Impression Distortion...Only a Technical Problem? A Doctor/Technician Liaison’s Perspective

If you are lucky, impression distortion is major, and you can see it. But more often than not, it is "minor" ; and can be invisible to the untrained or undiscerning eye. Further-more, you and your dental technician often do not fully appreciate the implications of even minor distortion until you actually attempt to seat a restoration. Minor impression distortion, in fact, is often major. It is one—if not the single largest—technical killer of profits, relationships, and self-esteem in our profession today. This is the essence of the problem. As such, we must make every effort to understand this problem fully and its costly ramifications. Then we need to take on the team responsibility to eradicate it from our practices and dental laboratories to the maximum extent possible.

WHAT DO OUR DENTAL LABORATORIES WANT?

 

Impressions, like photos, must capture details correctly to be of optimum use. Factors such as different types of impression materials, monophase versus dual-phase technique, cord selection and technique, and attention to moisture control can all greatly affect the accuracy and reproducibility of desired details.1 Our preparation is only as good as the impression that we send to our dental laboratory. A case with quality margins, fit, and function can only be created utilizing accurate, distortion-free impressions. Very few of us can lay claim to an impression-perfect practice. In my work as a doctor/technician liaison and lecturer I have heard many requests for better impressions from our dental laboratory colleagues. "Impressions! Impressions! Impressions!" ; stated a technician who recently answered the question, "What could doctors do better for their laboratory?" ; This seems to be a universal plea for help.

QUESTIONS MOST OFTEN PRECEDE ANSWERS

 

Why is impression distortion so universal and prevalent? Why does it remain a significant problem despite the material advances over the past decades? What is our role as doctors in the ultimate solution? What role can our dental staff, including our dental technicians, play in dealing with this challenge? What will motivate us to find solutions as a doctor/technician team to this dental industry dilemma? Is it just a technical problem? Do we need to take a radical, outside-the-box business approach to reducing the rate of remakes resulting from impression distortion? Could we build financial motivators into our business model to encourage solutions for the doctor and laboratory team members?

DISCUSSION FROM A DIFFERENT PERSPECTIVE

 

The usual technical reasons for the impression distortion problem, along with the associated technical solutions, have been frequently addressed. Some of the better known among them include the following: 
Flexure will cause distortion. Use strong impression trays, preferably perforated.
Figure 1. A plastic triple tray showing a distinct pressure point (burn-through) at the lingual aspect of the prepared tooth. The result of this problem, not detected before sending the case to the laboratory, can be observed in Figures 7 and 8.
Figures 2 and 3. A triple tray is not indicated in a situation such as this. The dental technician was expected to complete this 3-unit case with limited occlusal contacts and no contralateral arch information. A separate bite registration impression was not provided with the case.

Flexure from pressure points can be a common problem with many plastic triple trays (Figure 1). Triple trays should be as inflexible as possible. A metal tray with a metal posterior connector is often the best choice. Triple trays should be prefitted prior to anesthesia to check for tissue impingement and resulting flexure of the side walls. A tray without sides becomes an alternative if pressure cannot be avoided with a sided tray. Knowing when to use a triple tray and when not to can be a vital technical decision affecting the final outcome of a case (Figures 2 and 3).

Figure 4. In dental laboratories, close examination reveals no adhesive being used on a majority of triple tray side walls.

Polymerization shrinkage of the impression material and required multiple pours. Always use adhesive on all types of impression trays (Figure 4). This must be properly applied and dried to hold the impression in place through multiple stone pours and to overcome polymerization (setting) shrinkage, which occurs toward the center of the mass and away from the tray walls.

Working times not observed. Carefully observe mixing and setting times. Careful planning and coordination between the assistant and doctor are critical.

Injection technique. Learn to inject wash materials properly to avoid separations and folds when recording the margins.

Figures 5 and 6. Seating technique, movement, and setting times play big roles in the quality of impressions. The technician will not be able to visualize aesthetics properly for the lateral incisor involved with this impression.

Seating trays properly (Figures 5 and 6).

Movement. Do not move or "hand-off204; trays during the critical intraoral setting phase. Be aware that one of several negatives related to anterior triple trays is that you cannot control or prevent movement of the tongue against the palatal aspects during the critical setting phase.

Quality of impression materials. Use adequate amounts of high-quality impression materials manufactured with strict controls to ensure a consistent product.

Accurate alginate impressions used for opposing models, study models, and diagnostic wax-up models. Follow exactly the manufacturer mix, working/set times, and pour instructions.

With a list of basics that is so easy to understand, no more impression distortion, right? We have all seen the continuous stream of educational materials related to impression problems and solutions that have been presented to us over many years. These have included thoughtfully created color brochures, lectures, mini-seminars, VCR tapes, and DVDs, all of which were created to simplify impression taking and to eliminate any of the commonly identified problems, most notably impression distortion. All these efforts, however, have been at great expense with almost imperceptible results on an industry-wide basis as observed upon examination of impressions currently in our dental laboratories.

Perhaps we need to improve results by changing how we view and approach this problem. In equal importance to the recently mentioned technical aspects, maybe we need to learn what will motivate us to take the necessary actions to improve our business systems governing this important area of our practices. Leadership, management, financial, and relationship issues with all their inherent implications for success need to be involved in any process of self-improvement.

AN INDUSTRY-WIDE PROBLEM NEEDING A TOTAL TEAM APPROACH!

 

Impression distortion has always been, and always will be, an industry-wide problem as long as we are taking impressions with elastomeric materials. That in itself dictates to us, as leaders and managers in our dental practices, the ongoing nature of this challenge. It is a problem that has multifactorial causes that do not respond to a one-time, one-size-fits-all, quick fix. It requires a business system that the doctor and dental team create and implement, and that multiple staff members coordinate.

It should be a preventive process that keeps the problem in constant focus, along with its potential causes and solutions.

This equates to routine training and reviews. It must include motivators for all involved on the dental team to correct any erroneous technical procedures. It will entail a system that tracks the staff efforts of both the dental practice and the dental laboratory. This must also take into consideration any turn-over of employees involved and the constant retraining efforts that are needed.

This system should include pre-exit inspection of the impression (problem-versus-solution awareness and related training) at the dental office, and entry inspection of the impression (quality control and problem-versus-solution feedback) at the laboratory level.

ESSENTIAL TEAM KNOWLEDGE AND TRAINING NEEDED TO REDUCE THE INCIDENCE OF IMPRESSION DISTORTION

 

All team members must know how to define and visually recognize obvious signs of the potential presence of impression distortion. The author defines it as follows: Impression material deformation, originating from a single (or multiple) causative factor(s), leading to an inaccurate physical representation of the actual shape and dimensions of the object (teeth, tooth preparation, ridge, etc) impressed.

There must be awareness by all team members that the potential for impression distortion is universal in all dental practices. Routine checks by all involved team members to identify potential impression problems should occur before the patient is temporized and the impressions are packed for shipment to the dental laboratory.

Figure 7. The original crown fits nicely on the original model.
Figure 8. As found in the mouth at try-in, the old crown does not come close to fitting the new model.

The doctor, dental office staff, and laboratory technicians must know how to recognize and definitively diagnose the presence or absence of impression distortion after a failure in the ability to seat a restoration as returned from the dental laboratory. (Note: A diagnosis should never be made with the purpose of finding a party to blame. Instead, it ultimately seeks to prevent future occurrences by identifying causative factors.) This is done after taking a second impression and after the second restoration is completed and returned. To do this definitively you should have the original impression, the original model, and the original restoration (which can be returned to the laboratory after inspection if required). Along with these you will need the new model and the newly fabricated restoration. Before the patient arrives for the second seating attempt, do the following: take the original restoration and place it gently on the original model. Does it fit down easily and properly in all aspects, including margins and interproximal contacts (Figure 7)? If so, the laboratory created this restoration according to the blueprint you sent. Next, take the new restoration and check it in the same careful way on its respective model for accuracy. If accurate, this also was created according to the blueprint submitted. Logically, if both models are accurate, then the restorations should be interchangeable. Try the old crown on the new model and determine if it fits (Figure 8). If it does not, as found in the first failed attempt to seat in the mouth, then impression distortion is nearly always the culprit. (It is optimal to use solid models, if your laboratory returns them to you with your cases, to compare restorations in order to obviate any model differences related to die trimming.)

A powerful motivator to prevent impression distortion is to understand its tremendous negative financial impact on the practice. If we attempted to seat a restoration that did not fit, or the contacts were open, or the margins were short, or the occlusion was high, did we grind and adjust until it "fit?" ; Perhaps immediately when the ill fit was noted, or eventually after lots of adjusting, we chose to send it back to the laboratory to make it again. Whatever the action, it took lots of valuable chair time. Unintentionally, we often do not think much about the financial impact on our dental technicians who typically do not charge us for the associated remake. In addition, we do not carry a global awareness of the dental industry into our professional life due to our independent nature and limited business training. A seemingly small average number of remakes per month can potentially be a yearly loss to the dental industry amounting to billions of dollars. (See Table for an extrapolation of costs according to the author204;s observations in the industry.) Any dental laboratory owner that tracks remakes will state that the majority of remakes he or she experiences can be linked to impression-related issues. These include impression distortion of prep and/or opposing models, poor triple-tray technique, margin inaccuracy due to tissue packing/moisture issues, and PVS bite impression problems. This is why laboratories will always bring impressions up as an issue that is in need of improvement when asked.

In addition to the yearly chair time lost with resulting financial losses to the dental team, other potential issues should motivate us to treat this problem aggressively and methodically. These include relationship and self-esteem side effects that can eventually have far-reaching consequences for the doctor and the practice:

The relationship between the doctor/staff and patient can be affected, sometimes with a loss of the patient and/or the patient as a referral source.

The relationship between the doctor/staff and laboratory technicians will be affected if it is a repeated problem. This can be another potential loss of a patient referral source.

The self-esteem and self-worth of the doctor can be adversely affected with even a small but repeated number of failures occurring over time. This leads to higher personal stress levels.

The feelings of "practice-esteem" ; (staff is affected, too) can be adversely affected with yet another potential and important loss of patient referrals.

PREVENTION: BUILDING IN FINANCIAL INCENTIVE!

 

Do you know how many remakes occur in your practice every year and why? When asked, most doctors and many laboratories cannot accurately answer this question. The establishment of a monthly and annual remake tracking system within the dental practice and dental laboratory is a prerequisite for identification, analysis, and diagnosis of technical problems. More importantly, this information assists in making the appropriate management decisions and technical changes that will help prevent a future recurrence of the same problems. Determining the number of remakes, when they occurred (at the seat or after?) and, to the best of your ability, why they occurred, becomes essential information to help you and your laboratory owner manage your respective businesses more successfully.

ARE OUR LABORATORIES DOING THE RIGHT THING BY NOT CHARGING US FOR CERTAIN REMAKES?

 

Once you determine a remake occurred due to an impression distortion, how do you handle this matter between you and your dental laboratory? Most of us expect our laboratory to remake our cases at no charge. Actually, this may not be the wisest decision from either a relationship perspective with your dental technicians or from your own profitability standpoint. While at first it may seem to be a good thing that you can err and not pay any additional lab fees for it, this traditional viewpoint is rather shortsighted. By not agreeing to some level of financial responsibility with your dental laboratory owner for specific situations like impression distortion, you are in effect building in the continuation of counter-productive technique and management behaviors. This practice behavior, which is both learned and reinforced at every level, hurts your bottom line and multiple relationships repeatedly.

Instead, as part of the interbusiness doctor/laboratory relationship, clinicians could work out in advance a mutually agreed upon and customized remake charge policy with their laboratory owner. In this agreement you can build in responsibility for things that go wrong by either party. You can share in the financial incentive to change the erroneous procedures that are causing problems, thereby eliminating them as future unnecessary expenses. From a profitability standpoint, this novel approach of taking on responsibility for your actions and management decisions can save you literally thousands of dollars per year over a no-charge-for-anything remake policy. Clinicians certainly need to be cautious in this aspect of the business relationship with their laboratories and have a written plan for responsibility, coresponsibility, and subsequent actions. This plan must include mutually agreed upon rules used for determining responsibility for the remake in question. The idea here is to develop a positive, win-win team approach to solving and preventing significant problems.

CONCLUSION

Figure 9. Impression accuracy will dramatically improve when supported by proper techniques with a team-oriented system to monitor the effectiveness of your efforts. Shown is an accurate, polyether impression of a full-arch preparation.

Impression distortion is not just a technical problem requiring only technical solutions. Generally, in the dental office and in the dental laboratory it is absolutely necessary to slow down in order to improve the quality and consistency of our work. Whether we are performing a complete, "Dawson" ;-style dental exam, building a lasting patient or dental technician relationship, learning new technical skills, or simply establishing an in-office system for improving impressions, we are invariably making a decision to commit precious time to the process. It is always worthwhile to spend the necessary time in preparation and rehearsal for treatment to ensure consistent and predictable results (Figure 9). The time it will take to attempt to eliminate impression distortion from your practice and dental laboratory can return many diverse dividends. It will lead to better technical work for your patients, increased referrals, improved self-esteem, and even better relationships with your laboratory colleagues. Everyone wins!










 

Reference

1. Johnson GH, Lepe X, Aw TC. The effect of surface moisture on detail reproduction of elastomeric impressions. J Prosthet Dent. 2003;90:354-364.

Suggested Readings

Making Better Impressions: A Trouble-shooting Guide. Educational materials at Impression Systems page, 3M ESPE Web site. Available at: http://cms.3m.com/cms/US/en/221/ezzrEF/view.jhtml. Accessed October 12, 2005.

Impression Technique Guide. DENTSPLY Caulk Web site. Available at: http://www.caulk.com/pages/products/alphasearch.cfm?alpha=. Accessed October 12, 2005.



Dr. Adams, a graduate of the University of Michigan, is an assistant clinical professor at Medical College of Ohio, Division of Dentistry, Depart-ment of Otolaryngology, in Toledo, Ohio. He lectures both nationally and internationally for many dental organizations and dental laboratories. In addition to Dr. Adams204; years in private practice, he has had the opportunity to serve as the doctor/technician liaison for a high-end commercial dental laboratory for 10 years. This unique combination of experiences has enabled Dr. Adams to bring clinically relevant discussions and practical solutions to the challenges facing the entire dental team. He has written numerous articles on clinical, laboratory, insurance, and marketing topics for Dental Insurance Today, Dental Economics, Dental Practice Management, Journal of Dental Technology, Spectrum, Journal of the Canadian Dental Association, and Dentistry Today. Dr. Adams is currently listed in Dentistry Today204;s Top Clinicians in Continuing Education for 2006. He is a member of the ADA, MDA, AGD, AACD, ICOI, and a fellow of the International College of Dentists. Dr. Adams can be reached at This e-mail address is being protected from spambots. You need JavaScript enabled to view it