There are many factors that go into the choice of dental materials for restorations. Years ago porcelain to metal was the esthetic choice for crowns. There have been so many advances in dental materials since then that it is rarely necessary to make crowns in this manner. Metal-free materials can produce crowns that are more esthetic, more natural in their appearance, and still very durable. Hope that helps.
Hi:Please inquire why Zirconium or emax crowns are not being used. Please post photo and X-ray for more accurate advice.Best,Dr. Maddahi