Zirconia – All ceramic restoration

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Zirconia Bridge

What is zirconia?

It is zirconium dioxide ( ZrO2), a white solid used in ceramic glazes and refractory coatings, and as a synthetic substitute for diamonds in jewellery.

Zirconium_oxide

Zirconium dioxide

Zirconium

Periodic_tablePeriodic Table

This is a metallic element with the atomic number of 40 and the symbol Zr. Despite the fact that zirconium can only be found in a combined form in nature, it is very abundant on Earth, being a highly reactive element. This element belongs to the transition metals, a group of neighboring metals on the periodic table of elements which includes palladium, silver, cobalt, copper, zinc, and nickel, among many others

Despite the fact that zirconium can only be found in a combined form in nature, it is very abundant on Earth, being a highly reactive element. This element belongs to the transition metals, a group of neighboring metals on the periodic table of elements which includes palladium, silver, cobalt, copper, zinc, and nickel, among many others.

Before going into details, we decided to do an overview of zirconium. This is a metallic element with the atomic number of 40 and the symbol Zr. Despite the fact that zirconium can only be found in a combined form in nature, it is very abundant on Earth, being a highly reactive element. This element belongs to the transition metals, a group of neighboring metals on the periodic table of elements which includes palladium, silver, cobalt, copper, zinc, and nickel, among many others. – See more at: http://www.dental-zirconium.com/#sthash.wb622dwA.dpuf

Structure

Crystal_structure_Zirconium(IV)-oxid

Zirconium(IV) oxide

Three phases are known: monoclinic <1,170 °C, tetragonal 1,170–2,370 °C, and cubic >2,370 °C. The trend is for higher symmetry at higher temperatures, as is usually the case. A few percentage of the oxides of calcium or yttrium stabilize the cubic phase. The very rare mineral tazheranite (Zr,Ti,Ca)O2 is cubic. Unlike TiO2, which features six-coordinate Ti in all phases, monoclinic zirconia consists of seven-coordinate zirconium centres. This difference is attributed to the larger size of Zr atom relative to the Ti atom. [Taken from Wikipidia]

Chemical reactions

Zirconia is chemically unreactive. It is slowly attacked by concentrated hydrofluoric acid and sulfuric acid. When heated with carbon, it converts to zirconium carbide. When heated with carbon in the presence of chlorine, it converts to zirconium tetrachloride. This conversion is the basis for the purification of zirconium metal and is analogous to the Kroll process. [Taken from Wikipidia]

 

Zirconia in dentistry

Final06 porcelain bridge

Zirconia is a very hard ceramic that is used as a strong base material in some full ceramic restorations. The zirconia used in dentistry is zirconium oxide which has been stabilized with the addition of yttrium oxide. The full name of zirconia used in dentistry is yttria-stabilized zirconia or YSZ.

ceramic_layer

Cross-section of a zirconia crown

The zirconia substructure (core) is usually designed on a digital representation of the patients mouth, which is captured with a 3d digital scan of the patient, impression, or model. The core is then milled from a block of zirconia in a soft pre-sintered state. Once milled, the zirconia is sintered in a furnace where it shrinks by 20% and reaches its full strength of approximately 850MPa.

ceramic_milling

Milling of zirconia block

The zirconia core structure can be layered with aesthetic feldspathic porcelain to create the final color and shape of the tooth. Because bond strength of layered porcelain fused to zirconia is not strong, “monolithic” zirconia crowns are often made entirely of the zirconia ceramic with no aesthetic porcelain layered on top. Zirconia is the hardest known ceramic in industry and the strongest material used in dentistry. Monolithic zirconia crowns tend to be dense in appearance with a high value and they lack translucency and fluorescence. For aesthetic reasons, many dentists will not use monolithic crowns on anterior (front) teeth.

Translucent_zicornia

Translucency of a zirconia crown

By using crowns made of metal zirconia, then merge the porcelain on the outside, zirconia crowns allow light to pass as a normal tooth would and that gives a natural look, unlike other metal cores that block the light. The normal too hot/cold sensations that can be felt with other crowns does not normally occur because of reduced thermal conductivity, this being another strong point for zirconia.

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Dr. Ng HW

About Dr. Ng HW

Dr. HW NG is a dentist and an oral & maxillofacial surgeon. BDS (MALAYA), MDFS.RCS (ENGLAND), MClinDent (Oral & Maxillofacial Surgery)(MALAYA) Dr. H. W. Ng is an oral & maxillofacial surgeon. He obtained his basic degree as a dental surgeon from University of Malaya in 2001 and become the member of the Faculty of Dental Surgery, The Royal College of Surgeons of England in 2006. He passed his master degree, MClinDent (Oral & Maxillofacial Surgery) from University of Malaya in 2009. Dr. H. W. Ng has more than 5 years of working experience as a general dental practitioner and he worked as a trainee oral & maxillofacial surgeon in a few centres in Klang valley, namely University Hospital, Hospital Tunku Ampuan Rahimah in Klang and Hospital Kuala Lumpur. Currently, he is the visiting Oral & Maxillofacial Surgeon in Columbia Asia Hospital in Bukit Rimau and Puchong, visiting oral surgeon in a few dental clinics in KL and a part-time lecturer in the Oral & Maxillofacial Surgery Department in Dental Faculty, International Medical University (IMU) in Bukit Jalil. His fields of interest are cosmetic dentistry, oral rehabilitation, dental implant and orthognathic (corrective jaw) surgery.

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