This document discusses impressions and physiologic adjustment of removable partial denture frameworks. It covers topics such as impression materials like alginate, rubber base and silicones. It describes taking impressions with stock trays and custom trays, as well as altered cast impressions. It provides details on caring for impressions, making casts, inspecting RPD castings and physiologic adjustment of frameworks.

1. Impressions and Physiologic Adjustment
John Beumer III DDS, MS
Tak Ogawa DDS, PhD
and
Ting Ling Chang DDS
Division of Advanced Prosthodontics, Biomaterials and
Hospital Dentistry
UCLA School of Dentistry
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2. v Impressions for RPD frameworks
v Physiologic adjustment of RPD
frameworks
v Altered cast impressions
v Border molded master impressions with
custom trays

3. Impressions and Casts
Impression materials
v Alginate
v Rubber base
v Silicone
v Mouth temperature waxes
Impressions with stock trays followed
by altered cast impressions
v Boxing altered cast impressions and making
casts
Impressions with custom trays

4. Alginate (Irreversible Hydrocolloid)
Use
v RPD framework impressions
Advantages
v Can be used in the presence of saliva
v They are hydrophillic
v They have a pleasant taste and odor
v They are inexpensive
v They pour well with stone
Disadvantages
v Low edge strength
v Provide less surface detail than other materials
These materials must be stored in 100%
humidity and poured within 1 hour.

5. Rubber Base (Polysulfide)
Use
v Framework impressions
v Altered cast impressions of
edentulous extension areas
Advantages
v Betteredge strength than
alginate
v Moderately inexpensive

6. Rubber Base (Polysulfide)
Disadvantages
v Medium and heavy body are highly cross
linked and do not recover well from
deformation and should not be used when
large numbers of teeth display significant
undercuts
v The material must be held still during the
impression making procedure because the
material does not have a snap set
v Requires carefully fabricated custom trays
that ensure uniform thickness of the
impression material
v Unpleasant odor
v Stains clothing

7. Silicones
Use
v Framework impressions
Advantages
v The most accurate are addition reaction types
v Less polymerization shrinkage
v Low distortion
v High tear strength
v Fast recovery from deformation
v Short working times (3-5 minutes for addition reaction types and
5-7 minutes for condensation types)
v Can be used in a stock tray
v Available in both hydrophilic and hydrophobic forms
v Available in automixing devices
v Multiple pours are possible if poured within 1 week
Disadvantages
v More expensive compared to other materials

8. Mouth Temperature Waxes
Use
v For recording edentulous denture bearing surfaces in an
extension based RPD patient when making altered cast
impressions
Advantages
v They have the ability to flow and consequently while in the
oral cavity and allow equalization of pressure and minimize
the risk of tissue displacement while making the impression
v Good tissue detail
Disadvantages
v Requires an occlusal index
v More time consuming

9. Impressions with a Stock Tray
*Plastic trays are
contraindicated for
master impressions
because they lack
rigidity
Requirements
v Confine the impression material to assure close
adaptation to the teeth and soft tissues
v Must be rigid*

10. Impressions with a Stock Tray
v Posterior extension – add wax or compound when
necessary, check with mirror and mouth movements.
v Mandible – If necessary, add periphery wax on lingual
surface of tray, from premolar back to assist in
displacing the tongue.
v Maxilla – Add wax to posterior palatal border to keep
impression material from extending posteriorly.
v Warm wax for fitting, then chill with water prior to
impression.

11. Impression with a Stock Tray
Impression material: Alginate
Procedure:
v Follow powder-water ratio set by manufacturer. May be
occasionally necessary to reduce water slightly to
increase viscosity for soft tissue displacement.
v Keep impression in mouth then remove in one swift,
positive movement.
v Use warm or cold water to adjust setting time.
v Pour cast immediately
v Imbibition– distortion by water absorbtion.
v Syneresis – loss of water and shrinkage distortion.

12. Impressions with a Stock Tray
Compound support
where needed Don’t forget to spray
alginate adhesive
onto the inner
surface of the tray.
Requirements
v Provide for mechanical locking of impression
material to the tray
v Provide for an relatively even or consistent
thickness of impression material in the impression

13. Impressions with a Stock Tray
To avoid bubbles use a syringe filled with alginate to
apply impression material to rests, guide planes,
occlusal surfaces and the the gingival margins.

14. Care of Impressions and Making Casts
Thoroughly examine the impression to
determine its acceptability
Remove excess alginate
that extends beyond the
back of the tray
v Cut carefully and
towards the tray to
avoid pulling the
alginate away from the
tray.
While mixing stone place the tray in a holder to avoid placing the tray on
the bench-top. Avoid wrapping the tray in a cloth or paper towel since
uneven stress and/or moisture may distort the impression.

15. Care of Impressions and Making Casts
Carefully rinse the
impression with cold tap
water in order to remove
saliva* from the surface of
the impression
Failure to do so will result in a cast with a soft or chalky surface.
*Saliva can be identified on the cast by sprinkling stone on the
impression and gently rinsing it away with tap water.

16. Care of Impressions and Making Casts
Before pouring the cast
remove all moisture with a
gentle stream of air. Be
careful not to over-dry the
impression.
Never box an alginate impression with wax or a
mixture of plaster and pumice.

17. Double Pour Technique
v Do not invert first pour of stone.
v Base is 10-15 mm thick.

18. Care of Impressions and Making Casts
Problem Probable cause
Surface of the v Saliva in the impression when cast
cast soft or was poured
chalky v Improper water powder ratio used
v Water from rinsing remains in
impression
Distorted cast v Impression material separated from
the tray
v Air inclusion in impression that
distorts when stone is poured
v Nonrigid tray used for impression
v Premature separation of the tray from
the cast

19. Care of Impressions and Making Casts
Pouring the cast
v Measure the required amounts of water and powder
v Carefully mix the stone in a vacuum power mixer
v Using gentle vibration, flow the stone into the
indentations in the impression formed by the teeth.
v Use a small brush to avoid trapping air
v The bottom surface of the cast should be rough to
facilitate attachment of the base
v Suspend the poured impression by the handle in the
tray holder
v Once the stone is fully set invert the cast and add a
base. The base should be 10-15 mm thick.
v After 60 minutes of the first pour, separate the
impression from the cast.

20. Care of Impressions and Making Casts
Trimming the cast
Before trimming the cast
soak it in clear slurry water
for 5 minutes. Trimming
should not begin until 24
hours after pouring.
The cast should never be rinsed, or soaked in
water because dental stone is water soluble.

21. Care of Impressions and Making Casts
Trimming the cast
Failure to soak the cast
in slurry water will result
in sludge adhering to
and damaging the cast.
The cast should be trimmed so that its base is
10-15 mm thick. The land should be 4 mm wide.

22. Inspection of the RPD Casting
v Does
the RPD framework conform to the
drawing on the study cast

23. Inspection of the RPD Casting
v Inspect for roughness and bubbles
v Rests must well adapted to their rest
seats
v There should be no metal flash
extending beyond the rest area
v The casting must not rock
inappropriately

24. Inspection of the RPD Casting
v The retainers must be
precisely positioned per
the design
v The proximal plates must
be contoured per the
design

25. Inspection of the RPD Casting
Quality of the RPD casting
v Porosity
v Rough or irregular areas
v Sharp edges
v Contour of the connectors
v Proper bulk and thickness for strength
and rigidity

26. Physiologic Adjustment of RPD Metal
Frameworks
RPD’s must rotate freely around the axis of rotation in
order to prevent the RPD from delivering torquing
forces to the abutment teeth during occlusal function

27. Physiologic Adjustment
Purpose :
v To prevent the RPD framework from binding
on the abutments and minimize torquing of
teeth during mastication
v Areas of greatest concern
v Proximal plates
v Minor connectors
v Lingual plates
The objective is to permit the RPD is rotate freely around the axis
of rotation (fulcrum line) during function.

28. Physiologic Adjustment
Extension Based RPD’s
Movement of Proximal Plates
v In this example, when an occlusal force is applied to the
edentulous extension area, the proximal plates contacting
the distal surfaces of the abutments, will engage the tooth
surface, producing a torquing action.
v To avoid this problem, the RPD is “physiologically adjusted”

29. Physiologic Adjustment
Extension Based RPD’s
Movement of Minor Connectors
v In this example, when an occlusal force
is applied to the edentulous extension
area, the minor connectors will engage
distal surfaces of the teeth anterior to
the abutment preventing pure rotation
around the rests.
v To avoid this problem, the RPD is
“physiologically adjusted”

30. Physiologic Adjustment
Method
v Dissolve gold rouge with chloroform
v Apply this solution to the surfaces engaging the teeth of the RPD casting.
The chloroform will quickly evaporate, leaving a thin layer of rouge on the
casting
v The RPD casting is seated and pressure is placed on the extension area
v The rouge will be rubbed away from areas of the casting that are
inappropriately binding to the dentition.
v These areas are relieved with a suitable burr and a high speed air rotor
v The procedure is repeated until the framework rotates freely around the
axis of rotation

31. Physiologic Adjustment
Method
v A disclosing medium (gold rouge and chloroform) is applied to the
undersurface of casting. Pressure is applied in the extension areas. As the
casting rotates the rouge will be rubbed away from the casting.
v These areas are adjusted with a high speed hand-piece until the casting
freely rotates around the axis of rotation as designed without lifting.

32. Physiologic Adjustment
Method
v Inthis example the rouge has been rubbed off
from the minor connectors and areas associated
with the lingual plate

33. Physiologic Adjustment
Method
v When the procedure is complete the RPD framework will
rotate freely around the axis of rotation with out lifting out of
the rest seats that determine the axis

34. Altered Cast Impressions
For extension base RPD’s

35. Altered Cast Impressions
Preparation of the Extension Tray
Tray must be properly extended. However 1mm of relief
between tray and soft tissue surface of the preliminary cast
should be provided. In this case a thin layer of baseplate wax
has been applied to the preliminary cast in the extension areas

36. Altered Cast Impressions
Preparation of the Extension Tray
v Thewax is removed from the tissue
surface of the tray. Note the relief.

37. Altered Cast Impressions
Making the impression
v Insert
the RPD
casting and tray
into the mouth
v Checkthe borders
to ensure the tray
is properly
extended
v Thetray must
extend onto the
buccal shelf and
the retromolar pad

38. Altered Cast Impressions
Making the impression
Border mold the tray extensions with dental compound
v Make sure you extend the tray properly and cover the prime support
areas (retromolar pad and the buccal shelf)
v During border molding make sure the casting seats properly every time
you readapt the border molded extensions

39. Altered Cast Impressions
Making the impression
Extend your border molding to the opposing occlusion. This
enables you to make a tentative centric relation record at the
same time you are making the altered cast impression.

40. Altered Cast Impressions
Making the impression
v Perforate the tray along the finish line with a round burr (either #6 or #8)
v Cut back the compound extension to make room for the material used in
making the corrected impression
Make sure the casting seats perfectly
before making the corrected impression.

41. Altered Cast Impressions
Making the impression
v Apply the adhesive right up to the finish line.
v When making the wash impression apply a very thin layer
impression material along the finish line. Don’t overload this
area.

42. Altered Cast Impressions
Completed impression
The multiple perforations have prevented the wash material from spilling onto
the major connector. If wash material does spill onto the major connector
carefully remove it with a scalpel with a fresh blade.

43. Boxing altered cast impressions
v Remove the extension area past the finish line and onto the
major connector
v Cut multiple retention grooves onto the bottom side of the cast
as shown
v Seat the RPD framework onto the cast. Be sure all rests are
seated
v Lute the RPD framework to the cast with sticky wax
v Box the impression as shown

44. Boxing altered cast impressions
v Remove the extension area past the finish line and onto the major connector
v Cut multiple retention grooves onto the bottom side of the cast as shown
v Seat the RPD framework onto the cast. Be sure all rests are seated
v Lute the RPD framework to the cast with sticky wax
v Box the impression as shown

45. Care of Impressions and Making Casts
Completed
Cast
" Box the impression as shown with beading and boxing wax.
" Before pouring the impression soak the boxed impression in
slurry water for at least 5 minutes.
Do not soak the cast in tap water.
Dental stone is water soluble.

46. Mount the centric relation record
v Mount the tentative centric relation record with the compound
occlusal index
v This record must be verified at the try-in appointment

47. Mounted altered cast

48. Altered Cast Impressions
Problems Probable Cause
Second pour v Retention on original cast
separates from is inadequate
the first pour v Original cast at time of
first pour too dry
Dental stone on v Poor seal of beading wax
teeth of cast
Framework with v Impression material under
impression does rests or minor
not seat completely connector, or the ridge
on the cast areas of the cast not
trimmed adequately

49. Altered Cast Impressions
Problems Probable Cause
Difficulty in removing v Failure to heat compound
impression from before separating
altered cast v Undercuts in the impression
tray
Completed RPD v Framework not seated
rocks in the mouth when impression made
• Inadequate cutback
• Impression material under a
rest
• Impression material under the
major connector

50. Impressions with custom trays

51. Preliminary Casts
Hard and Soft Tissue Landmarks Visible.
Extensions Visible.

52. Custom Tray Fabrication
v Block-out Soft, Hard Tissue Undercut Areas.

53. Fabrication of Custom Trays
Apply spacer for impression
material.
v Elastomeric Material: 2-4 mm
v Alginate: minimum 3 mm

54. Custom Tray Fabrication
Carefully remove all wax from the tissue surface of the tray
with hot water. The impression materials we use will not stick
to the wax and there is risk of the impression material
separating from the tray distorting the impression.

55. Border mold extension with dental
compound
v Adjustlength of tray borders as needed
v Border mold all Borders with dental compound

56. Final Impression
Patient Preparation
v Prophylaxis – flour of pumice, prophy paste
v Pack arch with gauze. Block salivary ducts
v Block un-necessary undercuts. Soft and hard
tissues
v Instructions to patient
v Relax lips, tongue, and cheeks
v Advise patient that you will ask them to lift their
tongue
v Ask patient to concentrate on breathing.

57. Impression Tray Preparation
v Applyadhesive on internal surfaces and
external extension areas

58. Completed Impressions

59. Box and pour impression

60. Placement of Wax
Beading Wax Boxing Strips
Soft Tissue Undercut
And Tongue Areas To All Borders To Beaded Areas

61. Box and Pour Master Cast
Carefully remove salivary residues and dry
the cast. Polysulfide casts need to be
poured within 30 minutes.

62. Fabricate RPD framework
v Fabricate record bases
v Make CR or CO records

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