Better dentistry: never miss impressions
The defining moment for a crown and bridge case is when the final impression is removed from the mouth.
Willliam Strupp, DDS
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The defining moment for a crown and bridge case is when the final impression is removed from the mouth. If the impression is anything less than 100% perfect, the final case will simply be a failure of one degree or another. In many instances, the failure will be catastrophic the day the case is cemented — not for the dentist, but for the patient. Bad impressions are the antithesis of better dentistry. The patient suffers from both a financial as well as a biological perspective, while the responsible dentist diminishes the integrity of our profession. To avoid such an outcome, follow these six simple steps and achieve a perfect impression:
1. Do core buildups. It is difficult to make an impression of a small spike of prepared tooth structure. If the tooth is built up to full size with a core buildup, it can then be prepared as if it were a virgin tooth. Making an impression is much easier under these circumstances.
2. Do not cut the tissue. When the tissue gets hacked up during preparation, bleeding can become an insurmountable obstacle to making a good impression. However, this can be avoided if the burs and diamonds are kept away from the tissue and all of the final margination is done dry at very slow rpms using a high volume of air to keep the tooth cool. Magnification and extra light are mandatory to see how to avoid tissue contact.
3. Clean the sulcus before making the impression. Grinding debris, plaque, and bonding materials used to place core buildups inhibit the set of many impression materials, causing them to tear off in the sulcus. This is often blamed on low tear strength of the impression material, but the real culprits are the contaminants that do not allow the impression material to react completely chemically. Air/water syringes will not remove these contaminants. A more effective approach for removal is to scrub and rinse the sulcus with 4% chlorhexidine gluconate (Dial Surgical Scrub) in a 3 cc syringe with an Inspiral Brush Tip (Ultradent).
In addition, if an end-tufted toothbrush is used to brush all of the teeth in the arch that is being prepared, the teeth in the opposing arch, and the soft tissues around all of the teeth (including the inside of the lips and cheeks), the sulfur contaminants from operating gloves will also be removed. Glove contaminants cause a slimy residue to be left on the surface of the preps when the impression is removed.
4. “Bone” dry the preparations and retraction cord after using bilateral isolation for all four salivary glands. Research documents the fact that impressions are better when the object of the impression is dry. There is no documented evidence to support the theory that irreversible pulp damage is caused from excessive drying. Yet, there is a ton of clinical evidence (more than 45,000 units of crown and bridge that I have done) to confirm there is no damage.
5. Use full-arch impressions. The ability to see how the teeth on the other side of the arch look and fit is invaluable to construction of bilaterally symmetrical dentistry. Short or long bicuspids compromise the beauty of a patient’s smile and his or her satisfaction with the final case results.
6. Use custom trays. The evidence is in on this one. Custom trays provide superior impressions. Better than that, less impression material is necessary, so the cost per impression is less. In addition, the second cast retrieved from a custom tray is far more accurate than one retrieved from a stock tray. Stock trays are flimsy and can bend while being held in the mouth. Once removed, they rebound and, therefore, distort the impression. Restorations made from such distorted impressions usually will not seat all the way down into place.
There are numerous other factors that can make this task of impression-making less of a challenge, more gratifying for the dentist, and more valuable for the patient.
For an in-depth discussion, please refer to the Strupp Technique Manual under the topic, “13 Steps to a Perfect Impression.” The manual can be purchased at www.strupp.com, or comes free with seminar registrations or when dentists, their spouses, or staff receive dental treatment in my office.
Dr. Bill Strupp is a practicing clinician and inspirational speaker, acclaimed for his practical and predictable presentation, “Simplifying Complex Cosmetic and Restorative Dentistry.” He is an accredited fellow and founding speaker of the AACD. He is a member of the AAFP, AOD, APS, AES, AAIP, IASD, AAOSH, FACD (president and founding speaker) and other organizations. Contact him by phone at (800) 235-2515, by email at Bill@strupp.com, or visit his website at www.strupp.com.