\* this study aims to evaluate accuracy of fixation of the bone shells by a calculated distance which is always a challenging step for inexperienced surgeons to fix a cortical shells at the ideal position in the conventional protocol.
the fixation guides used to make the shells precisely fixed at the proper position and angulation the problem is if it fixed with insufficient distance with proposed volume loss leads to totally insufficient volume gain for future implant placement
* also to evaluate the efficacy of the CAD/CAM surgical guide during chin harvesting (harvesting guide ) procedure in reducing the risk of anatomical structure damage (mental neve) and patient morbidity with more accuracy compared with the standard technique and preserve the roots of the lower anterior teeth or any fracture to the inferior border of the mandible also allow to harvest the bone shells from the suitable area with cancellous bone which prevent bad split of the bone shells this trial versus free hand conventional cortical shell bone technique both harvested from symphysis area (chin), * also to evaluate thickness of implanted bone shells , the thickness should be enough to preserve the graft(autograft 50% and xenograft 50%) between the buccal and lingual bone shells * also aims to evaluate the vertical and horizontal bone augmentation achieved at the anterior mandible using computer-guided cortical shell bone technique.
Age ranges from 20-60 years. No sex predilection.
Intra-bony lesions (e.g., cysts) or infections (e.g., abscess) that may retard the osteotomy healing.