The daily tasks of taking impressions can be stressful for a lot of practices, yet taking good impressions are the foundation for good restorative work. Did you know that the main reason clinicians encounter high/low occlusion, crowns not seating or inadequate interproximal contacts is due to poor impressions?
We recently hosted a workshop in Vancouver, BC called “Making Great Impressions – Success Lies in the Details” – instructed by our Frontier Institute Canadian clinical director, Dr. Janet Roberts for our doctors and assistants to learn more about tips and techniques that they can adopt to improve upon their impressions. As Dr. Roberts puts it: “Success in dentistry is mainly dependent on doing the basics well.” Here is a quick summary and tips that you can takeaway from Dr. Roberts’ workshop:
Most Frequent Impression Problems:
- Material not fully set – Always use a timer and don’t rush the process.
- Posterior distortion – Select the right tray and use of full arch tray is always preferred.
- Re-lining, re-inserting – Never attempt this as you’ll never be able to reposition the tray in the mouth accurately enough to avoid distortions.
- Tray too small – Have a good selection of sizes and try them before taking the impression
- No light body – The accuracy of medium/heavy body is only about 1/3 of that of light body – always use light body.
- Not enough material – Not recording tissue (palate, vestibules, etc.) can make it difficult for your laboratory to work on a case, especially cases over 2 units.
- Material lifted off tray – Always use tray adhesive.
- Missing or inaccurate opposing impression / model – Alginate might not be able to capture level of detail that the laboratory needs especially when trying to position working side against opposing taken with Alginate and PVS bites have been used.
Keys to Success:
- Prep Design: Always start with the end goal in mind. If a patient shows heavy Bruxism prepping conservatively and requesting an Empress Crown for example might not be the best idea. Think of the final outcome before a bur touches the tooth and prep accordingly. Ask your Frontier Dental Lab technician/lab manager for prepping protocols for different materials available in the market.
- Soft Tissue Management: EXTREMELY important! You need Hemostatis and Retraction. You must be careful not to induce irreversible damage to tooth ligaments but retracting tissue is the ONLY way to ensure margins are captured and visible on a model from its negative (impression). According to most experienced clinicians, double cord retraction technique is the best way to displace tissue for an adequate impression. As secondary means of retraction, you can also use retraction paste and lasers but they are no match to double-cord technique. When heavy bleeding occurs, you might have to combine techniques for proper hemostasis and retraction. To learn more about hemostasis management, you can also read our blog article by Dr. Trevor Morhaliek.
- Impression Trays: Full arch trays are always preferred as the laboratory can manipulate models for lateral movements and avoid interferences better than using quadrant models. Triple trays are acceptable when doing single tooth cases but we advice against them on free end situations and cases over two units.
- Impression Materials: Always use materials that have not exceeded their expiration dates and have been stored under the right temperature and humidity. Never mix fast set and regular set materials, and always use timers. PVS materials are preferred as they remain stable for long periods of time. Key elements that your impression material should have include: dimensional accuracy, high reproduction of detail, wettability, good resistance to deformation, high tear strength and adequate dimensional stability
- If you don’t give the lab accurate information, they can’t given an accurate restoration.
- The fit of the restoration cannot exceed the accuracy of the impression.
- Time spent in preparation is rewarded at the insert appointment.
This summary was written by Carlos Robayo, CDT, Fixed Prosthetics General Manager at Frontier Dental Laboratories in Vancouver, BC, Canada.