Surgical procedures for bone defect filling are used to regain lost bone substance in the upper or lower jaw. Bone defect filling may be required, for example, after the removal of large cysts. Special techniques are also used to prevent collapse of the alveolus (collapse of the bony tooth compartment) after extraction (tooth removal). This can eliminate the need for far more costly methods of augmentation (jawbone reconstruction). In addition, bone defect fillings are an established component of implantological measures, without which a large number of implants could not be successfully placed.
Bone grafting materials
I. Autogenous bone graft substitute
The gold standard is considered to be the use of autologous (body’s own) bone. This is bone that must be previously harvested from another part of the patient’s body. The most suitable harvesting sites are the back of the upper jaw, the angle of the lower jaw or the chin region.If larger quantities are required, harvesting from the pelvis, the ribs or the splint bone is possible. These comparatively larger surgical procedures require a hospital stay. At the same time, the amount of bone available is nevertheless limited. A distinction is made between:
- Free bone grafts – non-vascularized grafts (without vascular supply).
- Microvascular anastomosed bone grafts – grafts with vascular supply for the supply of larger defects.
Meanwhile, there is also the possibility of regenerating (renewing) autologous bone extracorporeally (outside the body) in the context of so-called tissue engineering. Bone chips made in this way can be produced in any desired quantity and consist of the body’s own vital bone cells in a matrix. At the same time, harvest defects and rejection reactions are avoided.
II Allogeneic bone graft substitute
Allogeneic (nonbody human) bone from multiorgan donors is also used to fill defects. However, in this case, there is a risk of an immune response to the foreign material resulting in rejection. In addition, only frozen lyophilized bone (FDBA – freeze dried bone allograft) carries the risk of pathogen transmission, such as HIV infection, because the virus cannot be safely destroyed in the course of freeze drying. However, additional demineralization and virucidal treatment in the DFDBA (decalcified freeze dried bone allograft) process can safely inactivate HIV. Overall, the risk of HIV infection from this form of bone is 1:1,600,000. However, the reduction in risk due to demineralization is accompanied by a deterioration in osteogenic (promoting bone formation) potency: DFDBA heals fibrous (“rich in fibers”) in some cases, and conversion to bone fails to occur.
III Xenogenic bone graft substitutes
Inorganic bone of bovine origin (from cattle) is also used to replace lost bone. When bovine material is used, the patient must be informed of the residual risk of infection with prions (BSE agent). Deproteinization (removal of protein) takes place to reduce the risk of transmission and allergenization. What remains is the inorganic bone portion into which new bone is sprouted.
IV. Alloplastic bone substitutes
Synthetic (artificial) bone substitutes are referred to as alloplastic. Also used in combination with autologous bone, they initially fill the bone defect. Osteoblasts (bone-forming cells) colonize the synthetic surfaces. Subsequently, within a few months to years, the bone substitute material is transformed into autologous bone. Depending on the material used, it is either completely or partially degraded and replaced. Alloplastic materials include:
- Hydroxyapatite
- Β-Tricalcium phosphate
- ICBM – Insoluble collagenous bone matrix
- Copolymers of polylactate/polyglycolic acid
- Calcium carbonate
Hydroxyapatite and tricalcium phosphate are the most commonly used. Tricalcium phosphate is a synthetic, fully absorbable (degrading) material. Hydroxyapatite was initially obtained from bovine bone. Therefore, there was a residual risk of infection with prions or allergic reaction.Synthetically produced hydroxyapatite is now available, eliminating these risks.
Other therapeutic options
I. Growth factors
To further positively influence bone regeneration, growth factors are increasingly being used. These include, for example, bone morphogenetic proteins (BMP), which are used together with synthetic bone substitute material and stimulate the differentiation of mesenchymal cells (embryonic connective tissue cells) into osteoblasts (bone-forming cells).
II Guided Bone Regeneration (GBR)
Covering the bone graft substitute with an absorbable membrane is also known as guided bone regeneration or guided bone regeneration (GBR). The membrane prevents the rapidly regenerating soft tissue from growing into the defect, allowing the bone defect to heal more slowly through new bone formation.
The surgical procedures
All procedures, regardless of the bone graft substitute (KEM) used, serve the goal of stimulating osteoneogenesis (new bone formation) in the area of the bone defect. In this process, the implanted materials are gradually partially or completely degraded and replaced by the patient’s own bone. The surgical procedures that involve bone defect filling are each discussed separately elsewhere. These include, for example, the following procedures:
- Jaw bone augmentation by bone splitting – alveolar process splitting, e.g., before implants or after accidental or disease-related bone loss.
- Socket preservation technique – filling of the empty alveolus (the bony compartment of the tooth) after extraction (tooth removal) to prevent atrophy (bone loss) and create favorable conditions for subsequent implant placement.
- Jaw bone augmentation via the maxillary sinus (sinus lift) – before implant placement in the maxillary posterior region after atrophy.
- Periodontal surgery – Surgical measures to rebuild the periodontium (the periodontium) can be accompanied by bone defect fillings in addition to Guided Tissue Regeneration (GTR) via membranes.
- Cystectomy – Surgical removal of a cyst; the decision to defect filling depends here on the size of the resulting cavity.