Impressions in removable partial dentures
- Introduction :
- problem ͢ toothlessness.
- Solution ͢ prosthesis, for its realization, it is necessary to transfer the clinical reality to the laboratory.
How? By Footprints.
- There are different types of imprint:
- Primary, secondary,……etc.
- Unitary, partial or global.
- Higher or lower.
- Study or final.
- Techniques: anatomo-static or anatomo-dynamic.
- Materials: alginate, silicone, plaster, etc.
- Result: study or working model.
- Definitions:
Imprint = hollow or raised mark (LAROUSSE).
In dentistry:
“The impression is the negative recording of the dental arch allowing a positive model to be obtained either for study or for the creation of a prosthesis.”
There are different types:
* preliminary (primary) impression: made using a standard impression tray with the aim of having a primary model on which an individual impression tray (PEI) will be made.
*secondary impression: taken using a PEI in order to have a secondary model on which our future prosthesis will be made
- Objectives: To obtain:
*primary model: -‘study
– realization of PEI
-medium and short extension prosthesis.
*secondary model: in the Cl I, Cl II edentulism and a large intercalary edentulism.
- Materials:
There are several materials,
The qualities required of a material of choice are:
-Inexpensive and easy storage;
-Easy handling;
-Pleasant taste,
– Must not be irritating or toxic;
-Taking time of 3 to 5 minutes (depending on the procedure);
-Sufficient elasticity;
-Dimensional stability over time;
-Faithful ;
-Compatibility with all replica materials.
Req: There is no material that combines all of these qualities.
- Material: Is dependent on the choice of material.
- Patient installation:
*Impression of the upper jaw:
the patient (patient) must have the bust and head straight (perpendicular to the ground) to balance the forces of the bi-digital pressure and avoid the material being pushed back towards the pharyngeal tract, his oral cavity must be at a height that generally does not exceed the practitioner’s elbow. *Impression of the lower jaw:
-The bust is slightly tilted backwards so that when the patient opens his mouth the lower ridge will be horizontal.
-CB at the level of the practitioner’s elbow.
- Preliminary anatomical-static impression with Alginate:
1)- Definition:
It is the first impression reproducing an edentulous maxilla, made with a standard impression tray (PES), filled with a precise but inexpensive material. It is intended for the production of an individual impression tray.
2)- Goals:
-Perfect the diagnosis
-PEI preparation;
-Production of short and medium range prostheses.
3)- Material:
-Perforated standard impression tray (metal or plastic)
-Alginate bowl and spatula.
4)-Choice of standard impression tray:
-Have no influence on the physical and chemical properties of the material;
-Be rigid;
-Be adapted to the shape of the arch and cover all the anatomical elements to be used (without direct contact);
– Leave a space of 1 to 2 mm between its intrados and the surface to be molded.
-Does not cause any distension of peripheral organs.
5) – The imprint of the lower jaw:
It should be undertaken first (easier to bear compared to the imprint of the upper jaw)
-Trying and correction of the impression tray.
-Preparation of the impression material: Alginate.
-compliance with the dosage indicated by the manufacturer;
-the water/powder mixture is spatulated vigorously until a homogeneous mass is obtained.
*Imprint technique:
-Fill the PES with alginate
-PE is inserted, centered and held without movement for the entire duration of the setting.
-Removal of PE with a sharp blow without lateral pulling or hesitation in the longitudinal axis of the anterior teeth.
-Careful examination of the print
-Rinse with water (remove any mucin or saliva)
-Remove excess alginate
6) – The imprint of the upper jaw:
-PE tests and correction:
-Preparation of the material.
-Impression technique: after centering the PE, the patient’s head will be tilted slightly forward to avoid any risk of material flowing into the pharyngeal tract.
7)-Processing the imprint or casting the model:
The casting of the model can take place either immediately or after 10 minutes, not exceeding one hour.
-after a good cleaning of the imprint the plaster/water mixture is prepared;
-the imprint is placed on a vibrator;
– small portions of plaster are gradually deposited using a spatula, until the impression is completely filled;
– construction of the base;
-after the plaster has crystallized, separate the imprint from its model.
NB:
According to our clinical case, if there is an indication, we make a PEI to take a secondary anatomical-physiological impression (Cl I, Cl II and/or large intercalary edentulism).
Individual impression tray: Made of resin or thermoplastic plate
- Secondary Anatomical – functional Footprints :
1)-Definition:
This is a definitive impression from which the complete prosthesis will be built, obtained with an individual impression tray from the preliminary impression.
2)-Objectives:
- Records the free play of paraprosthetic organs.
- Obtain a working model as faithful as possible on which the prosthesis will be developed.
3)-Materials:
“Synthetic elastomer” (eg silicone) = viscosity + KERR paste.
4)- Materials:
-Mixing plate and spatula
-Spirit lamp
-Chisel or blade
5)-Technique:
1st stage Verification and control of the PEI on model
2nd stage : Verification and control of the PEI in the mouth (static and dynamic tests)
3rd stage: Creation or recording of the physiological play of the paraprosthetic organs (peripheral joint) at the level of the edentulous segments using:
Kerr paste: segmental method;
Medium viscosity silicone: global method.
The corresponding edge of PEI is covered with sufficient thickness of the material, then insertion, centering + movement of the corresponding region.
- Lower footprint:
- Sublingual region (from PM to PM) swallowing + retraction and elevation of the tongue.
- Middle lateral region: maximum opening.
- Posterior lateral region: maximum opening
- Anterior lateral region: contraction of the lip.
- Mylohyoid and retromolar region: swallowing + movement of the tongue (by its tip) from corner to corner.
- Upper footprint:
- Middle lateral region: maximum opening.
- Posterior lateral region: maximum opening + swing of the mandible from right to left.
- Anterior region: pull the lip down, and project it forward, then retract the corners.
- Posterior platinum region: the paste is placed in the intrados: emission of the phoneme “A” (movement of the veil)
4th step : Imprint of the support surfaces:
-Material preparation (homogeneous mixture)
-Fill the PEI with the “fluid” material
-Insertion and centering of PEI
-All movements corresponding to the regions to be recorded
-Analysis of the impression: after taking the material, the impression is carefully removed and examined then rinsed with water.
Imprint processing:
- For the realization of the working model:
- After cleaning the imprint, make the formwork
- Place the print on the vibrator
- Prepare the mixture; plaster-water
- The casting
Other types of prints:
Impression of corrections or split impressions: indicated in posterior classes (Cl I and Cl II or IV of large extent) = mixed osteo-mucosal and dental support.
Conclusion :
The transfer of clinical reality to the lab requires quality samples in order to ensure the adaptation of the prosthesis and its compatibility with the supporting tissues (durability of the prosthesis )
Impressions in removable partial dentures
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