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.
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
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
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
13.
14.
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
16.
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
18.
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
20.
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.