Comparative Evaluation of Dimensional Accuracy of Impression Techniques for Parallel Implants and Implants Placed with Angulation: An in vitro Study

Objective: This study aims to measure and compare the accu­ racy of various implant impression techniques in specimens with parallel implants placed at 90° to the horizontal plane and at 75°. Materials and methods: Polyether medium body (3M ESPE Impregum) was selected as the material of choice. Two metal samples with three lab analogs placed in each were used as the master models. One had implants placed at 90° to the horizontal plane, and the other at 75°. Ten impressions were made each of stock metal tray, closed custom tray and open custom tray techniques. Photographs were taken and measure ments were made using Adobe Photoshop software. Intragroup comparisons were done using the analysis of variance (ANOVA) and one way t­test. Intergroup comparison was done using two way t­test. Results: All the techniques studied showed some distortion and the difference had no statistical significance. However, closed custom tray technique gave better results for the 90° specimen, and open custom tray technique gave better results for the 75° specimen. Conclusion: Within the limitations of this study, it can be con­ cluded that provided operator error is minimized and guide lines are followed, it may be possible to achieve impressions of similar accuracy regardless of technique used. However, it was impossible to achieve a level of exactness that would ensure a completely passive fitting prosthesis.