good presentation

1. LAB PROCEDURES FOR
COMPLETE DENTURES AFTER
TRY-IN
GUIDED BY- PRESENTED BY-
DR. ASHISTARU SAHA DR. POOJAAGRAWAL
DR. TUSHAR TANWANI
DR. ANUPAM PURWAR
DR. NEHA NAVLANI

2. CONTENT-
 INTRODUCTION
 ACRYLIC RESINS
 DENTURE PROCESSING TECHNIQUES
 FLASKING
 DEWAXING
 APPLICATION OF SEPARATING MEDIUM
 MIXING AND PACKING
 CURING
 DEFLASKING

3.  REMOUNTING
 FINISHING AND POLISHING
 CONCLUSION
 REFERENCES

4. INTRODUCTION
 The Glossary of Prosthodontic terms defines a complete
denture as a removable dental prosthesis that replaces the
entire dentition and associated structures of the maxilla or
mandible.
 Processing converts the trial denture into a denture in its final
form.
 Success of complete denture is completely dependent on the
quality of processing.

5. ACRYLIC RESINS
 Since the mid-1940s, the majority of denture bases have
been fabricated using poly (methyl methacrylate) resins.
 Such resins are resilient plastics formed by joining multiple
methyl methacrylate molecules or “mers”.
 Poly methyl methacrylate denture base material usually is
supplied as a powder-liquid system.

6. Based on the method used for activation or curing
types of resins are-
 Chemically activated denture base resin.
 Light activated denture base resin.
 Heat activated denture base resin.

7. Chemically activated denture
base resin
 chemical activators used to induce the
polymerization or curing of denture base resin.
 referred to as cold curing, self curing or
autopolymerizing resins.

8. Light activated denture base
resin
activator
initiator
 This material has been described as a composite
having a matrix of urethane dimethacrylate,
microfine silica, and acrylic resin monomers.
Visible light
camphoroquinone

9. Heat activated denture base
resin
activator
Water bath/micro-oven
 As previously noted, denture base resin contain
benzoyl peroxide.
 When heated above 60 degree, molecules of
benzoyl peroxide decompose to yield free
radicals.
Thermal
energy

10. COMPOSITION
 HEAT ACTIVATED PMMA-
 POWDER-
 Polymethyl methacrylate
 Benzoyl peroxide – Initiator(0.5%)
 Pigments and dyed synthetic fibers
 LIQUID-
 Methyl Methacylate
 Hydroquinone- Inhibitor(traces)
 Glycol dimethacrylate- Cross-linking agent(10%)

11.  CHEMICALLY ACTIVATED RESIN-
 POWDER-
 Polymethyl methacrylate
 Benzoyl peroxide – Initiator(0.5%)
 Pigments and dyed synthetic fibers
 LIQUID-
 Methyl Methacylate
 Hydroquinone- Inhibitor(traces)
 Glycol dimethacrylate- Cross-linking agent(10%)
 NN-dimethyl-p-toluidine-Activator

12.  LIGHT ACTIVATED RESINS
 Single component, premixed composite sheets
and ropes
 Matrix- Urethane dimethacrylate
 Filler- Methacrylate resin beads, microfine silica
 Photoinitiator- Camphoroquinone

13. DENTURE PROCESSING
TECHNIQUES-
 Compression moulding technique
 Injection moulding technique

14. Compression moulding
technique
 Compression molding is a molding process during
which resin is placed between two dies of a mold
and subjected to pressure and heat to create a
finished part.

15. Injection moulding technique
 It is a complicated procedure requiring special
flask and equipment. In this technique the wax
pattern is sprued and the material is injected into
the mold. This process allows injection of further
material during polymerization to compensate for
the polymerization shrinkage.

16. COMPRESSION MOULDING
TECHNIQUE
 The most commonly used technique for acrylic resins-
 1.Preparation of the trial denture
 2. Disarticulation
 3. Flasking produce
 4. Dewaxing ( Boil out )
 5. Application of the separation medium

17.  6. Mixing of powder and liquid
 7. Packing
 8. Curing
 9. Deflasking
 10. Finishing and Polishing

18. PREPARATION OF TRIAL
DENTURE
 After try-in, the trial dentures are placed on the cast and
sealed to the cast using additional wax.
 This is done so that the relationship of the trial denture and
the cast is not altered during disarticulation.

20. DISARTICULATION
 The junction between the mounting plaster and the
cast is split with the help of a wax knife and a
plastic mallet.

23. FLASKING
 Flask: Is a metal case or tube used in investing
procedures.
 Flasking: The process of investing the cast and a
waxed denture in a flask to make a sectional
mould used to form the acrylic resin denture base.

24.  The flask is made of 3 major parts,
 (1) lower half (which contains the cast),
 (2) upper half and
 (3) the cover or lid.
 The lower half may have a round plate, covering a
round hole in the base of the lower half.

35. Steps in flasking
 The waxed maxillary denture on its wetted cast is
placed in the bottom part of a denture flask that has
been partially filled with plaster.
 It is forced into the plaster until the land of the cast is
relatively level with the brass sides.
 The wet plaster is then smoothened from the brass
edge toward the land of the cast so that no undercuts
exist, and all plaster is wiped from the edge of the
flask.

36.  When the plaster has set, a film of separating
medium is painted on the plaster and the land of
cast. This medium will separate this layer from the
next.
 The upper half of the flask is now placed in
position making certain that it is completely
seated on the lower half.
 The remaining part of the investment may be
totally of stone or totally of plaster.

37.  A combination of plaster and stone is
recommended. The stone is painted with a brush
into the interproximal spaces and around the
gingival spaces; it is then poured to the level of
the incisal and occlusal surfaces of the teeth.
 The remaining space is filled with plaster.

38. DEWAXING
 When the flasking materials have set, the flask
should be heated in boiling water for 4 minutes.
 The object is to soften the wax, not to melt it.
 If the wax is properly softened, it can be easily
lifted from the teeth, almost in one piece with the
trial base, and discarded.

41. APPLICATION OF THE
SEPARATION MEDIUM
 The flask is now allowed to cool to a point where
it can be held in the hand, and separating medium
is applied to separate the denture base material
from the investing stone or plaster.
 All the gypsum mold surfaces must be painted.

42.  Various types of separating media used are-
 Tin foil
 Cellulose lacquers
 Solution of alginated compounds
 Calcium oleate
 Soft soaps
 Sodium sillicate
 Starches

43.  Sodium alginate solution- It is commonly known
as “Cold mould Seal” and is the widely used
separating media because of it’s effective and easy
manipulation.
 Composition-
 Sodium alginate solution
 Sodium phosphate
 Glycerine
 Alcohol
 Preservatives

44. MIXING AND PACKING
 The monomer and polymer are mixed according
to the instructions supplied by the manufacturer.
 The ratio is 1 part monomer to 3 part polymer by
volume or 1 part to 2 parts by weight.
 When the powder and liquid components are
mixed in the proper proportions, a doughlike mass
results.

46. POLYMER-MONOMER
INTERACTION
 Sandy stage
 Stringy stage
 Doughlike stage
 Rubbery Stage/elastic stage
 Stiff stage

47.  DOUGH- FORMING TIME- The time required
for the resin mixture to reach a doughlike stage is
termed the dough-forming time.
 WORKING TIME- Working time may be defined
as the time that a denture base material remains in
the doughlike stage.

48. PACKING
 The placement and adaptation of denture base
resin within the mold cavity is termed packing.
 The placement of too much material, that is
overpacking leads to a denture base that exhibits
excessive thickness and resultant malpositioning
of prosthetic teeth.
 The use of too little material, that is underpacking
leads to denture base porosity.

49.  The packing process should be performed while
the denture base resin is in a doughlike stage.
 The resin form is bent into a horseshoe shape and
placed into the portion of the flask that houses the
prosthetic teeth.

55.  Then a polyethelene(nylon sheet) is placed over
the dough in the upper half and then the two
halves of the flask are closed until they are almost
in approximation, this is done to spread the dough
evenly throughout the mold.
 Then the two halves of the flask are separated, the
excess material at the borders of the denture is
removed by a wax knife, and additional resin is
added at any places that are deficient.
 At least two trial closures are done and before the
final closure the polyethelene sheet is removed
and then the two halves of the flask are closed
under pressure by bench press.

56. CURING
 After the final closure of the flask in the
compress, they should remain at room temperature
for a minimum of 1 hour or as much as 4 hours.
 This is termed as bench curing.

57.  It offers several advantages-
-it provide longer flow period,
thus permitting an equalization of pressures
throughout the mold.
-it allows time for a more uniform dispersion of
monomer throughout the mass of dough,
-it also provides longer exposure of resin teeth,
to the monomer in the dough.

58.  Curing is polymerization of the heat cure acrylic,
to produce the final denture.
 The material is cured by heating in a water bath.
 pressure is applied during curing for the following
reasons:
1- To decrease the effect of thermal expansion.
2- To decrease the polymerization shrinkage.

59. Curing cycle
 The heating process used to control
polymerization is termed the polymerization cycle
or curing cycle.
 Types of curing cycles for heat cure acrylic:
 1- Short curing cycle .
 2- Long curing cycle
 3- Ultra short curing cycle

60. 1- Short curing cycle: rapid processing
 Submerge the closed flask in water at 71o C for
one and half hour followed by boiling for one
hour.

61. 2- Long curing cycle: slow processing:-
 9 hours at a constant 71o C is considered adequate
for the average denture.
 If boiling also is desired in the slow cure, the
temperature should be held at 71oC for 9 hrs and
then raised to 100o C for 30 minutes.

62.  The amount of heat must be controlled while
processing acrylic resin, as the reaction is
exothermic and becomes very rapid at temperature
between 60o and 71oC.
 Once polymerization has begun , the temperature
of the resin may be considerably higher than the
temperature of water bath.

63.  For this reason, the temperature of the water
should be maintained at ,or below , 71oC for at
least 1 and ½ hrs so that the exothermic heat can
be conducted away from the resin.
 The boiling point of monomer is 100.8oC. If the
heat is not controlled, the exothermic reaction will
cause the monomer to boil and result in area of
porosity.

64.  3- Ultra short curing cycle-
polymerized in 100oC
for 20 min
immediately after being packed.
In hybrid acrylics both chemical and heat activated
initiator formulated to allow rapid polymerization
without porosity.
Hybrid
acrylics

65. Curing cycle according to
different manufacturer
Acrylic resin Curing cycle
Trevalon -immerse flask in boiling water
-turn off heat for 20 min.
-Re-heat 100oC for 10 min.
Triplex -immerse flask in cold water,
-heat up to 100oC
-& boil for 45 min.
Lucitone -90 min in 73oC
-then 30 min in boiling water.
pyrax -immerse flask in cold water
-heat up to 100oC for 30 min
-then boil for 30 min.
DPI -2 hrs in 74oC
-increase the temp up to 100oC &
processing for 1 hr.

66.  At the close of curing cycle, the flasks in their
compress are removed from the water and allowed
to cool on the bench.
 The compress must not be loosened until the
operator is certain that the centre of the flask has
reached room temperarure,

67. POLYMERIZATION VIA
MICROWAVE ENERGY
 Polymethyl methacrylate resin also may be
polymerized using microwave energy.
 This technique employs a specially formulated
resin and a nonmetallic flask.
 A conventional microwave oven is used to supply
the thermal energy required for polymerization.

68. DEFLASKING
 When deflasking complete dentures, it is best to
use a deflasker, which allows retrieval from the
flask without damage to the dentures or flask.
 The lid of the flask should be removed by prying
with wax knife.
 The flask is inverted and placed on the deflasker
and tightened with a thumbscrew.

76.  Pribars are inserted laterally to fit on to the slots
of the flask. Once these pribars are engaged, they
are lifted up , so that they separate the base and
the body by lever action. The body or counter will
slide out of the investment.
 Place a knife blade in contact with the junction
between the second and third pour investment.
Tap the back of knife blade with plastic mallet to
separate the stone cap and to expose the cusp tips
and incisal edges of the denture.

77.  With a saw and spiral blade, cut through the stone
that encloses the denture opposite the central
incisor teeth.
 Place more saw cuts at the distobuccal corners of
the flasked denture.
 Placing a knife in the anterior and posterior saw
cut and gently separate the stone from the buccal
and anterior flanges of the denture.

78. REMOUNTING
 The remounting procedure gives the operator the
oppourtunity to see the changes that occurred in
the teeth during processing and makes it possible
to restore the occlusion that existed on the
completion of waxing.
 The dentures on their casts are seated, by means
of the index notches that were cut on the cast
bases before they were mounted on the articulator,
on the original plaster mountings and attached
with plaster that is added to the sides.

81.  Normally the incisal pin will show a slight
opening.
 Articulating paper is placed between the teeth, and
the articulator opened and closed in the centric
position.
 The marks made by the paper indicate which areas
should be ground.
 This is continued until the original vertical
dimension has been restored.

84. FINISHING AND
POLISHING
 The dentures on their casts are now removed from
the articulator, and the casts separated from the
dentures.
 The borders, as well as all other areas reduced
with the arbor bands, then polished using a wet
mix of pumice on a wet rag wheel
 Highly polished denture surfaces are more
resistant to stains, are more easily cleaned by the
patient, and are more conductive to tissue health.

92.  The inside surface of the denture should be
examined both by the eye and the finger and all
sharp projections smoothed or removed.
 The dentures should then be thoroughly cleaned
with warm water, soap and a stiff brush and stored
in water until they are delivered to the patient.

93. Effect of different curing temperatures on the
distortion at the posterior peripheral seal: An in
vitro study
Pasam N, Hallikerimath RB, Arora A, Gilra S.
Indian J Dent Res 2012;23:301-4
 Most of the maxillary complete dentures do not
adapt accurately to the cast because of the changes
in the resin during polymerization.

94. Minimum
distortion
Maximum
distortion
no significance difference between the denture bases processed
from 68 to 72°C.
70°C
80°C

95.  Amount of distortion increases as the processing
temperature increases which was highly
significant.
 This study carried out on an ideal edentulous
maxillary cast to determine the discrepancy
incorporated into the posterior aspect of maxillary
denture bases by long curing cycle.

96. CONCLUSION
 All these laboratory steps are important for
complete denture construction. Esthetics, function
and patient satisfaction depend on a skillfully
waxed and properly processed prosthesis.

97. REFERENCES
 Sharry J J. Complete denture Prosthodontics. Third edition.
A Blakiston publication.
 Morrow R M, Rudd K D, Rhoads J E. Dental laboratory
procedures Complete dentures. Second edition. C. V. Mosby
company .
 Anusavice K J. Phillips’Science of dental materials.
Eleventh edition. Elsevier Publication.
 RangarajanV, Padmanabhan TV. Textbook of
Prosthodontics. Elsevier Publication.
 Effect of different curing temperatures on the distortion at
the posterior peripheral seal: An in vitro study
Indian J Dent Res 2012;23:301-4.