How to address a Dr. des.?
While the formal title is Dr. des., there are good reasons to simply use the form of address you would use to a “final” doctor: the title is only temporary, and the person will eventually have the title or Dr.; moreover, PhD candidates having freshly attained their goal will probably enjoy you using it.



For those who wonder what Dr. des. is, it's a temporary title, like US presidents are “president elect”:


  Following a successful defence, the title of Doctor designatus (Dr. des.) may be used until the doctoral degree is gained.