Dental treatments dose not just revolve around relieving pain and other symptoms but also deals with improving the function and look or aesthetics of a person, this is where Zirconia crowns come in as a part of Cosmetic Dentistry. There are many names for Zirconia crowns as called in the Industry – Zirconia, Ziconium and Zircon and many other.
Zirconium was first invented by a German chemist – M.H Klaproth in 1789 which is a silicate and is known to be extremely durable and is 100% bio compatible with human body. Due to its bio compatibility is has been used in orthopedic surgeries as well as hip, joint replacements, finger and ear replacements as well. The first instance of use of Zirconium in Dentistry was to fabricate endodontic posts and Implants in 1990’s and later the use in Dental crowns has taken over to get great success due to its durability, natural appearance.
FAQ’s about Zirconium Crowns:
Q. Are Zirconium crowns ‘Metal Free’?
Ans: No, Zirconium is a refined product of a natural mineral and it is reined to produce Zirconium Dioxide which is used in Dentistry.
Q. Is Zirconium a directly found mineral?
Ans. No, Zirconium is a modified form of Zircon which is the natural mineral found in earth. After modifications Zircon is converted into Zirconium or Zirconium dioxide which is used in Dentistry.
Q. What should we call Zirconium crowns – Metal or Ceramic crowns?
Ans. Zirconium Dioxide is called a Ceramic and it is the hardest form of Ceramic found. Hence we can call them as Zirconium or All Ceramic crowns.
Q. Which form of Zirconium is used in Dentistry?
Ans. Technical name of the Zirconium used in Dentistry is – ‘Tetragonal Polycrystalline zirconia partially stabilized with Yttrium Oxide‘.
Q. What are the types of Zirconia?
Ans. There are two types of Zirconia used in Dentistry – Solid and High translucent.
Q. What are the three phases of Zirconia?
Monoclinic phase when heated to 1170 degrees centigrade decreases in volume and enters the Tetragonal phase which when heated to 2370 degrees centigrade enters the Cubic phase.
Tetragonal phase is the toughest at room temperature which is the phase used in Dentistry. It also has the finest grain size in all the three phases.
Zirconia is used in Dentistry as two types – Monolithic Crowns and Layered Crowns
Monolithic Crowns: These are pure Zirconia crowns which are made of a single block of Zirconia making it more durable without any fear of cracks or chipping off but less aesthetic when compared to layered Zircnoia. It is used in posterior crowns and in bridges, but not indicated in anterior teeth due to less aesthetics.
Layered Crowns: These are not pure Zirconia crowns, as it comes with a Zirconia core layered with ceramic on top for improving the aesthetics. It is more aesthetically pleasing but there are chances of ceramic chip off. It is indicated in anterior crowns and anterior bridges only.
Indications of Zirconia Crowns:
- Anterior Crowns – better aesthetics, prevents gingival discoloration commonly seen in PFM or metal ceramic crowns.
- Non Vital or Fluorosis affected anterior teeth with discoloration – Ceramic crowns tend to show the underlying discoloration in such teeth whereas due to the opacity of Zirconia the severe discoloration is masked.
- Bruxism patients complaining of frequent chip off of ceramic seen in high stress areas (posterior teeth). Monolithic Zirconia crowns are best suited for these regions whereas Porcelain used to zirconia are not indicated.
- Patients allergic to other substances, as Zirconia is 100% bio-compatible and non allergic with no reported cases or allergy reported so far.
- Short teeth where less tooth removal should be done, Zirconia crowns require less tooth removal when compared to other crowns.
- High Strength: Monolith or Solid Zirconia crowns have high flexural strength of 1200 MPa
With Zirconia having both high strength for posterior crowns and natural appearance for anterior crowns they can be indicated in almost all cases requiring a crown be it a single tooth or a bridge. As Zirconium is a single material used in making the crown they can be thin and avoid the bulky appearance of the crown which is seen in PFM (Porcelain Fused metal) crowns.
Contra-indications or Disadvantages of Zirconium Crowns:
- Expensive: The first factor which makes patients reject this material is the cost, it is much costlier than it counterpart the PFM crown.
- Wear opposing teeth: If given in patients with bruxism or grinding of teeth, due to the high strength they can wear out the opposing natural tooth.
- Cantilever Pontic: These are not indicated in Cantilever cases where a single tooth is taken as an abudment to replace a missing tooth.
- When Abutment is Mobile
- Zirconium crown is not indicated in Abutment tooth whose height less than 4mm
How much does a Zirconium Crown cost?
A Zirconium crown is costly when compared to a PFM crown and the price varies depending on the country you live in and even the location of the Dental clinic you go to along with experience of the Dentist. On an average a Zirconium dental crown in United States of America costs anywhere between $1000 to $2000 USD based on the type and warranty the company provides.
Same Zirconium crown costs around $200 USD in India, $550 in Mexico etc where Dental tourism is known for.
Tooth Preparation for a Zirconium Crown:
Tooth preparation and the amount of reduction required is different depending on the type of crown being placed – Monolithic or Porcelain fused to Zirconia Crown
- Monolithic Zirconium Crown: 0.6mm thickness overall all around the tooth is sufficient in case of Monolithic crown
- Porcelain Fused to Zirconia Crown: 1.0 mm at the cervical region, 1.0 to 1.5mm in the middle third of the crown along with the occlusal and cusp tips.
Finish Line for Zirconium Crowns:
The advantage of Zirconia crowns is that they can be fabricated on any Finish line – Shoulder, Chmafer, feather edge, knife edge etc.
- For Single Crowns a Deep Chamfer finish line is best suited.
- For Bridges a Modified Shoulder finish line is indicated, where the shoulder with rounded internal angles are prepared.
Impression Material / Technique used for Zirconia Crowns:
Scanning of the Arch with the prepared tooth is the most accurate technique. In scanning there are three types – Direct scanning of the tooth preparation in the oral cavity, Indirect scanning of the model obtained from the impression and Indirect scanning of the Impression.
The Ideal Impression material used to record a Replica is Condensation Silicone or Addition Silicone (Gold Standard).
While taking an Impression a Mandibular Impression Tray is best suited for both Maxillary and Mandibular arches.