Purpose: To compare maximum bite force, masseter thickness, and oral health-related quality of life (OHRQoL) in elderly patients rehabilitated with conventional complete dentures (CDs) and single-implant overdentures (SIOs). Materials and Methods: A paired design was conducted, and 12 elderly patients were selected. Initially, a set of new CDs was manufactured and placed. After a 2-month adaptation period, the mandibular CD was transformed into an SIO by inserting one osseointegrated implant into the symphysis region. All variables were evaluated 2 months after both treatments (CD and SIO). Maximum bite force was evaluated using pressure sensors, while masseter thickness was obtained via ultrasound during muscle contraction and relaxation. The Oral Health Impact Profile for edentulous people (OHIP-Edent) was used to measure OHRQoL. Data were analyzed using Student t test and Wilcoxon test. Pearson coefficient of correlation between bite force and masseter thickness was calculated. Results: Values for maximum bite force and masseter thickness during contraction increased significantly after SIO use (P .001), indicating an improvement in muscle function. Considering OHRQoL, the general score and the domains functional limitation and physical pain were reduced (P .05), indicating better perception of OHRQoL, with SIO use. Moreover, masseter thickness during contraction was moderately correlated with bite force (r = 0.480; P = .018). Conclusion: Using SIO increased the maximum bite force and masseter thickness of elderly patients, leading to an improved OHRQoL.