الفهرس 
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Abstract
The first step in achieving an accurate, passively fitting implant-supported prosthesis is to reproduce the relationships of dental implants through impression procedures. It is critical to record the three-dimensional orientation of the implant as it occurs intraorally, since imprecise superstructure fit can result in mechanical and biologic consequences that disrupt the function of dental implants. This study was designed to investigate -in vitro- the passivity of implant superstructure fit using two types of implant supported prosthesis and two impression techniques.
A master model was constructed from cast acrylic sheets by using a computer software and a laser cutting machine. Then a drilling machine was used to drill 2 holes 10 mm apart and parallel to each other then each hole received an implant.
The main groups were classified according to the type of impression technique used as follows:
Group A: Open impression technique.
Group B: Closed impression technique.
Each group was subdivided into 2 sub-groups according to type of retention:
Subgroup I: Screw-retained.
Subgroup II: Cement retained.
Ten custom open trays and ten custom closed trays were also fabricated from cast acrylic sheets and medium body polyether was used for all 20 impressions. The impressions were poured using extra-hard stone. Then the 20 experimental casts were used to fabricate 20 metal framework (10 screw-retained, 10 cement-retained). Each framework was measured for strain development using strain gauges on the master model.
Data was tabulated and statistically analyzed. The results of this study showed that Regardless of Impression technique used or the type of framework retention used, there was no statistically significant effect.
Conclusions:
Within the limitations of this study, it can be concluded that:
1. Impression technique didn’t affect impression accuracy.
2. Screw retained and cement retained framework produces nearly the same strain.
3. Passive fit of implant supported superstructure cannot be acheived.
Clinical Recommendation:
The current study revealed that the passivity of fitting is a Challenging situation for achieving therefore accurate impression technique is paramount.