الفهرس 
Introduction.Only 14 pages are availabe for public view
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Abstract
This study was carried out to evaluate the effect of using resilient spherical attachment on the retention of mandibular overdenture retained by non parallel implant, and to evaluate the stresses induced on the ridge and the implants. A modified simulated three educational mandibular acrylic models were constructed with two bilateral implants placed in the canine region.
In model one the two implants were parallel to each other, placed at zero 0 angulation of vertical reference axis. In model two the two implants were divergent from each other, placed at 7 0 angulation of vertical reference axis. While in model three the two implants were divergent from each other, they were placed at 14 0 angulation of vertical reference axis. In all the three models mandibular overdentures are attached to the implants by spheroflex attachment.
An educational acrylic model was used after removing all the acrylic teeth, three special stainless steel tools were constructed and used to position the implants in the models at the required angles according to the angles in their shanks Zero0, 70, 140 respectively. All the empty sockets were filled with wax, the wax was carved to the shape of an edentulous ridge. The cast in wax was then converted into clear acrylic resin. The resilient caps inside their metal housing were placed over the attachments. Then trial denture bases were constructed on each model and setting of the teeth was made.
During the stage of waxing up the denture, a transverse bar was placed and attached from each of its two terminal ends to the lingual side of the overdenture at area between second premolar and first molar at both sides. A pull action was applied via constant speed via hook attached to the middle of the bar using universal testing machine until denture dislodgment. The device recorded the force at which denture dislodgment occurs; this was the retention force.
Two strain gauges were installed on the distal surfaces of the two implants to monitor the effect of the applied load on the implant. In addition two strain gauges was installed over the distal areas at the right and left sides of the ridge to monitor the effect of the applied load on the ridge. A special loading device was used to apply standardized static unilateral load within the physiologic limits of 80 N on the central fossa of first left molar. Four measures were recorded for each site, and then the data was collected and statistically analyzed.
The results of this study showed that at the implant site as well as the ridge site under vertical as well as oblique loads in the loaded sides, Model III showed the statistically significantly highest mean stresses, followed by Model II that showed statistically significantly lower mean value. While Model I showed the statistically significantly lowest mean stresses.
Comparing oblique and vertical load in all the three models oblique loading showed statistically significantly higher mean stresses than vertical loading at the left (loaded) and Right (unloaded) implant
sites, While at the right (unloaded) ridge sites, oblique and vertical loading showed no statistically significant difference in the mean stresses.
In all the three models when comparing the left (loaded) side with the right (unloaded) side under vertical as well as oblique loading, left side (loaded) showed statistically significantly higher mean stresses than right side (unloaded) at the implant as well as ridge sites.
There was no statistically significant difference between mean retention values of the three models However model II shows slight higher mean retention values than model I and model III. There was loss of the retention after the first pull for all the three models.