INTRODUCTION: One of the primary objectives of complete dentures is to restore masticatory function in people who have lost their natural teeth. Patients wearing conventional complete denture (CD) often complain of instability of the mandibular denture leading to a feeling of insecurity, inefficient mastication, and overall dissatisfaction with the prosthesis. Implant mandibular overdentures (IOD) constitute a secure therapeutic alternative, affording a great patient's satisfaction and masticatory efficiency. The most common problem in implant dentistry is the presence of insufficient bone volume to receive the conventional size of dental implants. The 2-pieces narrow diameter implants were introduced into the market combining the undisturbed healing period required for proper osseointegration and the avoidance of time, cost and morbidity of extensive surgeries for bone augmentation. OBJECTIVES: The aim of the current work was to evaluate and compare the electromyographic (EMG) activity of masseter and anterior temporalis muscles when using three different treatment protocols i.e. (conventional CDs, two and four IODs). MATERIALS AND METHODS: Eight completely edentulous patients were selected from the prosthetic department, Faculty of dentistry, Alexandria University. Implant mandibular assisted overdentures were constructed for each patient using narrow diameter implants and delayed loading protocol. EMG activity of masseter and anterior temporalis muscles during habitual chewing and maximal voluntary clenching were recorded for each of the studied patients in the three different treatment protocols. RESULTS: EMG activity of masseter and anterior temporalis muscles of IOD was significantly lower with conventional CD than with IOD. Patients with four IOD showed higher EMG activity of masticatory muscles and better function compared to two IOD. Masticatory muscles activity during clenching was significantly higher than during chewing. CONCLUSIONS: It was concluded that IODs have great masticatory efficiency when compared to CD. Implants number affect masticatory efficiency and muscle activity in cases of severely resorbed mandibular ridge.