Brief presentation of the basics of ceramics used in dentistry (classification and properties). Made for dentistry 2nd year prosthetic technology subject lecture.

1. Dental Ceramics
Adam Bilski
Palacky University, Olomouc, 2020

2. Dental porcelain (ceramic)
– material used by dental
technitians for creating
biocompatible dental
restorations (crowns,
bridges, veneers).
They are esthetic,
biocompatible, insoluble,
hardness 7 on Mohs scale
(out of 10).
They also have
translucent qualities,
giving them more realistic
look.

3. Use:
In all branches of dentistry, like:
• With metal for crowns, bridges (PFM-porcelain fused metal)
• Crowns, veneers
• Dentures
• Inlays, onlays, overlays
• All ceramic bridges
• Implants
• Orthodontic braces

4. Characteristics:
• High melting point
• Low thermal + electrical conductivity
• Hight compression strength + stiffness
• Highly esthetic
• Brittle
• Very biocompatible

5. „Ceramic restorations are indicated
where aesthetics is needed and when the
size of the preparation exceeds the limit
for the use of direct composite resins“

6. Contraindications for ceramic
restorations:
• Bad hygiene
• Deep subgingival preparation
• Impossible moisture control
• Bad cooperation with patient
• Low biological factor of the
tooth
• Price

7. Inner structure:
• Ionic and/or covalent bondings between
atoms – hardness, stiffness, being brittle =
they are strong to compression, weak to
tension
• Microstructure:
the more glassy (noncrystalline) - the more
transluscent
the more crystalline – the more opaque
• For translucency what matters – particle
size, particle density, refractive index,
porosity

8. Composition
• Depends on type of porcelain, can vary on producer as well
• Mixture of glass and crystal components
• There are 3 main components:
1. Feldspar (75-80%) (potassium aluminium silicate)
2. Quartz (silica) + SiO2 crystals
3. Kaolin clay (3-5%) (aluminium silicate) (for binding)
Additionally: glass modifiers, leucite (strength, toughness,
coefficient of thermal expansion), pigments (metallic oxides),
fluorescing agents

9. • Feldspars – mixtures of KAlSi3O8 – NaAlSi3O8 –
CaAl2Si2O8 that fuse during melting at 1150*C,
producing glass matrix, crystalline leucite. There can be
potash, soda and both feldspars combined with silica
network.
Feldspars are a MIX OF SILICA AND ALUMINA =
aluminosillicates with potassium and sodium, found in
nature
• Quartz – remained unchanged during firing, remains as
fine crystalline dispersion through the glassy phase

11. Classifications of ceramics:
• A lot of them…
• Ceramics can be classified by:
- Composition (including glass content – Kelly’s classification)
- Microstructure
- Manufacturing
- Type
- Substructure material
- Type of fusing
- and probably many more..

12. Composition
Predominantly glass:
- highly esthetic
- feldspathic porcelain
- veneers or vennering
metal-cer.
- produced BY HAND
(powder + liquid)
Particle-filled glass:
- fillers are added to glass
matrix (higher mechanical
properties)
- fillers = crystalline particles
of high melting glasses
- for all kinds of restorations
- produced by milling
(CAD/CAM) or sintering
(pressing)
Polycrystalline:
- NO GLASS
- aluminium oxide, zirkonium
oxide
- atoms packed regularly –
VERY tough
- good to put a nice veneer
on top of a polycrystalline
one

13. The glass-forming matrix of
dental porcelains uses the
basic silicone oxygen (Si-O)
network with the silicon atom
combining with 4 oxygen
atoms, forming a tetrahedral
configuration.
The larger oxygen atoms serve as a matrix,
with the smaller metal atoms such as
silicone inserted into spaces between the
oxygen atoms.
Reinforcing the ceramics we add leucite or
alumina, to form crystal glass composites.

14. Kelly’s classification

15. Microstructure
There are 4 categories:
Category 1: glass-based systems (mainly silica)
Category 2: glass-based systems (mainly silica) with fillers, usually
crystalline (typically leucite or a different high-fusing glass)
Category 3: crystalline-based systems with glass fillers (mainly
alumina)
Category 4: polycrystalline solids (alumina and zirconia)
*Leucite – to modify CTE (coefficient of thermal expansion)
and inhibit crack propagation, improving strength

16. Cat. 1 - containing mainly silica, and various amounts of alumina.
They have low flexular strength, therefore usually used for
veneers.

17. Cat. 2 – they are glass, like cat 1, but with added or grown
different crystals in the matrix (like leucite (increase potassium
oxide), lithium disilicate (add lithium oxide) and fluorapatite). You
can use premanufactured blocks of these materials in CAD/CAM
(VITABLOCS Mark II), proven the best machinable glass for
inlays and onlays manufacturing. Great, because there is no risk
of porosity. There are 3 sub-categories to these:

18. * Subcategory 2.1 - Low to moderate leucite-containing
feldspathic glass. AKA feldspathic porcelains. In the past they
had random distribution of leucite crystals, being weaker than
enamel. Now they are more even distribution, with finer crystals,
giving it more strength.
Most-commonly used as veneers, for metal-ceramic restorations.
Feldspathic veneer A metal–ceramic restoration

19. * Subcategory 2.2 - High leucite-containing glass (50%) e.g. IPS
Empress (increased fracture resistance, improved thermal shock
resistance, and resistance to erosion) - used on space vehicles
heat shields too. Adding 2nd phase crystals to the glass improves
strength.
Inlays, onlays, anterior crowns and veneers.
Pressable ceramic with leucite crystals Pressable ceramic restoration

20. * Subcategory 2.3 - Lithium disilicate glass ceramics e.g IPS
Empress II, IPS e.max. Crystal content increased to 70%
(improving strength), so we can call it highly filled glass matrix.
On top of it we can add some veneer porcelain with fluorapatite
(for final shape and shade of the restoration).
This material is quite translucent thanks to the low refractive
index of the lithium disilicate crystals present inside.
Can be used for almost all restorations.
A scanning electron micrograph of the
microstructure of a lithium disilicate
glass- ceramic. Acid etching reveals
the fine crystal structure.

21. e.max restoration

22. Cat. 3 – crystalline-based systems with glass fillers
(interpenetrating phase ceramic), e.g VITA In-Ceram (VITA
Zahnfabrik) – family of ceramics covering all ceramic
restorations, including veneers, inlays, onlays, anterior and
posterior crowns, and bridges.
Interpenetrating, as they have two phases that are intertwined
and extend continuously from the internal to the external surface
– great defence against cracks. According to the esthetics we
choose which one we use for what restoration.
VITA In-Ceram Alumina – visible 2 phases

23. VITA In-Ceram SPINELL crown

24. Cat. 4 – polycrystalline solids (aluminia + zirconia).
Solid sintered monophase ceramics are materials formed by
directly sintering crystals together without any intervening matrix
to form a dense, air-free, glass-free polycrystalline structure.
Newer zirconia – not pure – has metal oxides added - Partially
stabilised zirconia is one of the materials that allow production of
reliable multi-unit all-ceramic restorations for high-stress areas,
such as the posterior region of the mouth.
Zirconia has the apparent physical properties to be used for
multi-unit anterior and posterior fixed partial dentures.

25. Alumina ceramic

26. Guide:
http://www.moderndentistrymedia.com/may_june2014/mclaren.pdf

27. Important!
Glass-based systems (categories 1 and 2) are etchable and thus
easily bondable.
Crystalline-based systems (categories 3 and 4) are not etchable
and thus much more difficult to bond.
Categories 1–3 can exist in a powdered form that is then
fabricated using a wet brush technique, or they can be
preprocessed into a block form that can be pressed or machined.
As a rule, powder/liquid systems have much lower strength than
pre-manufactured blocks do owing to a much larger amount of
bubbles and flaws in the finished restoration.

28. Manufacturing
Powder/liquid system – either conventional or slip-casted
- Conventional:
a) compaction –
1. mix powder and water until it’s a paste
2. Brushing, whipping, vibrating (on a die previously coated with
platinum foil)
b) firing
c) glazing – to eliminate porosity (strength + bacterial
colonization) to create smooth, shiny surface, either by low
fusing glasses applied to crown construction and fused, or
by final firing done by fusing superficial layer.
- Slip-casted – condensation of aqueous porcelain on die.

30. Pressable ceramics:
- similar to injection moulding
- Empress restorations
- inlays, onlays, veneers,
single-unit crowns
- esthetic
CAD/CAM:
- short and easy

31. Compaction explained by Dr Voborna:
1. mixing of powder with water and binder to form a paste by
spatulation
2.brush application, whipping or vibrating, that is aimed at
compaction, which is painted over the die that is previously
coated with platinum foil -----) This paste is made from different
porcelain powders to mimic the esthetics of natural teeth ------)
Usually, an opaque shade (to mask metal core), a dentin shade
and then enamel shade is used -----) The enamel shade is
selected from shade guide matched to patients actual tooth
shade

32. Type:
- Feldspathic
- Leucite
- Aluminous porcelain
- Glass infiltrated (alumina or zirconia)
- Glass ceramics

34. Division according to fusing:
- High fusing
1300 – 1350*C
ONLY Denture teeth
highest strength and stability
- Medium fusing
1100 – 1250*C
all-ceramic restoratives
- Low fusing
850 – 1050*C
PFM restorations (Porcelain
Fused to Metal)

35. Substructure material:
• Alloy
- no noble metals
- corrosion prevention by surface oxide layer by chromium
- primarily nickel
• Zirconium oxide (ZrO2)
- for multiple-unit, all-ceramic posterior teeth restorations
- depending on minor components zirconia may be in different
phases
- flexural strength – 900-1100 Mpa
- may be in form of zirconia blocks – milled into framework,
crowns, bridges
- extremely resistant to chemical, mechanical and thermal
factors

37. PFM pros and cons:
+ strong core
+ easy cementation
+ less expensive than full ceramic
- not perfect aesthetics (not as translucent,
metallic margin, ions may discolor porcelain,
metal can fracture it too)
Silver discolorates, palladium eliminates the
discoloration and improves strength.

38. All-ceramic restorations
- Amazing esthetics
- Has to be made from reinforced ceramics (added glass,
alumina, leucite, magnesia and zirconia)

39. Etching
For glass ceramics – we etch with HF (9%)
Luting with composite - dual-cured materials
For no-glass ceramics – we don’t etch
Conventional luting – GIC

41. Thank you for attention 