Two groups of patient with horizontally deficient anterior maxilla indicated for bone augmentation ,one will be subjected to autogenous onlay bone block from retromolar bone and the other to cortical shell from retromolar bone also.

• Two groups of patients with horizontally deficient anterior maxilla indicated for bone augmentation, the first group will be subjected to autogenous onlay bone block from retromolar bone and the other group to cortical shell from retromolar bone also.
• periodontal therapy will be performed before any procedure and oral hygiene measures will be given to the patient.
• After injecting local anesthesia in the anterior maxillary region a trapezoidal flap will be performed in the area of horizontal bone defect (the recipient site).
• The recipient site will be decorticated and recontoured using a round bone bur for better adaptation of the graft and to improve graft-to-recipient bone contact.
• Bone harvesting will be carried out from retromolar region (the donor site) a crestal incision will be carried out 5 mm below and parallel to the gingival margin of the mandibular molars.
• subperiosteal dissection will be extended to expose the ascending ramus and the retromolar region.
• Using piezoelectric device a crestal cut and two proximal vertical cuts penetrating the cortex of the external oblique ridge will be performed then the inferior cut will be carried out.
• Using a mallet and chisel the bone block will be sheared off.
• The underlying cancellous bone will be gently retrieved and the collected bone will be conserved in sterile saline, followed by suturing the mucosal wound.
• Onlay bone block graft procedure (control group)
• In the first intervention, a bone block harvested from the donor site will be fixed with osteosynthesis titanium screws to the recipient site as an onlay graft to achieve a horizontal enlargement of the alveolar ridge.
• Cortical shell graft procedure (intervention group)
• The harvested cortical plate will be split longitudinally in two parts using a micro-saw and thinned with the bone scraper to achieve a plate of 1 mm thickness.
• The plate will be fixed at a distance from the residual ridge with 2 screws.
• Autogenous bone particles, collected with the bone scraper, were tightly packed into the gap between the plate and the recipient site.
• Radiographic assessment will be achieved by CBCT scan immediately and 4 months postoperatively to evaluate bone regeneration and final horizontal bone width.
• In the two groups, the screws will be removed 4 months postoperatively after final CBCT.
• The bone formed in the gap between the bone segment and the original bone will be measured from the CBCT scan.
• Before the intraoperative installment of the dental implants, bone core biopsies will be retrieved from each patient's recipient sites followed by implant placement.

Inclusion Criteria:

• Patients in both sex with partial edentulism of the maxilla and requiring horizontal ridge augmentation
• The ages of the patients ranged from 20 to 60 years.
• The residual ridge width in these patients are less than 4.m
• Sufficient bone in intra-oral donor sites are available (external oblique ridge)
• Patients free from any systemic conditions and bone metabolism diseases that might interfere with the surgical intervention, soft tissue or hard tissue healing.
• The vertical level should be in a favourable esthetic appearance with normal inter-arch space
• The minimum number of missing teeth in the anterior maxilla alveolar ridge is one single extracted teeth

Exclusion Criteria:

• Subjected to irradiation in the head and neck area less than 1 year before implantation.
• Poor oral hygiene and motivation.
• Uncontrolled diabetes.
• Pregnant or nursing.
• Substance abuse.
• Psychiatric problems or unrealistic expectations.
• Severe bruxism or clenching.
• Immunosuppressed or immunocompromised.

This trial is considered a randomized single blind clinical trial due to the following:

• The participants will be blinded to the technique that will be used during the surgical procedure.
• The operator will not be blinded for both techniques during the surgical procedure as the two techniques are different.
• The outcome assessor cannot be blinded. C) Data collection, management, and analysis: