The all-on-4 treatment approach for completely edentulous mandible is a proven concept. However, there are still issues regarding the use of metal substructure to support the prostheses such as allergy, metallic taste, and aesthetic. Therefore, other materials such as polyetheretherketone (PEEK) are being tested for its suitability and is showing good potential. However, available evidence is limited regarding its clinical performance. Thus, the aim of this study is to compare clinical performance of all-on-4 treatment concept utilizing PEEK versus conventional metal framework as substructure in fully edentulous mandible. Thirty suitable patients will receive either PEEK or conventional all-on-4 prostheses for fully edentulous mandible. The prostheses will be retained by four implants utilizing the all-on-4 principle. Clinical performance will be assessed during the follow up period of up 3 years concerning screw loosening, material chipping or fracture, wear or staining, prosthesis survival and success, implant survival and success.

The objectives of this randomized clinical trial are to 1) compare clinical performance of the two different treatment concepts during the follow up period of up to 3 years concerning prosthesis survival and success, 2) to assess the implants survival and success rates after 3 years, 3) to assess the accuracy of two surgical guides for full-arch implant surgery, 4) to assess the anticipated and actual pain following implant surgery, and 5) to assess patient satisfaction and quality of life will be assessed.

The study will be conducted according to the guidelines of the CONSORT statement for reporting randomized clinical. The study will be conducted at the College of Dental Medicine, University of Sharjah, United Arab Emirates.

Population and sample Study patients will be recruited from an existing pool of edentate adults referred for treatment to the College of Dental Medicine, University of Sharjah, United Arab Emirates. The patients will not be charged any treatment costs as part of this study. The target population will comprise patients requiring treatment for edentulous arches. Eligible patients for the implant phase of the study will be evaluated through a clinical assessment, panoramic radiograph, and cone-beam computed tomography (CBCT) exam. All study patients will be provided with a patient information sheet and provided written consent to take part in the study.

Conventional upper and lower denture constructions In the first phase of treatment, new maxillary and mandibular complete dentures with acceptable function and esthetics will be made and deliver to the patients. The conventional maxillary and mandibular complete denture constructions will follow the established methods which are primary impression with compound impression material, secondary impression with zinc oxide eugenol, jaw relation, try-in, issue and recall. The satisfactory mandibular complete denture will be converted into provisional all-on-4 mandibular prostheses immediately after implants placement.

Implant treatment planning The implant surgery planning will be performed using CBCT images of the anterior mandible obtained with a limited Field of View and standard protocols for minimizing radiation exposure. Implant placement planning and construction of surgical guides will be accomplished using available software and 3D printing machine. Implant placement will be fully guided surgery. The accuracy of two surgical guides will be assessed (milled and 3D-printed) by obtaining another CBCT after 3 months. The pre- and post-treatment scans will be superimposed and evaluated using Geomagic Control software.

Implant surgeries All implant surgeries will be performed by one surgeon. Surgeries will be carried out under local anesthesia. Four axial and tilted implants (All-on-4) will be placed in association with the treatment protocol. Four dental implants with a platform-switching design (Replace Conical Connection; Nobel Biocare, Zurich, Switzerland) will be placed with computer-guided technology (Nobel Guide; Nobel Biocare, Zurich, Switzerland) in the mandible at the lateral incisor and distal to first premolar sites. Primary stability of more than 35 Ncm will be achieved for all implants.

Pain Evaluation Anticipated pain will be recorded before surgery using visual analog scale (VAS) and actual pain levels will be recorded at day 1, 2 and 4 and at week 1, 2 and 3 after surgery using VAS.

Prostheses constructions Provisional prostheses Following implant placement, straight and 30-degree angled multiunit abutments will be torqued to the implants. Temporary abutments will be connected to the multiunit abutments, and the mandibular denture will be hollowed out to accommodate the temporary abutments. Rubber dam will be used to isolate the underlying soft tissue, and the temporary abutments will be connected to the denture with acrylic resin and picked up with the conversion prosthesis technique. The provisional prosthesis will be torqued to the multiunit abutments at 15 Ncm, and the screw access holes will be filled with Teflon tape and composite resin.

Definitive prostheses (conventional) Conventional hybrid prostheses combining metal frameworks as substructure, acrylic teeth and acrylic soft tissue will be constructed after three months of implants placement according to published protocols. Shimstock foil (GMH; Hanel Medizinal, Nu€rtingen, Germany) will be used for minor occlusal assessments during delivery of the prostheses. The prostheses will be torqued to the multi-unit abutments at 15Ncm, and the screw access holes will be filled with Teflon tape and composite resin (Z250, 3M ESPE, Minneapolis/St. Paul, MN). Oral hygiene instructions will be given to the patients. The follow up will be a week, three months, six months, a year, and 18 months or as needed by the patients. All prosthodontics procedures will be performed by the same prosthodontist.

Definitive prostheses (PEEK) Like conventional hybrid prostheses, the PEEK frameworks hybrid prostheses will also be constructed three months after implants' placement. The prostheses frameworks will be fabricated from modified PEEK (BioHPP; bredent GmbH & Co KG). The definitive impression will be made with a custom tray (Fastray LC; Harry J. Bosworth Co), medium viscosity polyether impression material (Impregum Penta; 3M ESPE), and low shrinkage auto polymerizing acrylic resin (GC pattern resin; GC America Inc) to splint the impression copings for better accuracy. The definitive cast will be poured with Type IV dental stone (Prima-Rock; Whip Mix Corp), and an accuracy transfer index will be fabricated on this cast. This index will be transferred intraorally to verify implant position. The implant misfit will be accommodated by sectioning the index and reconnecting it using the same low-shrinkage resin. This corrected position will be transferred onto the definitive cast by removing the analog from the cast and re-attaching and repositioning it with the transfer index in place. Once the accuracy of the definitive casts has been verified, a facebow transfer and an interocclusal centric relation record will be made using a conventional occlusal wax rim. The casts will be mounted on the semi-adjustable articulator (Denar Mark II; Whip Mix Corp). The cast with the implant abutments in place will be scanned with a laboratory scanner (Dental Create; Smart Optics GmbH); the implant framework will be digitally designed using digital software (Exocad; Exocad America Inc); and a wax implant framework pattern will be fabricated using CAD-CAM technology (DMU 80P duoBLOCK; DMG MORI). The wax frameworks will be made to fit over the selected abutments, which will be incorporated into the framework by using a sculpting wax (Thowax; Yeti Dental) and then cast in 1 piece from modified PEEK, using the conventional lost wax technique, using a special investment (Brevest; bredent GmbH & Co KG) and vacuum press device (2 press; bredent GmbH & Co KG) designed for this material. The fit of the PEEK framework will be verified intraorally, as is the space for the acrylic teeth and pink PMMA. The prostheses will clinically be evaluated to ensure correct tooth position, midline, esthetics, and phonetics. The PEEK framework will then be used to fabricate hybrid prostheses like conventional one. The implant supported prostheses will be tightened to 30 Ncm according to the manufacturer's instructions. Specific oral hygiene instructions will be given to the patients. The follow up will be a week, three months, six months, a year, and 18 months or as needed by the patients. All prosthodontic procedures will be performed by the same prosthodontist.

Inclusion Criteria:

• no contraindications for implant surgery (including uncontrolled systemic diseases)
• sufficient bone height in the inter-foraminal area for an implant length of at least 10 mm
• ridge width of 5.5 mm for implant insertion of at least 3.5 mm in diameter,

Exclusion Criteria:

• individuals who disagreed with being randomly allocated to the treatment study groups, those with signs of untreated temporomandibular disorders or uncontrolled systemic or oral conditions requiring additional treatment, participants unable to understand and answer the questionnaires used in the study, and unable to attend the scheduled post-treatment appointments for longitudinal data collection.

Individuals data will not be shared, data required normally for publication will be shared upon reasonable request.

Block randomization will be used to randomly assign participants. The sequences will be concealed in opaque, consecutively numbered envelopes for each block. One envelope will be obtained for each participant, corresponding to the assignment of the protocol (conventional versus PEEK). The outcome assessor will be independent and not involved in any treatment procedure