Impression techniques in implantology
I-Introduction
The impression, in implantology as in traditional prosthetics, is a crucial and essential step.
It is an opportunity to transfer as faithfully as possible any clinical situation to the prosthesis laboratory.
It is made in the mouth, it is then processed to produce, in the prosthetics laboratory, a working model also called a master model.
Chronologically, the impression is taken after the surgeon has validated the osseointegration. It determines the start of the so-called prosthetic phase.
The implant impression must take into account the particularities of the implant prosthesis. This type of impression requires high dimensional accuracy but requires little precision in recording details.
The implant impression can simply be called a positioning impression
In supra-implant prosthetics, the main difficulty is to obtain a passive adaptation of the prosthetic elements on the implants. The precision of the recording of the spatial positions of the implants is crucial.
A defective impression can cause fracture of the ceramic, screws, or even the implant. It can even lead to loss of osseointegration.
The implant impression allows the recording to be obtained:
– the position of the implants in the oral environment;
– of the gingival contour;
– of the emergence profile.
II-Preparation of the impression
This preparation is twofold:
– choice of the type of imprint;
– preparation of equipment and materials.
1 – Choice of print type
• a) Most used techniques: direct and indirect prints
• b) Less used techniques:
– Direct clipped impressions;
– Pillar prints
The two most commonly used fingerprinting techniques are called direct and indirect . They have radically different concepts, each with advantages and disadvantages.
The technique of direct clipped impressions has the advantage of simplicity but its lack of precision can be criticized.
Abutment impressions : very simple at first glance, this technique is very similar to conventional prosthetic techniques. It is reassuring for the novice practitioner because it closely resembles what they are familiar with elsewhere. However, it has the disadvantage of recording the surface condition and detail of the prepared abutments.
2 – Preparation of equipment and materials
• a) Impression tray
The use of an individual impression tray provides better adaptation to the clinical situation.
• b) Transfers
The transfer is selected according to: – the diameter of the implant or abutment; – the emergence profile of the healing screw; – the impression technique chosen.
1 – Transfers for indirect imprint;
2 – Transfers for direct impression
3 – Materials
• a) elastomers
The choice of material is mainly made between polyethers and silicones A
• b) hydrocolloids
Irreversible alginates or hydrocolloids are used for preliminary impressions or for impressions of the opposing arch.
• c) plaster casts
The dimensional variation of the impression plasters is very low, their rigidity is significant.
The first choice to make concerns the type of impression tray (open or closed). This determines the type of transfers used (transfers removed or repositioned). The other choice concerns the materials: silicones or plaster. Finally, the chosen transfer will also depend on the presence or absence of an intermediate abutment on the implant neck.
Implant impression: direct technique
Direct impression, which is characterized by the use of a perforated impression tray, is performed in several stages. While this technique is not the simplest, it appears to be the most reliable, making it the technique of choice.
1 – Unscrewing the healing pillars
2 – Screwing the impression transfers
3 – Radiographic control of the positioning of the impression transfer
4 – Fitting the individual impression tray
5 – Preparation of the individual impression tray and taking of the impression
6 – Detaching the imprint
7 – Retightening the healing pillars
8 – Positioning of laboratory analogues
1 – Unscrewing the healing pillars:
The healing abutments, placed during the final surgical stage, are unscrewed. The marginal gingiva is then checked. It is important to verify that nothing can interfere with the placement of the impression transfer. There must be no bony edge covering the prosthetic base.
2 – Screwing the impression transfers:
Screwing is performed manually (without torque control) using a hexagonal screwdriver. When mouth opening is limited, a needle-holding forceps is used to fix the transfers.
The screwing of the transfers must take place as quickly as possible after unscrewing the abutments.
When the number of implants is large, it is therefore advisable to use contact or injected anesthetics.
3 – Radiographic control of the positioning of the impression transfer
A periapical X-ray is taken to check the position of the impression abutment in relation to the implant. When all the coils are visible on the X-ray, this means that the angulation of the film is correct. The control is then precise.
The internal hexagon connection significantly reduces the risk of incorrect positioning of the transfer
4 – Fitting the individual impression tray
The individual impression tray can be perforated in the prosthetic laboratory.
When there are a large number of implants, the perforation is then done in the office after screwing the transfers.
The impression tray is inserted and removed several times while empty to memorize the insertion path.
5 – Preparation of the individual impression tray and taking of the impression
The impression is made in one step with one or two viscosities depending on the material chosen.
6 – Detaching the imprint
Once the material has set, the transfer screws are unscrewed and then removed from their housing by a few millimeters in height to ensure that they are completely unscrewed.
The impression tray is removed with a brief movement in order to minimize deformations.
7 – Retightening the healing pillars
As soon as the impression leaves the oral cavity, the healing abutments are screwed back in as quickly as possible. The impression is left aside during this step.
8 – Positioning of laboratory analogues
Implant analogs can be screwed in at the dental office or lab. Screwing is done gently, maintaining the transfer so as not to tear off any impression material when moving it.
Implant impression: indirect technique
This type of impression allows the use of a conventional impression tray and is very similar to the dental preparation impression.
More common in its procedure, it seems simpler. However, its lower precision limits its use to recording a small number of implants.
1 – Unscrewing the healing pillars
2 – Screwing the impression transfers
3 – Radiographic control of the positioning of the impression transfer
4 – Trying on the impression tray
5 – Making the impression
6 – Detaching the imprint
7 – Unscrewing the impression transfers and screwing the healing abutments
8 – Assembly of transfer-analogue pairs
1 – Unscrewing the healing pillars
2 – Screwing the impression transfers:
The transfers should be fixed as soon as possible after the previous step. Without a healing abutment, the marginal gingiva no longer receives support and sags. Screwing is done manually using a friction screwdriver.
3 – Radiographic control of the positioning of the impression transfer
A retroalveolar X-ray is performed to check that the impression post is correctly positioned on the implant neck. If there is a gap, the transfer must be unscrewed and the source of the discomfort during insertion determined.
In the indirect technique, it is not advisable to retouch the transfer because this retouching could harm the precision of its repositioning.
4 – Trying on the impression tray
The impression tray is tried in. During the trial, it must not interfere with either the dental tissues or the transfers.
5 – Making the impression
The impression is made like a conventional prosthesis, in one step, with one or two viscosities depending on the chosen material. The heavy material is positioned in the impression tray, the oral cavity is dried, and the more fluid material is injected around the impression transfers. The filled impression tray is inserted into the mouth. Constant pressure on the impression tray ensures its immobility.
6 – Detaching the imprint
7 – Unscrewing the impression transfers and screwing the healing abutments
The impression transfers are unscrewed using the same screwdriver that was used to screw them in. The healing abutments are screwed back in as quickly as possible. The impression is left aside during this step.
8 – Assembly of transfer-analogue pairs
Each transfer is screwed onto the analog of the corresponding diameter. The placement of the transfer-analog pairs in the impression can be done in the office or in the laboratory.
During transport, the print containing the transfers must be carefully protected so as not to damage it.
Impression techniques in implantology
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