Primary impression

Primary impression

1. Impressions in Complete DenturesImpressions in Complete Dentures
An imprint / negative likeness of the teeth
&/or edentulous areas where the teeth have
been removed, made in a plastic material
which becomes relatively hard or set while in
contact with the tissues.
A complete denture impression is a
negative registration of the entire denture
bearing, stabilizing & border seal areas present in
the edentulous mouth.s

4. ClassificationClassification
Depending on theories of impression making
Mucostatic / passive impression (Richardson
& Henry L. Page)
Mucocompression / functional impression
(Carole Jones & Greene brothers)
Selective Pressure impression (Boucher)

5. ClassificationClassification
Depending on the technique
Open mouth / Closed mouth technique
Hand manipulation for functional movements
(Dynamic impression)
Depending on type of tray
Stock tray / Custom tray impression

6. ClassificationClassification
Depending on purpose of the impression
Diagnostic / Primary / Secondary
Depending on the material used
Agar, Alginate, Impression Compound, Plaster,
Wax, Silicone, Thiokol rubber impression.

7. Principles of impression makingPrinciples of impression making
Oral tissues must be healthy
Impression should include basal seat within limits
Borders must be in harmony with anatomical & physiological limitations
of oral structures
Selective pressure tech. shd be used
Sufficient space should be provided within impression tray for imp.
material
Guiding mechanism (tissue stops & handle) shd be provided for correct
positioning of tray
Imp. Shd be removed from mouth without damaging the mucosa
Materials used shd be dimensionally stable
External shape of impression shd be similar to ext. form of complete
denture

8. Objectives of impression makingObjectives of impression making
PP – preservation of remaining natural structures – preservation of remaining natural structures
RR – retention – retention
EE – esthetics – esthetics
SS – stability – stability
SS – support – support

9. Preservation of remaining natural Preservation of remaining natural
structuresstructures
Impression shd record details in appropriate form to prevent
injury to the tissues
Relief to non-stress bearing areas, thus preventing damage
Avoid overextensions

10. RetentionRetention
That quality inherent in the prosthesis which resists the force of
gravity, adhesiveness of foods, and the forces associated with the
opening of the jaws
It is the ability of denture to withstand displacement against the
path of insertion
Factors affecting retention
Anatomical ----size & quality of denture bearing area
Physiological – viscosity of saliva (thick/thin)
Physical -------- adhesion, cohesion, surface tension,
capillarity & atmospheric pressure
Mechanical ---- undercuts, retentive springs, magnets,
adhesives, suction chambers/discs
Muscular ------ Neutral zone

11. StabilityStability
The quality of a denture to be firm, steady, or constant, to resist
displacement by functional stresses & not to be subject to
change of position when forces are applied
It is the ability of the denture to withstand horizontal forces.
Factors affecting stability
Vertical height of ridge -- resorbed ridge – poor stability
Quality of soft tissue ---- firm / flabby tissues
Quality of impression---- accurate, smooth, stable
Occlusal plane ------------ should be parallel to ridge
Arrangement of teeth --- balanced occlusion
Contour of the polished surfaces

12. SupportSupport
The resistance to vertical forces of mastication, The resistance to vertical forces of mastication,
occlusal forces & other forces applied in a occlusal forces & other forces applied in a
direction towards the denture bearing area.direction towards the denture bearing area.
Achieved by covering as much area as possibleAchieved by covering as much area as possible
This helps to distribute forces - snowshoe This helps to distribute forces - snowshoe

13. EstheticsEsthetics
Thickness of flangesThickness of flanges
Impression should reproduce width & height of Impression should reproduce width & height of
sulcussulcus

14. Recording the Preliminary ImpressionRecording the Preliminary Impression
TRAY – A receptacle into which a suitable material is placed to make
an impression
A device which is used to carry, confine & control an impression
material while making an impression
Stock tray – metal / plastic, 2-3mm clearance, shd cover tuberosity &
hamular notch
Special tray – A custom made device prepared for a particular patient
which is used to carry, confine & control an impression material while
making an impression
Material used shd be well adapted, stable, 2mm thick, contrast in
colour & 2mm short in sulcus
Fabrication of tray – shellac, self cure resin, thermoplastic resins,
vacuum formed Vinyl or Polystyrene
Storing the trays

18. The End