• Full thickness Buccal bone lid approach is well known and well reported technique with a superiority on preserving bone volume and better bone healing especially when done using piezoelectrical devices when compared to conventional technique for management of mandibular pathosis, however periosteum disturbance have a negative role regarding vascularity and bone healing, by comparing the split thickness VS full thickness flap design with buccal bone lid approach, this study will highlight if the periosteum preserved attached to the lid improve the healing on mandibular bony pathosis.
• Aim of the study:

determine the effect of split thickness flap vs full thickness flap using a guided bone lid in hard mandibular pathosis in term of bone healing.

Mandibular cysts, tumors, and impacted teeth are common pathosis that affect the oral and maxillofacial region, causing bone resorption, swelling, facial asymmetry, infection, and influence quality of life. Such pathosis requires its removal surgically for the preservation of mandibular structure and to avoid complex complications.

Conventional technique for removal of these pathosis requires excessive bone removal with limited accessibility and carries a high possibility of injury to vital structures. On the other hand, the buccal bone lid technique, especially when combined with piezoelectrical devices, demonstrates superiority in preserving vital structures, improving visibility, and enhancing bone healing.

The buccal bone lid acts as a barrier against soft tissue invasion and a reservoir for osteoblasts, that's why it is considered a technique for guided bone regeneration.

Computer-guided surgery and 3d printing guides are essential tools in managing oral and maxillofacial lesion providing patient-specific solutions with high accuracy and predictable outcomes.

A scoping review identified a gap of knowledge regarding the effect of computer-guided surgery in the buccal bone lid technique.

The periosteum is primarily structured by two layers: a superficial outer fibrous layer composed of collagen fibers, elastic fibers, and fibroblasts, and an inner cambium layer rich in fibroblasts, osteoblasts, and a specific type of undifferentiated mesenchymal cells known as periosteal skeletal stem cells (P-SSCs) Shi et al. had reported that P-SSCs have been shown to exhibit pluripotency in vitro, having the ability to differentiate into adipogenic, chondrogenic, and osteogenic lineages, and therefore Inner cambium layer has a great influence on bone remodeling and healing in cases of bone fractures and craniofacial bone injuries Debnath et al. revealed that, unlike bone marrow-derived stem cells (BMSCs), which are involved in endochondral ossification, P-SSCs directly differentiate into osteoblasts via an intramembranous pathway under normal physiological conditions in vivo. However, under pathological conditions, P-SSCs can acquire an endochondral osteogenic capacity after periosteal damage and participate in fracture healing and repair.

The periosteum may retain cell viability if handled properly and stored under appropriate conditions. It can remain viable for less than 1 hour in dry conditions; however, in moist conditions (e.g., saline-soaked gauze), viability may be maintained for up to 2-3 hours. Steiner and Ramp had reported up to 5H preservation in normal saline, Cryopreservation or storage in special preservation media can prolong viability for several days to weeks.

While with full thickness flap elevation, periosteum stripping and elevation from the cortical bone, then repositioned in situ, healing progresses predictably. Within just a few days, early reattachment begins thanks to fibrin deposition and cellular infiltration. By approximately two weeks post-surgery, a newly regenerated periosteal layer is established, complete with osteogenic cells and vascular networks, allowing normal bone-healing activity.

Several studies have examined the biological potential of the periosteum in regenerative contexts. Gamal and Mailhot reported superior clinical and radiographic results using marginal periosteal pedicle grafts (MPP) as guided tissue membranes for treating proximal intrabony defects compared to open flap debridement. Later, Gamal et al. observed coarse-fibered woven bone and cementum-like tissue formation in histological samples 9 months after using MPP.

Ghallab et al. also confirmed that autogenous pedicled periosteal grafts were as effective as bioresorbable collagen membranes in improving clinical and radiographic outcomes for intra-bony periodontal defects Puisys et al. Clinically evaluated connective tissue grafts from the tuberosity for increasing soft tissue thickness and keratinization in edentulous mandibles. They found that keratinization of non-keratinized mucosa was more pronounced in partial-thickness flap groups.

Fickl et al. examined the effect of flap thickness on bone loss and reported that partial-thickness flaps, although not preventing bone loss, resulted in less bone loss compared to full-thickness flaps Mounir et al. Similarly had reported reduced marginal bone loss in maxillary ridge-splitting procedures using split-thickness flaps compared to full-thickness flaps.

To our knowledge, the technique of using a split-thickness flap with a guided bone lid approach for managing mandibular pathosis is novel. Based on the periosteum's unique role in osteogenesis and regeneration, its preservation by keeping it attached to the bone lid during temporary removal may enhance healing. This technique requires investigation, particularly in the context of avoiding periosteum stripping and maintaining lid vascularity

Inclusion criteria:

• No sex predilection.
• Age: 18 to 40
• mandibular intra-bony hard pathosis with a diameter ≥1cm with a buccal cortex thickness ≥1mm

Exclusion criteria:

• Systemic or local disease/ condition that could affect bone healing
• Diabetics
• patients on systemic corticosteroid
• chemotherapy
• radiotherapy