Purpose: This cross-over study aimed at assessing masticatory efficiency in single-implant mandibular overdentures with different reinforcement materials (CO-Cr and PEEK). Materials and Methods: Eight completely edentulous participants have been delivered conventional complete dentures. One month later; they received a single midline mandibular implant. After three months of osseointegration, each patient received two mandibular overdentures; one was metal reinforced (Group I), and the other was PEEK reinforced (Group II). Masticatory efficiency for both groups (I & II) was carried out. Masticatory efficiency was measured by two colored chewing gums test at time of each overdenture insertion (T0). Thereafter, masticatory efficiency was evaluated subsequent to three months of using metal and PEEK reinforced overdentures (T3). Results: In regard to masticatory efficiency, no significant difference was noted between the studied groups reinforced with metal or PEEK at (T0) and three months after insertion (T3). Among chewing strokes, significant differences were revealed between varied chewing stroke counts among both groups (increased chewing efficiency with an increased number of chewing strokes). Conclusion: Respecting single midline implant overdenture, there was no significant difference between (Metal & PEEK) reinforcement regarding masticatory efficiency. SIMOs reinforced with either Metal or PEEK frameworks could be successful treatment options for assisting mandibular complete overdentures.