Impression for

complete denture

Impression: A negative likeness or copy in reverse of the surface of an object. Complete denture impression: is a negative registration of the entire denture bearing, stabilizing, and border seal areas present in the edentulous mouth Primary impression: is an impression made for the purpose of diagnosis or for the construction of a special tray. Final impression: the impression that represents the completion of the registration of the surface or object.

Requirements for making impression: 1-Knowledge of Basic anatomy 2-Knowledge of basic reliable technique 3-Knowledge and understanding of impression materials 4-Skill 5-Patient management

Objectives of impression:- 1-retention 2-stability 3-support 4-esthetic 5-preservation

1-incorrect tray position in the mouth2-excessive areas of the impression tray showing through the impression material.3-any void or discrepancy too large to accurately correct on the cast.4-incorrect border formation as a result of incorrect border length of the tray. 5-obviously distorted impression because of movement of the tray during the setting of the final impression material.6- poor detail in the impression because of a poor mixing technique

An impression must be remade for many reasons including:

Primary support area: -Maxillary:- a)posterior ridge b) flat areas of the palate-Mandibular:- a)buccal shelf area b)Posterior ridge c)pear shaped pad Secondary supporting area: - Maxillary :- anterior ridge ,rugae & all ridge slopes- Mandibular:- anterior ridge & all ridge slopes

1-Depending on theories of impression making:2-Depending on the technique 3-Depending on the tray type:4-Depending on the purpose of the impression:

Classification of impression:

1-Depending on theories of impression making:

mucostatic

mucocompressive

Selective pressure

The impression is made with the oral mucous membrane and the jaws in a normal, relaxed condition. Border molding is not done here. The impression is made with an oversized tray or called spaced tray.

Impression plaster or light body The mucostatic technique results in a

denture, which is closely adapted to the mucosa of the denture- bearing area but has poor peripheral seal.(stable but not retentive)

mucostatic

Mucocompressive Impression: Records the oral tissues in a functional and displaced form. The materials used for this technique include impression compound, zinc oxide impression material, and soft liners. The oral soft tissues are resilient and thus tend to return to their anatomical position once the forces are relieved.

mucocompressive

in reality it is likely that tissue adaption to the presence of either a denture made with a mucostatic or a mucocompressive technique make little difference between the two in the long term.

the impression is made to extend over as much denture-bearing area as possible without interfering with the limiting structures at function & rest. This is achieved through the design of the special tray in which the non stress-bearing areas are relieved and the stress-bearing areas are allowed to come in contact with the tray. Both the advantages of muco static and muco compressive techniques are achieved.

C-Selective Pressure Impression

Open mouth

Close mouth

2-Depending on the technique

a tray which carries the impression material of choice into the desired contact with the supporting tissues and into an approximate relation to the peripheral tissues when the mouth is opened and without applied pressure. The rationale behind this method is that the dentures do not dislodge when subjected to biting force.

Open-mouth

The patient is made to close on bite rims and the patient manipulates his tissues by closing, grimacing, sucking and swallowing to form peripheral borders.

Close-mouth

Stock tray

Custom tray

3-Depending on the tray type:

4-Depending on the purpose of the impression:

Diagnostic

Primary

Final or secondary

Primary impression

Final impression:

Impression technique for flabby ridge:

Impression technique for flabby ridge :

1-Full tracing technique of the special tray then the impression is taken with tracing compound after that the final impression done with zinc oxide or light body silicon material. 2-Neutral zone technique: neutral zone: the potential space between the lips and cheeks on one side and the tongue on the other, that area or position where the forces between the tongue and cheeks or lips are equal. The concept considers the actions of the tongue, lips, cheeks, and floor of the mouth during a specific oral function, to push the soft material into a position where buccolingual forces are neutralized.

Impression for severely resorbed ridge

Primary impression of the upper and lower jaws are taken in impression compound.

Upper wax rims and lower special tray are constructed.

The special tray is a plate of acrylic without a handle, with spurs or fins projecting upwards toward the upper arch. These help with retention of the impression material. Occlusal pillars have been built up on the top of the lower tray in green stick to the correct occlusal height.

Then thick mix of viscogel is then placed around the rest of the lower special tray distally and mesially to the occlusal pillars. The patient is the asked to swallow, talk…..etc.

After about 5-10 minutes, the set impression is removed from the mouth and examined. The viscogel material would have been molded by the patient's musculature into a position of balance

Technique of neutral zone impression using viscogel material:

-Impression between oral space and border of denture -Physiological molding by lips, cheeks and tongue improve function and comfort so that the polished surface of the denture is functionally compatible with muscle action.- Try in procedure was done and then, the wax surrounding the teeth was removed and replaced with light body elastomeric impression material or zinc oxide. Trial denture bases were reinserted into the patient's mouth & the patient was instructed to perform various orofacial movements so as to record the polished surface of the denture in harmony with the orofacial musculature.-after the impression material had set the trial denture removed, packing & curing then the final denture just polished lightly not over finishing in order not to destroy the details that recorded.

3-Polished surface impression technique:

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