Comparison of Retentive Force in Four Attachment Systems in Implant- Supported Overdenture of the Lower Arch

tement of Problem: Along with the rapid population growth in recent decades, there has been an increase in the number of edentulous patients who have complications with conventional denture. This entails the use of dentures, such as implant overdenture, which are more efficacious. Purpose: The purpose of this study is to compare four types of different attachm-ent systems; two prefabricated and two castable attachments. Materials and Method: A model of lower edentulous arch was constructed out of dental stone. Two parallel implants were placed in the canine region. A single cast metal chrome cobalt framework was fabricated to provide reinforcement for experimental overdentures and it splinted the two attachments on the cast. To conduct this study, four groups with six numbers of attachments in each group (superflex ball, locator, castable ball on bar, castable bar) were selected. All the samples were put in a Universal Testing Machine and a tension force with the speed of 50 mm/ min was exerted to separate the framework from the cast. The tension force was recorded and the first two prefabricated attachments (superflex ball and locator) were compared with the second two castable attachments (ball on bar, castable bar).Results: The findings of this study revealed that retention force of castable ball on bar was greater than the other three attachments (35.31±3.14N). With regard to the strength of retentive force, superflex ball took the second place (33.33± 3.11 N) and locator (20.90± 3.74N) and castable bar (14.74± 1.15N) took the third and the forth places, respectively ( p >0.001). Conclusion: The retentive force of castable ball on bar was similar to that of superflex ball. Therefore, the use of this cheap attachment; castable ball on bar, is preferred to its prefabricated counterparts. The retentive force of this kind of attachment is greater than expensive locators. The retentive force of castable bar was similar to that of locator, although the former was a bit weaker than the latter. Therefore, when less retention is needed, castable bar can be a suitable choice, and when more retention is needed, castable ball on bar is preferable.