The study will be conducted to compare three different mandibular implant- assisted complete overdentures. These overdentures were constructed from three different materials and techniques: CAD/CAM-milled poly ether ether ketone (CAD/CAM PEEK MOD), CAD/CAM-milled poly methyl methacrylate (CAD/CAM PMMA MOD), and conventional heat-cured poly methyl methacrylate (conventional PMMA MOD) to clinically evaluate the preiimplant tissues.

The participants enrolled in the current study were randomly assigned to one of three groups based on the material and technique of their mandibular overdenture bases. All participants were delivered new sets of conventional complete dentures implied bilateral balanced occlusal scheme. They were well instructed to wear their dentures regularly for 3 months prior to implant installment ascribed to enhancement of the neuromuscular adaptation. For each patient, the mandibular denture was duplicated with clear auto- polymerizing acrylic resin to fabricate the mandibular surgical template with gutta percha markers. By employing CBCT, all patients were scanned conforming to the dual scan protocol .The implants were installed virtually parallel to each other and perpendicular to the occlusal plane at the areas of canines and lateral incisors .This was carried out using 3D image planning software . The surgical stent with four sleeves was constructed by rapid prototyping .It was placed over the proposed implant locations.Four dental implants were surgically placed in the anterior region of the mandible.Three months afterward, the mandibular impression was registered. The primary impression was recorded and poured to gain the primary cast. Upon that primary cast, a closed custom tray was constructed. The positioner attachments were screwed to the implants, the processing caps and metal housings were secured over them. The custom tray was border molded. By using silicon impression material , the deﬁnitive impression was made at the abutment level. The processing caps and the metal housings were removed from the impression which was being poured by extra hard scannable dental stone to obtain the master cast. Maxillomandibular relations were registered .This was accomplished with mandibular conventional record blocks opposed by the existing maxillary complete denture. Semi anatomical acrylic teeth were arranged employing bilateral balanced occlusion .The waxed overdentures were tried in the patient's mouth. According to the mandibular denture base material and processing technique of the prostheses, the subjects were divided into three groups: The first group (I) included 10 participants whose mandibular overdentures were fabricated by milling pre-polymerized poly ether ether ketone PEEK discs (CAD/CAM PEEK MODs, the second group(II) included 10 participants whose mandibular overdentures were constructed by milling prepolymerised PMMA resin discs (CAD/CAM PMMA MODs), while the third group(III) included 10 participants received conventionally constructed heat-cured poly methyl methacrylate mandibular PMMA overdentures (conventional PMMA MOD).All needed adjustments were executed at the insertion visit. This is to assure appropriate border extension, proper denture base ﬁt, even occlusal contact besides patient comfort. The female housing attachment was picked up to the ﬁtting surface of the mandibular overdenture bases using self-cure acrylic resin. The white processing cap was removed and replaced by a blue one. The mandibular overdentures were delivered to all participants according to their group.

Patients' evaluation Clinical evaluation Peri-implant soft tissue changes as regards plaque, bleeding, and gingival scores were assessed employing the modiﬁed plaque index (PI), bleeding index (BI) and simpliﬁed gingival index (GI), respectively. These indices were evaluated at prosthesis insertion (T0), 3 months (T1) , 6 months(T3) and 12 month (T4) after insertion. A calibrated pressure-sensitive plastic periodontal probe was utilized.