Split thickness periodontal flap

Oral surgery in the dental region requires a good knowledge of the histological layers as manipulation of these layers can be used to serve different purposes. The connective tissue layer is formed of loose collagen, contains blood vessels that run parallel to the surface in the deeper layers. Periosteum is a thin layer of non stretchable fibres that attach directly to the bone. If it is raised as a flap or as part of a full thickness flap, the non stretchable nature of periosteum hinders advancement of the flap unless the periosteum is released with horizontal incisions or split from the superficial tissues.

If the flap needs to be advanced to close an extraction site, close an implant site or make room for bone graft material, you may want to release the flap. If you are going to be splitting a flap, it may be beneficial in cases where a bone graft is required as well as advancement of the flap. Splitting the flap allows separation of the connective tissue which allows advancement of this portion but also exposes the bone with the periosteum raising that allows bony contact of the bone graft particles which is necessary for integration. 

It is easier to split the flap from the very start and then raise the periosteum rather than to raise a full thickness flap then handle the loose flap to split the tissue. This is because the periosteal portion will be held down onto the bone as you are dissecting the tissue off. If you raise a full thickness flap then attempt to split, the flap can't be held as rigidly and the changes of perforation are high. When splitting flaps don't hold the connective tissue up away from the bone as you have higher risk of a button hole through the flap. As you proceed with the split thickness flap, either don't hold the tissue at all or stretch it parallel to the bone. You are aiming to hold the scalpel parallel to the surface of the tissue with wide, slow sweeping motions. Look from the external surface at the angulation of the blade and bone when splitting the flap. If the flap is too thin you will see the blade through the tissue and you need to back the scalpel off the surface so you cut slightly deeper.

The benefits of a split flap is that it allows advancement vertically (coronally) and horizontally (away from the bone). Horizontal advancement is important as it allows placement of as much graft as needed.

If the membrane is cut too big or too much bone is packed it, the flap won't be able to close.Teflon membranes can't be placed in contact with adjacent teeth, collagen membranes can touch the tooth but it can't be allowed to bunch up or it will hinder closure.
 

Steps for a full-split thickness flap for bone grafting
1. Incision to bone
2. Full thickness flap 4-5mm height
3. Use a 15 blade to split mucosa past this point
4. Raise the underlying periosteum to form a periosteal pouch flap: This acts as stable tissue to hold the graft. The stabilising sutures through the periosteum, will be firmer as the periosteum is less elastic so tension on this tissue layer is better tolerated. The periosteum is well vascularised so will provide additional blood supply to the bone graft which also receives blood from the bone itself. The graft acts as a scaffold to support a clot that grows bone.

-The initial part of the split flap should be thick on the mucosal side but then thin out below the mucogingival junction.

-Don't split with same scalpel used to touch bone as this will now be blunt. The scalpel used only on soft tissue will blunt as well but not as fast. Once the scalpel touches bone it will be too blunt for fine soft tissue work.

-Doing all the steps in one go leaves less room to correct errors as you proceed through the treatment plan and forces you to juggle more complex arms of a procedure. Staging things allows time to focus and make corrections i.e better quality work. E.g First providing a socket graft for after the extraction to plan for a future implant then sorting the soft tissue with a soft tissue graft then providing the implant with a concurrent hard tissue graft. Multiple appointments means multiple surgeries but the outcome may be more predictable.
 

-During upper implant placements don't rely on the osteotomy to guide your implant placement as it will want to push through thin buccal bone and deviate from the osteotomy angle. Put some palatal pressure to, push the implant to the palatal aspect to avoid this.