Impressions in removable
partial denture
DR. ABHINAV GUPTA M.D.S.
Contents
 Introduction
 Impression materials
 Impressions of the partially edentulous arch
 Distal extension rpd
 Factors influencing the support of a distal extension base
 Anatomic form impression
 Methods for obtaining functional support for the distal extension base
WHAT IS AN IMPRESSION ?
“a negative likeness or copy in reverse of the surface
of an object ; an imprint of teeth and adjacent
structures for use in dentistry.”
(gpt-9)
An impression of partially edentulous arch must record accurately the teeth in anatomic
form and surrounding tissues in a functional form.
Classification of impression materials
IMPRESSION MATERIALS
Factors influencing the selection of
impression materials
 Convenience of use
 Time of manipulation & setting time
 Cost
 Operator training & preference
 Need for special trays
IMPRESSION OF PARTIALLY EDENTULOUS ARCH
 Elastic impression materials are used
 This is due to the presence of undercuts in the partially
edentulous mouth
POSITION OF PATIENT AND DENTIST
 Dentist should stand &patient should sit upright
 Occlusal plane should be parallel to the floor
 MAXILLARY IMRESSION- dentist should stand at the right rear of patient
 MANDIBULAR IMPRESSION-dentist should stand at right front of patient
IMPRESSION TRAY SELECTION
Stock trays used for dentulous & partially edentulous arches are of 3 types Rimlock trays
 Perforated metal trays
 Plastic disposable trays
CHECKING TRAY SIZE
 There should be a clearance of 4-5 mm between teeth and inner flanges of
tray
 It should cover the desired anatomic areas
 Too Large tray may be difficult to insert& may interfere with the coronoid
process of the mandible while making maxillary impression
 In case of mandibular impression ,if the tray extends too far lingually , there
is a tendency to trap the tongue or floor of mouth
Extending an impression tray
 Sometimes impression tray of adequate width may not cover the desired
impression area
 In such cases , the tray is lengthened using modeling wax
LOADING IMPRESSION TRAY
 Place impression material in small amounts
 Tray should be filled in level with the flanges
 Overfilling should be avoided
MANDIBULAR IMPRESSION TECHNIQUE
 Inject some material over occlusal surface of teeth ,into vestibular areas &
alveolo-lingual sulcus
 Then tray is rotated into the mouth & carefully seated
 Patient is asked to do the tongue movements
 Maintain the position of the tray by placing the forefinger of each hand on
top of tray on premolar area& thumb under the patient’s chin
MAXILLARY IMPRESSION TECHNIQUE
 Inject alginate into occlusal surface and vestibular areas & wipe some
amount on the palate
 Tray must be centered and properly aligned & verify the position by looking
at the patient’s face from above
 After this tray is seated by using fingers of both hands over premolar areas
and stabilize the tray
INSPECT THE IMPRESSION FOR DEFECTS
Anatomical & functional form of ridge
Anatomical form of ridge
Functional form of ridge
Anatomic or Resting form
Supporting or Functional form
Materials Used
 ANATOMIC IMPRESSION
irreversible hydrocolloid
elastomeric impression materials
reversible hydrocolloid
 FUNCTIONAL IMPRESSIONS
fluid waxes
metallic pastes
elastomeric impression materials
soft liners
FUNCTIONAL IMPRESSION
“recording the functional form of residual ridge to
obtain uniformity of support when the functional
load is applied”
Therefore, the impression must,
Record and relate tissues under uniform loading
Distribute the load over as large area as possible
Accurately delineate the peripheral extent of the denture
base
Indications for Functional impression
Mandibular distal
extension partial dentures
• Mainly kennedy’s class I & II
edentulous arches.
SUPPORT OF DISTAL EXTENSION BASED
PARTIAL DENTURE
minor support abutment teeth
major support elastic fibrous connective tissue
pad
5 Factors influencing the support of
distal extension base
Contour & Quality of
residual ridge
EXTENT OF RESIDUAL RIDGE COVERAGE BY THE
DENTURE BASE
TYPE & ACCURACY OF IMPRESSION REGISTRATION
ACCURACY OF FIT OF DENTURE BASE
•Design of partial denture framework
METHODS OF FUNCTIONAL IMPRESSION
 PHYSIOLOGIC OR FUNCTIONAL IMPRESSION
McLean’s method
Hindel’s modification of McLean’s method
Functional relining method
the Fluid Wax technique
 SELECTED PRESSURE IMPRESSION TECHNIQUE
McLean’s Physiologic Method
 McLean “The basic problem of partial denture
stabilization is to equalize the resilient and non resilient
support”
Custom tray over a preliminary cast
Functional impression of extension area under
occlusal load
Hydrocolloid impression over the first impression
made under finger pressure.
Disadvantages-
Finger pressure not equal to biting pressure
Closely affect the direct retention
HINDEL’S MODIFICATION
impression is made with a modified tray applying
finger pressure.
Disadvantage
Tissues are in constant stage of
compression
Ischemia and bone resorption
Premature contacts at rest.
Functional Reline Method
Layer of relief given
The denture is processed & fitted in the mouth in
customary manner, except that the relief metal is left in
place.
It should be worn for a trial period of a week & all
needed adjustments are done
The relief metal is stripped off from the acrylic.
low fusing modeling compound is added in
increments
Border molding done.
1 mm Modeling plastic is removed from the
intaglio surface.
Impression made using one of the corrective
materials : fluid wax, Zinc-oxide Eugenol pastes or
any elastomeric impression material.
DISADVANTAGE
 OCCLUSION MAY BE ALTERED SLIGHTLY
 FINE LINE OF DEMARCATION EXIST BETWEEN THE NEWLY
ADDED & OLD RESIN
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
 Draw the outline of the denture base
 Cast is coated with separating medium
 Wax spacer is adapted over the crest of edentulous ridge
 Framework is placed over the spacer
 Auto-polymerizing resin is mixed to dough stage & is adapted and
contoured over the framework along the length of the ridge
 Borders of the tray are trimmed
IMPRESSION PROCEDURE
 Wax is softened at 51 to 54 degree Celsius
 Softened wax is painted on the tissue surface with a brush
 Wax is painted in excess near the border to record the sulcus
 Tray is seated and held in position
 Wait for 5 minutes to allow the wax to set
 The tray is removed and impression is examined
 Wax surface that has contacted soft tissue appear glossy & the other areas
that has not contacted the tissues will appear dull
THE MOST FREQUENTLY USED WAXES
 KORRECTA WAX NO.4 – Dr. o.c & S.G Applegate
 IOWA WAX – developed by Dr. Smith
Korrecta wax no.4 is slightly more fluid than Iowa wax
SELECTIVE PRESSURE IMPRESSION
 More force is applied to areas that can absorb stress without adverse response
& relieve the areas that are least able to absorb force
 This is also known as dynamic impression method.
MATERIALS USED-rubber base material - ZOE paste
ALTERED CAST TECHNIQUE
ALTERED CAST- a final cast that is revised in part before processing a denture base
AKA CORRECTED CAST or SPLIT CAST TECHNIQUE
It is mainly a modification of functional impression through lab procedure
Edentulous area cut from the
master cast
Framework with attached
impression seated on master
cast
Newly altered master cast with
newly added stone
COCLUSION
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.
references
 McCracken’s removable partial prosthodontics
 Stewart’s removable partial prosthodontics