Ridge Augmentation Success:Flap Design and Regenerative Cells
The initial incision is made in the buccal mucosa approximately 3mm apical to the mucogingival junction. The incision is through the mucosa and periosteum. The incision crosses the retromolar pad moving forward through the mucosa and periosteum one tooth forward of the most distal tooth. At this point, the incision is carried coronally through the keratinized gingiva then distal across the papilla. From here, a sulcular incision is made around the buccal of the distal tooth wrapping around the lingual and carried on the lingual across the lingual papilla. Depending on the patient, on occasion, a lingual vertical incision is needed at the same position of the buccal vertical incision to gain adequate flap reflection. This photograph shows the opening of the tissue without any dissection of the buccal mucosa.
The gingiva is elevated off the bone and pushed to the lingual. Cortical perforations are performed. The purpose of the cortical perforation when using science-based regenerative materials is to gain access to the cancellous bone and the regenerative cells that populate this tissue. The cortical plate must be completely perforated. However in this photo, note that three of the perforations (blue arrows) do not completely perforate the cortical plate, which may compromise the regenerative potential of the surgical procedure.
The reason for placing the incision in the buccal mucosa is to involve the periosteum in maintaining flap closure. The attached keratinized gingiva is a very passive tissue that provides very little resistance to sutures pulling through the tissue, which allows the flap to open. The periosteum is a very aggressive tissue, possibly the most aggressive tissue in the body, and the periosteum will resist suture pull. Irrespective of what periodontists believe, there is no periosteum under the attached gingiva. In order to engage the periosteum in maintaining flap closure, the periosteum under the buccal flap needs to be apposed to the edge of the periosteum attached to the keratinized gingiva. In this photo, the coronal position of the buccal flap periosteum is grasped, and it is obvious that the periosteum will not cover the graft site and reach the opposing flap.
After grafting with Ridge Graft Kit, it appeared that the graft volume might be inadequate. Therefore, 1cc of Socket Graft Plus (petal-shaped) was laid over the Ridge Graft to provide adequate graft volume.
The edge of the released periosteum is sutured to the edge of the periosteum remaining on the edge of the keratinized gingiva. Closure of the periosteum does not need to be perfect. The edges of the periosteum need to be approximated so the tissue recognizes its orientation. In regenerative medicine, it is not enough to just put cells in the area. The cells must be able to recognize the environment they are in so they know what needs to be regenerated. The incised ends of the periosteum will quickly grow together preventing the flap from opening. The edges of the periosteum are closed with resorbable 40 Look sutures.
The membrane is removed and the ridge is mineralized with resorption of the majority of the βTCP granules. However, the buccal portion of the ridge apical to the crest has retained the majority of the βTCP granules with a minimum of resorption. Note that the ridge is white to pale gray. All of this is bone, but the surface is not fully mineralized because the graft has been in place only 4 months. We will return to this image and compare it to a ridge that was allowed to grow for 8 months with a discussion on the process of mineralization and the cells involved.
As you recall in the step by step instructions, some of the perforations did not penetrate into the cancellous bone. As you can see where the cortical bone was not perforated, bone did not regenerate establishing that success of ridge augmentation surgery when using science-based regenerative graft materials requires direct access to the regenerative cells in the cancellous bone.
Implants in place. While bone regeneration was compromised where the cortical bone was not perforated, the rest of the ridge showed good regeneration with good regeneration of the crest. Fortunately, the area of failed regeneration did not affect the proper placement of the implants or the success of the surgery.
Day of surgery with implants and healing abutments in place. The same flap design was used in all of these successful ridge augmentation surgeries. The incisions are made into the mucosa and after surgery the periosteum is sutured with resorbable sutures and the mucosa is closed with Vicryl. All significant ridge augmentations performed in our clinic utilize these principals. On occasion, however, for minor ridge augmentations a crestal incision into the gingiva is utilized. The following case is an example of a failed bridge where the mandibular molar is extracted and the pontic area requires ridge augmentation. The same materials utilizing Ridge Graft Kit covered by a d-PTFE membrane was utilized:
Membrane removed. While exposure of a d-PTFE membrane does not always compromise a ridge augmentation surgery, opening of the flap does commonly result in graft failure. In our experience, a flap design that uses the unique properties of the periosteum to close the flap results in a much more predictable ridge augmentation procedure. When using science-based bone graft materials that are resorbable, the granules become encased in bone and some resorption occurs. However, until the bone is loaded, only slow bone resorption occurs. Resorbable science-based graft material rapidly begins resorbing when the bone is loaded because the bone remodels into a structure designed to ideally carry the load placed upon it and the granules are resorbed in the process. Dentists want to know how fast a graft material is resorbed. They often think that when they open a graft site and find bone graft granules the graft material has not performed well or has even failed. All of the grafts on this post will be fully resorbed within a few months of loading and only normal healthy bone with the ability to remodel and adapt with changing loads will be the result. We have discussed the benefits of incising and closing the periosteum to maintain predictable graft site closure. We have shown the need to provide direct access for regenerative cells into the graft material and we have purposely not talked of the need for blood or bleeding. You need blood and bleeding for cadaver bone grafts because the blood supply is the critical source of the inflammatory cells responsible for mineralization of these bone grafts. However, blood and bleeding is not needed for bone regeneration when using science-based bone graft materials that provide a matrix for cell migration. Science-based bone graft material is perfused by extracellular fluid which provides nourishment to the migrating regenerative cells and only after the osteoblasts and their precursors have migrated throughout the material will the vascular supply arrive. In the following image, the ridge is covered in pale gray newly formed bone. The regenerative cells populate the site and the vascular supply is then directed and controlled by the regenerative cells. Lecturers who use cadaver bone graft are correct is saying you must have adequate blood supply for graft mineralization. However, when you use science-based graft materials, you do not need blood–you need regenerative cells:
American Society for Bone and Mineral Research (ASBMR) Tissue Engineering and Regenerative Medicine International Society (TERMIS)