Porcelain fracture

DR. BAHJAT ABU HAMDAN
CONSULTANT PROSTHODONTIST
BDS,CES,DSO
DAMASCUS UNIV. PARIS V,VI,VII UNIVS.
Porcelain fracture, reasons
and management.

A. Introduction
 In spite of the sophisticated structure of the hard
tooth tissues, enamel and dentin are prone to
extended damage in the oral cavity. However it is
a real challenge to find a man made materials
that compete with these hard tissues.
 In addition to the mechanical properties, a
dental material should be biocompatible,
aesthetic, corrosion resistant, easy to process
and reasonable inexpensive.
2

A. Introduction.
 Ceramics are widely accepted and used in
dentistry with a high degree of general
success.
 However, fracture of these restorations does
occur and usually frustrates the dentist and
the patient.
 In case of PFM, incidence of porcelain
fracture is increased with the long term
survival due to cyclic fatigue.
3

A. Introduction.
 Incidence of porcelain fracture was the
second most common cause for FPD
replacement.
 Porcelain fracture is considered the most
common cause failure with PFM Crown.
(Walton et al)
Clinical study revealed that prevalence of
ceramic fractures is 5-10% over 10 years of
use.
4

A. Introduction.
 In all ceramic restorations, veneering porcelain
fracture remains one of the primary complication
affecting longevity.
 Clinical evaluation of 323 porcelain laminate
veneers, over a period of 3-11 years, reveals
failure due to porcelain fracture was 4% and 97%
of the cases was satisfactory.
(Maria G-Ruiz et al)
Chipping rates are 3 to 50% for FPD with
zirconia framework after 3 years and 2.9% with
metal framework.
5

B. Porcelain restoration
Types of porcelain restorations ;
 • Simple FeldspathicVeneers
 • Porcelain Jacket Crowns and Bridges ( PFZ)
• Metal-Ceramic Crowns and Bridges
 • Inlays and Onlays
 • Implant Superstructures.
6

C. DENTAL Porcelain composition
7

C. Dental porcelain…
 Indications for feldspathic porcelains • Highly esthetic veneers
or anterior crowns in cases where color masking is not an issue
 Indications for leucite-reinforced ceramics • Esthetic veneers
and anterior crowns • As a layering porcelain on leucite-
reinforced, lithium disilicate, alumina, or zirconia cores
 Indications for lithium disilicate ceramics; Veneers Premolars and
molars - inlays, onlays and crowns • Three-unit bridges – anterior
and premolar region
 Indications for zirconia-based ceramics • Anterior and posterior
crowns • Bruxers – full-contour crowns • Anterior and posterior
bridges (maximum 14-unit bridges, span depends on product and
number of abutments) • Endodontically treated teeth • Implant
abutments • Inlay bridges • Maryland bridges • Block-out of
darkened tooth structure or cores.
9

C. Dental porcelain…
 A summary of the strength of all-ceramic
materials is shown in below:
 Silica-based Ceramics Flexural Strength
Feldspathic porcelain 65-120 MPa
 Leucite-reinforced ceramic 120-140 MPa
Lithium disilicate ceramic 300-400 Mpa
 Non-silica-based
 Ceramics Alumina 650 Mpa
 Zirconia 800-1500 MPa
10

D. Contributing factors..
technical
1. surface treatment and design of the metal
coping; the oxide layer is necessary for
bonding the metal to the porcelain.Absence
of the oxide layer or thick layer have been
shown to increase the risk of bonding and
porcelain fracture at this level. (Graig et al).
 The design of the metal framework should
ensure strength, avoid sharp angles and has
no flexibility, and ensure uniform thickness of
porcelain.
11

technical
 With zirconia, form and thickness, copings
should resemble dentinal tooth substructures
with relatively even and uniform thickness of
enamel over dentin.
 Zirconia is a (milled) material and could not exist
without CAD/CAM, with the best zirconia using
“virtual design”. Copings of standard thickness
(that is, 0.5 millimeter) do not account for
individual anatomical crown.
 Anatomically designed copings are better able
to reduce chipping.
13

Technical.
 2. Compatibility between coefficient of
thermal expansion; difference of coefficient
about 0.5x1/1000000 between the metal and
the porcelain is desirable. Such relation put
the porcelain under compression after firing.
 For PFM veneering leucite is added to the
feldespath to adjust the thermal expansion
compatibility with the metal. Fast cooling
causes cracks, at any step of sintering, and
later on breaks.
15

technical
 In PFZ, mismatch of CTE between the core
and veneer has resulted in an increase in
failure loads for Zr-ceramic systems.
 (Denry I et al) Another
issue concerning the incidence of chipping in
PFZ is the low thermal conductivity of the
zirconia.
 (Baldassarri M. et al)
16

technical
 3. Ceramic build up and firing techniques;
porcelain cracks can be caused by air
entrapment and porosity due to lack of
densification.This lead to cracks coupled with
low fracture toughness.
 Rate of cooling affect the stress concentration at
the metal ceramic interface.
 Repeated firings or excessive temperatures are
regarded as causes of super facial imperfections.
(Baretto, M.T.)
17

technical
 4.Thickness of porcelain; Increased porcelain
thickness leads to a fragile restoration, this is
caused by the increase of stress concentration
and weakness of the porcelain under tension.
 A fairly uniform thickness of porcelain (1.5-2mm)
minimize the formation of microcracks.
 The incidence of cracks is expected to increase
with greater porcelain veneer thicknesses,
especially in combination with fast cooling rates.
 (Guazzato M et al).
18

technical
 5. Elastic modulus of the used alloy; modulus of
elasticity means resistance to deformation. Lack
of rigidity and distortion of the metal framework
is a frequent reason for porcelain fracture.
 EM of the framework should be higher than that
of the porcelain.
 Porcelain is at fracture risk when the framework
is perforated, if a trace of opaque is noticed
inside the crown, it means simply that the
framework is perforated.
20

technical
 6. Porcelain-metal contact lines; it is
important that the occlusal contact in centric
occlusion avoid the metal-porcelain junction,
so that the dentist and the technician should
discuss whether the occlusion will on the
metal or on the porcelain, ( it is up to the
clinical situation and tooth prep). Porcelain
metal junction should have 90 degree.
22

technical
 7. Substructure material used for fabrication
of crowns or FPD can be ;
 Metal alloy framework veneered by porcelain
(PFM), which has been used for over 40 years.
 Zirconia substructure material which is
regarded as offering high mechanical
qualities over the ceramic materials. (used
over the last 15 years)
23

technical
 Veneering ceramics designed to be used with
modern zirconia framework restorations have
been reported to fracture occasionally in vivo.
This veneer is leucite free, its fracture
toughness is 0.73 MPa , which is less than that
for the porcelain fused to metal (PFM)
veneering ceramic: 1.10MPa)
(Janet B. Quinn et al)
24

technical
8. Cutting process induce flaws of different size in
the tooth structures and dental materials.
 A sandblasted glass lose 67% of its strength.
Use burs with fine grains (not more than 50 mM)
 In the oral environment, the influence of water
and changing temperature, called stress
corrosion, can promote crack propagation and
decrease the fracture strength of an all-ceramic
restoration (Kelly 1995)
25

Restorative process
 Factors to Consider in the Restorative Process.
The following principles, described by Dawson,
based on the integration of the restoration in the
context of the gnathostomatic system decrease
and limit the post-cementation complications.
Of course porcelain fracture is one of these
complication.
 1. Properly designed centric stops; force
distribution is a timing issue, equal intensity of
contact have 2 purposes.
26

Restorative process
 The first is to distribute equally throughout
the mouth whatever force the patient can
generate.The second purpose of the centric
stop is to create both vertical and horizontal
stability of the teeth.To realize these
purposes these contacts should be in
harmony with the condyles in their CR
position which is necessary in the distribution
of occlusal forces between the teeth and the
TMJs.
27

restorative process
 2. Correct lateral anterior guidance;When the
mandible moves laterally, the goal is to have
immediate disclusion of the posterior teeth
on the working and balancing side.The
classic work byWilliamson and Lunquist
illustrated the neuromuscular advantage
obtained when posterior teeth are not
allowed to contact in excursive movement.
Anterior guidance should be worked on
provisional restoration.
29

restorative process
 Acceptable anterior guidance should be
coherent with the condylar guidance, so that
it will not cause tooth migration, mobility or
tooth fracture.
30

restorative process
 3. Correct protrusive anterior guidance;With
any protrusive movement of the mandible,
the goal is immediate posterior disclusion.
 Just like lateral movements of the mandible,
posterior tooth contact in a protrusive
movement increases the force on the anterior
teeth because of increased muscle activity.
32
Steep guidance patterns restrict the movement of the mandible that can
lead to instability; fracture being one of the possibilities.

restorative procee
 4. Correct crossover disclusion; In lateral
excursions, as the patient goes beyond the
cuspid, proper occlusal design dictates that
there is a smooth transition to the incisal
edge of the maxillary centrals.This transition
requires the proper alignment and position of
the mandibular as well as the maxillary
incisors.When this position is overlooked
excessive loads can be placed on the distal of
the lateral incisors, leading to fracture.
33

restorative factors
 5. Lingual Contours in Harmony with the
Envelope of Function; Protecting the posterior
teeth from contact in excursive movements is
one of the most important functions of the
anterior teeth.Working with the condylar
guidance, the lingual contour must be steep
enough for immediate separation of the
posterior morphology. Signs of instability such as
wear, fremitus, or migration of the anterior teeth
are all indications that a constriction occur.
34

restorative procee
 6. Parafunction; Bruxism, nail biting, sleep
disturbances, chewing on pencils/pens, or any
aberrant movement of the mandible that
brings the teeth together in an abnormal
pattern and creates signs of instability in any
part of the system need to be identified
during treatment planning. If it is identified
that the parafunctional issues happen while
the patient is asleep, a night guard should be
fabricated to cover the teeth during this time.
39

Restorative process
 Flexible appliance for protecting the
porcelain restorations.
41

restorative process
 7. Properly DesignedTooth Preparation; One
of the most common causes of fracture is
overreduction of the incisal edge. Porcelain
that has > 2 mm of unsupported material is at
risk for fracture. Result predictability is
ensured by evaluation of tooth length and the
esthetic on the study models.
42

Restorative process
 8. Properly FinishedTooth Preparations; All-
ceramic dentistry requires a high degree of
precision in both reduction and finishing.
Sharp line angles and rough preparations are
some of the major contributing factors when
fractured porcelain occurs. Proper finishing
will lead to cleaner impressions as well as
better fitting, fracture-resistant restorations.
43

Restorative process
 Finished tooth prep for all ceramic crown.
44

E. Porcelain fracture
management
 Fracture of veneering porcelain is a
complication that can occur in every dental
ceramic system. Based on the placement of
the fracture, two types are considered;
 a. cohesive which located in the porcelain.
 b. adhesive which affects the bonding
between the veneering and the framework.
 Single crown survival is similar for both PFM
and all ceramic, but in FPD all ceramic shows
higher failure. (Heintze SD, RoussonV)
45

management
 Fracture modes of all-ceramic restorations
have changed substantially with the
availability of zirconium oxide compared with
glass-ceramic. (mainly for the post.T.)
 Fractures of the veneering porcelain appear
to be a zirconia-specific problem.
 (Al-Amleh et al)
 Chipping rates are 3 to 50% for FPD with
zirconia framework after 3 years and 2.9%
with metal framework.
46

management
 Management of this complication is based on
the evaluation of each case, based on that,
treatment can be;
 a. By adjustment and polishing.
 b. Porcelain repair.
 c. Replacement of the restoration.
The frequency of chipping that can be treated
by a, b, is considerably higher for both PFM or
PFZ.
47

management
 What options are available to repair a
chipped all-ceramic or PFM restoration?
 1. Replace.
 2. Repair the ceramic restoration intraorally,
which is an interim, but reasonable, solution.
a. Polish the fractured surface. is possible
only for small chippings in the posterior
region and only when the metal or ceramic
coping is not exposed.
48

management
b. Replace the missing piece of porcelain
with composite-based resin;
c. Reapply the broken piece of porcelain with
resin cement;
d. Prepare the restoration for a new veneer
and adhesively bond the ceramic veneer onto
the existing restoration.This option is an
attractive solution.
49

management
 To achieve functional success, the clinician has
to establish reliable bonding of the veneering
porcelain to the core material.
 Surface conditioning is essential to the success
of intraoral repair.The challenge is to create a
strong, mechanochemical bond between the
hydrophobic resin-based composite or resin
cement and the fractured surface of the
restoration, which often is composed of two
different materials. this bond also involves
chemical interactions.
50

E. Porcelain fracteure
management
 Surface treatment depends on the exposed
substructure material which can be;
 Metal alloys, oxide-ceramic materials;
zirconia, alumina and glass- infiltrated
zirconia which are used for copings or
frameworks in all-ceramic restorations.
 Disilicate-ceramic materials: feldspathic
ceramics, which are used for anterior veneers
or veneering porcelain in PFM or all-ceramic
restorations.
51

management
 Glass-ceramics, which are indicated for inlays,
onlays, veneers and monolithic crowns.
 Micromechanical retention of the metal or
ceramic bond to resin is achieved by means of ;
 1. Air abrasion with the intraoral sandblaster.
2. Or by etching with hydrofluoric acid.
porcelain etching is done by the application of 2.5
to 10 percent hydrofluoric acid for 60-90
seconds. It is indicated for use only with silicate-
ceramic
52

management
 Etching breaks silicate bonds
 Unsaturated oxygen bonds are also generated,
which serve as bonding partners for the silane.
 However, intraoral use of hydrofluoric acid is
controversial because of its hazardous
properties. If hydrofluoric acid is spilled on the
soft tissue, it may take hours before symptoms
appear.Therefore, clinicians should use with
precaution and rubber dam is mandatory also
tooth tissue should well protected.
53

PORCELAIN FRACTURE
MANAGEMENT
 In the case of chaireside air-abrasion procedure
with 50 µm Al2O3, bothV and INC ceramic
surfaces exhibited similar rough surface patterns
that presented incorporation of sand particles
on their surfaces
55

E. PORCELAIN FRACTURE
MANAGEMENT
 Air abrasion.
 Minimal safety risks by using an intraoral
sandblaster.
 Al oxide particles of 50 mM at 2-3 bars air
pressure will clean, roughen, enlarge the surface
and activate the surface leading to a better
wettability and chemical accessibility.
 Lowering the pressure to.05 bar will reduce the
detrimental effects on oxide ceramic materials.
(high pressure cause flaws in the ceramic)
 It is difficult to limit the action on the target area.
56

E. PORCELAIN FRACTURE
MANAGEMENT
 The chemical bond between substructure
surface (metal,Al oxide,Zr oxide, silicate) and
the hydrophobic resin is created by
bifunctional molecules such as silanes or
phosphate monomers. Silanes bond to
silicate materials. On the other end of the
silane molecule, an additional polymerization
reaction of methacrylate groups generates a
bond to resin. (Söderholm KJ et al)
57

management
 Rrubber dam is indispensable, as contamination
of the silanized surface with water inactivates
the silane.
 Metal- and oxide-ceramic materials, which do
not contain silanol groups, also can be bonded to
silanes if they are silicatized in advance.
This procedure usually is referred to as
tribochemical coating.
Intraoral surface treatments become possible with
a chair side system.
58

management
 (CoJet silicate-ceramic surface treatment
system, 3M ESPE).The system consists of fine-
grained 30-µm Al oxide particles that are doped
by silica.This modification simultaneously will
allow roughening and the incorporation of silica
into the alloy, Zr oxide, or Al oxide.The silica
enriched surface then will react with the silane.
 4-META containing resin have been shown to
bond on non-noble alloy via the oxide (Panavia)
and are quite useful for porcelain repair.
59

management
 Bifunctional phosphate monomers.
(10- methacryloyloxydecyl dihydrogen
phosphate or 4-methacryloyloxyethyl
trimellitate anhydride) bond to oxides of the
metal or oxide-ceramic surface on one side
and to the resin on the other side.
( Uo M, Sjögren G. et al)
 Bifunctional phosphate monomers can be
part of the resin cement.
64

management
 In this case, they are called modified
phosphate-monomer– containing resin
cements.
 Modified resin cements should be applied
only on base alloys because they do not bond
sufficiently to noble alloys.
 (Antoniadou M. et al)
 Products also are available that contain
ceramic and metal primer, (silane and
phosphate monomer).
66

management
 The use of these combined primers is
appropriate for the intraoral repair of a
restoration if different materials are exposed
on the fractured surface. (silicate and oxides)
67

Conclusion.
 In spite of all the technical standards and the
clinical precautions, porcelain cracks and fracture
are still considered as a daily frustrating problem
that may be confronted. Management of this
failure needs meticulous diagnosis.
 Treatment may need complete replacement of
the restoration as last option, however certain
cases can be repaired.The nature of fracture
whether it is cohesive or adhesive is important
to decide the nature of the material to be
repaired, is it silica, Al oxide, Zr oxide or non
precious alloy?
69

 To obtain a good bonding on these different
material, a comprehensive knowledge about
the different type of bonding systems and
their indications is basic.
 These bonding systems include the fluoric
acid, the air abrasion system, the silane,the
Cojet system, the phosphate monomer
primer, combined primers, modified
phosphate-monomer– containing resin
cements.
70

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