The labs that say "Zirconia can also be used for anterior teeth with a facial veneer of porcelain for improved esthetics" describe the crown as Bruxzir. Maybe they are confused? This is exactly what the lab website says:
BruxZir® Anterior BruxZir® Anterior is the latest advancement in the BruxZir Solid Zirconia product line. This highly esthetic restorative material is designed specifically to satisfy the esthetic and functional requirements of the anterior region of the mouth. Exhibiting an average flexural strength of 650 MPa with translucency and color similar to natural dentition, BruxZir Anterior is an ideal, esthetic solution for your anterior cases. BruxZir® Anterior requires less reduction than monolithic glass ceramic restorations and does not create wear on the patient’s natural opposing dentition during occlusal and parafunctional activity.
Indicated for anterior crowns, bridges, inlays and onlays. An esthetic solution for bruxers and grinders when PFM metal occlusal/lingual or full-cast restorations are not desired or when patient lacks the preparation space for a PFM or has broken a PFM in the past. Zirconia can also be used for anterior teeth with a facial veneer of porcelain for improved esthetics.
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I canot find any dentist who does porcelain to gold. At least not one who is willing to do work for me. It seems to be dying technology anyway - and companies are putting lithium in the ceramics for that too. At least that's what Noritake indicated to me.