الفهرس 
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Abstract
Reproducing the intraoral relationship of implants through impression procedures is the first step in achieving an accurate, passively fitting prosthesis. The critical aspect is to record the 3-dimensional orientation of the implant as it occurs intraorally, along with reproducing fine surface details.
Therefore, improper recording of the fine details in impressions results in inaccurate cast that will affect superstructure fit resulting in mechanical and biologic consequences that disrupt the function of dental implants.
This study was designed to investigate –in vitro- the effect of implant placement depth and different impression materials on the stability of open tray impression coping.
Four plastic master models were constructed from cast acrylic sheets by using laser cutting machine. For each model, a drilling machine was used to drill one hole in the center of the top surface of the model. An implant analog was inserted in the hole drilled of each master model perpendicular to the top surface of the model at different depths.
The main groups were classified according to the implant placement depth as follows:
• group A: the implant analogs were placed 1mm below the top surface of the model.
• group B: the implant analogs were placed 2mm below the top surface of the model.
• group C: the implant analogs were placed 3mm below the top surface of the model.• group D: the implant analogs were placed 4mm below the top surface of the model.
Custom open trays were fabricated for each master model from cast acrylic sheets. Impression copings were adapted and fastened to the implant analogs using the coping screw. Medium bodied viscosity impression materials were used to take impressions for the transfer copings. Polyether and addition silicone impression materials were the materials of choice.
After polymerization of the impression, the tray was removed from the master model and an implant analog was connected to the transfer coping.
Load was applied to the implant analog and force needed to move the analog 1mm was measured in newton.
Data was tabulated and statistically analyzed using Statistical Package for Scientific Studies. The results showed that as the implant placement depth increased the stability of the impression coping decreased within the same impression material and that the polyether impression material showed more stability for the impression coping than the addition silicone impression material.