Twenty-five years ago someone gave me a set of carved ivory pins, which I used on my D-28. They certainly are more beautiful than any others. When my luthier Larry Brown built me a new bridge, the guitar came back with standard plastic pins. He didn't like my ancient ivory pins, but I think his opinion was "aesthetic" (they don't "belong" on a mid-40s guitar) rather than "acoustic". I played with the plastic pins for a few months, re-installed my pretty ivory ones, and never noticed any difference in sound either way.