Impression Its a negative reproduction of details of the prepared

teeth ,adjacent teeth , and surrounding soft tissue.

Obtaining the impression is the first step necessary to indirect fabrication of the prosthesis.

Types of impression

1-Zinc-oxide egenoul impression material

2-Compound impression material

3-Irreversable impression material (Alginate)

4-Elastomeric impression material

Impression materials

1 -to be nontoxic and non-irritant .

2 -have acceptable odor , and taste. (relief of gagging reflex)

3 -have suitable working and setting times.

4 -have strength to resist tearing.

Characteristics (properties ) of the ideal impression material to be clinically

acceptable

5 -have sufficient plasticity and fluidity before curing .To easy seating in mouth and to record fine details of

finish lines and preparations .

6 -have complete elasticity after curing.To allow removal from the mouth and from the undercuts

without any deformations of impression.

7 -have optimal dimensional stability.Its important , that the impression should be stable in dimension after curing without any changes and

shrinkage until its transporting in laboratory and pouring.

8 -impression material should be easy to use , mix and manipulation.

Zinc-oxide egenoul impression material ,used to make impression with individual tray for more details and outlines in edentulous arches for complete denture

Impression pasteImpression paste

Caves outline

1 -Zinc - oxide egenoul impression

Impression paste (z.O.E)

It’s a thermoplastic impression material in cakes and sticks form used as a base (primary) impression for edentulous and partially edentulous arches ,and used to correct outlines (periphery) of individual tray to make functional (secondary) impression for complete denture

Its hard material and soften by heating ( hot water)

2 -compound impression

Compound stick - Kerr

Peripheral impression ( border molding) for secondary (functional impression)

* The alginate impression material consist of basic ingredient – soluble salt (sodium) of alginic acid , which derived from seaweed and another chemicals as filler – gypsum (Ca So4)2.H2o + Barium sulfate (BaSo4) + sodium carbonate

(Na2Co3). * Soluble salt (sodium) of alginic acid in water make colloid

system – gel ,which after become hard by irreversible chemical reaction – gypsum returns soluble gel of sodium alginate to insoluble calcium alginate (hard).

* Alginate impression material is used to obtain impression for removable complete and partial dentures , for casts of opposing teeth to bite registration ( occlusion ) , for diagnostic casts in orthodontics to study the models and for

fabrication of removable orthodontic appliances .

3 -Alginate impression - irreversible hydrocolloid

Product name

Alginmajor (major) – tropicalgin , hydrogum (zhermack) , tulip (cavex) , dentalgin

Step – by – step impression taking

Powder + water measuring Mixing in rubber bowel Loading into tray

Inserting tray in mouth Setting alginate in the mouth

Complete impression after removal from

mouth

1 2 3

4 5 6

Alginot – alternative traditional alginate automixing system

Indications to use

1 -diagnostic study casts

2 -opposing arch impressions for mounting and occlusion record

Adantages

1 -hydrofphlic

2 -fast setting

3 -easily poured

4 -used with stock and custom trays (perforated )

5 -inexpensive

Disadvantages

1 -low flow , there for cannot record fine detalis

2-low tear strength ,therefore thin margins may tear upon removal of impression from the mouth

3 -low dimensional stability due to synersis and imbibtion

4 -single pour and cannot another time pour

)after removal of poured stone model from impression

, its become teared(

They are synthetic rubber and formed by chemical reaction the process of changing the elastomeric base into final rubber-like material known as polymerization There are 4 types of elastomeric impression material:

A- polysulfide rubber (polymer) – (as permlastic – kerr)B- polyether (as impregum material for monophase technique -espe)C- condensation silicone

D- addition silicone (poly-vinylsilaxone)

4 -Elastomeric impression material

This impression material is a silicone-based polymer called a poly(dimethylsilaxone) – liquid

Polymer is mixed with a powder silica (alkyl silicate) to form a paste (base paste).

Polymerization of material occurs by a condensation reaction between silicone base ( polymer) and alkyl-silicate in the presence of a catalyst (accelerator) . The by-product of the reaction is ethyl alcohol , which is lost by evaporation causing a dimensional contraction (shrinkage) , for that need to use a correction paste (light-bodied paste).

Condensation silicone (C-silicone)

Impression with C-silicone can make by two-phase (sandwich technique) This material is hand mixing and consist of:

C-silicone consist of heavy putty (base paste) – light body (correction paste) – and catalyst.

1 -Heavy body – as base paste 2 -Light body – as correction paste

3 -And catalyst – as accelerator

Impression with C-silicone make by : two-stage technique and one-stage sandwich technique (wash putty technique or double technique)

Product name

Zetaplus – (zhermack) – protesil (vannini) – condensil (septodont) –coltofllex (coltene)

C- silicone impression material ( sandwish technique )

Light body Heavy body

Base paste Correction paste

Advantages

1 -provided in all viscosities , good handling properties

2 -adequate working time and setting time

3 -reasonable tear strength

4 -accuracy is improved by minimal polymerization shrink

5 -pour within 24 – 48 hours

Disadvantages

1 -dimensional changes on storage due to loss of ethyl alcohol therefore pour within 24 hours

2 -hydrophobic ,therefor require dry field (to prevent fomation bubbels in impresstion)

3 -poor wetting , therefore difficult to pour

Sandwish technique (putty wash technique)

Its usually used with condesation and addition cured silicones , stock trays is usually used to high viscosity of the putty material.

Step – by – step procedure

1 -Give anesthesia

2 -Select a suitable stock tray ( shape and size )

3 -Apply retaction cord around the prepared teeth (remove after 10 min)

4 -Isolate and dry the area to eliminate bubbels formation

5 -Dispense equal amount of base and catalyst then knead till homogeonous mix is obtained

6 -Roll the material and place(load) it into the stock tray

7 -Seat the putty loaded tray inside the patient`s mouth

8 -After setting remove the putty impression

9 -relieve the impression with sharp knife to remove areas of severe undercuts and interdental areas as those areas may prevent resating of the putty impression

10 – Squeeze out equal length s of light body material and catalyst and mix with a spatual till homogenous mix occurs ( or use automix dispenser)

11 -Load part of the material into the syinge and the remaining part is then applied to the tay over the relieved impression

12 – Remove the retraction cord then immediately inject material from syringr into the sulcus of the prepared teeth

13 – Seat the loaded putty material tray in place (in the mouth again)

14 – Remove tray a fter material sets

1 -stock tray ( double or putty wash technique)

Relieving borders of heavy body impression material

Full arch impression with heavy and light body impression material by double technique

Double or putty wash technique – used stock tray

The base of the polymer of this silicone is a poly(vinylsilaxone). This material is supplied with two polymers :

One –terminal vinyl-group and other with terminal Hydrogen N Polymerization occurs by addition reaction between two polymers in the presence of the catalyst.

After polymerization , elastic solid is formed without volatile by-product which give the material high and excellent dimensional stability Material is odor free , clean and easy to mix (automixing – hand mixing)

-heavy body - light body - catalyst Techniques – sandwich technique( putty wash) –monophase technique

cH2

cH2

addition silicone (A-silicone or poly-vinylsilaxone pvs)

hand mix – double technique

Electro-mix mono phase technique

Auto-mix double technique impression

material

Auto-mix double technique

Auto-mix mono phase (one step) technique

Auto-mix impression material for bite registration

- impression trays

There two types of impression trays :stock tray and custom tray

Stock tray is:

1 -metal trays – perforated , non perforated

2 -plastic trays – perforated plastic and metal trays divided to full arch trays , semi arch trays

(unilateral ) , and closed-bite double arch trays.

Plastic perforated full arch tray upper

Plastic perforated full arch tray

lower

Semi arch (unilateral) tray

Metal perforated full arch tray

Metal not perforated full arch tray

Impression taking

Closed-bite double arch trays

Method of taking impression

Impression can be taken by;

1 -stock tray (ready made tray)

2 -custom tray (acrylic tray which fabricated in lab.)

3 -closed-bite double arch tray

2- custom tray – acrylic tray fabricated in lab for taking impression to removable partial denture , complete denture (individual tray ) , and for fixed partial denture

3 -closed-bite double arch tray – used for double and mono-phase technique of impression taking

Complete closure in centric occlusion

Tray is removed with smooth and fluid movement

tray is inserted in prepared teeth area

Verticulator – incisal pen should be in contact in

centric occlusion

Common errors of impression1 2

3 4

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Thanks for

attention