2. DEFINITIONS
• Ceram : A heat treatment process that converts a specially formulated
glass into a fine grained glass-ceramic material
• Ceramics :Compounds of one or more metals with a non metallic element,
usually oxygen. They are formed of chemical and biochemical stable
substances that are strong, hard, brittle and inert non-conductors of
thermal and electrical energy.
• Feldspathic porcelain : Porcelain fabricated from the natural mineral group
feldspar. The material is composed of compounds of oxygen with lighter
metals and non-metals and is predominantly an amorphous (non-
crystalline) matrix With one or more crystalline phases
3. Dental Ceramics
• Dental ceramics are usually
referred to as non-metallic,
inorganic structures primarily
containing compounds of oxygen
with one or more metallic or
semi-metallic elements, such as
aluminum, calcium, lithium,
magnesium, phosphorus,
potassium, silicon, sodium,
zirconium and titanium
4. PORCELAIN
• The term porcelain is referred to
a specific compositional range of
ceramic materials made by
mixing kaolin, quartz and
feldspar in proper proportioning
and fired at a high temperature.
5. • Porcelain is essentially a white,
translucent ceramic that is fired
to a glazed state. Dental
porcelains may be classified
based on their fusion
temperature, microstructure and
processing technique
6. Classification:-
• According to their fusion
temperature, porcelains are
classified into 4 types
High fusing Medium fusing
Low fusing Ultra low fusing
porcelains
7. • classified as “ low fusing because they sinter into a relatively dense, rigid
mass at temperatures several hundred degrees below those required to
fuse the denture tooth and pontic porcelain
• high- or medium-fusing porcelains can be made visually similar to low-
fusing “ bake-on porcelains, high-fusing porcelains are not designed to be
powdered and re-fused.
• The proportion of glass in higher fusing porcelains is sufficient to allow for
glazing of the surface when heated to temperatures in excess of 22(H) F
(1200° C), but such temperatures are unsuitable for metal veneering.
8. • Basically, three types of low-fusing porcelain are used;
• ( 1 ) porcelains for metal veneering,
• (2) stains and glazes,
• (3) aluminous porcelains for jacket crowns.
9. Stains and glazes
• Stains and glazes fuse at temperatures approximately 150° F (83.3° C) lower than
body or opaque porcelains.
• Their thermal expansion coefficients are probably nearly equal to or slightly lower
than low-fusing body porcelains.
• Stains are highly colored glasses that are added superficially to porcelain
restorations to adjust the shade or create special effect such as craze lines,
shadows, simulated restorations, hypoplasia, etc.
• Glazes, although chemically similar to stains, are uncolored (clear) and are used
to provide a glassy surface after occlusal, cosmetic, or morphologic corrections
have been made by grinding a previously glazed surface
10. Aluminous porcelain
• composed of a mixture of lowfusing powdered glass and powdered
aluminum oxide (alumina).
• Its principal use is in the construction of porcelain-jacket crowns or
special jacketlike crowns of porcelain fused to an oxidized tin-plated
platinum foil, which remains in place as an integral part of the
restoration.
• This technique can produce a highly cosmetic crown that resembles
the classic porcelain jacket, but has greater strength.
11. • Alumina is partly soluble in low-fusing glass, and its presence strengthens the
glass, making it less sensitive to crystallization and elevating its fusion
temperature.
• Aluminous porcelains are fired at temperatures up to 200° F (110° C) higher than
bake-on porcelains and are usually held at maximum temperature for several
minutes to allow for densification.
• susceptible to overfiring and loss of contour than are bake-on porcelains.
• Aluminous porcelain kits contain opaque body and modifying porcelain powders,
which are analogous in purpose to other low-firing porcelains.
12. FABRICATION
• The available materials for all-ceramic prostheses are fabricated
either as full contour/monolithic/anatomic constructions or as sub-
structures/copings/frameworks by usually employing one of the
following fabrication modes:
• 1. pressing
• 2. milling
13. • Pressed restorations involve pattern fabrication, in vesting and
burnout procedures similar to alloy casting procedures.
• The ceramic ingots are then heat-pressed into the mould cavity in a
special ceramic press furnace, cooled and retrieved.
• Usually, with the pressed technique, the sub-structure is obtained by
pressing, which is subsequently layered and stained to yield aesthetic
all ceramic restorations.
14. • Milled restorations can be fabricated either by manual designing and
hand milling or by computer-aided designing (CAD) and computer-
aided machining (CAM).
• Hand milling procedures involve fabrication of the desired pattern
manually which is then copied by the milling unit to mill the blank
simulating the fabricated blank. The term copy milling is also used to
denote this procedure since the pattern design is copied during
milling
15. The work is further subjected to either of the following:
1. staining and glazing procedures-if full contour units were fabricated
2. layering/veneering with ceramic followed by staining and glazing -if
sub-structures were fabricated
16. • The layering/veneering ceramics, stains and glazes are usually one of
the compatible feldspathic, fluorapatite or leucite-based powder-
liquid systems that are used for metal ceramic veneering.
• The layering, firing, glazing and staining procedures are similar to
those followed for metal ceramic prostheses.
• Lithium disilicate is also used as a veneering material and is usually
hot-pressed over the all-ceramic cores (IPS e.max ZirPress).
17. FABRICATION OF ALL-CERAMIC PROSTHESES
BY MILLING (CAD CAM) TECHNIQUE
• 'Digital Functional Prosthetics (DFP)', which is the method for
fabricating functional, interference-free, prosthetic restoration
digitally in the laboratory.
21. Data Acquisition/Scanning
• The scanning or mapping software aids data acquisition of the clinical
data, that is the hard and soft tissue details from the casts and dies,
the occlusal relationship and tentative design of the wax pattern are
scanned and con verted as digital files.
• This is the first step in the fabrication and is crucial because the
design process is based on and limited by the data acquired.
22.
23.
24.
25.
26.
27.
28. Milling (CAM)
• The software regarding the type of restorative material blank, blank
thickness, milling process (whether wet or dry), miling tools,
Sequence of milling (in case of multiple units) etc. Once the options
are selected and finalised, the virtual has options design is ready for
execution
29.
30.
31.
32.
33. Internal Colouring/Staining of Milled Units
• To achieve a better shade match, formulated colour solutions are
specially available that can be applied on the milled work prior to
sintering
• This is especially important for mono lithic works as they will not have
any porcelain layering done to improve the aesthetics later
34. • 1. Dilute the concentrated
colour appropriately as per
manufacturer's instructions
• 2. Carefully apply the colour
with a thin brush to the
body
• 3. Copings are tinted with
one uniform base shade
only
35. • 4. Seat the work carefully onto a retractory
sintering tray/bowl containing yttrium-
stabilised spherical zirconia sintering bead
36. Sintering
• Sintering is carried out in a special sintering furnace. The partially
sintered (green) zirconia is converted to dense, fully sintered stabi
lised zirconia.
• During sintering, there is homogenous distri bution of temperature
throughout the furnace chamber and constant temperature control
due to the heating ele ments present. This ensures that frameworks
reach their optimal density and strength.
37.
38. • Select the sintering programme/cycle depending upon the number of
units/ sinter bowls.
• For single crowns, a shorter cycle is available.
• For multiple units or large frameworks, the longer sintering cyee 1s used
for ensuring complete sintering.
• The sintert; temperature can range between 1450 and 1500°C depending
on the sintering programme. lypc sintering cycles have a heating stage, a
tempera stage (Fig. 14.57C), there is a rise in the temperature holding stage
and a cooling stage.
39. • During the heating within the furnace at a constant rate (eg. 8°C/min)
to reach the peak temperature.
• The peak temperature is held constant for the set holding period ro
1-2 h followed by cooling down to 200°C (detault temperature) at a
steady cooling rate (e.g. 5°C/min) which may be between 6 and 12 h
dependiing on the selected cycle.
40. Layering
• This is achieved with any of the compatible commer cially available
feldspathic or leucite veneering ceramics
47. SUMMARY
• The procedures to fabricate all-ceramic crowns by CAD and computer-
aided milling has been outlined in this chapter.
• Milled units can be finished with either staining and glazing
procedures if full anatomic constructions are made or by layering with
suitable ceramics followed by staining and glazing
48. REFRENCES
• RUDD AND MORROW DENTAL LABORATORY PROCEDURES 2ND
EDITION
• RUDD AND MORROW DENTAL LABORATORY PROCEDURES SOUTH
ASIA EDITION
