Is dental zirconia a metal or a ceramic?
There is a lot of confusion about whether dental zirconia is a metal or a ceramic. To clarify exactly what this material is, let us look at the origin of these terms.
Zircon - A mineral, and the source of the metal zirconium. The mineral form is zirconium silicate. This mineral form is not directly used in dentistry.
In the image (Fig 1), the zircon crystal is perched on a matrix of calcite (Image credit: Rob Lavinsky)
Zirconium - a transition metal, and is used mainly in nuclear reactors, NOT in dentistry. It is seen right below Titanium in the periodic table, which means zirconium and titanium are in the same family of elements – a transition metal. (Fig 2) (Image credit: Alchemist-hp)
Zirconia - A metallic oxide of zirconium, namely zirconium dioxide. It occurs in nature as the mineral baddeleyite. In dentistry, we use various stabilized forms of Zirconium dioxide (primarily Yttria stabilized).
(Fig 3) (Image credit: Rob Lavinsky)
Before we can define whether dental zirconia is a metal or a ceramic, let us look at the definition of a ceramic according to the Glossary of Prosthodontic Terms:
ceramics\sa-ram ́iks\n (1859): 1. compounds of one or more metals with a nonmetallic element, usually oxygen; they are formed of chemical and biochemically stable substances that are strong, hard, brittle, and inert nonconductors of thermal and electrical energy.
Going by this definition, ceramic is a metal compounded with a non-metallic element, such as oxygen. Hence, it is most appropriate to refer to dental zirconia as ceramic and not metal.
Other examples of this type, are:
1. Zinc in its elemental form is a metal (hard, dark color), but is a white powder as Zinc oxide.
2. Lithium in its elemental form is a metal, but lithium disilicate is a glass (popularly available as Ivoclar Vivadent’s e.max).
Although dental zirconia is ceramic, I do think it is disingenuous to refer to zirconia restorations as "metal-free".
If I am asked this question by a patient, I say "zirconia is a ceramic – but it’s not metal-free”.
Even lithium disilicate is not actually "metal-free" – since it has lithium in it.
Hopefully, this dissection into one of our most frequently used materials hasn’t left you feeling more confused than before!
Dr. Varun Acharya
B.D.S., M.S., F.A.C.P.
Diplomate, American Board of Prosthodontics
Dr. Varun Acharya is an American board-certified maxillofacial prosthodontist practicing in Chennai, India. He completed his BDS degree at Saveetha Dental College, postgraduate prosthodontics at the New York University College of Dentistry, and a fellowship in maxillofacial prosthodontics at the University of Texas MD Anderson Cancer Center. He has published several articles in international peer-reviewed journals, and lectures both nationally and internationally.
More about Dr. Varun Acharya:
Dr. Varun Acharya obtained his Bachelor of Dental Surgery degree from Saveetha Dental College, Chennai. He graduated at the top of his class and was selected as the Outgoing Student on graduation.
He pursued his post-graduate education in the United States of America where he completed 4 years of prosthodontic training at the New York University, College of Dentistry where he specialized in dental implants, veneers, crowns, bridges, inlays, onlays, and dentures. At NYU, he was a recipient of the Adisman Award for the most outstanding graduating prosthodontic resident.
After New York, he continued his post-graduate education at the University of Texas MD Anderson Cancer Center in Houston, where he completed a fellowship in Maxillofacial Prosthetics and Oncologic Dentistry. At MD Anderson, his focus was primarily on the maxillofacial rehabilitation of the cancer survivor. Besides intra-oral prosthetic devices, Dr. Varun also focuses on facial rehabilitation with silicone facial prosthetics.
Dr. Varun has presented numerous table clinics and research papers in conferences in India and abroad. His research and scholarly articles have also been published in peer-reviewed international journals such as the Journal of Prosthetic Dentistry and the International Journal of Prosthodontics. Dr. Varun is currently the consultant prosthodontist at Acharya Dental and the consultant maxillofacial prosthodontist at Tata Medical Center, Kolkata.