this is a presentation that describes the laboratory procedure in RPD framework fabrication also has a flow chart in the beginning explaining steps to be done by dentist and steps to be taken by laboratory technician https://youtu.be/aaJ6gpQohcs https://youtu.be/REMKSUty0cE https://youtu.be/fv3_tWZPJIU https://youtu.be/GeZIbCwqKYU if you want me to make ppt on some topic do let me know on the comment section of my youtube channel

1. Laboratory Procedure In RPD
Framework Fabrication
Piyali Bhattacharya
2nd Year PGT
HIDSAR

2. Steps In Fabrication Of Cast RPD
DENTAL
CLINIC
DENTAL
LABCOURIER
1. PRIMARY IMPRESSION
MADE,CAST POURED , 1.CAST SURVEYED,
2. UNDERCUTS MARKED,
3. SURVEY LINES DRAWN,
4. GUIDE PLANES
DETERMINED,
5. DESIGN ESTABLISHED
1. EXTRACTION OF HOPELESS
TEETH,
2. RESTORATION OF CARIOUS
TEETH
3. CROWN PREPARATION (TO
MAINTAIN PARALLELISM),
4. REST SEAT PREPARATION
5. IMPRESSION MADE
SECONDARY CAST SURVEYED
(IN THE SAME TILT OF THAT OF
DIAGNOSTIC CAST)

3. DENTAL
CLINIC
DENTAL
LAB
1. SECONDARY CAST IS DUPLICATED
USING AGAR
2. RPD DESIGN TRANSFERRED FROM
DIAGNOSTIC CAST TO SECONDARY
CAST AND CHECKED
3. BLOCK OUT AND RELIEF DONE ON
MASTER CAST
4. DESIGN TRANFERRED TO
REFRACTORY CAST AND SPRUED,
INVESTED, CAST, TRIMMED,
POLISHED AND FINISHED
METAL FRAMEWORK tried in
patient’s mouth

4. DENTAL
LAB
METAL FRAMEWORK SENT
BACK TO THE LAB
DENTAL
CLINIC
FABRICATION OF OCCLUSAL
RIM ON FRAMEWORK
JAW RELATION DONE MOUNTING OF CAST,
ARRANGEMENT OF TEETH
TRY-IN
FLASKING,DEWAXING AND
ACRYLYZATION, TRIMMING,
POLISHING
INSERTION

5. Laboratory procedures for metal
framework fabrication
Why metal framework…??
1. Maintains the accuracy of form without change
in mouth
2. Maintains contact intimacy of contact that
contributes to retention of prosthesis
(interfacial surface tension)
3. Inherent cleanliness of metal base contributes
to oral health

6. 4. Temparature changes are better transmitted to
the underlying tissue
5. Bulk and weight of metal denture base is much
lesser compared to acrylic resin yet provides
adequate strength and rigidity

7. Design transfer from diagnostic cast to master cast
STEPS-

8. Cast preparation
Beading is the act of scraping outline of the maxillary
major connector into the master cast
0.5 mm depth, prevents food lodgement
Not performed in mandibular cast RPD as the
margin rests on gingival tissues and are incapable of
withstanding the pressure.

9. Block out
• The act of placing wax and other materials into
undesirable undercuts on the master cast.
• Blockout is made by using different styli in the
surveyor to establish O-degree, 2-degree, or 6-
degree taper in the blockout wax
• Types of blockout-
Parallel blockout
Shaped blockout
Arbitrary blockout

10. Parallel Blockout
Areas Blocked out-
Interproximal surfaces to be used as
guiding plane
Beneath all minor connectors
On soft tissue undercuts to be
crossed by rigid connectors
Beneath bar clasp arms to gingival crevices

11. • Deep interproximal
spaces to be covered
by minor connectors
and linguoplates
Thickness-
Only undercut
remaining below
contact of the surveyor
blade with tooth surface

12. Shaped/ledged Blockout
Areas to be blocked out-
On buccal and lingual surfaces to locate plastic or wax
patterns for clasp arms

13. • Ledges for location of retentive clasp arm to be
placed as cervically as possible.

14. Arbitrary Blockout
• labial and buccal
tooth and tissue
structures not
involved in denture
design
Areas to be blocked –
Gingival crevices, gross tissue undercuts situated
below the design of denture framework, in maxilla
beneath deep palatal cleft to avoid sharp areas on
intaglio surface

15. • Tissue undercuts distal to the cast framework,
• Thickness-
Enough just to eliminate the gingival crevices

16. RELIEF
Any addition of wax intended to make the
framework stand away from master cast is known
as relief and also used to form internal finish lines
Material used-
Adhesive wax or hard baseplate wax
Areas to be relieved-
Beneath lingual bar
connectors or the bar
portion of liguoplates

17. On areas in which the major connector will
contact thin tissue e.g; Lingual or mandibular
ridges or elevated palatal raphes, Beneath
framework extension onto ridge areas , for
attachment of resin bases, beneath palatal tori

18. • After the relief wax is firmly attached to the cast,
it is trimmed with a sharp instrument , to act as a
tissue stop.
• A 2 x 2 mm section is removed
Maxillary stop Mandibular stop

19. Where is relief not advisable??

20. Problems in wax-up
Space exists between
upper border
of lingual plate and tooth
Blockout wax placed too
high
Pattern waxed over
blocked out area of
refractory cast
Take care to not overdo
blockout of master cast
Extend pattern above
blocked out region to
contact tooth
Lingual plate or maxillary
major connector too thin in
some areas
Casting wax was
overthinned by finger
pressure when pattern was
adapted to refractory cast,
Pattern was thinned when
smoothing with soft cloth
or alcohol torch
Do not use too much finger
pressure when adapting
soft casting wax
Take care when smoothing
to not overthin; do not use
alcohol torch to smooth
casting wax
Components are misplaced Brown pencil outline not
placed properly or outline
was not followed closely
when waxing components
Make certain brown pencil
outline follows exactly
outline on master
cast; when placing and
waxing components, make
certain that they follow
brown outline precisely

21. Sprue Guide placement
1. Sprues should be large enough for the molten
metal not to solidify in them until after the metal
casting has frozen.

22. 2) Sprues should lead into the mold cavity as
directly as possible and still induce minimal
amount of turbulence
3) Sprues should leave crucible from a common
point of attachment and be attached to the
bulkier section.
Two basic types of sprues are used –
8-12 guage round wax shapes for main sprues
12-18 guage round wax shapes for auxiliary
sprues.

23. Casting
• Induction casting has become the method of
choice
• Temperature is about 1371⁰c(2500⁰F)
Factors Influencing The Excellence Of Casting
1. Care and accuracy of cast reproduction
2. Intelligent designing of framework
3. Care and cleanliness in waxing up cast
4. Consideration of wax expansion caused by
temperature

24. 5. Size, length, configuration, points of
attachment, and ,manner of attachment of
sprues
6. Choice of investments
7. Location of the pattern in the mold

25. 8. Temparature of the mixing water ,
9. Degree of spatulation of the , setting time
10. Burnout temparature
11. Casting defects
12. Shrinkage on cooling
13. Removal from investment after casting
14. Scrubbing, pickling
15. Polishing, finishing
16.Heat handling

26. Casting Defects
Excessive cracks in mold
during Casting
Casting ring not lined
Investment too dry when
placed in oven
Temperature raised too fast
Line casting ring with
substitute asbestos
Liner
Soak ring in water for few
minutes before placing in
oven; do not place in
preheated oven
Start burnout in cold oven
and raise temperature
gradually
Pitted and discolored
casting
Investment overheated Do not overheat
investment: start in
cold oven and raise
temperature
Gradually

27. Portions of framework did
not cast
Metal too cold when cast
Improper spruing
Gas trapped in mold
Have metal fluid and at
proper temperature
Sprue framework to
eliminate casting
thick portions through thin
portion
Do not vacuum spatulate
outer investments
Pattern failed to cast Pattern separated from
crucible former during
investing
Reinforce main sprue with
bur or wire;
use proper diameter sprue;
handle carefully during
investing;
do not vibrate too heavily

28. Finishing and Polishing
Rough finishing and polishing:
Discs, Metal trimming burs, points,Rubber wheels
are used to give a “satin” finish. Nodules are
removed from the surfaces that contact the teeth
The intaglio surface of critical framework
components such as rests, retentive clasp tips, and
proximal plates must receive an absolute
minimum finishing .

29. Electropolishing
A form of electrolytic stripping is usually the first
step in polishing framework. In this process the
ions of metal from rough projections on the
framework go into the solution before the
smooth areas do.
Each sq. inch metal requires 2 amperes of current
for 6 minutes.

30. • Fitting The Framework
Final polishing
1. 2.
3. 4.

31. 5.
6.

32. Problems with finishing and polishing
Polished surface is dull
with fine scratches
Sequence of finishing
steps not followed
Steps not carried to
completion
before proceeding to
next step
Follow steps as outlined; do
not ‘'jump'’ steps
Complete each step before
proceeding to next one
Major or minor
connector overthinned
and flexible
Casting too thin as a
result of incorrect wax-
up
Framework overthinned
with abrasive stones
during finishing
Use care when finishing
connectors to avoid
overthinning;
Check frequently during
finishing

33. Clasp is nicked or notched
Clasp was miscast
Clasp was nicked with
stone or bur during
finishing
Use correct wax
thickness on pattern
Take care to avoid nicking
framework with bur or
wheel
Framework distorted Framework caught in
lathe during finishing
Take care when using lathe
to prevent framework from
being caught in polishing
wheel

34. Bacterial Colonisation In Cast RPD Framework
• It is considered that the bacterial species
adhered to the Co-Cr surfaces may differ from
that of acrylic resin surfaces.
• RPD clasps harbors a highly diverse bacterial
population and the bacterial community on the
RPD metal clasp develops into a complex mature
community, including putative periodontal and
opportunistic pathogens.
*Cristiane Machado Mengatto et. al, Partial denture metal framework may harbor
potentially pathogenic bacteria, J Adv Prosthodont 2015; 7:468-74

35. Titanium Removable Dentures
1 The use of titanium for the production of cast
RPD frameworks has gradually increased.
2 There are no reports about metallic allergy
apparently caused by CP titanium dentures.
3 The laboratory drawbacks still remain, such as
the lengthy burn-out, inferior castability and
machinability, reaction layer formed on the cast
surface, difficulty of polishing and high initial costs.

36. 4 The clinical problems, such as discolouration of
the titanium surfaces, unpleasant metal taste,
decrease of clasp retention, tendency for plaque to
adhere to the surface, detachment of the denture-
base resin and severe wear of titanium teeth have
gradually been resolved.
5 Titanium RPD frameworks have never been
reported to fail catastrophically.
*C. OHKUBO et al, Present status of titanium removable dentures – a review of the literature,
Journal of Oral Rehabilitation 2008 35; 706–714

37. Most Suitable Material to Be Used as Partial
Denture Clasps
• Acetal resin proved to be the non-metallic
material of choice due to its superior properties
regarding roughness, retention and deformation,
while Valplast(belongs to the Nylon family) is the
lowest at the end of one year follow up.
• Utilising Acetal resin is the best nonmetallic
partial denture clasp, while the Cr Co can be used
as the metallic one.
Sherif Aly Sadek et al,Comparative Study Clarifying the Most Suitable Material to Be Used as
Partial Denture Clasps ; J Med Sci. 2018 Jun 20; 6(6):1111-1119.

38. References
1. Dental Laboratory procedures, vol III, removable partial dentures,
KENNETH D. RUDD, ROBERT M. MORROW, JOHN E. RHOADS,
2. McCraken’s Removable PartialProsthodontics,
4th Edition
3. Stewart’s Clinical Removable Partial Prosthodontics, 4th Edition
4. Cristiane Machado Mengatto et. al, Partial denture metal
framework may harbor potentially pathogenic bacteria, J Adv
Prosthodont 2015; 7:468-74
5. C. Ohkubo et al, Present status of titanium removable dentures – a
review of the literature, Journal of Oral Rehabilitation 2008 35;
706–714
6. Sherif Aly Sadek et al,Comparative Study Clarifying the Most
Suitable Material to Be Used as Partial Denture Clasps ; J Med Sci.
2018 Jun 20; 6(6):1111-1119.