using Yin-Yang Release at the point when he erased Tobirama. Though it is weird they don't erase things in some cases like when Madara hit Sakura, since there was no reason for him not to do so if it's optional.