The duality of support that characterizes distal extension removable partial dentures is often characterized by time-dependent adverse changes in both the abutment teeth and edentulous areas. Consequently, adjunctive implant has been proposed for mandibular class I and II removable partial denture designs. This current study evaluated the effect of locator attachment system and ball abutment with O-ring female metal housings in implant retained mandibular partial overdenture by measuring peri-implant crestal bone level. Twenty partially edentulous male patients exhibiting bilateral distal extension edentulous areas were selected. Two implants were installed in the first molar region following the two stage surgical technique. Patients were randomly divided into
2 equal groups; Group 1 locator attachments were used and Group 2 ball attachments were used. The mesial, distal, buccal and lingual marginal bone height around the implants was evaluated using cone beam CT. The measurements were carried out at insertion, six and twelve months post insertion. The results of this study showed a statistically significant increase in crestal bone height loss around the implants in both groups during the follow up period. In conclusion, ball -retained mandibular overdenture are associated with more marginal bone compared to locator abutments.