Hello. My PFM crown on a first molar has cracked to the point where food traps between my teeth. I am going to request a full cast crown from my dentist. I heard that nonprecious is very hard to polish, so is it reasonable to ask for ask for semiprecious? Also, if a dentist were to ask to for a full cast crown for the same price as a PFM crown, what alloy would you use?