DR MOSTAFA ELSAYED SEM 1

26/3/2020

Impression for Complete Denture

Reproduce a positive form and shape of the same oral tissues (Cast) .

Dental Impression:

Is a negative imprint of the oral structures used to produce a positive

replica (cast) used as permanent record or in the production of

dental restoration or prosthesis.

Denture Bearing Area (Denture Foundation): Is the surface of oral structures available to support

denture.

Complete Denture impression:

Is a negative registration of the entire denture bearing stabilizing and border seal areas present in the edentulous mouth.

is to optimally reproduce the surface of the denture-bearing tissues.

fabrication of a denture base provide the best possible distribution of

physical forces by merit of its accurate adaptation of the tissues.

1. Primary impression. 2.Final impression (Secondary impression).

Is a negative likeness made for the purpose of

diagnosis, treatment planning and fabrication of Special tray.

1. To provide the study cast. 2.To provide a cast for the fabrication of

special (custom) tray. 3. In some techniques the impression itself is

modified for use as a final impression tray.

The primary impression Should: 1. Record all the denture supporting areas. 2. Record the oral anatomy adjacent to the

denture supporting areas. 3. Record the natural form and physiologic

extension of oral tissues.

Preliminary Impression

Study cast

USES

As a study cast to study :

1. Ridge shape .

2. Palatal Vault shape .

3. Denture bearing areas .

4. Areas of undercut .

5. Relief areas .

6. Posterior palatal seal area .

7. Sharp bony edges .

8. Depth of the sulcus .

9. Inter-ridge space

10. Inter-ridge relations .

As a cast on which the final impression try is fabricated.

Material used for primary impression: 1. Irreversible hydrocolloid (Alginate). 2.Impression compound (modeling plastic

modeling compound). It is usually made by alginate impression

material with metal stock try.

TYPES OF TRAY

STOCK TRAYS

For Dentulous Pt. For Edentulous Pt. For Partially Edentulous Pt.

IMPRESSION TRAYS

“A tray is an instrument used to carry the impression material to the mouth ,

holding it in position against tissues until the material hardens ,it helps

in removing the impression from the mouth “.

Parts

1 . Body

2 . Handle Body Body

Handle Handle

DENTULOUS TRAY EDENTULOUS TRAY

Dentulous Tray

Edentulous Tray

Body

Handle

Body

Handle

Floor

Flange

Floor

Flange

Straight

L - Shape

Flat

Long

Round

Short

Stock trays Compound impression

1. Selection of the Stock impression Try:

2.Adjustment of the stock tray:

Impression Making:

Pouring The impression by stone plaster:

SPECIAL OR INDIVIDUAL (Custom) TRAYS

1. Shellac base plates 2. Self curing acrylic resin .

3. Cast or swaged metal .

TYPES:

Advantages of Special Trays:

1 . Fit more accurately the individual arch of the patient.

2 . Bulk of the impression material is reduced .

3 . More accurate border contour

4 . Less impression material is used .

5. More comfortable to the patient .

Advantages Of Acrylic Resin Special Tray

2. More rigid than shellac trays .

3. Accept border tracing material.

1. Easily constructed .

4. Easily trimmed .

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Definition: Is the impression that represent the

completion of the registration of the surface of an object.

1. Preservation of the remaining residual ridges. 2.Maximum coverage within the anatomical and

physiological limits provides wide distribution of forces over the supporting structures and helps in stability ad denture retention.

3. Improve esthetics through border thickness. 4.Retention is achieved by physical properties and

lock of muscle control.

Final impressions techniques

Position of the mouth

Closed mouth

Open mouth

Amount of pressure exerted during

impression making

Minimal pressure

impression

Definitive pressure

Selective pressure

I. Muco-static impression technique

II. Muco-compression impression technique

III. Selective pressure impression

It is the negative representation of denture supporting area under static load. So the tissues are recorded under static condition with minimal displacement.

It is made by special tray constructed over spacer with stopers.

The material used have high flow property as impression plaster

SHIM OR SPACER

It is one thickness of modeling wax or shellac

base plate adapted on the study cast under the

special tray

Primary cast

Spacer

Special tray

It is called also functional impression or closed impression technique.

It is a negative representation of denture supporting area under functional pressure while the impression material sets. So it is carried under biting force.

It is recorded by closely fitting special tray with bite blocks.

The material used have low flow

property as zinc- oxid impression material.

Occlusion rims constructed at

proper vertical dimension

Functional

impression

Denture can be used for definite pressure impression

( functional impression)

It combines pressure over certain areas as

ridge area and little pressure over others as middle palatine raphe, sensetive areas and flabby areas.

Tray relief

Selective pressure

Sufficient relief and

escape hole drilled in special tray opposite to flabby tissue to ensure relief of pressure over this area and proper load

distribution.

Impression is taken of the firm area using zinc oxide paste.

An impression of the flabby tissue left uncovered by the tray is obtained

by applying a thin mix of impression plaster using a spatula ,brush or

syringe

Steps of

A sectional impression technique

(Two part impression technique)

The tray is tried in the mouth and checked to make sure that it is not displacing the flabby tissue. The borders are corrected in normal way.

Step 2

Impression is taken of the firm area using zinc oxide paste.

If this impression proves to be satisfactory . It is replaced in the mouth .

An impression of the flabby tissue left uncovered by the tray is obtained by applying a thin mix of impression plaster using a spatula ,brush or syringe.

Amount of pressure applied

Minimal pressure

impression

Sometimes called muco-static, open mouth or passive non-pressure. This technique aim to record the denture bearing area under minimal amount of pressure and so the tissues in relative rest state.

Definitive pressure

impression

It is also called muco-compressive or closed mouth. The impression record the bearing mucosa under biting force. The greater the biting force the greater the displacement

Selective pressure

impression

This technique combine the previous techniques by applying pressure over certain tissues and minimize pressure over other tissues.

Materials used

Minimal pressure

impression

Materials with high flow and low viscosity like plaster of paris and alginate

Definitive pressure

impression

Materials with high viscosity and low flowing properties. They also have adequate setting time to allow functional movement.

These material as zinc oxide eugenol.

Selective pressure

impression

Compound impression material over the tissue to be compressed and plaster of paris wash over tissues needed to be recorded at rest

Tray used

Minimal pressure

impression

Trays should have spacer of even and enough thickness. 3 to 4 stops properly distributed. 1 to 2 holes to allow excess material escape.

Definitive pressure

impression

Trays constructed without spacer and have occlusion rims at the proper vertical dimension.

Selective pressure

impression

Compound impression is used as a tray after scrapping for the final plaster of paris wash. Another technique used special tray with window at the movable tissue.

Advantages Disadvantages

Minimal pressures

impression technique

1- allow visualizing the proper border molding 2- minimal tissue distortion 3- suitable for flabby ridge and thin wiry ridge 4- tissues receive minimal pressure so less interference to blood supply

1- not fit all times due to changes in mucosal typography. 2- neglect wide distribution of force. 3- consider the interfacial surface tension is the only retentive mechanism.

Definitive pressure impression technique

1- allow patient masticatory forces during setting of impression material 2- proper lingual border molding due to closed mouth during molding

1- over-extended denture 2- denture not fit at rest due to tissue rebound 3- tissue may become permanently deformed 4- deprive denture bearing mucosa from adequate blood supply.