This document discusses different impression techniques used for removable partial dentures. It describes anatomic impressions, which record teeth and ridges in their resting form, and are used for tooth-supported partial dentures. Functional impressions compress soft tissues to record them under load and are used for tissue-supported partial dentures. Pick-up, functional reline, and selective pressure impression techniques aim to record ridges functionally. Anatomic impressions capture teeth anatomically, while functional impressions record soft tissues under loading for optimal partial denture support and stress distribution.

1. IMPRESSION TECHNIQUES IN
REMOVABLE PARTIAL DENTURE

2. CONTENTS
• Introduction
• Anatomic impressions
• Functional impressions
• Classification
• Conclusion

3. INTRODUCTION
• In tooth-supported removable partial dentures (class III and many class IV partially
edentulous arches), the occlusal forces transmitted to the abutment teeth are directed
vertically along the long axis of the teeth through the occlusal, incisal or lingual rests.
• The edentulous ridges do not contribute to the support of the partial denture.
• Since abutment teeth are the sole support of the tooth-supported prosthesis, they can be
constructed on a master cast made from a single, pressure free impression that records the
teeth and the residual ridge in their anatomic form (anatomic impressions).

4. • A tooth- and tissue-supported removable partial denture (class I and class II)
obtains support from both the abutment and the residual ridge.
• If the prosthesis is constructed on an anatomical impression, it will exert excess
pressure on the abutments as the soft tissue under the denture base is compressed
and moves under occlusal loading.
• A dual impression technique is used to distribute the forces to the abutment teeth
and the residual ridge such that support is provided by both.

5. • The impression of the teeth should be made with a material that captures the teeth
in the anatomic form, as teeth do not change position under function.
• The impression of the soft tissue, on the other hand, is made in such a manner so
as to record the tissues in their functional state (functional impressions).

6. ANATOMIC IMPRESSIONS
• Anatomic form is the surface contour of the ridge when it is not supporting an occlusal
load.
• These are indicated for tooth-supported partial dentures and most class IV.
• Most maxillary distal extension bases can also be recorded with this technique.
• A single impression with medium body/regular body/monophase elastomeric impression
material using a custom tray is the preferred technique.
• Putty with light body wash in a stock tray can also be used.
• Irreversible hydrocolloid – alginates, may also be used.
• Addition silicones are preferred.

7. PROCEDURE
• Fabrication of custom tray
1. Outline of the tray is marked on the primary cast.
It should extend up to the vestibule
2. A wax spacer 2 mm in thickness is adapted on
the cast and at least three tissue stops (one
anteriorly and two posteriorly on either side) are
created in noncritical areas to provide space for the
impression material.
3. A custom tray is fabricated with
autopolymerizing acrylic resin.

8. Impression making
1. Evaluate the custom tray in the mouth and correct the
extension.
2. Impression material is mixed and loaded onto the tray after
application of tray adhesive. In case of alginate, perforations
in tray provide retention.
3. Tray is seated in the mouth and held steady till material sets.
4. Impression is removed, washed and checked for any
imperfections.
5. A master cast is poured after beading and boxing

9. Functional impressions
• Functional form is the form of the residual ridge recorded under some loading or compression.
• This could be achieved by occlusal loading, finger loading, specially designed individual trays or
consistency of recording medium.
• It is indicated for distal extension bases (class I and class II), especially in the mandibular arch.
• Maxillary distal extension ridges are covered by firm mucosa, stress is borne by crest and slopes of
the ridge and hence a functional impression may not be needed.
• Another indication for this type of impression is a long span anterior edentulous ridge (class IV).
• A dual impression technique is used along with a combination of impression materials – one that
records the teeth in anatomic form and the other that records the residual ridge in functional form

10. REQUIREMENTS
1. Record the tissues under the same loading as the teeth.
2. Distribute the occlusal load over a large area.
3. Demarcate accurately the extent of the denture base.

11. Factors influencing support of distal extension base
The following factors determine the extent of displacement of the residual ridges thereby indicating the support:
1. Quality of soft tissue covering edentulous ridge
2. Type of bony architecture of denture bearing area
3. Design of partial denture
4. Amount of tissue coverage of denture base
5. Amount of occlusal force
6. Support from denture bearing area
7. Fit of denture base
8. Type of impression registration

12. Quality of soft tissue covering edentulous ridge
• A firm, tightly attached thick mucosa will offer the greatest support.
• The more displaceable tissue is present over the edentulous ridge, less is the support.
• Surgical removal of flabby tissue is indicated to increase the support.

13. Type of bony architecture of denture-bearing area
• Cancellous bone has less ability to resist vertical forces compared to cortical bone. This is
due to its irregular surface which acts as an irritant to overlying soft tissue when stress
occurs. This results in chronic inflammation of soft tissues which leads to resorption of the
cancellous bone.
• The crest of the maxillary and mandibular ridge is composed mainly of cancellous bone
and hence should not be considered as a prime source of support.

14. Design of partial denture
• Rotational forces on the ridges in distal extension bases can be controlled by our design
considerations
• The most efficient method to control rotational stress is by using indirect retainers.

15. Amount of tissue coverage of denture base
• The broad stress distribution design philosophy demands that the denture base must cover
the maximum amount of surface area of the edentulous ridge to effectively distribute the
functional stresses.
• Overextension must be avoided, as it can cause soft tissue irritation, ulceration and even
lifting or dislodgement of the base leading to leverage forces on the clasped abutment teeth.

16. Amount of occlusal force
• Greater the occlusal load on a denture base, greater should be its support.
• A denture base that is opposed by a full complement of natural teeth requires more support
than that opposed by a complete denture.
• Narrowing the food table of the artificial teeth will help reduce the load transmitted to the
denture base.
• Supplemental grooves and sluiceways on artificial teeth increase the masticatory
efficiency thereby reducing the load transmitted.

17. Support from denture-bearing area In the maxillary edentulous
ridge
• Crest of the ridge provides the maximum support and is the primary stress-bearing area.
• The buccal slopes of the ridge, though covered by a layer of cortical bone, is not placed
perpendicular to the vertical forces, so it offers little resistance to them. It will, however,
resist lateral forces, reducing the total force.
• Hard palate also provides some resistance to vertical displacement.

18. Support from denture-bearing area In the mandibular edentulous
ridge
• Buccal shelf area, composed of very dense cortical bone, bordered by the external oblique
ridge, is an excellent primary stress-bearing site.
• The soft tissue covering the cortical bone in this region is also firm and dense.
• It is also positioned perpendicular to the vertical occlusal stresses.
• The slopes of the residual ridge contribute to resisting horizontal forces.

19. Fit of denture base
• To derive optimum support from stress-bearing areas, accurate fit of denture is mandatory.
• Type of impression registration Impression plaster and zinc oxide eugenol impression
paste are best suited to record the ridges in the resting or anatomic state because of their
low viscosity, though it can also be recorded by other materials like elastomeric materials
and hydrocolloids.
• This largely depends on the fit of the tray and the thickness of the spacer. Functional
impressions to compress the tissues are better made with higher viscosity materials like
waxes, impression pastes and elastomers.

20. CLASSIFICATION
Functional impression procedures can be classified as follows:
1. Physiologic impressions: Those impressions which record the residual ridge under generalized
compression.
i. Pick-up impressions
a. Mclean’s technique
b. Hindels’ technique
ii. Functional reline impressions
iii. Ridge correction technique using fluid wax
2. Selective pressure impressions: Those which selectively compress the stress-bearing tissues.

21. Impression procedures –
Pick-up impressions
1. Mclean’s technique
• Custom tray is fabricated only for the
distal extension base area with wax occlusal rims.
• Functional impression is made of the
residual ridges with zinc oxide eugenol
impression paste or polyvinylsiloxane (PVS), by
recording the impression with patient biting on
the occlusal rims

22. • After this impression has set, without removing the same, a second
impression is made over the functional impression and the teeth, in
a stock tray with alginate. It is called as overimpression or pick-up
impression as the first impression made with custom tray is
contained in it.
• While making the overimpression, finger pressure is applied
posteriorly to push the first impression down towards the ridge, to
its functional biting position
• A master cast is poured after beading and boxing.

23. Disadvantages:
1. Finger pressure on second impression will not produce the same amount of functional
displacement of the tissue that biting forces produced in the first impression.
2. Hence compression of the tissues will not be the same and the functional impression
will not be recorded as per the patient’s biting force.

24. 2. Hindels’ technique
• Hindels and coworkers developed this technique to overcome the disadvantage of
Mclean’s technique.
• The first impression of the edentulous ridge was an anatomic impression made in a
custom tray with tissue stops so that pressure could not be applied to the ridge.
• The impression was made with zinc oxide eugenol impression paste.

25. • Hindels and coworkers developed stock trays with a large hole on
either side posteriorly so that finger pressure could be directly
applied to the first impression through the holes on the tray.
• With the set anatomic impression in the mouth, the second
overimpression was made in the specially designed stock tray with
alginate, maintaining finger pressure till the material sets.
• It was contended that the finished impression is related to the teeth
and the ridge as if masticatory forces were taking place on denture
base.
• A master cast is poured after beading and boxing.

26. Disadvantages of both Mclean’s and Hindels’ technique
• As tissues are recorded in compressed state, if clasp retention is good, even at rest position (when
patient is not biting) the soft tissues are constantly displaced as the clasps will maintain the denture
in this position.
• This will lead to interruption of blood supply to the ridges and bone resorption.
• If clasp retention is not adequate, the denture will always remain slightly occlusal to the
functionally recorded position.
• Hence the artificial teeth will first come into contact with the opposing teeth, when patient applies
biting force.
• This will produces premature contacts which is uncomfortable to the patient.

27. Functional reline technique
• This is done after fabrication of the metal framework and denture base. It consists of
adding a new layer to the fitting or tissue surface of the denture base.
• The procedure may be performed before the insertion of the partial denture, or it may be
done at a later date to any cast partial denture, if because of bone resorption, the denture
base no longer fits the ridge adequately and relining is necessary.

28. • To allow some space for the reline material, a layer of relief metal (ash metal), is added to
the ridge area of the cast prior to packing the acrylic resin denture base material.
• Space can also be provided by trimming the tissue surface of the denture base, but metal
spacer provides a uniform thickness.
• After processing, the metal spacer is attached to the acrylic resin.
• The partial denture is tried in the mouth and once the fit is confirmed, the metal spacer is
removed and functional reline impression procedure carried out.

29. • Low-fusing green stick impression compound is flowed onto the tissue surface of denture base,
tempered and placed in the patient’s mouth. This procedure is performed several times along with
border moulding so that an accurate impression of the ridge as compressed by the impression
compound is obtained.
• The tissue surface of the low-fusing compound impression is trimmed uniformly by 1 mm and final
impression is made with zinc oxide eugenol impression paste, fluid wax or medium body
elastomeric impression materials.
• It is like making a primary impression with green stick compound and a final wash impression with
the other materials.
• If fluid wax is used to produce a functional reline, green stick compound is eliminated and only
wax is used for making the impressions.

30. • The amount of soft tissue displacement can be controlled by the amount of relief given to
the green stick compound before the final impression is made.
• The greater the relief, the less will be the tissue displacement.
• Patient must keep the mouth half open during the impression procedure to:
• Control the border tissues, cheek and tongue.
• Enable the operator to ensure proper placement of framework on teeth during the
procedure.

31. Disadvantages
1. Occlusion may be altered by reline procedure and needs adjustment.
2. A visible junction may be created between new acrylic and old denture base.
3. May be difficult to maintain correct position of framework on teeth during impression
making.

32. Ridge correction technique using fluid wax
• This impression of the ridge is made after fabrication of the framework, but before
denture base is processed.
• Following fabrication of framework using an anatomic impression, special tray is made
for the distal extension segment attached to the denture base major connector

33. Fabrication of special tray
• Framework is placed on master cast after checking in the mouth.
• Outline of tray is marked on cast and uniform relief of 1–2 mm is provided with a spacer of
baseplate wax.
• Cast is coated with separating medium and autopolymerizing acrylic resin is mixed to a dough
consistency and adapted over the edentulous ridge and denture base minor connector.
• The tray is trimmed 2 mm short of its estimated functional length.
• In the mandible, it should cover retromolar pad and extend onto buccal shelf, and in maxilla it
should extend up to hamular notches.

34. Impression technique using fluid wax
• Fluid wax: These are waxes that flow at mouth temperature and are firm at room temperature.
• Frequently used are Iowa Wax – developed by Dr Smith and Korrecta Wax No. 4 – developed by
Drs. O.C. and S.G. Applegate.
• Korrecta wax has more fluidity than Iowa wax.
• Tray extension is checked for any overextension by manipulating the border tissues.
• Wax in a container is placed in a water bath maintained at 51–54°C, which makes it fluid.
• The fluid wax is uniformly painted onto the tissue surface of a dry special tray with a brush.

35. • The tray is placed in the mouth and border moulding is performed.
• At all times correct positioning of framework on teeth is ensured by finger pressure on the
abutments.
• The wax is allowed to remain for 5 min with mouth half open.
• Framework is removed and impression is dried and inspected.
• Areas in good functional contact with tissues will appear glossy, while insufficient contact
will be dull.
• Wrinkled areas indicate insufficient time for wax to flow, and areas of tray exposure need
to be relieved.

36. • After all the corrections are made and impression shows complete tissue contact, the
prosthesis is reinserted and left in the mouth for 12 min to ensure that wax has completely
flowed and released any internal strains.
• The final cast is poured using the altered cast technique.
• The procedure can also be performed by using low-fusing green stick compound for
border moulding and making final impression with zinc oxide eugenol impression pastes
and medium body elastomeric impression materials.
• The amount of tissue compression depends on the thickness of spacer provided and
viscosity of impression material

37. Selective pressure impressions
• This technique directs forces to areas of ridge capable of
withstanding stress and protects areas of ridge unable to absorb
stress by relieving them.
• As discussed earlier, only mandibular distal extension ridges
require functional impressions.
• The buccal shelf area is the primary stress-bearing area, but the
crest of the ridge is not a stress-bearing area and hence needs to
be relieved

38. • This procedure is similar to the ridge correction technique described previously, except for the
spacer provided for the special tray.
• In this technique no spacer is provided and a close fitting special tray is fabricated on the distal
extension ridge on the denture base minor connector.
• The tissue surface of the tray is relieved in the ridge crest area by trimming the tray by 1 mm.
• The buccal shelf area of special tray is trimmed very slightly so direct contact will be maintained
and more pressure can be transferred here.
• The lingual slope of ridge should be trimmed similar to buccal shelf as it may offer some support.
• If the soft tissue covering the ridge is very soft and displaceable, relief holes may be made in the
special tray to dissipate the pressure even more.

39. • After border moulding with low-fusing green stick compound,
final impression can be made with a free flowing impression
material like zinc oxide eugenol impression paste.
• This is the material of choice when residual ridge is free from
undercuts and when soft, flabby tissue is involved.
• Other impression materials like medium body elastomeric
materials can also be used to make the final impression.
• These are indicated for patients with undercuts in the edentulous
ridges. They have higher viscosity than impression pastes.
• The amount of pressure placed on the ridge will depend on the
viscosity of the impression material and relief should be given
accordingly

40. MASTER CAST
• Pouring the cast for anatomic and pick-up impression is similar to making a cast with
dental stone for diagnostic casts and master cast for complete dentures.
• For the functional reline, ridge correction and selective pressure impressions, an altered
cast technique is desirable.

41. Altered cast technique
• This involves altering only the distal extension part of the
master cast after a functional impression is made of the
residual ridges.
• The framework is fabricated on an anatomic impression in a
refractory cast duplicated from the first master cast.
• The framework fitted to the master cast is sent to the dentist
by the laboratory

42. A special tray is made for the distal extension segment attached to the denture base
major connector. A functional impression is then made of the ridge area.
The master cast is then altered to accommodate the functional impression as follows:
• The area to be altered is outlined on the master cast.
• It consists of two lines one buccolingual and other anteroposterior along each
distal extension ridge.
• The buccolingual line is made 1 mm posterior to the distal abutment at right
angles to the long axis of the ridge.
• The anteroposterior line is drawn at right angles to the first, just lingual and
parallel to the lingual sulcus.
• The outlined area is cut and removed with a handsaw

43. • Longitudinal retention grooves are made on the cut
surface of the cast to provide mechanical retention
for the attachment of new stone to the old.
• The framework with the functional impression is
placed on sectioned master cast. Impression must
not have any contact on the cast.

44. • The framework is secured firmly to the cast with sticky wax
after ensuring correct position of all components on the cast
• The impression area is beaded with utility wax and boxed
with boxing wax. The cast is immersed in slurry water for
10 min to provide saturation of dry stone.
• The functional impression is poured with low-expansion
dental stone without much of vibration so that the
framework is not disturbed. After final set, cast is trimmed
and is ready for completion of the denture base part of the
cast partial denture.

45. conclusion
• Impression making is an important aspect of any prosthesis as the tissues need to be recorded
accurately to ensure proper fit.
• In cast partial dentures, an anatomic impression will suffice in most clinical situations.
• When the load on the abutments needs to be transferred to the residual ridges, a functional
impression is essential, in long-span edentulous spaces and distal extensions.
• Altered cast technique is the method of choice to make master casts with functional impressions.
• Once the master cast is poured, the prosthesis design is transferred and fabrication of the
framework is commenced.