This document discusses dental impressions, including the materials used, steps in the impression making process, and techniques for different types of impressions. It defines a dental impression as a negative likeness of the teeth and edentulous areas made of plastic material. The main materials discussed are reversible and irreversible hydrocolloids and elastomeric materials. The steps outlined are patient and dentist positioning, tray selection, mixing and loading the material, making the impression, and inspecting the final impression. Specific techniques covered include McLean's physiologic impression and fluid wax functional impression.

1. By:AhmedAliAbbas

2. INTRODUCTION
An impression is defined as a negative likeness of the
teeth and/or edentulous areas where the teeth have
been removed, made in a plastic material which
becomes relatively hard while in contact with these
tissues

3. MATERIALS AVAILABLE FOR MAKING
IMPRESSION
Reversible hydrocolloids (agar-agar)
Irreversible hydrocolloids (Alginate)
Elastomeric impression materials

4. STEPS IN IMPRESSION MAKING
Position of patient & dentist
Tray selection
Mixing the material & loading into the tray
Impression making & removal
Inspecting, cleaning & disinfecting the impression

5. POSITION OF PATIENT & DENTIST
Dentist should stand & patient should sit upright
Occlusal plane should be parallel to the floor
MAXILLARY IMPRESSION- dentist should stand
at the right rear of the patient
MANDIBULAR IMPRESSION- dentist should
stand at the right front of the patient

6. Mandibular impressionMaxillary impression

7. IMPRESSION TRAY SELECTION
Stock trays for dentulous & partially edentulous
arches are of 3 types:
Rimlock trays
Perforated metal trays
Plastic disposable trays

8. MIXING IMPRESSION MATERIAL
Bowel Spatula Scoop and
Measuring jar

9. REMOVAL OF IMPRESSION FROM MOUTH
Clinically the initial set of alginate is determined
by loss of surface tackiness
Release seal by retracting lips & cheek
Then impression is removed by a sudden jerk

10. INSPECT THE IMPRESSION FOR DEFECtS
Mandibular impressionMaxillary impression

11. IMPRESSION TECHNIQUES
Mc LEAN’S PHYSIOLOGIC IMPRESSION
FLUID WAX FUNCTIONAL IMPRESSION
SELECTIVED PRESSURE IMPRESSION

12. Mc LEAN’S PHYSIOLOGIC IMPRESSION
Procedure
A custom impression tray is constructed over a
preliminary cast
Functional impression of distal extension ridge is
made. Patient applies some biting force with
occlusion rims
Then an Alginate impression is made with the 1st
impression held in it’s functional position with
finger pressure

15. FLUID WAX FUNCTIONAL IMPRESSION
Make an anatomic impression of the arch using alginate
Fabricate a refractory cast using this impression
Fabricate the partial denture framework over the refractory
cast

17. Draw the outline of the denture base
Cast is coated with separating medium
Wax Spacer is adapted over the crest of the
edentulous ridge

19. Framework is placed over the spacer
Auto-polymerizing resin is mixed to dough stage and
is adapted and contoured over the framework along
the length of the ridge
Borders of the tray are trimmed

21. SELECTIVED PRESSURE IMPRESSION
• More force are applied to areas that can absorb stress
without adverse response & protect that areas that is least
able to absorb force
• Stress bearing areas are the buccal shelf area & the lingual
slopes of residual ridge stress bearing areas
• The denture base made from this impression will be closely
adapted to & in firm contact with the tissues in buccal shelf
area

22. CONCLUSION
An accurate impression is vital for the success of a cast
partial denture. So proper selection of material,
impression technique and the skill of the dentist plays
a key role in the success of the overall treatment.

23. REFRENCE
Mc Cracken’s Removable Partial Prosthodontics
REMOVABLE PARTIAL PROSTHODONTICS-STEWART’S 4TH EDISION