One of the most important stages of the restoration process is taking a quality impression. To provide the appropriate transferring of implant’s position, two methods of taking impressions are used – closed tray impression and open tray impression techniques. Now let us look at the examples of both.
CLOSED TRAY IMPRESSION TECHNIQUE
is typically the standard one, and actually is no different from a traditional double-layer impression applied in dental prosthetics. But first let’s look at the healing cap: it should be screwed in tight; the mucosa around should differ in colour and condition from the mucosa around the adjacent teeth; while you are tapping slightly with the handle of a dental probe or an intraoral mirror, you should hear a distinct high metallic sound. Of course, at this moment the patient should not feel any pain. Only after this, we can turn out the healing cap. The screwdriver should always be placed into the cap’s slot very tightly until it stops, otherwise while turning the cap in or out you can damage the slot. Examine the gingival tissue inside: it should not bleed. If it does, we should apply some Solcoseryl dental adhesive paste on the healing cap again, insert it into the implant, and instruct the patient to wait a few more days.
The internal surface of the implant should be cleaned carefully. Then we install a closed tray impression coping. This is needed to accurately transfer the implant’s position from the mouth to the gypsum master cast (as a rule, this impression coping includes an outer case and an internal screw).
Insert the impression coping, turning it slightly in both directions, to check that its polygon enters the implant’s appropriate polygon. And only then we can tighten the internal screw. Next, we rub the screw’s slot with warmed wax and take the first layer of the impression. Then we get the impression out from the mouth (on the hardened impression mass, cut off undercuts and interdental septa, which can prevent the repeated insertion of this impression), put the second [adjustment] layer and take the final impression.
After this, we turn off the impression coping and insert it into the taken impression at the relevant place. If you took several impressions of different implants at once, it is important not to confuse them. In the same way we install the healing caps, which had been removed a few minutes ago.
While you were taking impressions, your assistant was to wash carefully and to apply antiseptics. Now, the impression with the copings is sent to the dental laboratory.
In the laboratory, a dental technician takes out the implant impression coping, turns the implant analogue on it and put it into the impression again, aligning the surfaces of the coping’s flats appropriately. Then he places the implant surrounding surface with so-called gingival mask, and after the mask sets he casts the base of die stone.
In a few hours, the die stone sets, and we open the model.
Then unscrew the healing cap again, attach the suprastructure chosen by the dental technician, and try on the framework. The framework should be put on the suprastructure without effort. Of course, the framework should be located in the mouth in the same way as at the master cast. If a bridge construction is supposed to be used, it should not be balancing while being fit.
If the prosthetic construction is implant-supported not with cement, but screw retention, to determine the construction fitting, a Sheffield fit test should be conducted: place the construction on the implants and tighten it with a single occlusal screw. The construction should not be balancing itself.
Unscrew the occlusal screw from the implant and screw it into the other implant — the construction also should not be balancing itself in the mouth. Do it in this way with each implant that is used in the construction.
In such cases, the framework should not squeeze or traumatize the surrounding soft tissues. When this is not the case, you should make an appropriate fitting procedure (if it is necessary, together with a framework try-on you can take a reference X-ray). Choose the colour of the prosthetic construction, take the suprastructure and the framework off, and send them to the laboratory. Insert the healing cap into the implant in the mouth.
When the prosthetic construction is fully ready, attach it with the occlusal screw or fit with cement, depending on what technique was planned. At the stage of the final fixation of the suprastructure, it is important that the requirements of cleanness and dryness (both of the suprastructure and the internal surface of the implant) should be observed, as well as the required torque values to tighten the fixing screw or the suprastructure. This should be done with a torque wrench (implant manufacturers always specify the recommended torque values).
While fitting the construction on cement, close the slot of the screw, used to attach the suprastructure to the implant with a gasket (gutta-percha one, for example). Otherwise, cement will harden in these slots and will not allow turning out the screw when it is needed.
For CONMET implants, the following torque values are recommended:
Remember that every time after it use, the torque wrench should be completely disassembled and sterilized.