REVIEW ARTICLE

CONTEMPORARY ALL-CERAMIC MATERIALS, PART- 1

Shriharsha Pilathadka, Dagmar Vahalová

Charles University in Prague, Faculty of Medicine and University Hospital in Hradec Králové, Czech Republic:
Department of Prosthodontics

Summary: Over the past 35 years, multiple types of all-ceramic materials have been introduced as an ideal alternative for
metal-fused to ceramic. This review covers state-of-the-art development of all-ceramic systems in terms of history, material
composition, fabrication technologies, and structural and strength properties. These materials are proved to be ideal in
terms of mechanical properties and biocompatibility, making metal-free ceramic restorations a realistic clinical alternative
for conventional metal-fused-to ceramic.

Key words: All-ceramic; Glass-ceramic; Particle-filled ceramics; Polycrystalline ceramic; Substructure ceramic; Strength;
Fracture toughness

Introduction review outlines the developments in evolution of all ceramic

systems over the last decade and considers the state-of-
Dental ceramics are the most natural appearing replace- the-art in several extended materials and material proper-
ment material for missing tooth substance available in ties.
a range of shades and translucencies to achieve life like re-
sults. Ceramics were the last to move into the high-techno- Historical background
logy phase of development. During the past decade, the
demand for non-metallic highly biocompatible dental resto- Dental ceramics are composite materials (2, 7). Con-
rative material has, however, markedly increased. The esthe- ventional metal-fused ceramic material composition con-
tic demands made on dental restorations have resulted in tains 75 to 85 % (by volume) vitreous phase (matrix) contains
an increased use of dental ceramics. Esthetically, these ma- and is reinforced by crystalline phase (fillers). Most of the
terials are a preferred alternative to traditional materials ceramics used for metal-fused ceramic contain 15 to 25 %
and ceramics are also regarded as bio-compatible and inert Lucite as crystalline phase. Leucite is a potassium-alu-
materials. Furthermore, the introduction of bonding proce- mino-silicate with a large coefficient of thermal expansion
dures and new luting techniques has increased the general (20x10-6/°C). All-ceramic systems use different types of
acceptance of these all- ceramic systems. In an attempt to crystalline phases. The nature, amount, particle size and
meet the requirements of dental materials and to improve coefficient of thermal expansion of crystalline phases in-
their strength and toughness, several new all-ceramic mate- fluence the mechanical and optical properties of the ma-
rials and techniques have been developed during the past terials (2). In 1965 Mclean and Hughes (13) reported on
decade. These recent developments have attempted to over- strengthening feldspathic glass by adding of aluminium
come the principal disadvantages of inherent brittleness oxide particles (70 % vol), Thereby increasing the strength
and strength by either the use of increasingly complex tech- and fracture toughness. The introduction of “shrink free”
nology or by simplification of existing techniques and/or (16) (Cerastore, coores Biomedical, Lake wood, Colo) and
materials. castable glass-ceramic crown system (12) in the 1980s pro-
Recent material, technical and clinical innovations in vided additional flexibility for achieving esthetics with new
restorative dentistry have increased the complexity of treat- innovative processing methods. The application of compu-
ment planning and decision-making. Many of these ad- ters to ceramic processing started during the late 1980s and
vances have not replaced, but have rather augmented a wide through the 1990s led to introduction of high strength, 100 %
variety of already existing materials or treatment protocols, polycrystalline “substructure” ceramics. This type of cera-
as well as clinical technique and skills. Dentists today can mic doesn’t have glassy components. This allows us to un-
choose from a variety of all-ceramic material systems and derstand that higher strength substructure ceramics are
hence should be familiar with the range of all-ceramic ma- generally crystalline, and highly aesthetic dental ceramics
terial available for fabrication of ceramic restorations. This are predominantly glassy (9).

ACTA MEDICA (Hradec Králové) 2007;50(2):101–104 101

 Classification Tab. 1 and 2 give some commercial examples and com-
position of different ceramic systems,
The term ‘all-ceramic’ refers to any restorative material
composed exclusively of ceramics, such as feldspathic por- Predominantly glassy ceramics
celain, glass ceramic, and alumina core systems and with
any combination of these materials (4). In 2004 Kelly (9) Ceramics can best reproduce the natural optical proper-
also clarified that ceramics as “composite” means a com- ties of natural teeth. They contain an amorphous (non-cry-
position of two or more distinct entities. He proposed the stalline) matrix of glass (vitreous phase). The glass-forming
most simplified way of organizing the panorama of all ce- matrix uses the basic silicon-oxygen (Si-O) network. The sili-
ramic systems as, con atom combines with 4 oxygen atoms, forming a tetra-
a. Predominantly glassy materials, hedral configuration. The larger oxygen atoms serve as
b. Particle filled glasses, a matrix, with the smaller metal atoms tucked into spaces
c. Polycrystalline ceramics. between the oxygen atoms. Thus each silicon atom (Si) is

Tab. 1: Esthetic ceramics: composition, usage, and commercial examples.

Base Fillers Usage Commercial examples
Predominantly glassy ceramics
Feldspathic glass Colorants Veneer for ceramic Alpha, VM7 (Vita)
Pacifiers substructures, inlays, Mark I I (Vita)
High-melting glass particles inlays, veneers Allceram (Degudent)
Moderately filled glass ceramics
Feldspathic glass Leucite (17–25 mass %) Veneer for metal VMK-95 (Vita)
Colorants substructures, inlays, Omega 900 (Vita)
Opaciffers veneers Vita Response (Vita)
High-melting glass particles Ceramco11 (Dentsply)
Ceramco 3 (Dentsply)
IPS d.SIGN (Ivoclar-
Vivadent)
Avante (Pentron)
Reflex (Wieland dental)
Highly filled ceramics
Feldspathic glass Leucite (40–55 mass %) Single-unit crowns, Empress (Ivoclar)
Colorants inlays, inlays, veneers OPC (Pentron)
Pacifiers Finesse All-Ceramic
(Dentsply)

Tab. 2: Substructure ceramics: basic composition, usage, and commercial examples.

Glass Fillers Usage Commercial examples
Highly filled glassy ceramics
Feldspathic glass Leucite (40–55 mass %) Inlays, Onlays, Veneers, Empress (Ivoclar)
Single-unit crowns OPC (Pentron)
Finesse All-ceramic
(Dentsply)
Feldspathic glass Aluminum oxide (55 mass %) Single-unit crowns Vitadur-N (Vita)
Lanthanum Aluminum oxide (70 % vol %) Single-unit crowns, In-ceram
Zirconium oxide (20 vol %) Anterior three-unit bridges Zirconia (Vita)
Modified feldspathic glass Lithium disilicate (70 vol %) Single-unit crowns, Empress2 (Ivoclar)
anterior three-unit bridges 3G (Pentron)
Polycrystalline ceramics
Aluminium oxide More than 0.5 mass % Single-unit crowns Procera (Noble Biocare)
Zirconium oxide Yittrium oxide (3–5 mass %) Single-unit crowns Procera (Noble Biocare)
Zirconium oxide Yttrium oxide (3–5 mass %) Single-unit crowns, Cercon (Dentsply)
Three-unit bridges, Lava (3M-ESPE)
Four-unit bridges Y- (Vita)

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surrounded by four oxygen atoms (O). The atomic bonds in shrinkage can be exactly predicted. These new high strength
this glass structure have both covalent and ionic characteris- materials are used as substructure materials upon which
tics which make them stable. Several such linked silicate unit glass ceramics are veneered, to attain the highest esthetics.
chains form the continuous SiO4 (tetrahedral) network in Due to its more opaque color, to attain better esthetics it
glass. A stable structure, with strong atomic bonds and no- can also be stained (13). The esthetic effect of different all-
free electrons, not only makes glass an excellent insulator for ceramic veneer and core material has been well documen-
thermal and electrical conduction, but also chemically inac- ted (14). Polycrystalline ceramics are formed from powders
tive. The strong covalent and ionic bonds make this ceramic that can be packed only to 70 % of its density. Hence, po-
biocompatible, resistance to chemical and heat attack (2). lycrystalline ceramics shrink about 30 % by volume when it
is fired to attain density. To manufacture well-fitting resto-
Particle-filled glasses ration, the amount of shrikage is predicted and compen-
sated by enlarging the die (1).
Fillers are used in this glass matrix to improve mechani-
cal properties and to control optical effects such as opales- Transformation-toughened ceramic
cence, colored, and opacity. These fillers are basically
crystalline but can be also particles of a higher melting glass. This technique relies on a crystal structure change
One of the first fillers used in ceramic (for conventional under stress to absorb energy from cracks. It involves the in-
metal fused ceramic) is leucite. It is a potassium aluminum corporation of a crystalline material that is capable of
silicate mineral with a large coefficient of thermal expansion undergoing a change in crystal structure when placed under
(20 x 10-6/oC) when compared to feldspathic glasses (8 x stress. The crystalline material usually used was zirconium
10-6/oC). Adding the leucite 17 to 25 mass % to feldspathic oxide. At sintering temperature zirkonia is a tetragonal
glass to match thermal expansion of the alloys used in metal form, and at room temperature it will be in monoclinic
ceramic prevents thermal mismatch. Along with this, leucite form. The monoclinic form occupies about 4.4 vol % more
has the same refractive index as that of feldsapthic glass. than the tetragonal form. This monoclinic phase is unstable
The strength of ceramics was increased considerably by at room temperature. Stabilization can be achieved by
dispersing the suitable fillers through out glass, called “dis- adding a small amount of (3–8mass %) of calcium and
persion strengthening”. The first filler used for this was alu- yttrium. When the stress is localized, any areas on this ma-
minum chloride 50 mass %. In 1965 MacLean developed terial is sufficient to transform the grains in the vicinity to
aluminum porcelain, using this to improve the strength of a monoclinic stage. The volume increase of 4.4 % squeezes
ceramic without sacrificing the esthetics. This alumina rein- the crack closed. These are the potential substructure ma-
forced core material was used to fabricate the all-ceramic terial for posterior crowns and FPDs (9).
restoration (4). Leucite is also used for dispersion strengt-
hening. The all-ceramics having leucite as fillers are hot pres- Strength and Fracture Toughness
sed into mold to attain the substructure for crowns: example
Empress, Empress 2 Ivoclar-Vivadent [Schaan Liechtenstein]; Strength and fracture toughness consideraion is impor-
and Finess All-ceramic, Dentsply [York, Pennsylvania]. tant for the assessment of structural value. In 1999 Kelly,
suggested the ideal methods to test the failure testing so as
Polycrystalline ceramics to mimic clinical failure (8). New all-ceramic systems have
improved flexural strength and fracture toughness. The
This type of ceramic has no glassy components. All the most documented failure mode of all-ceramic is by cone
atoms are packed into a regular pattern making it dense and cracks, radial cracks and quasiplastic damage (11). But ra-
stronger. They are difficult to fabricate into different shapes. dial cracks, which originate from the cemented surface, are
The availability of the computer made fabrication possible. the dominant failure mechanism. It was also suggested that
In 1993 Anderson M. and Oden A (1), with the coopera- strength and selection of core material is important than
tion of Noble Biocare AB (Sweden), introduced the Procera the veneer porcelain because core material supports more
system. This is a computer-aided designing and computer- of the flexural load during function.
aided manufacturing system (CAD-CAM). At the design
station, a computer-controlled optical scanning device Strength
maps the surface of the master die and sends it via modem
to the production facility (3). This 3-D data set is used to It is the more frequently encountered physical property
create an enlarged die upon which ceramic powder is packed of all-ceramic systems in professional literature. But it is the
(Procera; Noble Biocare, Goteborg, Sweden) or to manu- universal measure of the type and nature of cracks (re-
facture an oversized part for firing by machining blocks of sistance to crack initiation), fracture toughness (resistance
partially fired ceramic powder (Cercone, Dentsply Proste- to crack propagation) and influence of water. Strength is
tics; Lava, 3M-ESPE [Seefeld, Germany]; Y-Z, Vita Zahn- not a measure of inherent material property in judging the
fabrik [BadSackingen, Germany]). These approaches rely material. Fracture toughness is better to compare the struc-
upon well-characterized ceramic powders for which firing tural performance of different systems (9, 5).

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Tab. 3: Comparison of Flexural strength and Fracture toughness values.
System manufacturer Core material Flexural-strength Fracture toughness
(Mpa) (Mpa/m1/2)
Empress II (Ivoclar North America, Amherst, NY) Lithium Disilicate 300–400 2.8–3.5
InCeram Alumina Glass-infiltrated alumina 236–600 3.1–4.61
(Vita Zahnfabrick, Bad Sackingen, Germany)
In-Ceram Zirconia Glass-infiltrated alumina 421–800 6–8
(Vita Zahnfabrik, Bad sackingen, Germany) with 35 % partialy
stabilized zirkonia
ProceraAllCeram Bridges Densely sintered 487–699 4.48–6
(Noble Biocare, Goteborg, Sweden) high-purity alumina
Cercon (DENTSPLY Ceramco, Burlington, NJ) Y-TZP 900–1200 9–10
DCS-Precident DC-Zircon Y-TZP 900–1200 9–10
(Dentsply Austenal, York, Pa)
Lava (3M ESPE, St. Paul, Minn) Y-TZP 900–1200 9–10

Fracture toughness the success rate, selection criteria, and clinical aspects of
all-ceramic systems.
Because ceramics fail via crack growth from existing
flaws, it is better to measure how it happens. Cemented all- References
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Submitted December 2006.

Accepted April 2007.
Corresponding author:

Shriharsha Pilathadka, M.D., University Hospital Hradec Králové, Department of Prosthodontics,

Sokolská 581, 500 05 Hradec Králové, Czech Republic, e-mail: shreeharsha_70@yahoo.co.in

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