The document discusses errors that can occur during the denture fabrication process, from initial impressions through final processing. It notes that errors may stem from clinical procedures, laboratory techniques, or material properties. Specific errors are described for impression taking, jaw relation records, tooth arrangement, processing techniques like flasking, packing, and curing, and final polishing. Attention to each step is important to avoid defects that can compromise the fit, function, or aesthetics of the final dentures.

3. Dr. Amal Fathy Kaddah
Professor of Prosthodontic,
Faculty of Dentistry,
Cairo University.

5. Errors may be made at any of individual
treatment procedure and are not apparent
until denture insertion.
The importance of early recognition can
mean the difference between failure and
success.
Introduction

6.  Clinical errors.
 Technical discrepancies and Inherent
deficiencies in the material itself.
 Laboratory Errors.
Causes of Denture Errors

7.  Errors in impressions
 Ill-fitting trial denture bases.
 Inaccurate jaw relation records.
 Errors during transfer of the records to articulator.
 Incorrect arrangement of teeth.
 Dimensional changes during curing.
 Laboratory and Processing faults.
Causes of clinical and laboratory Errors

8. Technical discrepancies could be due to:
1- Dimensional Changes in the wax due to variation in
temperature.
2- Expansion of the investing material during the processing
(plaster and dental stone).
3- Errors which may occur during packing of acrylic resin.
4- Changes in the acrylic resin material during processing
procedures (polymerization shrinkage).
5. The pressure of the flask press.

9. Procedures involved
 Casts and special tray fabrication
 Setting up of teeth
 Try-in
 Wax contouring
 Disarticulation
 Errors of Denture processing
• Flasking
• Wax elimination
• Packing and curing
• Finishing and polishing
Laboratory Faults and Errors

11.  Setting Anterior
Teeth
Esthetics & Phonetics

12. Symmetry
Perfect
Symmetry
Gross
Asymmetry

13. Any defect in anterior teeth arrangement affects
esthetic, phonetics and denture stability
Nasolabial angle ≈ 90°
If insufficient support, the vermilion
border will be reduced

14. Cervical necks tilt posteriorly from the central
incisor to the canine
Setting Maxillary Anteriors

15. Setting Mandibular Anteriors
 Incisal edges are placed at the same level
 Even with the occlusal plane

16. No Anterior
Contact in Centric
Correct
Insufficient
Excessive

17. Canine Offset
Correct
Insufficient
Improper offset
results in a
space or half
tooth
replacement
Most critical tooth
relationship

18. Intraoral Assessment of Anterior Teeth
Incisal edges of
maxillary incisors
should follow line of
lower lip when
smiling (‘smile line’).

19. Central & lateral incisors must begin to turn along
the curvature of the arch.
Circumference Follows Arch
Shape

20. Facial Support, OVD & Tooth Setup Can
Dramatically Affect Appearance

21. Phonetic Assessment
• Maxillary centrals should
lightly touch vermilion border
of lower lip for ‘F’, ‘V’ sounds.
• ‘S’ sounds - incisal edges
should approximate each
other.

22. Effect of incisor length and width

23. Effect of incisor length and width

24. Setting Posterior Teeth
Set for Function
• Set teeth as close to:
• Maximum intercuspation.
• Balance.
• All setups will need some adjustment.

25. Set mandibular premolars & 1st
molar :
• Level with occlusal plane.
• Centered over ridge.
Occlusal plane
Line indicating the crest of the ridge

26. Second molar elevated by ~ 15° from the
occlusal plane.
15 degrees

27. Max. lingual cusps contact
central fossae/marginal ridge.
~ 1mm space between buccal
cusps.

28. Maxillary lingual cusps firmly contact
bilaterally simultaneously

29. Verify centric
No max. buccal cusp contacts in:
• Centric
• Lateral excursions
Centric Position

30. Verify excursive contacts
Anterior teeth are in
contact during lateral
excursions.
Working Excursions

31. Note the balancing contacts
Balancing Excursions

32.  THE TRIAL DENTURE BASES

33. Importance of Wax Try-in
• Chance to change
setup
• An opportunity to
improve the final result

35. Don’t accept the try in
from the Lab. If any of
those errors exists

36. Waxing-up for try-in
Final wax-up

37. It is the contouring of the trial denture bases
to reproduce the original form of tissues.
 Waxing up

38. The form of the polished surfaces and the
proper location of the artificial teeth plays a
major role in:
Stability of the dentures.
Influences its retentive quality.
Influences the esthetics of the denture.
Support the cheeks, lips and tongue.

39. Upper denture
1.The wax at the periphery must extend to
the full depth of the vestibule.
2.Fully round, well extended and polished.

40. 3. Improper waxing up in the palate may
also cause faulty phonation particularly
of the "S" sound.
The palate should have an even
thickness of 2.5 mm.

41. 4. The labial waxing may be
thickened in order to restore lost
facial contour.
5. Festooning and cuspid eminence
should be provided.
Gingival crests should be trimmed
exactly to the finished line.
6. Stippling of the facial surface.

42. Lower Denture
1- The labial surface is concave.
2-The peripheries are fully rounded well
extended and polished.

43. 3- In the premolar region the buccal surface is
flat and thin.
In the molar region the wax is thick.
4. The lingual surface must be concave.

44. Denture base contours
• Affect phonetics,
comfort and retention.
• Should not be convex
in shape.
Convex X Concave

45. The tongue brings the food onto the occlusal plane then
it holds the food between the upper and lower teeth
cooperating with the buccinator muscle so that the food
can be easily crushed.

46. Phonetic Tests

47. These sounds are made with
the tip of the tongue against
the palate in the rugae area
with small space or slit like
channel for the escape of air
between the tongue and hard
palate. The size and shape of
this small space or channel will
determine the quality of the
sound.

48. •Always check on the total
length of the upper and
lower teeth (including their
vertical overlap).
•The upper and lower incisors
should approach each other
end-to-end, but they should
not touch that indicate a
possible error in the amount
of horizontal overlap of the
anterior teeth.

49. Lisping
• Palatal contour too
constricted
•Remove wax to provide more
room
• Arch form too broad

50. 50
If the channel formed
between the hard palate
and the tongue is too
narrow and deep
Whistling (Rare with
denture construction)
Lisping “Sh” sound
if the depth of the
channel is further
decreased or
obstructed
Lisping and whistling are opposite phenomena
If this channel is too
shallow (broad and
thin)
Lisping (th or etts)

51. Finalize TRIAL INSERTION STAGE

52. • Finalize Wax up

53. When you realize you've made a mistake,
take immediate steps to correct it.

54.  DENTURE PROCESSING
• Flasking
• Wax Elimination
• Packing and Curing

55. Processing faults and errors
1. Errors of sealing
2. Errors of disarticulation
3. Errors during flasking
4. Errors during wax elimination
5. Errors of mixing the resin
6. Errors of packing
7. Errors of curing
8. Errors of cooling
9. Errors of deflasking
10.Errors of finishing and polishing

56. 1. Sealing of the waxed denture base to the
cast using base plate wax.
When festooning is completed Seal the periphery of the
denture flange to the inner edge of the land of the cast.
Before Flasking

57. Sealed and filled peripheries
. Wax contouring ( festooning ).
. Sealing.
Improper sealing lead to change the relation between
the trial denture and cast.
Errors of sealing

58. • Soak casts and mounts
in water.

59. After soaking the master casts and mountings
Plaster in water for a few minutes, gently
remove the casts from the mountings.
2. Disarticulation

60. • The mounting plaster is
carefully separated from the
cast.
• Split the junction between the
mounting plaster and the cast
with help of wax knife and
plaster mallet.
. After separation, the cast’s soaked in water.
2. Disarticulation

61. Before Flasking
Soak casts and mounts.

62.  Errors of disarticulation
Distortion of trial denture and the remounting
plates may result during disarticulation.

63. 3. Flasking
1. Centralize the waxed denture in stone with the
occlusal surface parallel to the base.
2. Invest the trial dentures in the lower half of the flask
with dental stone.

64. 3. Smoothen the dental stone.
Notice that there is no stone on the flask edge,
preventing seating of the middle part of flask.

65. 4. Apply separating media to the dental stone.

66. Lubricated with
the Vaseline
• If the separating medium
is contaminated with
stone, the stone adhere to
the surface of the denture.

67. 5. Pour dental stone till
the incisal and
occlusal surfaces.
6. EXPOSE THE TEETH.

68. 7. Paint separating medium (to facilitate deflasking)
except occlusal surfaces of teeth.

69. 9. The lid of the flask is pressed into place while the
investing stone is still soft.
8. Pour the third mix of stone to fill the flask and cover
with its cover lid.

70. The advantage of three pour technique is that it
facilitate easy removes of the denture after curing.
Completed flasking for mandibular
and maxillary complete denture

71. Holes allow the excess
material to come out.
10. Clean flasks, ready for wax removal.

72. The clamp is tightened to hold the flask in position
Leave the flask for 30-60 minutes to reach final
setting time of the stone.

73.  Failure to close flask completely.
 Too much pressure while closing the flask.
 Tooth movement during flasking or packing
 Failure to cool flask before deflasking.
 Distortion due to improper flasking.
 Errors during flasking

74. 2. Stone adhere to the surface of the denture:
• The application of separating medium contaminated
with stone.
• Space between the teeth and resin base.
 Errors during flasking
1. Causes of Tooth movement:
• The use of plaster instead of stone. (Its low
capacity to resist the pressure)
• Incomplete closure of flask.

75. Incomplete closure of
flask causes tooth
movement.

76. 4. WAX ELIMINATION
1. The flask is soaked in boiling water (100 C ) for
5 minutes to soften the wax.
It is done to remove the wax, so that a mould space is
created for acrylic to fill in.

77. 2. Before placing the flask into the water bath, the
clamp should be loosened.
3. Dewaxing is done to just soften the wax and not
melt it.
4. The softened wax is flushed out using hot water
or wax solvent or soap solution.
5. Even the finest traces of waxes should be
removed.

80. It is painted with e. g. tinfoil
medium carefully and must
prevent the penetration of the
media to the teeth.
Separating medium is applied
to the mould space to
Lubricate the stone surface
only prior to packing the
acrylic resin.

81. -To prevent the passage of water from gypsum to resin.
-To minimize the passage of monomer to the plaster.
-To facilitate separation of the flasks.
Separating medium
Various types of separating media used are:
- Cellulose lacquers.
- Soft soaps.
- Sodium silicate.
- Starches.
- Evaporated milk.
- Tinfoil.
- Sodium alginate.

82.  The soap solution is said to react with
the gypsum forming a membrane
impervious to wax.
 Any traces.
 Errors during wax elimination

83. 5. Mixing of powder and liquid
Heat cure acrylic is used
 Polymer / monomer is mixed according to manufacture
instruction.
 Usually 10cc of monomer , and 30cc of polymer will be
enough to pack an average- sized denture. (1:3 ) M / P.
 When the material reaches the dough stage, it is ready for
packing.

84.  Greater polymerization shrinkage.
• More time is needed to reach the packing
consistency.
• Porosity can occur in the denture.
a. If too much monomer is used will lead to:
 Errors of mixing the resin

85.  Not all the polymer beads will be wetted by monomer
and the cured acrylic will be granular.
 Dough will be difficult to manage and it may not form
a continuous mass during processing.
b. If too little monomer is used will lead to:
c. Improper mixing & contamination of the mixture with
dirty hand or instrument may lead to color streaks.
 Errors of mixing the resin

86. 6. Packing
• Packing is introduction of denture base resin into the mould
cavity.
• The powder liquid mixture should be packed into the flask
at the dough stage.
• Divide acrylic in half and place in tooth portion of flasks. To
trial pack, cover with plastic sheet before closing flasks so
flasks can be re-opened to add acrylic, remove flash or
insert names.

87. • Use cellophane or polyethylene film as a separator for the
half of the flask which is lower half ( on the cast ).
• Place flasks together and press to remove excess acrylic.
• The flask is opened and the flash is trimmed away.
• Before final closure the separating film is removed.
• Final closure of the flask or metal to metal contact of the
flask halves then completed in the process .
• Transfer flasks to compress and tighten completely.

88. PACKING

89. Trial packing
keep flasks closed
during curing.

90. Flasking for Processing

91. • Insufficient separating medium.
• The introduction of too much material termed over
packing.
• The introduction of too little material called under
packing.
• Adding the resin material in layers during trail packing
• Packing the resin in sticky stage.
• Lack of pressure, lead to presence of fine pits.
Errors of packing

92. Insufficient separating medium will lead to:
a) Entering the water to the mould and may affect the
rate of polymerization, color and crazing.
b) Penetrating of the monomer into the mould
material causing plaster to adhere to the acrylic
resin and producing a rough (porosity ) surface
Errors of packing

93.  Too much material (over packing) leads to:
excessive thickness of the denture base
and movement the teeth.
 Too little material ( under packing) lead to
denture base porosity.
Errors of packing

94. • Adding the resin material in layers during
trial packing may lead to color streaks
• Packing the resin in sticky stage may lead
to porosity.
• Lack of pressure, leads to presence of fine
pits.
Errors of packing

96. 7. Curing (polymerization)
• Bench curing: After final closure the
flasks are kept at room temperature for
30 to 60 min.
• Purpose of bench curing: permit an
equalization of pressures throughout the
mould space.

97. Curing cycle: It is polymerization
cycle. The curing cycle
selection depends on the
thickness of the resin.

98. • Long cycle: flasks are placed in water at
160OF (60-70OC) for nine hours.
• Short cycle: flasks are placed in water
at 160OF (70OC) for two hours, then
maintained at 212OF (100OC) for one hour.

99. Immediate curing after closure of the flask without
allowing the packed flask to bench set for at least
30 minutes before curing, lead to presence of fine
pits in the resin.
Rapid rise of temperature during the initial curing,
lead to gases porosity, crazing and fractured in the
acrylic denture base or teeth.
 Errors of Curing

100. Incorrect time and temperature of curing,
lead to incomplete curing.
Too much delay in the curing after
packing, cure of the denture lead to sandy
appearance in the resin material.
 Errors of Curing

102. 8. Cooling
• The flask should be cooled slowly
(bench cooled).
• Cooling for 30 min.
• Then placing under tap water for
15 min.

103. Rapid cooling after curing, leads
to cracked, warpage or fractured
of the denture base or the teeth.
 Errors of cooling

104. • Deflasking is done using a deflasker and
pribar.
• The lid (cover) of the flask should be
removed.
• The flask is inverted and placed on the
deflasker and tightened with a thumbscrew.
9. Deflasking

105. • Pribars are inserted laterally to fit in to the slots
of the flask.
• Separate the base and the body by lever action.

106. • Three incisions are
made one in the anterior
mid-point and two at the
posterior corners.
• Use plaster knife to remove plaster around the
denture.
• The body will slide out of the investment.
• The 2nd and 3rd pour are separated with
plaster knife.

108. - During deflasking: be careful to preserve the cast, also
do not left or remove the denture from the casts
 Clean the denture and cast from plaster.
 Remove any stone or bubbles from the exposed acrylic
resin and from the occlusal surfaces of the teeth.
 Remove any particles of stone from the base of the cast
and index grooves.
 Using a stiff brush, soap and water clean the denture
and cast before starting the laboratory remount.

109. • Improper deflasking as used the
hammer for knocking the flask, may
lead to cracked or fractured of the
denture base or the teeth.
 Errors of deflasking

110. Dentures being re-mounted on the original articulator and
adjustments carried out to provide correct articulation
(Laboratory Remounting).

111.  Laboratory Remounting
The cast with the processed denture should be remounted
on the articulator using the V-shaped notches for laboratory
Remounting.
using the split-cast method

112. The processed denture on the master cast is
repositioned to its old position on the articulator by
means of remounting indices made in the master
cast before mounting.
 Laboratory Remounting

113. Remount and Adjust for Processing Errors`
1. Errors of sealing
Improper sealing lead to change the relation between
the cast and plaster.

114. 10. Finishing & Polishing
1- Trimming
2- Sand papering
3- Pumice wash

115. Finishing and Polishing

116. Before trimming plaster at the necks of the teeth
is removed using a chisel.
Borders are trimmed using a laboratory size
carbide bur.
Frenum relief is given using a straight fissure bur.
The thickness of palatal surface is reduced using
a large egg-shaped bur.
Trimming:

117. The denture should be held against the light
and checked for translucency.
Guide for trimming:
Areas of opacity or darkness indicate excessive
thickness of the denture base. Uniform thickness
of 2 to 2.5mm must be maintained.

118. Sand paper finishing:
 Sand paper should be fixed on to a lathe
mounted sand paper mandrel.
Even the finest of all scratches should be removed
during this procedure.
Some technicians prefer the use of a wet sand
paper to improve the finish.

119. Polishing (Pumice wash)
• Pumice powder mixed with water is coated
over a rag wheel.
• The finished denture should be polished by
intermittently pressing against the rotating
rag wheel.

120. • A hand piece mounted rubber cup or a medium bristle
brush can be used to polish the inaccessible areas.
• After polishing, the denture should be thoroughly washed
in soap water.
• A tooth brush can be used to remove the remaining
plaster and pumice. After finishing, the denture are
stored in water and stored till the day of the insertion
appointment.

121. • After finishing, the denture are
stored in water and stored till the
day of the insertion appointment.

122. Errors during finishing and polishing
• Reduction should never be carried out on
the tissue surface.
• Care should be taken to avoid excessive
pressure on the denture to prevent Warpage
due to overheating during polishing.

123. Common laboratory Errors
a. Insufficient dough
b. Packed at sticky stage.
c. Rapid rise in temperature.
d. Lack of metal to metal contact.
1. Porosity
a. Contamination.
b. Rapid rise in temperature.
c. Rapid cooling.
2. Crazing
Small cracks which may vary in
size from microscopic dimension
to the visible size it indicates
beginning of fracture . cross
linking of resin reduces this fault
considerably .
a. Dry mix. (no enough monomer).
b. Evaporation of monomer.
c. Delayed curing.
3. Sandy
appearance

124. Stone not properly spatulated.
Air bubbles within the stone.
4. Denture base
with nodules
a. Improper flasking or deflasking.
b. Rapid curing or cooling.
c. Too much monomer.
5. Cracked or
fractured teeth
a. Plaster instead of stone in investing the trial denture.
b. Not enough time for plaster setting.
c. Late packing or over packing.
d. Incomplete closure of the flask.
e. Rapid pressure.
f. Teeth not retained.
6. Tooth
movement

125. 7. Incomplete cure
of the denture
a. Incorrect time and temperature of curing.
b. Organic solvents in contact with the acrylic resin.
8. Bleaching of
acrylic resin
a. An undercure.
b. Incorporation of the tin foil substitute with the acrylic
resin on its surface.
c. Incorporation of wet cellophane into the resin.
d. Contamination with same organic solvents.

126. 9. Stone adhere
to the surface
of the denture
a)Insufficient separating medium on the mold before
packing.
b)The application of separating medium contaminated
with stone.
c) Incomplete elimination of wax during washing out thus
rendering separating medium ineffective.
10 . Space
between the
teeth and resin
base:
a) Delayed curing leaving the flask without curing for a long time
.
b) The application of separating medium on the teeth.

128. References:
• Boucher, C. O., Hieckey, J. C. and Zarb, G. A.: Prosthodontic treatment for edentulous patients. 2nd ed., C. V. Mosby Co. St.Louis, 2000.
• Eissman, M.R.: Dental laboratory procedures, complete denture, C.V. Mosby company, St. Louis, Toronto, London, 2000.
• Hassaballa, M. A.: Clinical complete denture prosthodontics. 1st edition. Academic Publishing and Press, Riyadh, Saudi Arabia, 2004.
• Iwao Hayakawa: Principles and Practices of Complete Dentures creating the mental image of a denture, Tokyo Medical and Dental University, Tokyo, Japan. Quintessence
Publishing Co., Ltd. 1999.
• Iwao Hayakawa: research profile on BiomedExperts,The Journal of prosthetic dentistry 2007;98(2):141-9. 2007.
• Iwao Hayakawa: Principles and practices of complete dentures: creating the mental image of a denture, rapidshare.com, 27 Dec 2009.
• Kaddah, A. F.: OCCLUSION IN PROSTHODONTICS, Varieties, Aberrations & Management. Dar El-Etehad. First Co. First ed. Cairo Egypt. 98/7071, 1998.
• Tamer El-Gendy: Introduction to complete denture, Didactic and Laboratory Manual, Course Director: Tamer El-Gendy BDS, MS. Assistant Professor. COLLEGE OF
DENTISTRY, THE OHIO STATE UNIVERSITY.2000.
• Winkler, S.: Essentials of complete denture prosthodontics. 2nd ed., PSG Publishing. Co. Inc., 2005.
• Zarb, G. A., Bolender, C. L., Hickey, J.C. and Carlsson G. E.: Boucher’s Prosthodontic Treatment for Edentulous Patients, ed. 12th . St. Louis Mosby, 2000.
• Internet Sites:
• Full denture relining using Tokuso Rebase, By Dr. David J. Sultanov, DMD, Pittsburgh, PA. Information provided by J. Morita USA. The British Dental Journal is
published by Nature Publishing Group for the British Dental Association.© 2002 British Dental Association
• http://www.dentistry.bham.ac.uk/ecourse/pros/casetreat_w3.asp
• http://www.tpub.com/content/medical/14274/css/14274.
• The School of Dentistry, Birmingham UK
• Treatment options for edentulous spaces. Dr David C. Attrill d.c.attrill@bham.ac.uk
• Lectures and PowerPoint® presentation slides:
• Full denture relining using Tokuso Rebase By Dr. David J. Sultanov, DMD, Pittsburgh, PA. Information provided by J. Morita USA
• Lectures Posted by dental products .net. Originally published in the April 2001 Dental Products Report. Copyright 1999-2005 Advanstar Dental Communications.
• Lectures Produced in the United States of America. ISBN 0-7216-9770-4
• Related Links: About Tokuso® Rebase; Rationale for relining; Tips for success.

129. Thank You
and Good Luck