Evaluation of the Stability of Open-Tray Impression Coping Using Two Different Impression Materials at Three Different Subgingival Implant Placement Depths.

Objective To evaluate and compare the stability of the open tray impression coping within the set impression while attaching the lab analog when polyether (PE) heavy body and polyvinyl siloxane (PVS) putty impression materials were used and the implant platform was placed sub-gingivally at three different depths. Methods Two impression materials, PE and PVS, and custom-made plexiglass models with embedded single implants to simulate implant positioning depths of 0 mm, 2 mm, and 4 mm, sub-gingivally, were used in the study. Open tray impressions were made after attaching impression coping to the implant embedded in the model. Implant lab analog was attached to the impression coping in the set impression, and its stability was measured using a universal testing machine. Forty-two open tray impressions were made in six groups, with seven impressions in each group. Descriptive statistics such as mean and standard deviation were calculated. A comparison of the mean stability between the two impression materials at each depth was done using an independent t-test. Comparison of the mean stability between the three different subgingival implant depths in each material was done by one-way ANOVA with the Scheffe multiple comparison test (post-hoc analysis). The level of significance was set at p<0.05. Results The stability of the impression coping was measured as the force in Newtons required for the displacement of the analog attached to the impression coping embedded in the set impression. PE with the embedded impression coping at a depth of 0 mm gave the highest mean stability value (4.37+/-0.41), and the least mean stability was offered by PVS with the embedded impression coping at 4 mm depth (1.88+/-0.37). When an independent t-test was done to compare the mean stability values of PE and PVS, there was a statistically significant difference at 0 mm, 2 mm, and 4 mm. On doing one-way ANOVA to compare the mean stability between the different depth groups, there was a statistically significant difference between the three depth groups in PE and PVS. Scheffe multiple comparison tests (post-hoc analysis) revealed a statistically significant difference between 0 mm, 2 mm, and 4 mm subgingival depths of the impression coping placement in both PE and PVS. Conclusion The accuracy of the master cast is an important determinant for the precise fit and long life of the final prosthesis. In the case of maxillary anterior implant placements where deep subgingival placement of the implant platform is needed for aesthetic and functional reasons, the impression material should be selected carefully to ensure the stability of the impression coping. Among the materials included in the present study, the PE impression material offered the maximum stability for impression coping compared to PVS.