dr mostafa elsayed sem 1 26/3/2020 f… · record the natural form and physiologic extension of...
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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.