Subjective Impression Rating and Objective Evaluation of the Preparation Margin

Objectives: The quality of final impressions often is rated subjectively by the investigator. The follow-up from impression to master cast and a combination with an objective evaluation is yet missing. The subjective rating of final impressions and an objective computer-aided analysis of the preparation margins was analyzed in a clinical trial.
Methods: The same study design was performed twice with 52 patients per center (university (U) and dental office (DO)). Patients were eligible if they were in need of a single crown. The two experienced prosthodontist in both centers rated each of the three impressions made with three different impression techniques (“Romeo”=flawless impression, “Sierra”=minor flaws, clinically suitable, “Victor”=major flaws, unapt for use). Impressions were poured and digitized. Monophase (M) and two-stage putty-wash (TS) data was aligned to the one-stage two-phase (OS) data chosen as reference. At six measuring points around each prepared tooth (mesial-vestibular, vestibular, distal-vestibular, distal-oral, oral, and mesial-oral), the differences at the margins were measured. Analysis of variance was used for statistical evaluation (SPSS 21.0, IBM, USA).
Results: The subjective ratings of both investigators showed comparable results for the impression techniques applied: TS was rated better than OS and both better than M. However, DO gave more “Sierra” ratings, while U gave more “Romeo” and less “Sierra” ratings. Looking at the objective results from the computer-aided evaluation, there was no influence of the impression technique M or TS for the university investigator, while the dental office investigator achieved better margin results with TS. However, despite the different subjective ratings, there was no statistically significant difference for the six margin measurements (p between 0.592 and 0.907) with exception of the oral aspect (oral p=0.023 and mesial-oral p=0.050).
Conclusions: Subjective final impression ratings are highly depending on the investigator and do not necessarily agree with an objective analysis.