الفهرس 
LITERAT URE REVIEWOnly 14 pages are availabe for public view
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Abstract
Implant placement presents a great challenge in the posterior regions of the maxilla and mandible. Any attempt to place standard implant length in such regions will considerably increases the risk of injury of the anatomical landmarks. Complicated surgical procedures may be required, however, they include higher morbidity and cost. Short implants provide a simple, less invasive and less complex treatment modality in such regions. In the last few years, short implants had shown high success rates and great predictability in edentulous regions with reduced bone height.
Recently, the application of CAD⁄CAM technology in dentistry offers an innovative, state-of-the-art dental service to patients as well as general practitioners. This advanced system had been applied in the fabrication of dental restorations with great accuracy, reduced time and superior fit. Currently, restorations are provided of newly available materials such as Biologically High Performance Polymers (BioHPP) as well as zirconia.
Biologically high performance polymers have been known for their high biocompatibility, good mechanical properties, high esthetic properties and high fatigue resistance. They are as elastic as bone that can reduce stresses transmitted to the implant and peripheral bone. In addition, zirconia is highly esthetic material, highly biocompatible, translucent, and thermal insulator. It provides superior mechanical properties and low bacterial surface adhesion. It has high elastic modulus and can be used with minimal occlusal thickness of 0.5 mm that can withstand a high bite force.
The aim of this in-vitro study was to assess and compare the strains developed around both short dental implants (7 mm) and standard implant
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length (12 mm) using two different crown materials (BioHPP and zirconia) which are fabricated using CAD/CAM system.
In this study, twenty polyurethane test blocks have been used to resemble human cancellous bone. They were equally splitted into two groups. group A included ten blocks which received ten standard implant lengths of 12 mm, and group B included ten blocks which received ten short implants of 7 mm. Each group were divided into two subgroups according to crown material (BioHPP and zirconia). Five implants of group A were restored with BioHPP material (subgroup A1), and the other five implants were restored with zirconia material (subgroup A2). group B was subdivided similarly like group A. Bounded saddle was created with maxillary canine, maxillary second premolar, and missing maxillary first premolar where implants were drilled.
A surgical guide was created using 3D printer to guide and limit implant insertion. A hole was then drilled using the conventional drilling protocol according to implant diameter and lengths. Implants were screwed in place using torque wrench. The abutments were then screwed to the implants. After that, the abutments were scanned using digital scanner for designing and fabricating BioHPP and zirconia restorations through the CAD/CAM system. The restorations were cemented to the abutments as recommended by the manufacturer.
Strain gauges were fixed on flat channels that were prepared opposite to the implants on the buccal and palatal surfaces. The free ends of the strain gauges were connected to multichannels strain meter to magnify the strains resulted from load application. Strain meter was connected to a computer to record the data. Axial and oblique (45°) loads were applied with universal
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testing machine. Microstrains were, then recorded on the computer. Data were statistically analyzed and evaluated.
In the final analysis, we can summarize that,
When axial loads (central fossa, mesial marginal ridge, and distal marginal ridge) were applied