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Dental impression techniques

author icon By Dr. George Ghidrai

There are various types of dental impressions. The technique that will be selected for a particular situation may depend on different factors:

It is very difficult to make a thorough classification of dental impressions. According to several factors, here is a possible and logical classification:


  1. Depending on the extent of the impression

    • Full or complete dental impression

      A complete impression captures all teeth and surrounding tissues inside the mouth cavity. Basically, three distinct impressions are taken:

      • upper arch impression
      • lower arch impression
      • occlusion impression or bite registration

      Features:

      Complete dental impressions provide full details on the existing oral structures: teeth and surrounding soft tissues.

      They can be used in almost any clinical situation and, because of the detailed information, complete dental impressions are widely preferred by dental practitioners.

      Various techniques may be used to perform complete impressions: one-step technique, two-step technique, custom tray technique etc.


      complete dental impression

      complete dental impression

      Application:

      Many physicians prefer to utilize the complete impression even for simple dental crowns.


    • Partial or segmental dental impression

      The partial impression captures only a part (segment) of the oral cavity, namely the part where the prosthetic reconstruction is designed.

      Features:

      Partial impressions can be taken in partial coverage trays, designed to fit over several teeth, or without trays. In the second variation, the upper teeth, the lower teeth and bite registration are captured on the same impression.

      A partial impression may utilize the one-step or the two-step technique.

      Partials do not provide complete details but they are quicker and easier to make.

      partial impression

      partial impression

      Application:

      • Dental crowns

      • Small dental bridges



  2. Depending on the impression technique

    Note: The name of the techniques may vary from region to region


    • One-step technique

      This technique requires only one step and, in most cases, uses a single impression material. The impression fidelity is not as high as in the case of the two-step or individual tray techniques but it is easier and faster to make.

      Impression materials: rigid or elastic impression materials: putty silicones, alginate, plaster etc.


      Technique

      A stock impression tray that accurately fits the dental arch is selected.

      The dentist prepares the material then places it in the impression tray. The tray is positioned in the mouth and pressed over the dental arch. After the material sets, the tray is removed, washed and sent to the dental laboratory.

      dental impression procedure: impression trays

      impression trays of various sizes

      dental impression procedure: impression tray selection

      an impression tray is selected


      dental impression procedure: rigid impression material before preparation

      the impression material
      is prepared

      dental impression procedure: impression material is placed in the impression tray

      the impression material is placed in the impression tray


      dental impression procedure: impression tray positioning

      the impression tray is pressed over the dental arch

      dental impression procedure: impression after the material sets

      the impression after the material sets and the tray is removed


      Application:

      • Preliminary impressions for the custom tray technique. These impressions are used by the dental technician to fabricate the custom tray.

        The custom tray technique can be utilized in any situation but is especially indicated when large bridges, dentures or implant-supported restorations are manufactured.

      • The impression of the opposite arch: these are the teeth opposite to the designed restoration.

        If no essential details are located on this arch (details that are important for the design of the restoration), the one-step technique is accurate enough.

      • Impressions for case studies: these are used if complex reconstructions are designed or very high aesthetic is demanded.

        These impressions allow the practitioners to study various details before the preparation begins and compare them in different stages of the clinical case. More such impressions can be taken for a single case.


      complete impression using the one-step technique with alginate

      complete impression using the one-step technique with alginate


    • Two-step technique

      It is also known as the wash technique.

      The procedure requires two steps and uses two distinct impression materials, one for each stage. The accuracy and fidelity of these impressions is excellent.

      Impression materials: a rigid impression material for the first step and a fluid material for the second step. The combination of putty and fluid silicones can be a good choice.


      Technique:

      1. In the first stage, the dentist makes an impression with a rigid material. The process runs similar to the one-step technique.

        After material sets, the impression becomes hard and solid. Basically, it forms a tray (or a container) for the fluid material that is used in the second stage.

        dental impression procedure: impression material is placed in the impression tray

        the rigid impression material is placed in the impression tray

        dental impression procedure: impression after the rigid material sets

        the impression after the rigid material sets


      2. Before the second impression, many practitioners prefer to place a retraction cord on the gum lines around the prepared teeth.

        The cord will temporarily retract the gum from the tooth, allowing the fluid impression material to capture an accurate representation of the tooth preparation (which goes slightly below the gum).


        dental impression procedure: retraction cord placement

        retraction cord placement


      3. For the second impression, the fluid material is placed inside the rigid material formed tray. The impression is then repositioned over the dental arch.

        The running fluid material will capture all the fine details of the prepared teeth and surrounding structures.

        dental impression procedure: fluid material placement

        the fluid material is placed in the rigid impression material container

        dental impression procedure: impression after fluid material sets

        the impression after the fluid material sets


        After setting, the fluid material usually gains an elastic consistency. The fidelity of the reproduction is outstanding. The impression is washed and sent to the dental laboratory.


      Application:

      • Dental crowns

      • Fixed dental bridges

      • Some restorations supported by dental implants


      two step technique impression

      two-step technique impression
      rigid material with blue
      fluid material with red
      prepared teeth with arrows


    • Custom tray technique

      The custom tray technique is a particular variation of the two-step technique that involves the participation of the dental lab.

      The technique is widely utilized because of its high precision and fidelity. The only disadvantage is that it requires an extra session.

      Impression materials: fluid impression materials: fluid silicones, polyether etc.


      Technique:

      1. In the first stage, the practitioner makes a preliminary impression with a rigid or elastic material using the one-step technique. After the material sets, the impression is sent to the dental laboratory.

      2. The dental technician pours gypsum into the impression to obtain a dental cast. On this cast, the technician manufactures an impression tray that fits the dental arch as accurately as possible.

        This particular tray is called individual tray or custom tray and can be made of different plastic or composite materials.


        custom tray

        custom tray on a dental cast


      3. The custom tray is sent back to the dental office. The dentist adjusts it in the mouth and places the fluid material inside the custom tray. The tray is repositioned and pressed on the dental arch until it reaches the final position.

        After the material sets, the tray is removed and sent back to the dental lab.


        custom tray impression

        custom tray impression


      Application:

      • Functional impressions for various kinds of removable dentures.

      • Complex restorations supported by dental implants.

      • Extended dental bridges, full ceramic or zirconium prostheses.

      • Any other clinical situation that requires a highly precise impression.



  3. Depending on the functional moves during the impression


    • Static impression

      Features:

      During static impressions, no functional movements are performed.

      Application:

      Dental crowns or fixed bridges when there is no need for any functional movements.


    • Functional impression

      Features:

      During the functional impression, the patient, helped by the dentist, performs certain movements of the cheeks, tongue or lips that try to imitate the movements during the functional processes: mastication and speech. This way, the edges of the impression are actively shaped by the patient.

      Application:

      When removable dentures or other large restorations are designed, it is very important to know how much the margins of these restorations can extend.


Examples

Let's take 2 examples:


complete impression using the one step technique with alginate

1

partial impression

2


Impression number 1

Impression number 2

Last review and update: May 2019



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