Precision of master-casts made from one- and two-stage-impressions: a RCT

Objectives: The reproduction of the finishing-line in the master-cast is one major factor while assessing the quality of dental impressions. The aim of this study was to assess the quality of master-casts made from impressions taken with different dental impressions techniques (monophase, one-stage, two-stage) in a randomized controlled trial performed in a private dental office. Methods: For 61 patients with teeth prepared for single crowns, monophase- (MP), one-stage- (OS) and two-stage-impressions (TS) were taken in a randomized order. Master-casts were manufactured according to the Zeiser-technique using a type IV die stone for each impression. Clinical parameter (bleeding while impression taking, blood/moisture at the impression), subjective grading of the impression itself (modified CDA criteria) as well as the quality of the mater-casts were assessed. The data were statistically analyzed (chi-square-test, p<0.05, SPSS 18.0). Results: Impressions taken subsequently in a patient tend to be rated better compared with the first impression taken. TS-impressions were rated twice as often ,Romeo' compared with MP-impressions. Bleeding while removing the retraction cord and blood at the impression around the prepared tooth was associated significantly more often with worse ratings compared with no-bleeding cases. ,Victor' rating of the impression was associated significantly more often with incorrect master-casts. Non-prepared tooth structures below the finishing-line were captured significantly more often by the TS-impression. Conclusion: The TS-impression showed superior capturing of the finishing-line if the retraction cord was removed prior to the application of the wash material. ,Victor' rating of an impression is a valid parameter for an insufficient impression. This study was supported in part by 3M ESPE AG, Seefeld, Germany.