If you want to get the most of out your lab work, it all starts with an accurate, reliable impression, but even the most experienced practitioner can encounter difficulties when taking one.
I’ve got special permission from 3M ESPE to share with you a number of tips developed by that company.
1. Tearing/rough surfaces: Rough occlusal and/or incisal surfaces, tearing on the margin of the preparation, and poor lamination between the tray material and wash can be due to a number of causes. To avoid these issues, pay close attention to your retraction technique. Additionally, pay close attention to the recommendations for the material’s oral working time, and set a timer to ensure the tray is left in the mouth for the full set time.
2. Tight crowns: This problem can be caused by early removal of the impression tray from the mouth, a poor bond of the material to the tray, or seating an impression tray with material that is partially set. Again, closely follow the recommended working and setting times, and always use a VPS tray adhesive according to instructions.
3. Short crowns: Trays with weak or low walls can provide insufficient support during impressioning, leading to short crowns. To address this issue, use custom or inflexible trays — preferably metal. Short crowns can also be due to teeth coming into contact with the tray. Before seating confirm that teeth do not touch the tray.
4. Voids: Voids are one of the most common impressioning issues. Voids can compromise the restoration’s fit and function. This issue may indicate a needed improvement to your syringe technique. Use a stirring motion while syringing, making sure to keep the syringe tip immersed to avoid trapping air.
5. Tray seating: This step presents the possibility for a number of errors.
• Ledges — Position the tray before seating, and use a slow, steady, vertical seating motion.
• Drags — This can occur when the tray is placed and seated in one motion or when teeth rebound off the tray and slide into position. Seat the tray slowly after carefully positioning it in the mouth, avoiding contact of teeth with the tray.
• Rocking crowns, slanted or wavy teeth — Eliminate tray movement after seating using passive pressure on the tray to immobilize it for the full recommended oral set time.
6. Bite registration: When excessive occlusal adjustment is necessary for restorations, poor interocclusal records are likely a factor. To combat this, use a dimensionally stable bite registration material, and ensure it is trimmed properly. Additionally, monitor patients to confirm they do not move during the procedure.
7. Surface inhibition: If the surface of the impression material is not set, tacky to the touch, and visually resembles the surface of an orange peel, a number of factors may be the culprit; exposure to air-inhibited methacrylates or residues from custom temporary materials, for example. Avoid this problem by waiting to fabricate the temporary crown until the final impression has been made, then remove the air-inhibited layer on any composites, adhesives, or core build-ups in the impressioning area.
I suggest that a reliable impression material, such as 3M™ ESPE™ Impregum™ Soft Polyether Impression Material, and the right technique, impression-taking can be predictable and highly accurate.
I hope you found this guide helpful. If you’d like to discuss this article or other dental subjects, feel free to leave a comment here or get in touch on our social media accounts:
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