Voids on Margin
Voids on the Margin

What causes voids on the margin for dental impressions?

Voids are commonly identified as "holes" on the margin of the prepared teeth. Sometimes voids can lead to margins which are incomplete. This can cause short crown margins and/or open margins in the final restoration. Learn common ways to adjust the dental impression procedure to minimize voids.

Browse this page to read about common issues and find solutions and tips to eliminate voids on the margin. You can also request to download a PDF of the full guide.

Blood and Saliva contamination around preparation

  • Using Retraction Capsule
    Watch the video to see how the 3M™ Astringent Paste helps control bleeding

    What can you do:

    Rinse and dry the prepared area properly and stop any bleeding by using appropriate retraction/hemostatic agents. Liquid hemostatic agents and pastes based on aluminum chloride, aluminum sulfate or iron sulfate are suitable.

    3M™ Astringent Paste supports your impression work with excellent gingiva retraction with or without cord and hemostasis.

Improper syringe technique

  • Syringe Technique
    Watch to see how to apply wash material exactly where it’s needed to capture every marginal detail

    What can you do:

    Keep the mix tip permanently immersed in the paste to avoid the formation of air bubbles. Apply a liberal amount of wash material into the sulcus. Start from the bottom up and cover the whole abutment tooth with syringing material. Always keep the tip in close proximity to the surface.

    3M™ Intra-oral Syringes Green (for VPS materials) and Purple (for polyether) are easy to handle and give better control of the syringing process.

Working time exceeded, flowability already impaired

  • Dental Impression working time

    What can you do:

    Select material with sufficient working time (i.e. regular set instead of fast set). Make a choice depending on the individual situation and preference of material. Do not exceed working times given in the instructions for use. In case of 3M Oral Care materials follow given intra-oral syringing times for wash materials.

    Pay attention to storage temperature. Working times are reduced due to higher temperatures of the product, while intra-oral setting times might be longer if the temperature of the product is lower.

    3M™ Impregum™ Soft Polyether Impression Material offers a very long working time with constant flow. And, polyether impression material is less temperature sensitive in its setting reaction than VPS materials.

    3M Imprint™ 4 VPS Impression Material offers both a fast and a regular setting material. Select Quick Set for 1 to 2 unit cases and Regular Set for cases that involve 3 or more units.

Air bubbles in elastomer syringe or intra-oral syringe

  • Bleeding Impressions Syringe
    Watch to see how to properly prepare and bleed a syringe

    What can you do:

    Bleed cartridge prior to loading syringe and keep flow of material consistent. Do not stop and start while loading the syringe.

Tray not seated properly

  • Maxillary arch Impression tray Placement

    What can you do:

    Slowly (approx. 5 seconds) insert the loaded tray into the mouth parallel to the long axes of the prepared teeth, and hold it in place without applying pressure.

    Maxillary arch:
    Seat the impression straight up. Make sure the handle is aligned with the patient's midline. Always hold the impression tray in the premolar area for stability.

  • Mandibular arch Impression tray Placement

    Mandibular arch:
    Seat the impression straight down over the arch while pulling out the patient's cheek. Make sure the tray handle is aligned with the patient's midline. Apply passive pressure in the premolar areas with your thumbs for stability.


    • Apply passive pressure while holding the impression tray in place
    • Never ask the patient to hold the tray
    • Never ask the patient to bite down on the tray

Storage at elevated temperature

  • Storing Temeprature for Impregum

    What can you do:

    Store impression material at room temperature. Usually, times given in the manufacturers’ instructions for use are valid for a storage temperature of 23 °C/74 °F. Working times are reduced due to higher temperatures of the product, while intra-oral setting times might be longer if the temperature of the product is lower.

    Due to its lower temperature sensitivity, 3M™ Impregum™ Soft Polyether Impression Material is less affected by fluctuations in storage temperature than VPS materials.

Troubleshooting Dental Impressions
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Download our comprehensive guide to troubleshooting most common dental impressioning issues, including a bonus section on 10 Golden Rules for Taking Perfect Dental Impressions.