secondary impression for partial

1. The Final Impression for
RPD
Prof.Dr. Waleed Maryod
Professor of prosthodontics, MSA University
Faculty of Dentistry
Removable
Prosthodontic Dept.

2. LECTURE OUTLINE
• Principles of RPD.
• Types of impression techniques.
• Impression materials.
• Anatomic and functional impression techniques.
• Selective pressure impression technique.
• Objectives of final impressions.

3. LECTURE ILOs
• Having knowledge about different impression techniques.

4. Principles of RPD Design
R- B -S
1. R = Retention.
2. B = Bracing.
3. S = Support.

5. Tooth Supported RPD

6. Tooth-Tissue Support RPD

8. Types Of Impression Techniques
• 1.The Anatomic Form.
• 2. The Physiologic or Functional form.

9. 1.The Anatomic Form Impression
It’s a single stage pressure free impression technique that
records the teeth and supporting structures at rest in their
anatomic form. The residual ridge with no pressure or
occlusal load.
• used in cases of totally tooth supported PD, where the
edentulous ridge will not contribute to support the denture.

10. 2. Physiologic, functional impression Technique
• DEFINITION:
It is a dynamic registration of The teeth & edentulous ridge made under
functional load for the purpose of equalization of stresses on the teeth and
distal extension segment.

11. Impression Materials

12. Impression
Materials
Non-
elastic
Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Plaster
Compound
ZnO - Eugenol
Waxes

13. Impression Materials
• Materials for recording the Anatomic form:
• 1. Agar Agar.
• 2. Alginate
• 3. elastomeric.
• Materials for recording functional form:
• 1. compound.
• 2. Zinc oxide paste
• 3. Imperession wax.
• 4. polyether and silicon.

14. 1.The Anatomic Impression Technique

15. Impression Procedures
• After all steps of mouth preparations are completed, the impression
procedure is made using the special tray and alginate material taking in
mind that:
• 1. No air bubbles should be around or in rest seat perpetration or in any
area where the connectors present.
• 2. The tray should not be showing through the cusp tips.

16. Special tray construction

22. 2. FUNCTIONAL IMPRESSION Technique

23. Periodontal ligament
(0.25mm)
Mucosa
(2.0mm)
Different Displacement Between PDL & Mucosa

24. NEED FOR FUNCTIONAL IMPRESSION
1. Equalize support from residual ridges and teeth.
2. Distal extension cases require functional impression to record & relate tissue under
same loading.
3. Distribute the load over large area as possible.
4. Accurately delineate peripheries of the denture base.
5. Failure to make a functional impression will cause improper orientation between the
denture base and abutment teeth and cause pathologic leverages for the abutment
teeth, tissue atrophy, occlusal imbalance, irritation and frustration of the patient.

25. Factors influence (Support) the amount of tissue displacement covering the
edentulous ridge.
• 1. Contour and quality of the ridge.
• 2. The extent of the residual ridge coverage.
• 3. Design of RPD.
• 4. The total occlusal load applied.
• 5. Accuracy of the fit of denture base.
• 6. Accuracy of impression registration.

26. 1. Contour and Quality of the Residual Ridge
• The best foundation to give denture support is provided by a broad ridge crest formed
from cancellous bone and covered by cortical bone and dense fibrous connective tissue.
• The mandibular ridge is formed from cancellous bone so, it is not considered as primary
stress bearing area, while the buccal shelf of bone is considered as a primary stress
bearing area.
• The maxillary ridge may be considered as primary stress bearing area because it is
formed from cancellous bone and covered by dense and firm mucoperiostum. Buccal
and lingual slopes of the ridge give more resistance for lateral forces.

28. 2.The extent of residual ridge
• The broader the coverage, the greater the distribution of load/unite area.
So, the denture base should cover the maximum possible area of the
residual ridge within the physiological tolerance of the limiting structures.

29. 3. RPD design.
• By moving the fulcrum line more anteriorly, more of the residual ridge may be used to
support the denture base, so more stress distribution over a wider area, so, the occlusal
rests can be placed more anteriorly for better ridge support.

30. 4.Total occlusal load applied
The ridge support can be improved though:
1. Maximum ridge coverage.
2. Narrowing of the occlusal table of the artificial teeth.
3. Increasing the cutting efficiency of the denture teeth

32. 5. Accuracy of the denture base
• Support is increasing by intimate contact of denture base with the tissues
that cover the residual ridge.

33. 6. Accuracy of impression registration
• The more accurate impression registration, the more fittenes of the denture
base to the underling tissues.

34. Objectives of the impression in distal extension RPD.
• Provide maximum support, so distribute the load on large area as possible.
• Equalize support from the ridge and the abutment teeth.
• Direct forces to the primary stress bearing area.

35. • To achieve those objectives the impression technique must be:
• 1. Record and relate the supporting structures under some loading.
• 2. distribute the load over the largest possible area.
• 3. Record the peripheries of the bases accurately.

36. Different impression techniques for distal extension cases.
• 1. Functional impression techniques. (prior to framework construction).
• A. McLean’s physiologic impression technique.
• B. Hindel’s impression technique.
• 2. The selected pressure impression technique (after framework
construction).
• 3. The functional relining method. (after denture construction).

37. a. MacLean’s Physiologic impression technique
• Tray construction:
• 1. An acrylic special tray is constructed on the study cast covering only the
distal edentulous ridges and connected by a lingual bar (metal or acrylic).
• 2. An occlusal rim is formed on the tray for the patient to bite on.

38. a. MacLean’s Physiologic impression technique
• Impression Making:
• 1. Before impression making the wax rims are adjusted in both the vertical and centric
relations.
• 2. The impression for edentulous ridge is made using zinc oxide and eugenol material
under biting force.
• An overall alginate impression is made with the first impression held in place with finger
pressure. From this impression the master cast is obtained.
• The drawback of this technique is that the second impression is made under finger
pressure that not record exactly the functional displacement of the tissues that biting
force produced.

40. b. Hindel’s technique
• On the study cast, an acrylic special tray is made covering the distal edentulous areas and connected to
both sides by metal or acrylic connector.
• Border molding for the peripheries is carried out, the impression for edentulous area is made using zinc
oxide paste under light finger pressure.
• An overall alginate impression using stock tray with holes, these holes are used to maintain the finger
pressure on the first impression and eliminates its movement until the alginate is set, but it did not
eliminate the variable of the dentist’s individual interpretation of what constitutes functional loading.

42. 2.Selective pressure impression technique
• This technique helps to equalize the support between the abutment teeth
and the residual ridge, and directs the force to the primary stress bearing
areas.
• A. Altered cast technique.
• B. One stage selected pressure impression technique.

43. A. Altered Cast Technique
• It is made after construction of
the framework on a cast obtained
from anatomic impression.
• Mainly used in mandibular distal
extension cases (class I and class
II).

44. A. Altered Cast Impression
procedures
• Tray construction:
Before the construction of the impression tray , the
framework is tried in the patient’ mouth.
• Relief areas that need relief as internal oblique ridge if
it is prominent, and the crest of the ridge using wax,
while the buccal shelf of bone is left without relief.
• An acrylic resin special tray is constructed over the
ridge areas, and attached to the mesh of the
framework.

47. A. Altered Cast Impression
procedures
• Impression making:
• The framework with the tray is tried in the patent mouth.
• The borders are shortened and border tracing is made using green stick compound
• The trays are loaded by the impression material and seated in patient’s mouth accurately with occlusal
rests and indirect retainers in its seats and maintained in positions by three fingers of the operator ( two
fingers in main occlusal rests and third one on the indirect retainers –Tripoiding-).
• The impression materials that can be used as zinc oxide paste, rubber base and impression wax

48. .
The
framework
with the tray
is tried in the
patient
mouth

49. Border
extensions
are refined
with
modeling
compound,

50. • Material is
mixed, the tray
is loaded, and
the casting is
• firmly seated
on the teeth
and held in
position over
the rests
• until it is
completely set
Do not place or allow movement on the edentulous area!

53. • After the impression is made and accepted, the distal extension areas are
cut off from the cast, by sawing and retentive grooves are cut on the sides
of the cast along the cut off areas.
• The framework and the impression is reseated in position on the cast,
boxed, and pouring by stone plaster with different color.

54. Cast Alteration:
The edentulous area of the master cast is cut, and the
metal casting is seated in place on the teeth.
The casting is secured to the stone cast with sticky wax.
Note: Only the metal will touch the cast.
All impression areas must be out of contact

56. Retention grooves are placed in the cast. The impression is beaded and boxed and
ready to be poured in vacuum-mixed stone

58. B. One Stage Selected Pressure Impression Technique
• It is made before framework construction.
• Tray construction:
• On the study cast two layers of wax are adapted over the teeth and the ridge areas, and
aluminum foil is burnished over the wax spacer
• Occlusal stops are made over the teeth by cutting though the aluminum foil and the wax
spacer.
• An acrylic special tray is constructed over the wax spacer with short borders 2mm. Then
remove the wax spacer from the cast.

59. B. One Stage Selected Pressure Impression Technique
• Impression procedures:
• Apply softened molding compound on the tissue surface of the
tray corresponding to the ridge area, then seat the tray over
the cast.
• Reheat the compound and place the tray in the patient’s
mouth with finger pressure over ridge areas.
• Reheat the compound again and reseat the tray with border
molding for the tray.
• Relief the compound 1mm except buccal shelf area (primary
stress bearing area).
• An impression is made using rubber base material and finger
pressure over the ridge areas.

60. 3. Functional relining method
• It is an open mouth procedure.
• The denture borders are shortened, and relieved to allow space for impression material.
• Molding compound is applied to tissue surface of the base and inserted in the patient’
mouth and held the denture by three fingers ( Tripoiding).
• The compound is scraped to about 1 mm. then taking the impression using zinc- oxide
material with open mouth technique.
• An overall alginate impression using stock tray.
• After processing the occlusal errors should be adjusted.