الفهرس 
Introduction.Only 14 pages are availabe for public view
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Abstract
This study was including two parts: (in-vivo and in-vitro study), the in-vivo study was carried out as follow:
Fourteen completely edentulous patients were selected to participate in this study. from the outpatient clinic of Prosthodontic Department, Faculty of Dentistry, Ain Shams University
The selected patients were free from any systemic diseases that affect bone resorption, temporomandibular joint disorders and with no history of para-functional habits.
Patients were examined intra-orally and extra orally to detect any abnormalities in the ridge, mucosa or temporomandibular joint and for each patient, a diagnostic panoramic radiograph was made. All patients were rehabilitated with upper and lower complete dentures following the conventional technique.
The upper complete denture was used as a radiographic stent upon which four cones of gutta percha were attached in the planned positions of implants (canines and second premolars) Cone beam computed topography (CBCT) scan was taken for the maxillary arch while the patient wearing the maxillary and mandibular dentures.
Patient’s CBCT while wearing the denture with the markers was superimposed over a CBCT of the denture, and proper planning for the exact implant position and designing the surgical guide was made using a special software. Then printing of the surgical guide has been done.
Patients were divided into two equal groups according to the type of implants used:
group A: Straumann BLX® implants were selected with the following criteria: tapered, self-tapping, aggressively threaded, SLActive, roxolide (15% zirconium and 85% titanium), 3.7 mm in diameter, and 10 mm in length.
group B: JD EVOLUTION PLUS implants were selected with the following criteria: tapered, self-tapping, threaded, two-piece, with the same length and diameter.
After implant placement using surgical guide, smart peg and ostell device were used to measure the primary stability of the implant. After assessment, the smart peg is removed and replaced by cover screw, then after six weeks, secondary stability was measured for both groups.
After four months, the second stage started in which exposure of the implant fixtures took place. And pick up was carried out using novaloc attachment for group II and spheroflex attachment for group II patients.
Patients were recalled frequently for post-insertion inspection and adjustment.
The results were collected, tabulated and statistically analyzed.
The results showed that both the primary and secondary stability of group A were higher than group B, and it was of statistical significance.
In the in-vitro part of the study: it was conducted on 3D printed models simulating a maxillary completely edentulous arches with four implants placed at the canines and second premolars bilaterally, the models were divided into two groups equally.
group A: six maxillary overdentures were constructed on a 3D printed maxillary model with four BLX® Straumann SLActive implants (bone level roxolide) at the canine and second premolar areas with Novaloc attachments.
group B: six maxillary overdentures were constructed on a 3D printed maxillary model with four conventional acid etched implants at the canine and second premolar areas with a Spheroflex attachments.
On the virtual cast, four implant beds were designed in each group representing the planned sites for the implants, with the following dimensions 10 mm length and 3.7 mm diameter.
Then via exocad program, eight grooves were designed mesial and distal at each implant site for the attachment of the strain gauge.
Then 2 mm layer thickness was removed from the virtual model, which represented the future mucosa with their specific attachments.
The STL was imported to the 3D printing machine.
Mucosa simulation, was done via rubber base material, Multisil-Mask soft. Then Implants were installed in their designed sites in the printed models.
Construction of maxillary over dentures following the conventional technique were done then pick up of attachment in their fitting surface.
The strain gauges were installed in their grooves on the distal and mesial aspect of each implant. Using the universal testing machine unilateral and bilateral load were applied starting from zero up to 100N at the central fosse of first molar bilaterally by the T- shaped load applicator bar of the machine.
The values of micro strains of the eight strain gauges were recorded All the data obtained were collected, tabulated, and statistically analyzed.
After recording the strains resulted from applying static loads by the universal testing machine, the chewing simulator machine was used to apply dynamic cyclic loading to the dentures. The specimen chamber was filled with prepared artificial saliva for simulated salivary medium.
The amount of stresses was measured twice for each group. The first measurement was after 63,000 cycles and the second was after 125,000 cycles which represent 3 & 6 months sequentially. Each measurement was repeated for five times. The mean of these measurements was recorded.
The collected data were tabulated and statistically analyzed.
The results showed that the amount of stresses distal to the implants in both groups was higher than mesial. And amount of stresses induced in group A was lower than in group B.