This randomized controlled trial compares a mandibular overdenture retained by one implant placed in the parasymphyseal or canine region with a mandibular overdenture retained by two implants placed in the interforaminal region in completely edentulous adults. Primary outcomes are oral health-related quality of life, patient satisfaction, and masticatory performance measured by a two-color chewing gum mixing test, assessed at baseline before implant surgery and at 3, 6, and 12 months after overdenture insertion.

Eligible completely edentulous adults will be randomized to receive either one endosseous implant in the mandibular parasymphyseal or canine region on the preferred chewing side or two endosseous implants in the mandibular interforaminal region, followed by restoration with a locator-type attachment retained mandibular overdenture. Oral health-related quality of life, patient satisfaction, and masticatory performance assessed by a two-color chewing gum mixing test are collected at baseline before surgery and at 3, 6, and 12 months after overdenture insertion. Secondary outcomes include postoperative pain recorded during the early postoperative period, radiographic marginal bone level change, peri-implant clinical parameters, prosthetic maintenance events, and clinician chair time from implant surgery through overdenture insertion.

Inclusion Criteria:

• Men and women ≥40 years.
• ASA I-II; favorable general health or adequately controlled systemic disease (e.g., hypertension, diabetes).
• Skeletal Class I relationship.
• Completely edentulous mandible and maxilla.
• Technically acceptable complete dentures in both jaws for ≥3 and ≤24 months; dissatisfaction limited to mandibular retention/stability.
• Adequate anterior mandibular bone for implant ≥3.5×10 mm confirmed on CBCT; no bone augmentation needed.
• Normal mucosal resilience (~2 mm displacement).
• Implant sites healed ≥4 months since extraction.
• Willingness to be randomized and attend follow-ups; written informed consent.
• Primary stability target ≥25 N-cm.

Exclusion Criteria:

• Uncontrolled systemic disease; neurodegenerative disease; osteoporosis requiring antiresorptives.
• Chronic systemic antibiotics/steroids; bleeding disorders; active cancer therapy; metabolic bone disease; HIV.
• Investigational drug use within 30 days.
• Alcohol dependence/illicit drug use; xerostomia (stimulated flow <0.7 mL/min).
• Heavy smoking >20 cigarettes/day.
• TMD/orofacial pain; severe bruxism; moderate/severe cognitive impairment.
• Prior implant therapy.
• Non-adherence risk or inability to attend longitudinal visits.
• Insufficient prosthetic space for attachment housing: inter-arch vertical distance <8.5 mm at parasymphyseal/canine region.
• Concurrent participation in another interventional study.
• Erosive lichen planus or other significant oral mucosal disease; head-and-neck irradiation history.
• Mandibular pathology on CBCT (e.g., cyst, tumor).
• Ridge dimensions <6 mm width or <10 mm height at planned sites.
• Active intraoral infection.

De-identified individual participant data (including data dictionary/codebook) underlying the primary and secondary outcomes will be shared.

Available beginning after publication of the primary 12-month results, for 3 years.

Available to qualified researchers upon reasonable request, submission of a methodologically sound proposal, and execution of a data-use agreement; data will be shared via secure file transfer.

Outcome assessments (questionnaires and chewing gum mixing test) are performed by a blinded assessor; participants and treating clinicians are not blinded due to the nature of the interventions.