Dental implant restoration is an essential treatment to replace missing tooth, better function and enhance aesthetics for patients. An understanding of dental implant design & placement for optimum dental clinical results is common knowledge for the Dental clinician. This is not the case when it comes to the bone grafting needs and procedures that are the foundations for implant treatment.
This article will address the basic principles for bone grafts in implant dentistry: the rationale, indications, locations, requirements, types, materials, and some guiding consensus on surgical techniques and materials. This will help clarify a somewhat murky new area for the general practitioner who needs to know more – whether it is to provide guidance to patients, or to increase understanding of the surgical protocols of implant treatment.
The Rationale for Bone Grafts
Placement of implants requires sufficient bone volume and biologic quality. This is due to the macro design of the implant, which demands certain dimensional properties for long-term success.1
Other factors which make bone grafting necessary are:
• The resorption of the edentulous ridge post extraction.
• Presence of bony defects due to infection or trauma.
• The need to place implants in strategic sites for functional and aesthetic success. In aesthetic areas, soft tissue requires a bony base since “soft tissue follows hard tissue”
Treatment planning for bone graft placement requires the selection of an appropriate surgical technique and graft material. Poor planning or execution may lead to resorption of the graft material or its failure to integrate. In addition, the lost tissue may be replaced by fibrous tissue rather than functional bone.
Grafts are suitable for a variety of clinical situations.
Outline of topics
Locations/Indications for Bone Grafts in Implant Treatment
Bone graft materials are placed in different locations for various indications:1
• In alveolar sockets post extraction
• To refill a local bony defect due to trauma or infection
• To refill a peri-implant defect due to peri-Implantitis
• For vertical augmentation of the mandible and maxilla
• For horizontal augmentation of the mandible and maxilla
Following the extraction of a tooth, 40 to 60 percent of the original height and width of the surrounding alveolar bone is expected to be lost; the greatest loss is in the first 2 years.
With this loss of hard and soft tissue, conditions are less favourable for the proper axial alignment of the implant for function and esthetics. To minimize alveolar atrophy post extraction, healing procedures termed “socket preservation” or “ridge preservation” have been developed. These procedures involve filling the socket with bone or bone substitute material, with or without a membrane.
Bone substitute materials (BSM) were developed to counteract the difficulties of autogenous grafts. They can either replace autogenous bone entirely or expand the autogenous graft. Materials need to be effective for procedures both before insertion of the implants (time-delayed procedures) and for optimization of the recipient site at the time of implant placement (simultaneous procedures).
( Bone grafting of Dental Implant in India is still not a very popular procedure because of religious beliefs surrounding the manufacturing and extraction process)
Grafts are classified as:
Autograft (autogenous graft):
Tissue transferred from one location to another within the same individual
Allograft:
A graft between genetically dissimilar members of the same species i.e. human tissue
Xenograft:
A graft taken from a donor of another species i.e. bovine, porcine etc
Alloplast:
Inorganic, synthetic or inert foreign material implanted into tissue
The autograft is the patient’s own bone. It is chiefly harvested intraorally or from the iliac crest. It is the ideal bone substitute since in contains living cells and human growth factors. It has greater osteogenic potential than any other bone substitute as well as inherent biocompatibility.12
The allograft can be derived from cadavers or living donors (tissue harvested from hip replacement surgery). It has natural bone composition and structure. This tissue is osteoinductive as well as osteoconductive but lacks osteogenic properties because of the absence of viable cells.12
A controversy exists as to the association of allogenic material and the risk of transmission of infections such as HIV, hepatitis B and C, prions, malignancies, systemic disorders or toxins.
Aggressive allograft processing gives it a less intense immunologic response, but reduces the osteoinductive properties. Frozen allografts induce stronger immune responses than freeze dried allografts, hence they are no longer used.12
The donor tissue is cleaned and then undergoes ultrasonics to remove blood and tissue components and to eliminate fat from the cancellous bone structure; this improves penetration of the surrounding tissues into the graft material.
Then chemical treatment denatures non-collagenic proteins, inactivates viruses and destroys bacteria. Further oxidative treatment denatures persisting soluble proteins and eliminates potential antigenicity. Dehydration preserves the structural integrity of the material. Final sterilization by gamma radiation ensures sterility.
Allografts are available in different shapes from demineralized bone matrix granules to complete bone segments. Granules can be used in socket preservation for future implant placement, ridge reconstruction for prosthetic therapy, filling osseous defects and maxillary sinus floor elevation.
Allograft bone segment blocks are a predictable and effective alternative to traditional autogenous block grafting and ridge augmentation.13 When very large areas need to be grafted, a shell of autogenous bone is often used as a biologic container; this creates the necessary space for the incorporation of the particulated bone graft material. The bone cells in the autogenous bone die within a few days and then the boneplate functions as a stable, avital, slowly resorbable membrane.14 Allogenic bone blocks can also be used for this shell technique as a substitute for autogenous bone. This avoids the time consuming harvesting and splitting of the autogenous bone blocks.
The space between the local bone and surrounding shell can be filled with a variety of different particulated bone grafting materials (autogenous, allogenic, xenogenic or alloplastic).
Histologic studies have shown no difference in the final stage of incorporation between allografts and autografts.15
The xenograft is derived from other organisms, mainly bovine. It provides long-term volume stability. Porous natural hydroxyapatite can be obtained from animal bones.
Bovine bone has a long well-documented tradition. It is deproteinized by heating to eliminate the risk of allergic reactions and disease transmission.16 The removal of all proteins transforms it into biologically derived hydroxyapatite ceramic.
