Which are more safer?

I haven't heard of Zirconium being used much. Perhaps it is much newer? Porcelain seems to be much more widely used. The most important thing is using what the dentist has the most experience with, so that it is installed properly. Did he say a crown is definitely needed, and that an inlay or onlay would not suffice?

Yes a crown is required. He told me that zirconium are much more pricier but safer because they have no metal in them. He said that they only been around for 2-3 years.Porcelain once have metal on the inside, zirconium once don't.

Many porcelain crowns don't have a metal liner. Only one of my porcelain crowns has a metal liner.The rest are all porcelain. He could ask the dentist if a porcelain crown without a metal lining would be okay.