Bone Grafts in Implant Dentistry

Introduction:

The human bone is the slowest growing tissue and also the strongest amongst the other tissues. In implant restoration, an essential requirement for replacing the missing tooth is primarily to enhance patient aesthetics (looks/cosmetic needs) and also advanced function (chewing or biting hard - masticatory forces). The dental implant becomes a failure if it does not achieve either of the expectations in the long run. When the site where the dental implant needs to be fitted is deemed unsuitable due to certain factors or circumstances, then a bone graft will be an added advantage for the implant stability.

What Is Bone Grafting?

Bone grafting is a surgical procedure in which bone tissue is transplanted to fix the damaged or repaired bones. It also helps in the growth of bone around the implanted device.

What Are the Different Types of Bone Grafts?

Bone grafts are basically chunks or blocks of bone that are transferred to the recipient site (the site of dental implantation) from a donor site that might be either

1) From the individual's own bone tissue - also called Autograft or autogenous graft where the tissue is transferred from one location to another location. In regard to dental implantology, it is the site of a dental implant within the same individual.

2) Another individual's bone tissue - called Allografts wherein graft is between dissimilar members of the same species. For example, to graft a human tissue from another individual (human donor).

3) From a different species - called Xenograft, which is the tissue obtained from another species like animal tissue (bovine or porcine, etc.).

4) From foreign material sources – called Alloplasts that are synthetically designed substances and are inorganic by nature. These sources are inert and deemed suitable for dental implantation specifically.

What Are the Different Ways of Collecting Bone?

Bone grafts in the case of autografts (as it is from the patient's own tissue) are mainly obtained by bone collection methods from the iliac crest or the portion of jaw bone like symphysis/mandibular tori or the mandibular ramus. The bone obtained from this portion should be corticocancellous (mixture of the two types of bone - cortical and cancellous bone) in origin.

The different ways of collecting bone are by four major methods:

• Bone harvesting or block grafts.

• Bone milling.

• Bone scrapers.

• Bone traps.

Rationale for Bone Grafts:

Placement of implants demands dimensional stability and certain dimensional fulfillments for long-term success. The dimensional stability of a dental implant is mainly achieved by two factors:

1) Sufficient Bone Volume - When the bulk of bone needed for dental osseointegration (implant threads binding to the bone tissue) is missing as in certain cases of bone resorption post-extraction or defective bone due to trauma or infections (an increased prevalence in old age and systemic health diseases), then the bony base for implant needs to be substituted by grafting.

2) Biological Quality of the Bone - Bone strength is not uniform in all areas of the upper and lower jaw (maxilla and mandible). The density of bone fluctuates from area to area in the jaws (locations like the lower jaw having thick density, for example). Hence the type of bone graft needed to substitute the missing or defective bone depends to a great extent on the location of the dental implant site.

Apart from these two important criteria, appropriate selection of the graft and proper surgical technique are extremely important factors to be determined by the dental surgeon before the grafting procedure. Poor execution either in technique or material selection can lead to the resorption of graft material. Hence instead of osseointegration of the implant (where bone fuses with the implant), fibro-osseous integration may take place (soft tissue or fibrous tissue fusing with the implant rendering it weak and unstable).

What Are the Requirements for Ideal Bone Graft?

The bone is always in a constant process of renewal involving two aspects, formation and resorption. These are the ideal requirements for a bone graft to be successful:

1. Formative/Regenerative Capacity - For the bone graft to be successful, the bone cells should have a proliferating or formative capacity (by forming and inducing new bone cells, also known as osteoblasts). If the number of osteoblasts are less, then the bone matrix will not be dense or thick/ strong to be a base for a dental implant. The principle of bone grafting in dental implantology is by regeneration, not repair. Repair is simply regaining the lost tissue, but regeneration is a biological process in which the tissue is remodeled to form and function.

2. Blood Supply - The bone graft should receive a good blood supply for cell viability and clot formation. The clots serve as a base or anchorage for the proliferation of bone proliferating cells/osteoblasts.

3. Stabilizing Materials - For the graft to be stable and fixed in the position, GBR (Guided Bone regeneration), collagen membranes, bone screws, or titanium meshes will act as support systems. These materials act as a placeholder for the new regenerating bone and help promote the growth of blood vessels and bone cells.

What Are the Bone Grafts Materials Used In Dentistry?

The bone graft materials used in dentistry are mostly Bovine, Alloplast Reprobone Novabone Perioglas. No risk of cross-infection at all. The osteogenic potential is not as high as Autografts Synthetic. A thorough understanding of these biomaterials used in the bone graft both by the operator and the patient will allow a well-balanced, well-informed, and evidence-based discussion between the dental surgeon and the patient.

Conclusion:

The incorporation of sufficient bone and the quality of bone grafted hence remain the key components of bone graft success prior to dental implantation.