Bone Grafting

Bone Grafting

Bone regeneration or, simply, pre‐implant bone grafting is an important aspect of dental implantology. In fact, bone regeneration is often mandatory following tooth extraction and prior to implant placement, and there are several reasons for this. The successful placement of implants requires sufficient bone volume of high biological quality for the implant to osseointegrate prior to its subsequent restoration. Specifically, the rule of 6’s applies where 6 mm of bone is necessary in a vertical and horizontal dimension. When an implant is treatment planned, it is generally because the patient’s tooth is deemed non‐restorable. This “hopeless” prognosis is reached based on several factors including caries at or below the bone level, failing endodontic treatment, perio‐endo lesions, advanced periodontal disease, and tooth fracture. All of these conditions potentially affect the underlying hard and soft tissue.

Other factors necessitating bone grafting include post‐extraction resorption of the edentulous ridge, the presence of bony defects due to trauma or infection as well as the need to place implants in specific sites for proper functionality. Further, in esthetic areas, a satisfactory emergence profile of the soft tissue requires a bony base because it is well‐established that soft tissue follows its hard tissue base. Finally, in situations where there has been significant loss of bone and the tooth is deemed unsalvageable, guided bone regeneration (GBR) is used to facilitate bone regeneration when the bone thickness in the jaw is insufficient for implant placement.

In other words, bone grafting or GBR has two primary purposes:

  • To meet the criteria of bone volume for implant placement, or
  • To improve the results of an implant prosthesis by allowing a more ideal position of the implant.
Photos depict (a) Tooth number 30 with severe bone loss. (b) Tooth extracted and graft of mineralized cortico-cancellous bone placed with a non-resorbing membrane. (c) Implant placed five months post-GBR. (d) Implant level impression. (e) Final restoration.

Figure 9.1 (a) Tooth #30 with severe bone loss. (b) Tooth extracted and graft of mineralized cortico‐cancellous bone placed with a non‐resorbing membrane. (c) Implant placed five months post‐GBR. (d) Implant level impression. (e) Final restoration.

A typical example of a situation requiring GBR is shown in Figs. 9.1a,b,c,d,e, covering the replacement of a “hopeless” situation with tooth #30.

The basic rules of bone grafting in an extraction site with a wall defect (generally, the defect will occur on the buccal plate) are the following:

  1. Raise a flap to visualize the defect.
  2. Carefully curette all granulation tissue out of the socket and create blood flow.
  3. Irrigate with sterile saline.
  4. Place barrier membrane along defect.
  5. Place bone graft material.
  6. Close site with
    1. Primary closure which entails advancement of the flap to cover the graft – a resorbable or non‐resorbable membrane can be utilized. If a non‐resorbable membrane is utilized, it must be retrieved at the time of re‐entry.
    2. Secondary closure – a non‐resorbable membrane is generally utilized to “cover” the graft. Generally, the non‐resorbable membranes are made to withstand the acids and enzymes in the oral cavity.

Bone Grafting

Graft materials are discussed in detail in Appendix C but for convenience, a few comments are made here. There are basically four classes of material utilized for GBR:

  • An allograft – a tissue graft from a donor of the same species as the recipient but not genetically identical.
  • An autograft – a graft of tissue harvested from the patient, e.g., bone harvested from the iliac crest or patella plane for gap filling or sinus lifting.
  • A xenograft – tissue harvested from a species other than human.
  • Synthetic graft material.

Theoretically, autografting is the optimal approach to bone grafting but, as this procedure usually involves an ancillary surgical procedure to harvest the bone, it is not the preferred approach despite certain inherent advantages. The first of these advantages is that there is no need for sterilization or sanitization of the graft material. Second, the risk of rejection by the recipient site is minimized although it must be borne in mind that once bone is harvested from the donor site and separated from its vascular supply, that bone may die before it can heal. Although rejection is uncommon, it can still occur because the transplanted material will be “foreign” to the recipient site.

Similar considerations regarding rejection apply to allografting and xenografting. In both cases, sanitization/sterilization is necessary to ensure a pristine and bacteria‐free implantation. On the other hand, the advantage of both these approaches is that the particle sizing of the grafting materials and their sanitization/sterilization are performed prior to their use, and they are commercially available. As noted, graft materials are discussed in detail in Appendix C.

Regarding the selection of a graft material, the general consensus is:

  • Survival rates of implants placed into grafted areas are comparable with survival rates of implants placed into pristine bone [1].
  • Bone quality at the recipient site determines the type of graft material to be used. Cortical bone is inferior to cancellous bone at the recipient bed. Cells within cancellous bone are responsible for at least 60% of bone healing capacity. The periosteum in a young, healthy patient contributes an additional 30% whereas cells in cortical bone only contribute about 10% to overall bone healing.

When bone resorbs after extraction, the cancellous bone shrinks relative to cortical bone. As the cancellous component of the jawbone diminishes, there is a corresponding decreasing in the reservoir for osteoblasts. However, computerized tomography (CT) can indicate the ratio of cancellous to cortical bone at the recipient site prior to surgery, this ratio facilitating graft material selection as follows:

  1. Only cortical bone: autograft.
  2. Cortico‐cancellous bone: selection depends on which predominates but if there is a preponderance of cancellous bone, the choice is less critical.

Ridge Preservation

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Mar 12, 2022 | Posted by in Implantology | Comments Off on Bone Grafting

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