Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-11829889-20161218211452

Aizen specifically stated that in order to trap someone in Kyoka Suigetsu, the target needs to see its release. If the target doesn't see it, it can't fall under the hypnosis. Aizen trapped countless amount of entities in his Kyoka Suigetsu without even uttering the summoning chant, which means he has achieved materialization and is presumed to have bankai.