The aim of this study will be the evaluation of patient satisfaction and oral health-related-quality of life (OHRQoL) of two versus four implants supporting fixed full-arch screw-retained metal acrylic hybrid mandibular prosthesis.

• Six completely edentulous patients will be selected for this study from the outpatient clinic of the prosthodontic department
• All patients will be informed about all surgical and prosthodontics procedures that will be done for them. All patients will sign the consent form of the ethical committee in faculty dentistry Mansoura University.

The patients will be divided into 2 groups

1. Control group: will receive implant-supported mandibular fixed metal acrylic prosthesis on 4 implants that were placed according to the "All on four concept".
2. Study group: will receive implant-supported mandibular fixed metal acrylic prosthesis on two implants placed according to "All On two concept".

Inclusion Criteria:

• • Eligible patients needed must have Sufficient interarch space (at least 15 mm from the occlusal plane to the mandibular ridge) to provide space for fixed prosthesis construction all patients should be completely edentulous patients with resorbed mandibular ridge all patients must be angle class I

Exclusion Criteria:

• systemic diseases that contraindicate implant placement bone metabolic diseases such as diabetes mellitus irradiation of the head and neck region chemotherapy within the past 3 years smoking habits.