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Journal Bites - Frequency of Impression Errors (Operative Dentistry)

Despite improvements in accuracy and handling properties of modern impression materials, evidence shows the quality of impressions sent to commercial laboratories appears to be declining. In this laboratory study, three calibrated examiners using x2.5 magnification loupes assessed 1,157 impressions from four commercial dental laboratories. Analysis of the findings revealed:

  • At least one error was discovered in 86 percent of the 1,157 impressions.
  • The five most common errors were:
    • Tissue over the finish line (49.9%)
    • Lack of unprepared tooth stops in dual-arch impressions (25.6%)
    • Pressure of the tray on adjacent soft tissue (25%)
    • Voids or bubbles on the finish line (24.3%)
    • Show-through of occlusal or incisal edges (17.4%)
  • Only 3.2% of the dentists asked for the dies to be returned so the clinicians could trim and mark the finish lines.
  • Almost 83 percent of the trays were plastic, and the dual-arch impression was the most frequently used technique (62.2%). Noteworthy was the finding that the chance of a critical error was 1.68 times more likely for dual-arch versus single arch impression trays.
  • The presence of blood yielded a 2.31 times greater likelihood of a critical error.

The authors in this study urge dentists to carefully examine their tooth preparation procedures and impression techniques, in order to reduce or avoid the production of critical errors during impression taking.

Source: Rau CT, Olafsson VG, Delgado AJ, et al: The quality of fixed prosthodontic impressions: An assessment of crown and bridge impressions received at commercial laboratories, The Journal of the American Dental Association 148:654-660, 2017