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protho seminar
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IMPRESSION procedures FOR
Removable partial denture
Presented byShiji margaret
Final Year BDS
INTRODUCTIONAn 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
MATERIALS AVAILABLE FOR MAKING IMPRESSION
Reversible hydrocolloids (agar-agar)Irreversible hydrocolloids (Alginate)Elastomeric impression materials
STEPS IN IMPRESSION MAKINGPosition of patient & dentistTray selectionMixing the material & loading into the
trayImpression making & removalInspecting, cleaning & disinfecting the
impression
POSITION OF PATIENT & DENTISTDentist should stand & patient should sit uprightOcclusal plane should be parallel to the floorMAXILLARY IMPRESSION- dentist should
stand at the right rear of the patientMANDIBULAR IMPRESSION- dentist should
stand at the right front of the patient
Mandibular impressionMaxillary impression
IMPRESSION TRAY SELECTIONStock trays for dentulous & partially edentulous arches are of 3 types:
Rimlock traysPerforated metal traysPlastic disposable trays
MIXING IMPRESSION MATERIAL
Bowel Spatula Scoop and Measuring jar
REMOVAL OF IMPRESSION FROM MOUTH
Clinically the initial set of alginate is determined by loss of surface tackiness
Release seal by retracting lips & cheekThen impression is removed by a sudden
jerk
INSPECT THE IMPRESSION FOR DEFECtS
Mandibular impressionMaxillary impression
IMPRESSION TECHNIQUESMc LEAN’S PHYSIOLOGIC IMPRESSIONFLUID WAX FUNCTIONAL IMPRESSIONSELECTIVED PRESSURE IMPRESSION
Mc LEAN’S PHYSIOLOGIC IMPRESSIONProcedure
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
FLUID WAX FUNCTIONAL IMPRESSIONMake an anatomic impression of the arch using
alginateFabricate a refractory cast using this impressionFabricate the partial denture framework over the
refractory cast
Draw the outline of the denture baseCast is coated with separating mediumWax Spacer is adapted over the crest of
the edentulous ridge
Framework is placed over the spacerAuto-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
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
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.
REFRENCEMc Cracken’s Removable Partial ProsthodonticsREMOVABLE PARTIAL PROSTHODONTICS-STEWART’S 4TH EDISION
THANK YOU