RESUMEN
Considering to patient's complications with conventional denture in the lower arch, the requirement of a denture with more efficacy and cheaper than conventional ones, is definite. One of the most conventional ones is an overdenture with 2 implant. The purpose of this study was comparison of four types of different attachment systems including two prefabricated and 2 castable attachments. Four groups with 6 numbers of attachments [Superflex ball, locator, castable Ball on bar, castable Bar] were selected. 2 castable groups were casted; these attachments were put on implant fixtures. Then a Cr-Co framework was made. It was put on cast and attachments and an acrylic base was made on this assembly. All the samples were put in universal testing machine and a tension force of 50 Newton was loaded to seprate framework from cast. The tension force was recorded. After data collection, the data were analyzed through SPSS version 16 by One-Way ANOVA and Teukey test. Results showed that retention force of castable ball on bar [35. 31N] was the greatest followed by ball [33.33N, P=0.007], Locator [20.90N] and castable bar [14.74N], respectively [P<0.001]. Castable ball on bar was comparable to ball regarding the retentive force. Therefore this cheap attachment could be used in patients instead of prefabricated one. These attachments have more retention compared to locators which are expensive. When less retention is needed, castable bar can be used, and when more retention is needed, castable ball on bar is recommended