الفهرس 
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Abstract
The benefits of implant-retained/ supported mandibular implant over denture (IOD) treatment relative to conventional mandibular denture treatment have been well documented. Half of all conventional mandibular dentures demonstrate problems with prosthesis stability and retention, with retention being the single most important deficiency. It has been reported that a two-implant overdenture treatment should be the standard of care relative to conventional denture treatment.
Accordingly, our study aimed to measure the effect of cantilevered bar length on strain produced around two-implant and four-implant supporting a mandibular over denture ,and evaluating the amount of stress reaching the supporting structures using strain gauge analysis.
For our study one maxillary and two readymade completely edentulous acrylic resin models were used. A layer of mucosa simulating material (Mollosil) was placed on each heat cured acrylic resin mandibular model.
The two readymade mandibular completely edentulous acrylic models were classified as group A receiving two implants and the other model as group B receiving four models. On both group A (model with two implants) and group B (model with four implants) the mucosa simulating material was removed and the root form implants were placed. On each implant, a castable readymade plastic multi-unit abutment was placed and the multi –unit internal screw was tightened.
For both groups , one readymade plastic bar segment was luted between each two castable abutments using sticky wax, leaving 2 mm clearance space between the bar and the ridge.
For both models, all the plastic abutments and plastic bar segments were removed from the model, sprued, invested, casted, finished and polished according to the manufacturer’s instructions
After proceesing, processed abutments and bar segments were returned back on both models and fixed using a tightening screw. Resilient retentive clips attachments were adapted over each bar segment attachment and the clips were picked up using direct pick up technique.
For both groups: two linear strain gauges were bonded to the acrylic resin model at mesial (M) and distal (D) surface of each implant Also, for both groups : eight strain gauges were connected to the fitting surface of the implant overdentures.
The strain gauges were connected to strain meter circuit and loads of 60 N were applied over the first molar area of the two models.
The data was collected,tabulated ,and statistically analyzed providing the following conclusions.