Success and failure andproblem solving in prosthodontics complact final

Scenario
 Impression
 Framework check


SUCCESS AND
FAILURE
Problem solving in fix prosthodontics

INTRO…….
 Failure means, to be unsatisfactory, and in
C&B, it’s the inevitable.
 Repairment is the work that is done to get rid
of the failure.
 Recent large surveys of bridges made in
practice and elsewhere in different countries
show that about 90% of bridges last at least 10
yrs.(Smith, 2000)

Inhibited or Slow Setting
 Visual Appearance:  Result:
 Shiny, no detail  Inadequate surface
detail on cast
 Poor fitting
restorations.

Inhibited or
Slow Setting
CAUSE SOLUTION

 For Vinyl  Wear gloves proven
Polysiloxane not to contain traces
Materials of sulfur.
 Sulfur inhibition due  If contamination is
to contact of latex suspected, scrub
gloves with affected area with
tissue/tooth/retraction diluted hydrogen
material or impression peroxide.
material.

Inhibited or Slow Setting

CAUSE SOLUTION

 Do not use impressions
 Residues from already used to fabricate
custom temporary or the temporary restoration.
 Fabricate the temporary
 provisional cements crown or bridge after final
(acrylics) present. impression has been
made.
 Remove air-inhibited layer
on the exposed
 surface with an alcohol
wipe before making final
impression.

Inadequate mix
Result
Visual Appearance
Non-homogeneous mix. Slow setting impression
material.

 Use mix tip according
to manufacturer’s
instruction for use.
 When using hand-mix
materials ensure
correct mixing ratio
and thorough mix of
catalyst and base
paste.

Lack of Impression Detail

Result: Crowns may be too
Visual Appearance: Muted
tight, or loose, and not fit
detail reproduction.
correctly.


CAUSE SOLUTION

 Impression material  Store impression
stored at material at room
elevated temperature. temperature.


CAUSE SOLUTION

 Impression material  Keep impression
stored at too low a
temperature material at a
 prolongs the setting temperature of
reactions  18°C/64°F at least
 changes viscosity and one day prior use.
requires exceptionally
 high extrusion forces
for automix materials


CAUSE SOLUTION

 Thick blood/saliva  Remove blood and
pooled around prep. saliva prior to
making impression.
 Use 2-step
impression
technique.


CAUSE SOLUTION

 Inadequate  Use good retraction
retraction of sulcus technique
around prep.  proper moisture
control.


CAUSE SOLUTION

 Exceeding the  Follow
working time. manufacturer’s
working time
specifications.
 Choose material
with longer working
time.


CAUSE SOLUTION

 Inadequate  Use water based
disinfection effects disinfectants
 surface quality according to
(detail reproduction)  FDA guidelines.
and
 Follow
 dimensional stability.
manufacturer’s
instructions for use.

Voids on the Margin
 Visual  Result:
Appearance:  The fit and
Voids/holes on function of the
margin of the final restoration
prepared teeth. may be
Incomplete margin. compromised.
 Short crown
margins
 and/or open
margins.

Voids on the Margin

CAUSE SOLUTION

 Improper syringe  Keep syringe tip
technique. immersed in wash
material to
 avoid entrapping air.
 Wiggle and stir while
syringing. Push
 material forward.

Voids on the Margin

CAUSE SOLUTION

 Inadequate  Use wash material
coverage of liberally on
marginal area with preparation
light body  and abutments.
impression material.

Voids on the Margin

CAUSE SOLUTION
 Use good moisture control
 Blood and saliva technique.
contamination  Rinse and dry prep area
before taking the impression.
around prep.  Stop bleeding by using
appropriate retraction
technique and hemostatic
agent. Leave cord in sulcus
until no blood or saliva are
present before syringing the
light body impression
material.
 Consider two-cord retraction
to displace tissue and control
fluids.

Tearing at the Margin
 Visual  Result: Short
Appearance: Rip, crown margins
or visible tearing and/or open
on the margin of margins.
the preparation.


CAUSE SOLUTION

 Expired impression  Check expiration date
material. of impression
material.

 Ensure mixing
 Inadequate mix. instructions are
followed and
materials have a
streak-free
appearance.


CAUSE SOLUTION

 Insufficient  Displace tissue to allow
the impression material
retraction. to access prepared
area.
 Consider two-cord
retraction. Leave pilot
cord in the sulcus when
taking the impression.
 Use impression
material with sufficient
tear resistance.


CAUSE SOLUTION

 Do not use impressions
 Residues from already used to fabricate
custom temporary or the temporary restoration.
 Fabricate the temporary
provisional cements crown or bridge after final
(acrylics) present. impression has been
made.
 Remove air-inhibited layer
on the exposed surface
with an alcohol wipe before
making final impression.

Facial-Lingual Pulls
 Visual  Result: Failure to
Appearance: V- capture complete
shaped void, and accurate
trough-like. dentition.


CAUSE SOLUTION

 Exceeding the  Follow
working time. manufacturer’s
working time
specifications.
 Choose material
with longer working
time.


CAUSE SOLUTION

 Tray movement or  Do not move tray
repositioning after seating.
 after seating.


CAUSE SOLUTION

 Insufficient amount  Use more material
of impression to create back flow
material used. effect.


CAUSE SOLUTION

 Impression tray  Use lingual stops.
does not support  Use an impression
flow of impression tray that supports
material. the flow of the
material.

Tray-Tooth Contact
 Result:  Visual
Restoration may Appearance:
have slight Show-through of
distortion at tray. Impression
marginal area, or tray exposed.
rocks.

Tray-Tooth Contact

CAUSE SOLUTION

 Prepared teeth  Use proper size tray.
contact the sides or  Test various tray
bottom of sizes to ensure
impression tray. proper size.

Tray-Tooth Contact

CAUSE SOLUTION

 Tooth contact with  Carve out tray
the pre-set tray material properly
material when using before applying
the two-step wash.
technique.

Tray-Tooth Contact

CAUSE SOLUTION

 Insufficient  Fill tray adequately.
impression material
used.

Delamination
 Visual  Result:
Appearance: Restoration will
Heavy body and not seat or fit
light body properly.
materials not
blended, or mixed
together.

Delamination

CAUSE SOLUTION

 Exceeding the working  Follow manufacturer’s
time. working time
specifications.
 Choose material with
longer working time.

 Impression material  Store impression
stored at elevated
temperature. material at room
temperature.

Delamination

CAUSE SOLUTION

 Avoid contact with sulfur
 Sulfur or acrylic contaminants:
contamination of  Wear gloves proven not to
contain traces of sulfur.
pre-set heavy body  Avoid contact with acrylic
material in two-step and methacrylic
contaminants:
technique.  Ensure impression
materialdoes not come into
contact with methacrylate
residue from acrylate
temporary materials.

Poor Bond of Impression
Material to the Tray
 Visual  Result: Crown(s)
Appearance: may be tight and
Impression pulling not seat fully, or
away from the require excessive
sides/bottom of internal
tray. adjustment.

CAUSE SOLUTION

 No tray adhesive  Use tray adhesive.
used.

CAUSE SOLUTION

 Incompatible tray  Use appropriate tray
adhesive used. adhesive.
 VPS adhesive for
VPS.
 Polyether adhesive
for polyether
materials.

CAUSE SOLUTION

 Inadequate drying  Follow
time for tray manufacturer’s
adhesive.. instructions for
application, and
drying time

CAUSE SOLUTION

 Thin plastic trays  Use a tray that fits
allow deflection, better, and is stiffer
which can cause and more rigid.
rebound upon
removal.

Stone Model
Discrepancies
 Visual
Appearance: Voids
on margin,
powdery cusp tips
on incisal edges
on prepared tooth.
“Golf-ball”
appearance of
 stone model.
Result: Incomplete
seating of indirect
restorations

Stone Model
Discrepancies
CAUSE SOLUTION

 Tooth contact with  Instruct patient to
 impression tray bite passively in
 gauze of double bite centric occlusion
tray when using dual
 causes water to arch trays.
leach out of the tray,  Fill tray with
dehydrating the sufficient amount of
stone.
material.

Stone Model
Discrepancies
CAUSE SOLUTION

 Cast not made  Provide as much
according to model information as
preparation possible to the lab.
 Indicatetype of
guidelines and lacks
impression material
detail. (polyether or VPS)
 and whether or not
the impression has
been disinfected.
 VPS  Follow manufacturer’s
 Hydrogen gas emission. instruction for casting time.

WHY C&B WORKS FAIL?
 MECANICAL FAILURE
 CHANGES IN ABUTMENT TOOTH
 DESIGN FAILURES
 INADEQUATE CLINICAL OR LAB
TECHNIQUE

Mechanical
Failures….
 Porcelain/PJC #
 Failure of solder joints
 Distortion
 Occlusal/Incisal wear & perforation
 Lost facings

Porcelain #
 Stresses are developed within PJC’s as a
result of contraction on cooling after the firing
cycle. These stresses produce minute cracks,
some of which originate at the fit surface &
propagate to produce failure if the crown is
subjected to sufficient force. These stresses
are concentrated around sharp internal angles
of the fit surface, so the external angles of PJC
preps should be rounded to reduce them.

Porcelain #
 Distortion of metal-ceramic
framework invariably results in the loss of
porcelain
 Inadequate metal support
 Excessive porcelain thickness
 Technical flaws
 Normal function (occlusal forces)
 Trauma

Failure of solder joints
 A flaw or inclusion in the solder itself
 Failure to bond to the surface of the metal
 The solder joint not being sufficiently large for
the conditions in which it is placed.

CHANGES IN
ABUTMENT TOOTH….
 Progression of perio disease
 Abutment tooth may become non-vital (pulpal
problems)
 Recurrent caries occurring at margins of
retainers:
 change in diet.
 lapsed oral hygiene.

 inadequate restoration

 design

Distortion
 May occur to all-metal bridges if pontics are
too thin or if a bridge is removed with too much
force.
 Framework distortion may occur during
function or as a result of trauma.

Occlusal/Incisal Wear &
Perforation
 Crowns tend to wear down substantially over a
lifetime
 All restorative materials wear in use, and the
rate is determined by
 the occlusion
 the diet

 and parafunctional (bruxing) habits

3) DESIGN FAILURES…..
 Abutment prep. design
 Inadequate bridge design
 Under-prescribed bridges
 few abutment teeth
 Over-prescribed bridges

Marginal deficiencies
 Positive ledge (overhang)
 excess of crown material protruding beyond the
margin of the preparation.

Negative ledge
 deficiency of crown material that leaves the
margin exposed but with no major gaps between
the crown and the tooth.
 Often arises because the impression did not
correct at the try-in stage.

Casting difficulties
 “External angles of crown preps for metal
castings should be rounded to prevent one of
the faults that may occur in the following chain
of events:”
 Stone die may not flow into the impression
adequately, trapping air bubbles in the sharp
angles of the imp.

Casting difficulties
 Sharp edges may be damaged at the wax-up
stage.
 Investment material may not flow adequately into
the wax pattern to produce rounded internal
angles on the casting, preventing the casting from
seating fully.
 It may be difficult to remove the investment
material entirely from sharp internal angles
without damaging the casting.
 Cement will flow less rapidly around sharp angles,
increasing the likelihood of an unnecessary thick
cement layer at the margins.


REPAIRMENT TIME…
 Some things are really beautiful!

 But nothing lasts forever!

 HOW CAN WE REPAIR THESE C&B
FAILURES?

TECHNIQUES FOR ADJUSTMENTS,
ADAPTATIONS AND REPAIRS TO CROWNS
AND BRIDGES

 Assessing the seriousness of the problem

 Leave it alone if not causing any serious harm
 Adjusting or repairing the fault
 Replace the crown or bridge

Adjustments by grinding and
polishing in situ
 In some situations, margins of crowns with
good ledges can easily be adjusted.

 If margin is porcelain (or specially designed),
finishing instruments should be used,
example, heatless stone or diamond point
followed by various composite finishing burs
and discs.

In case of metal margins
 diamond stone followed by green stones,
tungsten carbide stones or metal and linen
strips may be used.
 Interdentally, a triangular shaped diamond and
an abrasive rubber instrument with special
handpiece (esp overhangs).
 Margins should be polished with prophylactic
paste with brush/rubber cup, and interdentally
with finishing strips.

Repairs by restoring in
situ…….
 Occlusal Repairs
 Occlusal effects in metal retainers can be fixed
by amalgam which usually gives good results.
 A small gold inlay may also be preferred.
 In metal-ceramic or porcelain restorations,
composite material can be used but repair may
need to be done periodically.

Repairs at the Margins
 Should never try to repair margins of a poorly fitting bridge
during insertion.
 Secondary caries/early erosion and abrasion can be treated
with composite or GIC.
 Cavity prep at margins should not endanger strength
although all caries should be removed. If poor access, then it
is better to remove part of the crown margin rather than
excessive amount of tooth structure.
 In some cases, raising a full gingival flap may be justified.
 Retainer margins can be adjusted and restored with good
visibility.
 Any necessary periodontal therapy or endodontic surgery can
also be carried out.

Repairs to Porcelain
 Materials such as basic composite with a
separate silane coupling agent for optimum
bonding can be used to modify or shape
ceramic restorations.
 It is not an acid etch bond to enamel and is not
strong. Therefore, the use of the material is
limited to sites with minimal occlusal forces.

C&B – METABOND WITH
COMPOSITE TO REPAIR
PORCELAIN…..

3.Ceramic facings
 When porcelain is lost from a metal-ceramic unit and
composite repair is not possible – often better to
replace whole crown.
 Sometimes possible with a pontic. A hole is drilled
through the backing and an impression is taken with
suitable pins for a new pin retained metal-ceramic
facing.
 - It could be a little bulkier than the original!
 Sometimes possible to fix retainers or pontics by
removing all the porcelain and reprepare the metal
part using a “metal ceramic sleeve crown” which
covers the skeleton of the old retainer or pontic.
 Sometimes made with heat cured acrylic or laboratory
light cured composite.

4.‘Unit construction’ bridge
facings
 Before the routine use of metal ceramic
materials, bridges were often made with
Separate PJC’s cemented to it.
 However, they often broke as they were
usually reduced approximally for connector
accomodation
 Patients sometimes were given a spare set
when bridge was cemented


Removing and/or replacing entire
sections of a bridge
 A good purpose for removable, telescopic crown retained
bridges and of dividing multiple unit bridges into smaller
sections.
 When a part of a bridge is removed, the remainder can be
modified like cutting a slot for a movable joint and replacing
the lost section.
 Bridges can also be extended using same principles if more
teeth are apparently lost


Removing C&B’s
 In removing any crown or bridge, in
particular posts and caries, often helpful to
break up the cement by vibration of ultrasconic
scaler. It works best with zinc phosphate
cement.


Removing Crowns
 Metal crowns
 Good leverage at margins for either complete or
partial metal crowns.
 Some instruments used are;
 - cumine or mitchels trimmer
 - even a slide hammer type crown
 - bridge remover may be used
 Crown can be cut off if all else fails.


Removing Post & Cores
 Using extraction forceps and using sharp
twists – carefully…
 Several other devices can be used


Removing PJC’s
 Cannot be removed intact and should be cut
off.
 A vertical groove is made with a diamond bur
in the buccal surface just through to cement.
 Then Removed with suitable heavy duty
instrument.


Removing Metal – Ceramic
Crowns
 Possible to remove with normal devices but are
more rigid than gold and porcelain may break –
usually better to cut off.
 cast metal is best cut with a solid tungsten carbide
bur with very fine cross cuts (beaver bur).
 Eye protection is important for everyone.
 Vertical groove cut on buccal as metal is usually
thinner here with better vision.
 Diamond bur can cut porcelain favourably !


Removing Bridges
(3 situations)



Abutment teeth need to be extracted
Bridge is removed with crown and bridge remover
 Easy for cantilever
 Others - Dividing the bridge through pontic or connector and remove teeth individually with
retainers in place


Cont…..

 2. When abutment teeth are needed to be retained either for support of partial denture or
overdenture or for making a new crown. Retainers are cut and bridge removed carefully as
preparations are protected.
 3. Some temporary measures require removing whole bridges and making adjustments. Neither
bridge nor preparation should be damaged.


Removing Bridges intact
 All metal bridges and minimal preparation bridges
are slightly more flexible and can be removed
more easier than metal ceramic conventional
bridges.
 Slide hammers can fit under margins, under
pontics and embrasure spaces, even in drilled
holes on palatal surfaces of retainers or pontics.


Other Techniques…..
 Ultrasonic vibration with a scaler can loosen crowns
and bridges.
 Loops of soft wire and sliding hammer
 If no slide hammer, than heavy duty instruments like
mallet is passed through the loops well outside the
mouth and sharp blows are applied. – need to warn
patient beforehand ( rather dramatic approach)


Practical Points
 A large proportion of failures are partial, a level of
acceptability must be reached by dentist and
patient (esp min prep bridges)
 Periodontally affected teeth can frequently be
treated.
 Never should be used to cover up poor design
 Bridge can be made with fail safe procedures


PFM evaluation

1. Proximal contact
2. Marginal integrity
3. Stability
4. Occlusion
5. Characterization and glazing

PFM evaluation
Proximal contact Marginal integrity/complete seating Occlusion Characterization and
glazing

MARGIN CHECK /
COMPLETE SEATING

PFM evaluation
Proximal contact Marginal integrity/complete seating Occlusion Characterization and
glazing

Overhan
Small
g
ledge
Careful
Acceptabl
Adjustme
e
nt
Risk of
caries
Open
margin

Making
new
casting

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