Influence of impression technique and screw access hole configuration on distortion in conventional impressions of prepared CAD-CAM abutment geometries.

PURPOSE: The aim of this study was to evaluate the influence of impression technique and screw access hole (SAH) configuration on distortion in conventional impressions of prepared CAD-CAM custom abutment geometries. MATERIALS AND METHODS: A master cast with implants placed at the maxillary first premolar and first molar was fabricated. CAD-CAM abutment geometries were designed with SAH positions corresponding to 0°, 15°, and 30° buccal angulation designs. In the first experiment, six groups representing different polyvinyl siloxane impression techniques were tested. In the second experiment, groups were formed based on SAH position and filling (filled vs unfilled). Fabricated stone casts were scanned, and STL datasets were superimposed onto reference data. Total, horizontal, vertical, and angular deviations were analyzed using the Kruskal-Wallis test and two-way ANOVA. RESULTS: The 2-step ML technique showed lower total deviation than the 1-step-L technique (24.35 µm [IQR, 6.28] vs 82.37 µm [IQR, 68.02]; P < .05). Unfilled SAHs showed reduced horizontal deviation but increased vertical and angular deviations. Angular deviation ranged from 3.60° to 4.37° in the filled SAH groups and from 5.05° to 5.13° in the unfilled SAH groups. CONCLUSION: Impression technique and SAH configuration were associated with differences in impression distortion patterns. Within the limitations of this in vitro study, the 2-step triple phase technique showed reduced deviation, whereas increased implant angulation and unfilled SAHs were associated with greater vertical and angular deviations.