A common-sense approach to Impressions

Sept. 1, 2002
Imagine that you are in the midst of one of the craziest days of your career. Smoke is rising, teeth are flying, women and children are diving for cover ... and one of your office administrators sneaks into your operatory to interrupt you.

by Dr. Mark Hyman

Imagine that you are in the midst of one of the craziest days of your career. Smoke is rising, teeth are flying, women and children are diving for cover ... and one of your office administrators sneaks into your operatory to interrupt you.

"Joe Blaes' office is calling on behalf of Dental Economics!! They want you to write an article!"

"Great," I thought. My mind raced into overdrive, thinking of my favorite topics: practice leadership, team building, high technology, intraoral cameras Then, reality struck.

"They want 1200 words, by next Monday. On impressions."

Me? An article on impressions? Are you kidding? All I could think of was - impressions of whom? Jack Nicholson? Forrest Gump? Rain Man? So I said "OK" and started thinking.

What are the key criteria in selecting impression materials? In our office, we have five major qualities that guide our selections.

•Accuracy - The cost of remakes is deadly; they kill our profitability, upset our schedule, and create a tremendous amount of ill will with busy patients.

•Working time/setting time - We want adequate working time, especially for complex restorative cases or cases with patient management challenges. We want prompt setting times for clinical efficiency and patient comfort.

•Patient experience - Chris Sager, the executive director of the Pankey Institute, says that 97 percent of our patients have no clue what we are doing to them technically. It's the experience that counts. Patients want a pleasant taste, smell, and colors that are visually pleasing.

•Versatility - We want materials that work well for crown and bridge, removable prosthetics, and bite guards.

•Cost - Can we get all of the attributes we want in an impression material and save money?

The answer is "Yes." There are some great impression materials that are very attractively priced. So, look around, check them out, and save some money!

However, these criteria beg the question: Is it the material or the technique that makes the difference? All things being equal, I think it is the technique. Many of us spend more time practicing our golf putts than we do practicing our impression techniques. Everyone should know what their role is in producing excellent impressions the first time, and every time! Decide what works in your hands and for your team. Your patients will benefit from a high level of quality and comfort. Predictability and consistency are vital for a successful crown and bridge practice.

Here are 10 keys to quality impressions:

  • All preparations must be clean and dry - consider dry angles, fresh cotton rolls, using two CDAs to manage the tongue, and moisture. Remove extra moisture on abutment teeth and on the opposing dentition. Educate the patient on the importance of cooperation during this critical step.

  • All margins must be clearly visible. Choose whatever technique is predictable in your hands - one or two cords, electro surgery, laser, infiltrate extra local anesthetic (with Epi) with your ligajet into bleeding areas. Use Hemodent, Superoxol, Expasyl, or whatever works best to clean out the area.

  • Use a rigid tray to provide stability and minimize distortion. Full-arch plastic trays and an accurate CR Bite are optimal.

    If you choose a triple tray, check your occlusion and evaluate tori, bony exostosis, third molars, or cross bites that can compromise accuracy. Try-in the tray and make patient expectations clear.

  • We must have good adhesion between the tray material and the wash - put holes in a solid tray, and dry triple trays following preimpression try-ins.

  • Adhesive used on the floor and walls of the tray must be material-specific and placed at least five minutes before the impression is taken. Too much adhesive can clog up the holes.

  • If you choose the two-step putty wash technique, the tray must be properly seated for the second impression to prevent putty from showing through the wash material. Trim away excess regular putty and confirm complete seating. Mixing heavy- and light-body material from different systems may compromise the quality of the impressions.

  • If you choose the double-bite, triple-tray technique, use rigid trays, and use med-ium/monophase or heavy bodied base material. Communication with your CDAs is critical so that mixing materials are initiated with close to identical start times. When in doubt, leave the impression in a minute longer instead of pulling the impression five seconds too soon. If you have any doubt about the complete set of the material, start over.

  • There must be a smooth transition between the wash material and the heavy body. If your wash material is consistently pushed away off the preps, note your starting times and consider creating space on your base material before seating the impression.

  • Watch for contamination of the materials. When using Superoxol or any other hemostatic agent, rinse thoroughly and gently rub the preparation with a moist cotton pellet to ensure complete removal of the agents.

  • Strive for perfection; accept excellence (but not much less). When in doubt, spend a few extra pennies and seconds to remake the impression. If you don't have time to do it right the first time, when will you have time to remake the case?


    •Surface inhibition - The surface of the impression material does not set, is tacky to the touch, is wipeable with a cotton swab, or usually has the surface texture of a football.

    Cause: Powdered glove inhibition. Use gloves that are unpowdered or treated with cornstarch (which will not inhibit the set of vinyl polysiloxane.) Do not use gloves prepared with talcum powder.

    Cause: Rubber dam inhibition. Rinse thoroughly before taking the impression.

    Cause: Hemostatic agents. These agents - especially those containing ferric sulfate - may transfer sulfur to the preparation site. Thoroughly rinse and dry the tooth after use and before taking the impression. You also can stop using these types of hemostatic agents. There are plenty of good ones that do not contain ferric sulfate.

    Be an educated dental materials consumer. If you are not, take one of Dr. Joe Blaes' courses on dental materials.

    Cause: Residue from temporary crown materials (Methacrylates) or air-inhibited composite material. After using these materials, scrub the tooth surface with pumice and rinse thoroughly.

    •Lack of adhesion in the simultaneous putty wash technique - Lack of occlusal detail and poor blending of wash to putty material.

    Cause: Seating of partially set putty. Seat the tray within 45 seconds of mixing putty and ensure that the working time of the wash is observed.

    •Stone model voids - Small voids present on the stone model that compromise the integrity of the prepared margins.

    Cause: Hydrogen gas evolution (A byproduct of the polymerization of vinyl polysiloxane impression materials.) Delay pouring up the model for one hour after the material is set.

    •Powdery cusp tips on incisal edges on stone model - Cause: Tooth contact with the impression tray causes dehydration of the stone. Avoid any contact with the teeth

    •Voids on the marginal preparation - Cause: The syringe is not immersed in the material. Keep the syringe tip immersed in the sulcus around the prep while syringing to avoid trapping air. Try using a stirring or "figure 8" motion. Be sure to remove excess fluids.

    •Voids on margins with poor adhesion of wash to the putty materials - Carefully follow the recommendations for working time. Check gloves for contamination.

    •Micro bubbles in impression - Cause: Improper removal of Superoxol. Rinse and gently rub the tooth with a moist cotton swab.

    •Streaky or unset putty - Cause: Inadequate mix. Use putty packs, mix until uniform in color.

    •Slow-setting putty - Cause: Improper ratio of catalyst to base or contamination. Use putty packs for more accurate ratios and eliminate wearing vinyl gloves for manually mixing putty.

    •Improper tray seating or lack of proper tray dimension - Cause: Crowns that are too tight, too small, seat improperly, or rock when seated are caused by the prepared teeth contacting the sides or bottom of the impression tray. Always avoid contact of the teeth and use a rigid tray to counter the "spring back" effect.

    •Poor adhesion of impression material to tray - Pulls away from the sides and bottom of the trays.

    Cause: Adhesive was not completely dry or the wrong adhesive was used. Make sure the adhesive has set at least five minutes, or use retentive trays.

    •Delamination - Wash and tray material have not chemically joined together.

    Cause: Strictly timing. You have taken too long to place the wash material, and the tray material has already begun to set. You have placed the wash material and the assistant is still filling the tray.

    Try practicing your timing with your assistant. Remember that as soon as that material begins moving through the mixing tip, the material has begun to set. In order to get the best chemical reaction, you need to follow directions and get the wash and tray material together as soon as possible.

    It's been said that you never get a second chance to make a first impression! If you follow these steps, your results will be predictable, the office will run smoothly, and your patients will be truly "impressed."

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