1. Complete denture Impressions

2. Impression
A complete denture impression is a negative registration of the entire denture bearing, stabilizing, and border seal areas present in the edentulous mouth.
A preliminary impression is an impression made for the purpose of diagnosis or for the construction of a tray.
A final impression is an impression for making the master casts. The master casts are used in constructing the dentures.

3. Types of Impression tray
Impression tray It is a device used to carry & control impression material while making an impression
Types of Impression tray
1-stock tray
The tray we use in the primary impression
2-custom tray
The tray we use in the final impression ,
and constructed on diagnostic cast

4. Types of stock trays Metallic it can be aluminum or stainless steel.
Non metallic:-
Plastic tray which can be sterilized.
Disposable plastic trays.

5. Types of stock trays 1. Perforated trays (used with alginate)
Non perforated or plain trays
(used with impression compound)

6. Primary impressions
Objectives 1. To obtain an impression of the whole of the denture-supporting area of each jaw. 2. To record the full extent of the sulcus. 3. To obtain an impression in which certain landmarks on the edentulous jaws are recorded.

7. Primary alginate impression
Stock perforated metal (plastic) impression tray
The form of the tray correspond the form of residual ridge as closely as possible
Allow enough thickness for alginate impression material (2-3 mm)
The length of the tray can be extended with wax to correspond the morphology of the denture bearing tissues as closely as possible

8. Primary impression with thermoplastic material
Stock non perforated metal impression tray
The form of the tray correspond the form of residual ridge as closely as possible
Allow enough thickness for impression material

10. Custom tray Individually made for each mouth Rigid & stable
Adequate relief at frena attachment
Borders are under extended from the functional borders of the anticipated prosthesis
Tray & its handle should not interfere with the functional movements of oral structures

11. Final impression Objectives
To obtain an impression from which a retentive denture base can be constructed.
The function of an impression material is to make a –ve copy, which records the dimensions of the oral tissue and their relationships.
The impression must be accurate so that the model, cast, or die will be accurate. That is the positive copy of the oral structure will be accurate.

12. Requirements of impression material
Must be a semi-liquid material that will flow and adapt itself around the structure of interest.
It must set and harden into a solid that is rigid enough to be removed from the mouth without becoming deformed.
Copy details accurately
Dimensional stability after removal from the mouth
Appropriate working time (from the start of mix)
Appropriate time to harden in the mouth (setting time)
Bio-compatibility/Aesthetic, odor/taste
Chemically compatible with material used to pour cast

13. Impression materials for complete denture:
Primary impression :
a) impression compound
b) Alginate
Secondary impression :
Rubber base
Zinc oxide Eugenol
plaster of paris

14. By Application or Mechanical Properties
Classification
By Setting Mechanism
By Application or Mechanical Properties
non-elastic
Elastic
Chemical reaction
(irreversible)
Plaster of Paris
ZOE
Alginate hydrocolloid
Elastomers
Temperature changes
(reversible)
Compound
Wax
Agar hydrocolloid

15. Impression materials Elastic Rigid / Inelastic Temperature change:
Chemical reactions:
(Irreversible)
Alginate
Elastomers
Polysulphides
Polyethers
Condensation silicon
Addition silicon
Temperature change:
(Reversible)
Agar hydrocolloid
Chemical reactions:
Plaster of Paris
ZnO Eugenol
Temperature change:
Impression compound
Waxes
Rigid / Inelastic

16. Impression plaster
Impression plaster used to record final impression for completely edentulous arch.
Impression plaster is similar in composition to the dental plaster used to construct models and dies.
The material is used at a higher water/powder ratio (approximately 0.60) than is normally used for modelling plasters.
The fluid mix is required to enable fine detail to be recorded in the impression and to give the material mucostatic properties.
Freshly mixed plaster is too fluid to be used in a stock impression tray and is normally used in a special tray, constructed using a 1–1.5 mm spacer.
Before casting a plaster model in a plaster impression, the impression must be coated with a separating agent (soap), otherwise separation is impossible.

17. The mixed impression material is initially very fluid and is capable of recording soft tissues in the uncompressed state.
In addition, the hemihydrate particles are capable of absorbing moisture from the surface of the oral soft tissues, allowing very intimate contact between the impression material and the tissues.
The fluidity of the material, combined with the ability to remove moisture from tissues and a minimal dimensional change on setting, results in a very accurate impression which may be difficult to remove.
The water-absorbing nature of these materials often causes patients to complain about a very dry sensation after having impressions recorded.
Disinfection of a plaster impression can be achieved with a 10 minute soak in sodium hypochlorite solution .
The material is, therefore, not suitable for use in any undercut situations (rigid material).

18. Impression waxes
Impression waxes are rarely used to record complete impressions but are normally used to correct small imperfections in other impressions, particularly those of the zinc oxide/eugenol type.
They are thermoplastic materials which flow readily at mouth temperature and are relatively soft even at room temperature.
They are applied with a brush in small quantities to ‘fill in’ areas of impressions in which insufficient material has been used or in which an ‘air blow’ or crease has caused a defect.

19. Zinc oxide/eugenol impression pastes
These materials are normally used to record the final impressions of edentulous arches.
These materials are normally supplied as two pastes which are mixed together on a paper pad or glass slab.
The zinc oxide paste, typically, being white and the eugenol paste, a reddish brown colour.
This enables thorough mixing to be achieved as indicated by a homogeneous colour, free of streaks, in the mixed material.
The pastes are normally dispensed from toothpaste- like tubes and are mixed in equal volumes.
The proportioning is achieved, simply, by expression equal lengths of each paste onto the mixing pad or slab.
The impression is normally recorded in a close-fitting special tray, constructed on the model obtained from the primary impression.
Defects sometimes arise on the surface of the impression but these can be corrected using an impression wax.
(rigid material).

20. Elastomers • Polysulphides.
Often called rubber materials since they have properties similar to rubber.
Clinical uses:
Bridges
Implants
Partial dentures and complete dentures
Indirect esthetic restorations
Four types of elastomers are in general use:
• Polysulphides.
• Silicone rubbers (condensation curing type).
• Silicone rubbers (addition curing type).
• Polyethers.

21. Polysulfides
These materials are generally supplied as two pastes which are dispensed from tubes One paste is normally labelled base paste whilst the other is labelled catalyst paste.
Setting times of 10 minutes or more particularly for light-bodied materials.
The polysulphide elastomers have very good tear resistance.
It has an unpleasant odour.
The colour contrast between the two pastes is an aid to efficient mixing, which is continued until a homogeneous colour, with no streaks, is achieved.
An adhesive is used to promote adhesion between the impression material and tray.

22. Clinical considerations when used
Used with custom trays
Allow 2mm thickness
Use tray adhesive
Setting time 10 min.
Have very good tear resistance.

23. Silicon rubber Condensation silicon
Developed as alternative to Polysulfides
Has more desirable qualities in comparison:
Easy mix
Better taste and odorless
Shorter setting time (5-7 minutes)
Proportioning of the paste/liquid materials is by mixing a given volume of paste with a fixed number of drops of liquid.
For paste/paste materials equal lengths of pastes are mixed together. A colour contrast between the pastes enables the operator to see when proper mixing has been achieved.
In order to obtain optimum accuracy, the models should be cast as soon as possible after recording the impression.

24. Addition silicon Desirable clinical qualities:
Dimensional stability
Accuracy
Clean
Easy to mix
No foul odor or taste
However, they are among the most expensive
Proportioning is carried out by extruding equal lengths of each paste onto the mixing pad. A good colour contrast between the pastes enables thorough mixing to be achieved.
The standard disinfection regime of a 10 minute immersion in sodium hypochlorite will have no effect on the dimensional stability of these materials.

25. Polyethers
Also used for crown and bridge work since they are very accurate and also more hydrophilic than other silicons
The two pastes are proportioned by volume.
Equal lengths of paste are extruded onto a mixing pad giving a base paste/catalyst paste volume ratio of about 8 : 1.
The good colour contrast between the pastes aids mixing.
very good dimensional stability.
A ‘standard’ disinfection routine of 10 minutes immersion in sodium hypochlorite is unlikely to have a deleterious effect on the accuracy of these materials.

26. Properties Stiff, difficult to remove from undercuts
Short working and setting times
Setting time 3-5 minutes
accurate

27. Final impression
techniques

28. Mucodynamic technique
Also referred as close mouth technique.
Record the tissues in there functional position.
The patient applies pressure by closing against occlusal rims or teeth.
Patient exerts pressure and executes muscle actions.
Displaced soft tissues unseated denture base.
Pressure limits normal blood supply resorption.

29. Mucostatic technique Also referred as open mouth technique.
Record the tissues in there undisplaced position.
dentist exerts pressure.
Spaced special tray with no border seal.
Close adaptation of the denture base to the undistorted mucosa.
Border seal retention .

30. Selective pressure technique
Extension for maximum coverage within tissue tolerance.
Light pressure or intimate contact with the movable loosely attached tissues in the vestibules.
Minimum pressure.
Impression compound tray & zinc oxide eugenol paste.
Special tray with border refinement.

35. Extends from one hamular notch to the other.
The vibrating line
Its an imaginary line drawn across the palate that marks the beginning of motion in the soft palate, when the individual says “ah”.
The position of fovea palatine also influences the position of posterior border of the denture. Denture can extend 1-2mm across it.
In patients with thick saliva, the fovea palatine should be left uncovered or else thick saliva flowing between the tissue and the denture can increase the hydrostatic pressure and displace the denture.
Extends from one hamular notch to the other.
It passes about 2mm in front of the fovea palatine.
This line should lie on the soft palate.
Distal end of the denture must cover the tuberosities and extend into hamular notches. It should end
1-2mm posterior to the vibrating line.

36. Posterior Vibrating Line:
Anterior Vibrating Line:
“ Its an imaginary line lying at the junction between the immovable tissues over the hard palate and slightly movable tissues of the soft palate ”
The anterior vibrating line is cupid bow shaped due to projection of posterior nasal spine.
It can be located by asking the patient to perform the “valsalva” maneuver.
Posterior Vibrating Line:
“ Its an imaginary line at the junction of the aponeurosis of tensor veli palati muscles and muscular portion of soft palate ”
This line is usually straight.
Its recorded by asking the patient to say “ah” in short but normal non-vigorous fashion.

37. POSTERIOR PALATAL SEAL / POSTDAM
Definition:
“ Soft tissue at or along the junction of hard and soft palates on which pressure within the physiological limits of the tissue can be applied by a denture to aid in retention of the denture ”

38. Significance Of PPS
Prevents air passage between the tissues and denture base.
Serves Primarily in denture retention by making contact with anterior portion of soft palate.
Reduces patients awareness about the area hence decrease gag reflex.
Prevents food accumulation between posterior border of denture and the soft palate.
Compensates for polymerization shrinkage of denture base resin