Purpose: The aim of this study was to assess the outcome of treatment with implantsupported mandibular overdentures in terms of biting and chewing, in entirely satisfied and not fully satisfied patients. Materials and Methods: Twelve edentulous patients who had worn dentures for at least 5 years participated. They were in good health but had retention problems with their mandibular dentures. First, all patients received new dentures. After 3 months, two Astra Tech implants were placed in the anterior part of the mandible, and 6 months later the abutments were connected. Patient assessment (questionnaire) and functional recordings (chewing ability, bite force, electromyographic activity) were performed with the new dentures, and again 3 months, 1 year, and 5 years after overdenture treatment. Results: After treatment, all patients were able to comminute hard and tough food, the maximum bite force and the chewing activity increased in parallel, and the duration of the chewing cycle was reduced. Every patient felt improved function and reduction of chewing pain. However, the seven patients not fully satisfied with the function of the implant-supported mandibular overdentures were characterized by lower muscle activity, even before implant placement, than the entirely satisfied patients. Conclusion: Implant-supported mandibular overdenture treatment permits better biting and chewing function than conventional complete dentures.