Alexandra and OTMA had fillings made of platinum, if I remember correctly.
Actually, it was only Alexandra who had the platinum dental work (a bridge I believe). The others (except NII) had very well taken care of teeth. NII being prone to periodontal disease.
Tooth decay was very much on the Empress's mind. Even royalty didn't eat foods that supported good dental health as well as the cold frigid temperatures of the Russian winters. The Empress knew this and insisted that meticulous care should be kept of her and her daughters teeth. Much has been speculated whether or not NII didn't go to the dentist, was afraid, etc. IMO, there simply wasn't a whole lot to do about gingivitis back then, even good brushing isn't enough. And it IS inherited.