الفهرس 
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Abstract
This in-vitro stress analysis study was conducted on computer generated 3D models supporting lower fixed detachable prosthesis to evaluate and compare stresses induced in the implants using strain gauge technology. According to the position, configuration and axial orientation of the implants the models were classified into:
Model 1: Fixed detachable denture supported and retained with four conventional interactive implants 11 mm length and 3.5 mm diameter with The All-on-4™ configuration. Model 2: Fixed detachable denture supported and retained with four conventional interactive implants 11 mm length and 3.5 mm diameter implants positioned in the interforaminal region with an axial orientation. Model 3: Fixed detachable denture supported and retained with two conventional interactive implants 11 mm length and 3.5 mm diameter implants positioned in the canine region area and two short implants 8 mm length and 4 mm diameter implants positioned posteriorly.
Three nearly identical complete acrylic dentures were construction on educational models. Three computer generated 3D models were fabricated using liquid photo-polymerized resin, cured in a layered manner by using LASER beam. An educational stone model was scanned via 3Shape desktop scanner (3Shape dental Denmark). Then an STL file was generated. In this STL file four implant beds were designed and two grooves were designed at the lingual and distal aspect of the posterior implants, a third groove was also designed at the lingual aspect of the anterior implants to receive the strain gauge. A key index with 2 mm thickness and 2 mm offset with tissue stops was designed for the purpose of creating a space for the mucosa simulator representing the future mucosa. The STL files were ready to be directly sent to the additive manufacturing device ULTRA 3SP, the Envision TEC (Ferndale, MI) Perfactory to print the casts using liquid photo-polymerized resin, cured in a layered manner by using LASER beam.
Self-cure acrylic resin was used to fix the implants in their implant beds and multiunit abutments were attached to the dentures which were converted into fixed hybrid prosthesis:
Universal Testing machine (LLOYD Universal Testing Machine, U.K.) was used for applying unilateral vertical static loads ranging between 0-100 Newton.
Based on the data obtained from this l in vitro study, it can be concluded that:
Widely distributed implants cause proper distribution of imposed occlusal load
Short implants decrease the chance of implant overloading.
The use of tilted implants and angled abutments reduces the forces transmitted to the implant.
Recommendations:
The results of this study are only descriptive because the physical properties of acrylic resins do not simulate the complex nature of living bone regarding mechano-biology and osseointegration. These results must be confirmed by future clinical studies with longer follow-up.