Zirconia in Dentistry :
Mohamed Mahmoud Abdul-Monem
Dental Biomaterials Department
• What is Zirconia ?
• History of Zirconia as a biomaterial
• Zirconia phase transformation
• Zirconia (Ceramic steel)
• Properties of Zirconia
• Uses of Zirconia
• Uses of Zirconia in dentistry
• Bonding to Zirconia
• Ceramics are very important in the science of
• Among all dental ceramics, Zirconia is the dental
biomaterial of choice in contemporary
What is Zirconia ?
• Zirconium oxide (ZrO2), or zirconia, is a metal
oxide that was identified as a reaction product of
heating the gem( zircon) by the German chemist
Martin Heinrich Klaproth in 1789 .
• The name of the metal, zirconium, comes from
the Arabic Zargon (golden in colour) which in
turn comes from the two Persian
words Zar (Gold) and Gun (Colour).
• Zirconia occurs as a natural mineral called
• Baddeleyite was first found in Sri Lanka in 1892.
It was named for Joseph Baddeley.
• This mineral contains 80–90% zirconium
oxide(zirconia). The major impurities are usually
TiO2, SiO2 and Fe2O3.
Zirconia phase transformation
• Zirconium oxide exists in three different crystal
structures: monoclinic at room temperature,
tetragonal at ~1200°C and cubic at 2370°C.
• Zirconium oxide is transformed from one
crystalline state to another during firing.
• At the firing temperature, zirconia is tetragonal and
at room temperature, it is monoclinic, with a unit
cell of monoclinic occupying about 4.4% more
volume than when tetragonal.
• The volume expansion caused by the cubic to
tetragonal to monoclinic transformation induces
large stresses, and these stresses cause ZrO2 to
crack upon cooling from high temperatures.
• When the zirconia is blended with some other
oxides, the tetragonal and/or cubic phases are
• Effective stabilizers include magnesium oxide
(MgO), yttrium oxide (Y2O3, yttria), calcium oxide
(CaO), and cerium(III) oxide (Ce2O3).
• Zirconia is often more useful in its phase 'stabilized'
state. Upon heating, zirconia undergoes disruptive
• By adding small percentages of yttria, these phase
changes are eliminated, and the resulting material
has superior thermal, mechanical, and electrical
• In some cases, the tetragonal phase can be
• If sufficient quantities of the metastable
tetragonal phase is present, then an applied
stress, magnified by the stress concentration at a
crack tip, can cause the tetragonal phase to
convert to monoclinic, with the associated
• This phase transformation can then put the
crack into compression, retarding its growth,
and enhancing the fracture toughness.
• This mechanism is known as transformation
toughening, and significantly extends the
reliability and lifetime of products made with
Zirconia = Ceramic steel
• It may be noted that zirconia has many features
in common with systems based on iron
(stainless steel )as :
1. Three allotropes
2. Martesnitic transformation
3. Metastable phases
Thus it is known as ceramic steel (Garvie et al ,
Properties of Zirconia
Physical properties :
• Low thermal conductivity (20% that of alumina)
• Chemically inert and corrosion resistant
Hydrothermal degradation of zirconia
• Hydrothermal degradation of zirconia occurs
between 200-400 ˚C .
• Longer exposure times at oral temperature may
also degrade zirconia leading to increased
surface roughness , fragmanted grains and
Uses of Zirconia
• Protective coating on particles of TiO2 pigments.
• Refractory material .
• In Oxygen sensors.
• Thermal barrier coating (low thermal
conductivity) in jet and diesel engines.
• Ceramic knives.
• Diamond simulant (cubic zirconia).
Uses of Zirconia in dentistry
• Crowns and bridges
• Inlays and Onlays
• Endodontic post and cores
• Fillers in dental composite
• Implant abutments
• Orthodontic brackets
• Pedodontic crowns
Zirconia as fillers in dental composite
zirconia/silica with a median
particle size of approximately
3 microns or less
Zirconia CAD/CAM Blocks
Soft machining Hard machining
• Mostly, they are
fabricated from a porous
block, milled oversized by
about 25%, and sintered
to full density in a 4 - 6
• Alternatively, fully dense
blocks are milled.
• However, this approach
requires approximately 2
hours of milling time per
unit whereas milling of
the porous block
necessitates only 30 to 45
minutes for a three-unit
Zirconia sintering Temperature
• Currently available zirconia for soft machining
of dental restorations utilize final sintering
temperatures varying between 1350 and 1550 ◦C
depending on the manufacturer.
• The microstructure of 3Y-TZP ceramics for
dental applications consists of small equiaxed
grains (0.2–0.5 µm) in diameter, depending on
the sintering temperature
Zirconia toughened alumina ZTA
• 70-90% alumina
• 10-20% zironia
• Toughened by a stress-induced
transformation mechanism of
zirconia leading to
compressive stresses within
• The strength of alumina is
doubled and toughness is
increase 2-4 times .
Surface treatment of zirconia implants
• Changing the surface chemistry using bioactive
coating with different materials (calcium
phosphates, bisphosphonate, collagen, etc.)
• Optimizing surface architecture and
microroughness using different techniques.
Scanning electron microscopy (SEM) observation of fibroblasts cultured on
zirconia: cells grow on the whole zirconia surface, covering it with a cellular
Zirconia individualized CAD/CAM implants
• Austrian Surgeons have
designed a system to produce
via CAD/CAM individualized
Zirconium Dental Implants for
use in case of immediate
• In short, after a tooth is
extracted it is scanned and a
zirconium copy is milled.
• The milled copy has macro-
retentive features which help
secure the new implant in the
extraction socket. They report
a 90% success rate.
Bonding to Zirconia
• One problem of zirconia application is its adhesion
to different substrates.
• Surface treatment of zirconia produces an activated
surface in different applications.
• Since zirconia is resistant to aggressive chemical
• Very aggressive mechanical abrasion methods
must be used to provide sufficient surface
Conventional surface treatment
(1)acid etching with hot acids
• This procedure based on corrosion–controlled
process and metallic nature of pure zirconium.
• It selectively etches the zirconia and creates
micro-retentions on the surface by modifying
the grain boundaries through removal of the
less arranged atoms .
• Hot acid etching with combinations of highly
corrosive acids (HNO3, H2SO4, and HF)
improves both initial bond strengths and
• Sulfuric acid in solution with hydrogen
peroxide (H2O2) (Piranha solution) appeared
to have a positive effect on the bonding of
zirconia with resin cements .
(2)Abrasion with diamond (or other)
rotary instruments (can cause microcracks)
(3)Coatings of low melting temperature
porcelain micro pearls.
(4)Selective infiltration etching (SIE)
• SIE uses a heat-induced maturation process to
pre-stress surface grain boundaries in ZrO2 to
allow infiltration of boundaries(1) with molten
• The glass is then etched out (2)using HF,
creating a network of inter-granular porosity
that allows nano-mechanical interlocking of
resin cement .
(5)Fusion sputtering :
• Fusion sputtering is a new technique used to create
rough zirconia surface by spraying an air-water jet
carrying microscopic zirconia particles onto
unsintered zirconia frameworks.
• Upon impact with the surface, the particles achieve
good contact and adherence.
• After sintering, these particles become
structurally fused with the underlying framework
and create undercuts suitable for establishing
mechanical retention with resin adhesives.
(6) Air abrasion with alumina (Mechnical)
low pressure particle abrasion (LPPA)
(7)Application of different laser types
(8) Plasma oxyfluoride
This process presents a method to chemically
modify zirconia by creating thin oxyfluoride
conversion layer on its surface that is receptive
to organosilane attachment .
Conclusion in bonding to zirconia
• The use of phosphate monomer luting cements
on freshly air-abraded zirconia is the simplest
and most effective way for zirconia
• These resin cements have shown good
MDP resin cements
• MDP-containing resin cement
continues to be a popular
choice for luting ZrO2
prosthetics in clinical
applications due to its low
failure rate and loss of
• The hydroxyl groups of the
passive zirconia surface bond
to the phosphate ester group of
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