This document discusses common problems that can occur with dental impressions and stone models, and their potential causes and solutions. It describes issues such as voids, tears or pulls in impressions that could result in poor fitting restorations. Specific problems covered include inhibited or slow setting impressions, lack of detail, voids or tears at margins, facial-lingual pulls, tray-tooth contact, delamination, poor bonding to trays, and discrepancies in stone models. For each problem, potential causes such as expiration, contamination, inadequate technique, or material incompatibility are identified along with recommended solutions.

1. Problem solving in fix prosthodontics

2. INTRO…….
 Failure
 Repairment
 About 90% of bridges
last at least 10
yrs.(Smith, 2000)

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

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

5. Porcelain fused to metal
 Distortion of metal-ceramic framework
 Inadequate metal support
 Excessive porcelain thickness
 Technical flaws
 Normal function (occlusal forces)
 Trauma

6. Failure of solder joints
 Inclusion
 Failure to bond
 Small solder joint

7. CHANGES IN ABUTMENT TOOTH….
 Perio disease
 Pulpal problems
 Recurrent caries

8. Mutiple aboutment better to index
and solder

9. Mutiple aboutment better to index
and solder

10. Distortion
 Pontics are too thin
 Bridge is removed with
too much force.
 Trauma.

11. Occlusal/incisal wear &
perforation
 Composite crowns
 Belle glass
 Targis vectris
 Wear down substantially over a lifetime
 Rate
 Occlusion
 Diet
 Para functional (bruxing) habits

12. 3) DESIGN FAILURES…..
 Abutment prep. design
 Inadequate bridge design
 Under-prescribed bridges

13. Inadequate clinical/lab technique
 Problems to 1 of 3 groups:
1. Minor problems
2. Can be corrected in situ.
3. Those that cannot.

14. Marginal deficiencies
 Positive ledge (overhang)
 Negative ledge

15. Casting difficulties
 External angles of crown
 should be rounded
 Sharp edges
 Stone die
 wax-up stage.
 investment material flow
 difficult to remove the investment material
 Cement thickness

16. REPAIRMENT TIME…
 Some things are really beautiful!
 But nothing lasts forever!
 HOW CAN WE REPAIR THESE C&B FAILURES?

17. Seriousness of the problem
1. Leave it alone if not causing any serious harm
2. Adjusting or repairing the fault
3. Replace the crown or bridge

18. fit checker

19. Grinding and polishing in situ
 Metal margins of crowns with positive ledges
 Porcelain margin
 Heatless stone
 Diamond point
 Followed by various composite finishing burs and discs.

20. Metal margins
1. Diamond stone
1. Green stones
2. Tungsten carbide stones
3. Metal and linen strips
2. Interdentally,
1. Triangular shaped diamond
2. Abrasive rubber instrument with special handpiece
3. Margins should be polished

21. Repairs by restoring in situ…….
 Occlusal Repairs
1. Amalgam
2. gold inlay
3. composite material

22. Repairs at the Margins
 margins of a poorly fitting bridge
 Secondary caries/early erosion and abrasion
 composite or GIC
 Cavity prep at margins
 poor access >>> remove part of the crown margin
 raising a full gingival flap
 good visibility

23. Repairs to porcelain
 Ceramic restorations
 Composite
 Separate silane coupling agent
 Limited to sites with minimal occlusal forces.

29. Ceramic facings
 Porcelain is lost and
composite repair is not
possible
 Often better to replace
whole crown
 Pontic.
 Drilled through
 New pin retained metal-
ceramic facing
 Removing all the porcelain
 Metal ceramic sleeve
crown

30. Removing c&b’s
1. Vibration of
ultrasonic scaler.
2. Good leverage at
margins
3. A slide hammer Bridge
remover
4. Crown can be cut off

31. Removing post & cores
 Using extraction forceps and using sharp twists –
carefully…
 Files
 Ultrasonic

32. 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.

33. Removing Metal – Ceramic Crowns
 Possible to remove with
normal devices
 usually better to cut off.
 cast metal
 solid tungsten carbide bur
with very fine cross cuts
 Eye protection!!!
 Vertical groove cut on buccal
 metal is usually thinner here
 with better vision.
 Diamond bur can cut
porcelain favourably !

34. Cutting
How to cut a pfm

35. Removing Bridges
(3 situations)
 1. Abutment teeth need to be
extracted
 Bridge is removed Intact
 Dividing the bridge
 2. abutment needed to be
retained
 Retainers are cut and bridge
removed carefully
 3. temporary measures
 removing whole bridges and
making adjustments.

39. Inhibited or Slow Setting
Visual Appearance:
Shiny, no detail
Result:
Inadequate surface detail on
cast, poor fitting restorations.
 S ulfur inhibition For Vinyl
Polysiloxane Materials
 latex gloves .
 Residues
 custom temporary
 provisional cements

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

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

43.  Expired impression material
 Inadequate mix.

44. Lack of Impression Detail
 Visual Appearance:
Muted detail
reproduction.
 Result: Crowns may be
too tight, or loose, and
not fit correctly.

45. Lack of Impression Detail
CAUSE SOLUTION
 Impression material stored at
elevated temperature.
 Store impression material at
room temperature.

46. Lack of Impression Detail
CAUSE SOLUTION
 Impression material stored at
too low a temperature
 (prolongs the setting
reactions,
 changes viscosity and
requires exceptionally
 high extrusion forces for
automix materials).
 Keep impression material at a
temperature of
 18°C/64°F at least one day
prior use.

47. Lack of Impression Detail
CAUSE SOLUTION
 Thick blood/saliva pooled
around prep.
 Remove blood and saliva
prior to
 making impression.
 Use 2-step impression
technique.

48. Lack of Impression Detail
CAUSE SOLUTION
 Inadequate retraction of
sulcus around prep.
 Use good retraction
technique, with proper
 moisture control.

49. Lack of Impression Detail
CAUSE SOLUTION
 Exceeding the working time.  Follow manufacturer’s
working
 time specifications.
 Choose material with longer
working time.

50. Lack of Impression Detail
CAUSE SOLUTION
 Inadequate disinfection
effects
 surface quality (detail
reproduction) and
 dimensional stability.
 Use water based disinfectants
according to
 FDA guidelines.
 Follow manufacturer’s
instructions for use.

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

52. Voids on the Margin
CAUSE SOLUTION
 Improper syringe technique.  Keep syringe tip immersed in
wash material to
 avoid entrapping air.
 Wiggle and stir while
syringing. Push
 material forward.

53. Voids on the Margin
CAUSE SOLUTION
 Inadequate coverage of
marginal area with light body
impression material.
 Use wash material liberally
on preparation
 and abutments.

54.  Blood and saliva
contamination around prep.
 Use good moisture control technique.
 Rinse and dry prep area before taking
 the impression.
 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.
Voids on the Margin
CAUSE SOLUTION

55.  Tray not seated straight.  Insert impression tray
straight.

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

57. Tearing at the Margin
CAUSE SOLUTION
 Check expiration date of
impression material.
 Ensure mixing instructions
are followed and materials
have a streak-free appearance.
 Expired impression material.
 Inadequate mix.

58. Tearing at the Margin
CAUSE SOLUTION
 Displace tissue to allow the
impression material 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.
 Insufficient retraction.

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

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

61. Facial-Lingual Pulls
CAUSE SOLUTION
 Follow manufacturer’s
working time specifications.
 Choose material with longer
working time.
 Exceeding the working time.

62. Facial-Lingual Pulls
CAUSE SOLUTION
 Do not move tray after
seating.
 Tray movement or
repositioning
 after seating.

63. Facial-Lingual Pulls
CAUSE SOLUTION
 Use more material to create
back flow effect.
 Insufficient amount of
impression
 material used.

64. Facial-Lingual Pulls
CAUSE SOLUTION
 Use lingual stops.
 Use an impression tray that
supports the flow
 of the material.
 Impression tray does not
support flow of
 impression material.

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

66. Tray-Tooth Contact
CAUSE SOLUTION
 Use proper size tray.
 Test various tray sizes to
ensure proper size.
 Prepared teeth contact the
sides or bottom
 of impression tray.

67. Tray-Tooth Contact
CAUSE SOLUTION
 Carve out tray material
properly before
 applying wash.
 Tooth contact with the pre-
set tray material
 when using the two-step
technique.

68. Tray-Tooth Contact
CAUSE SOLUTION
 Fill tray adequately. Insufficient impression
material used.

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

70. Delamination
CAUSE SOLUTION
 Follow manufacturer’s
working time specifications.
 Choose material with longer
working time.
 Store impression material at
room temperature.
 Exceeding the working time.
 Impression material stored at
elevated temperature.

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

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

73.  No tray adhesive used.  Use tray adhesive.
Poor Bond of Impression
Material to the Tray
CAUSE SOLUTION

74.  Incompatible tray adhesive
used.
 Use appropriate tray
adhesive.
 VPS adhesive for VPS.
 Polyether adhesive for
polyether materials.
Poor Bond of Impression
Material to the Tray
CAUSE SOLUTION

75.  Inadequate drying time for
tray adhesive..
 Follow manufacturer’s
instructions for application,
and drying time
Poor Bond of Impression
Material to the Tray
CAUSE SOLUTION

76.  Thin plastic trays allow
deflection, which can cause
rebound upon removal.
 Use a tray that fits better, and
is stiffer and more rigid.
Poor Bond of Impression
Material to the Tray
CAUSE SOLUTION

77. 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

78. CAUSE SOLUTION
Stone Model
Discrepancies

79.  Tooth contact with
impression tray, or gauze of
double bite tray causes water
to leach out of the tray,
dehydrating the stone.
 Instruct patient to bite
passively in centric occlusion
when using dual arch trays.
 Fill tray with sufficient
amount of material.
CAUSE SOLUTION
Stone Model
Discrepancies

80.  Cast not made according to
model preparation guidelines
 and lacks detail.
 Provide as much information
as possible to the lab.
Indicate
 type of impression material
(polyether or VPS) and
whether
 or not the impression has
been disinfected.
CAUSE SOLUTION
Stone Model
Discrepancies

81.  VPS
 Hydrogen gas emission.
 Follow manufacturer’s
instruction for casting time.
CAUSE SOLUTION
Stone Model
Discrepancies