الفهرس 
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Abstract
Purpose: this study aimed to examine the retention and stability of Locator attachment with different type nylon insert and Bar attachment for 4-implant supported maxillary over denture. Materials and Methods: An acrylic resin model of an edentulous maxilla without alveolar ridge undercuts was fabricated and 4 laboratory implants were inserted in the canine and second premolar areas. Mucosal simulation was fabricated over the model. Maxillary experimental overdenture were constructed over the model and connected to the model with either Bar attachment (group I) or Locator attachment with different type nylon insert (group II). The universal testing machine was used to apply vertically oriented 4 points tensile loads on a metal plate attached to the model with 4 metal chains until the attachments separated from the abutments. Maximum load needed to dislodge the experimental overdenture from the maxillary test model (retentive force) were calculated. Initial retentive and stability forces and final retentive and stability forces were evaluated. Results: Regarding initial and final retentive and stability forces for vertical dislodging, posterior dislodging ; anterior dislodging and lateral dislodging forces, Locator transparent recorded the highest retentive forces followed by locator pink, locator blue and Bar attachment recoded the lowest retentive forces. Conclusions : Locator transparent recorded significant higher retention forces compared to other types of locators and Bar attachment. The lowest retention was recorded with locator blue and Bar attachment.