Accuracy of Polyether vs Plaster Impressions for Implant-supported prostheses

Impression materials and techniques used for master cast fabrication in the construction of implant-supported prostheses play a key role in the accuracy of fit and passivity of the cast metal framework. Failure to fabricate a passively-fitting prosthesis may place undue forces and stress concentration around implants which could lead to excessive marginal bone loss and implant failure (osseodisintegration), losening of the screws, and fatigue fracture of the implant components. Objectives: The objective of this study was to compare the dimensional accuracy of polyether and plaster impressions which would enhance the success of an implant-supported prosthesis. Methods: Theses two materials were evaluated and compared with respect to the accuracy with which abutment postions were reproduced from a stainless steel master model containing five implant analogues. A total of twenty samples were prepared, ten for each of the two materials. The position of the precision impression copings on the twenty impressions were measured using a Reflex Microscope. The positions of the implant analogues on the twenty casts were also measured and compared to the positions on the stainless steel master model. Abutment positions were calculated analytically by manipulation of 3-dimensional co-ordinates within the menu-driven Comp 3D software package of the Reflex Microscope. Results: Experimental data were analysed statistically and the two impression materials were compared. The difference was significant as tested by ANOVA. Conclusions: The results of this study suggest that plaster impressions resulted in smaller inter-abutment error but with less predictable variance in dimensions.