A Clinical Evaluation of Fixed Partial Denture Impressions
Howard E. Strassler, DMD
Samet N, Shohat M, Livny A, Weiss EI. J Prosthet Dent. 2005 Aug; 94(2):112-7.
STATEMENT OF PROBLEM: Providing the dental laboratory with an accurate replication of the hard and soft tissue of a patient is important. Therefore, it is essential to examine whether clinicians critically evaluate impressions routinely before sending them to the laboratory. PURPOSE: This study evaluated the quality of impressions sent to commercial laboratories for the fabrication of fixed partial dentures (FPD) by describing the frequency of clinically detectable errors and by analyzing correlations between the various factors involved. MATERIALS AND METHODS: A total of 193 FPD impressions were evaluated, immediately after arrival at 11 dental laboratories, by 3 calibrated examiners. The impression technique and material used, tray type, and number of prepared units were recorded for each impression. Data relating to errors and faults, including defects in material polymerization, retention to tray, tissue contact by tray, crucial areas beyond tray borders, heavy-bodied material exposure through the wash material (for double-step impressions), inadequate union of materials, retraction cords embedded in impressions, and air bubbles, voids, or tears along the margin were also documented. The data were analyzed with the Pearson chi-square test (alpha =.05). RESULTS: Of the impressions, 89.1% had 1 or more observable errors. Significant correlations were found between material type and voids or tears at the finish line (Rv = 0.17, P< .025) and between material type and polymerization problems (Rv = 0.223, P< .004). CONCLUSIONS: Within the limitations of this study, impressions made with polyethers had the most detectable errors, followed by condensation-type silicones. The high frequency of detectable errors found in impressions sent for FPD fabrication is of concern.
This study provides all of us with staggering data: of 193 impressions for FPDs from 11 dental laboratories, 172 (i.e., 89.1%) had 1 or more detectable errors. From the design of this research study, the types of errors documented are those that can be easily visualized and evaluated by the clinician making the impression. Of the criteria of errors that were reported, the nature of what dentists are willing to send to the dental laboratory for the fabrication of FPDs are impressions that demonstrated voids and tears at the finish lines (50.7%); putty exposure through wash (double-step technique) (44.0%); air bubbles at the finish line (40.4%); pressure of the tray on soft tissue (38.3%); inadequate retention of the material to the tray (33.7%); flow problems (23.8%); and retraction cord attached to the impression (6.2%). These inaccuracies lead to unacceptable restorations.
The authors picked impressions that were made for the fabrication of FPDs. A licensed dentist that a patient trusted with his or her treatment sent in inadequate, inaccurate, and unacceptable impressions for the fabrication and, it is assumed, the ultimate cementation of questionable restorations. Making accurate impressions should not be a coin toss, but an exacting, most important procedure.
What is also frightening is the fact that laboratories used these deficient impressions and fabricated questionable restorations, returning them to dentists who had minimal complaints regarding the accuracy of fit. The dental laboratory is in a quandary; do they return the unacceptable impressions and then lose the business of that dentist, or do they keep their mouths shut and let it all fly by?
We need to be responsible for the treatment we provide our patients. The conclusion of this article summarized the clinical implications of the study results. More critical evaluation of impressions for fixed prosthodontics on the part of the dentist is recommended.
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Howard E. Strassler, DMD