الفهرس 
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Abstract
Background : Increasing the number of dental implants to assist mandibular overdenture may decrease the peri-implant stresses. Aim : This in vitro stresses analysis study was done to compare the stresses around three versus four mini-implants used for assisting complete mandibular overdenture. Materials and Methods : One completely edentulous mandibular epoxy resin models covered by polyurethanes soft liner to stimulate alveolar mucosa by using five mini implants with ball attachment installed into epoxy master cast in midline, canines and first molars area by using milling machine to achieve mini-implants parallelism. Two groups studied. group A Mandibular complete overdenture assisted by three mini-implants (one mini- implant in midline area and two mini-implants in first molars area). group B Mandibular complete overdenture assisted by four mini-implant (two implants in canine’s area and two in first molars area). The female housings and ball attachments picked up into the fitting surface of the overdenture. Strain gauges seated around each mini-implant at (mesial, distal, buccal and lingual) by using adhesive material to measure the axial and non-axial stresses around the mini-implants during application of load (70N) by using universal testing machine. Results : when comparing between the peri mini-implant stresses in the two groups, it was found that anterior mini-implants in group (A) recorded a statistically significant higher peri mini-implant stresses than in group (B), while the posterior mini-implants in two groups recorded insignificant difference during bilateral and unilateral loading (on the loading side). Also the Comparison between the two groups regarding the means of stresses around mini-implants during bilateral loading revealed that the stresses around mini-implants in group (A) were significantly higher than around implants in groups (B).Conclusion : (1) Regarding the peri-implant stresses, the four mini-implants can be considered more advantageous than the three mini-implants used for assisting the mandibular complete over denture, (2) When using the three mini-implants designs, the stresses induced around the midline mini-implant during functional loading of mandibular over denture will be higher than stresses around anterior mini-implants with the four mini-implants design.