Which is a New Crown?

Mr. Chen is a Cambodian refugee. He grew up in an environment where oral care was unavailable.  Although he has had a lot of cavities, they are under control.  He keeps good oral hygiene.  Recently a new crown is added to his front teeth.  There are two old crowns.  Can you guess which is the new among the three (Fig.1: 1,2,3)?  What is your basis for guessing? 

Here is the answer.

Xin Wei, DDS, PhD, MS 1st edition 06/14/2012, last revision 06/14/2012