This 10-year retrospective study investigates residual ridge changes in edentulous patients treated with mandibular overdentures (ODs) retained by either four Locator attachments or a four-implant bar system. Although two-implant ODs are well established, four-implant configurations may offer enhanced stability and function. Locator and bar attachments are commonly used, but their long-term effects on bone resorption patterns-especially posterior mandibular and anterior maxillary resorption-remain unclear. By standardizing implant positions, this study aims to directly compare the two systems to help guide clinicians in selecting the most effective attachment type for long-term success.

Implant-supported mandibular overdentures (ODs) have become the preferred treatment for edentulous patients, particularly after the endorsement of this approach by the McGill and York consensus statements. Although the use of two implants is well established, emerging research supports the use of four implants to enhance denture stability, improve masticatory function, and better maintain the surrounding oral structures.

Among the available attachment systems, Locator and bar-retained attachments are the most frequently utilized, each offering specific benefits. Locator attachments are known for their simplicity, affordability, and ease of maintenance. In contrast, bar-retained systems provide more rigid splinting between implants and more even stress distribution. These systems differ biomechanically, especially regarding their impact on bone resorption in the posterior mandible, which plays a vital role in denture retention and function.

While some research has compared different attachment types, few studies have standardized implant number and position. Moreover, there is a lack of long-term comparative studies assessing four-implant mandibular ODs using both Locator and bar attachments. Critical outcomes such as posterior mandibular ridge resorption (PMandRR), marginal bone loss (MBL), and anterior maxillary ridge resorption (AMaxRR) must be examined to evaluate the long-term effectiveness and biomechanical performance of these attachment systems.

Inclusion Criteria:

• Completely edentulous mandible and maxilla for at least 12 months.
• Four interforaminal dental implants placed in the lateral incisor and first premolar regions.
• Opposing maxillary complete denture constructed using a muco-compressive impression technique, with maximum denture base extension and lingualized occlusion.
• Mandibular bone height between 15-25 mm at the symphysis region as measured on panoramic radiograph.
• Minimum 10-year follow-up with adequate radiographic documentation.

Exclusion Criteria:

• Systemic diseases affecting bone metabolism.
• Parafunctional habits (e.g., bruxism).
• Smokers of more than 10 cigarettes/day or those with alcohol abuse.
• Patients with implant failures, missing follow-up data, or implants placed outside the interforaminal region.

The study population consisted of completely edentulous patients who received mandibular overdentures retained by four dental implants placed in the interforaminal region. Patients were selected retrospectively based on having been treated with either four Locator attachments or a four-implant bar attachment system and followed for a minimum period of 10 years. All participants had similar implant positioning (lateral incisor and first premolar areas) and were free from systemic conditions that could affect bone healing or implant success. Inclusion criteria required good oral hygiene compliance and regular follow-up records. Exclusion criteria included uncontrolled systemic diseases, history of head and neck radiation, and lack of long-term follow-up data.

Upon reasonable request from the corresponding author