A clinical evaluation of fixed partial denture impressions

Abstract

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.

Material 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.