Background: Single symphyseal implant-retained overdentures have been suggested as an alternative to the standard two implant treatment. There is, however, a need for more studies to compare the functional and patient outcome aspects of both treatment modalities. Objective: The aim of this prospective study is to compare the effect of single symphyseal versus two implant mandibular overdentures on the objective variables: maximum bite force (MBF) and masticatory efficiency (ME), in addition to patient satisfaction (PS) as a patient based outcome. Materials and methods: A total of 60 completely edentulous male patients were initially included in this investigation: 50 from three previously published studies and simultaneously participating in this study in addition to 10 new subjects. 53 participants concluded the study. All subjects received new conventional complete dentures. After 2 months adaptation period, patients allocation was carried out into 3 groups based on the type of implant retained mandibular overdenture that will be constructed: Group (1) single symphyseal implants with locator attachments; Group (2) two interforaminal freestanding implants with locator attachments; Group (3) two splinted interforaminal implants with bar-clip attachments. A capacitive sensor was used to evaluate unilateral MBF. Sieve method was implemented for ME assessment. PS was evaluated in 7 functions using visual analogue scale. MBF and ME were assessed 2 months after conventional complete dentures insertion (baseline); and then at 6months, 1year and 2 years after implant functional loading. PS was monitored at baseline and 24 months after implant loading. Level of statistical significance was set at p < 0.05. Results: All subjects reported a significant improvement in MBF, ME and most of PS variables when implants were used in comparison to the baseline status with conventional dentures. No significant differences were observed between MBF and ME findings among the three groups after implant placement. PS function of maintaining hygiene showed less favourable outcomes in group 3. Conclusions: Mandibular implant retained overdentures in contrast to complete dentures improved maximum bite force, masticatory efficiency and patient satisfaction. Outcomes with one and two splinted and unsplinted implants were comparable. Bars, however, complicated hygiene.