Zirconia crowns are also metal-free but are considerably stronger than ceramic crowns. They are an excellent choice for restoring back teeth where space is limited. Zirconia is also good for people with bruxism. The material is very resistant to wear and will not harm the opposing teeth.Some zirconia crowns are made entirely from this material, while others have a zirconia substructure covered with porcelain. The resulting restoration looks natural and life-like. The original zirconia crowns did occasionally cause problems because the material used to be bone white and was difficult to mask entirely with porcelain. Nowadays, zirconia crowns do not have these disadvantages, and the material is often pre-shaded to match your tooth.