Locator Attachment Versus Ball Attachment: 3-Dimentional Finite Element Study

Objectives: The mode of connection between the overdenture and its supporting implants should control transmission of potentially harmful forces to supporting structures. The locator attachment being characterized by a low profile design, its ease of seating in the oral cavity by the patient, its self-locating feature to fit non-parallel implants up to 40°divergence may be advocated as a suitable alternative to the classical widely used ball attachment. Hence, this study was designed to investigate the stresses induced by ball and locator attachments as connecting mechanisms between implants and overdentures. Methods: Finite element stress analysis was carried out on both locator and ball attachments. Both attachments were attached to the same width and length of a hexed-implant embedded in a bone block. Vertical load (100N) and oblique off-central load in different angles (10°/20°/40°) were applied on both model assemblies at the top of the locator- patrix & ball-matrix of attachments. Resultant stresses were evaluated. Results: Vertical (0°) and oblique (10°/20°/40°) loading on both attachments induced nearly the same stress distribution patterns except at the area of ball neck which suffered most. Maximum stresses were observed around the junction of either attachment with corresponding implant. However, less stresses were generated by the locator attachment on cortical and spongy bone as well as around the implant than by ball attachment. With oblique forces, maximal stresses were observed on the contralateral side of load application. Stress values were directly proportional to different degrees of angulations from the vertical direction. Conclusion: Within the limitations of the simulation study, the locator attachments may provide an adequate attachment system with respect to reducing the stress on the implant body and supporting structures when compared with the ball attachments for implant-retained overdentures. Further in-vitro and in-vivo studies focusing on the whole assembly of implant-locator-retained overdenture are still needed.