Principles, Harvesting & Healing of Bone Grafts in Dental Implant Cases

Abstract

Successful implant dentistry can be directly co-related to quality and quantity of bone at the recipient site of implant. The use of bone grafts for management of various osseous defects has been available for many years. Interest in bone reconstruction for the oral cavity has increased dramatically over the past decade with widespread acceptance of dental implant. Many patients who request implant rehabilitation require ancillary procedures to increase the quantity and quality of their recipient bone.Bone has an internal structure described in terms of quality which reflects the strength of bone. The density of available bone in an edentulous site is a determining factor in treatment planning, implant design, surgical approach, healing time and initial progressive bone loading during prosthetic reconstruction.Atrophy of the alveolar processes is expressed as reduction of height and width. This review provides a contemporary and comprehensive information about various bone graft used in dental implant management. Keywords: Dental implants; bone grafts; graft material

Introduction

Many patients who request implant rehabilitation require ancillary procedures to increase the quantity and quality of their recipient bone. Bone has an internal structure described in terms of quality which reflects the strength of bone. Atrophy of the alveolar processes is expressed as reduction of height and width. The density of available bone in an edentulous site is a determining factor in treatment planning, implant design, surgical approach, healing time and initial progressive bone loading during prosthetic reconstruction.

Healing of bone grafts

Incorporation of the grafts happens in concert with a process of initial remodelling and resorption, which is associated with a loss of bone volume. The amount and rate of this resorption depends on many factors, such as

• dimensions of bone graft
• quality of recipient site
• biomechanical properties and
• fixation to surrounding bone.

Graft healing occurs in one of 3 ways: osteogenesis, osteoinduction or osteoconduction. The proportion of these processes in each case depends largely on type of graft and conditions of host site(s).

Osteogenesis occurs when the graft itself supplies viable osteoblasts (osteogenic cells) as the source of new bone. It is well known that bone source (for instance, the iliac crest) with high proportions of marrow have better osteogenic properties due to all increased number of in differentiated cells. During healing phase of graft there is competition between bone-forming cells and soft-tissue-forming cells to fill the defect. The graft is replaced in a period that lasts between 3 to 6 months. When this occurs the hypervascularity gradually disappears. There is a histological response running parallel to vascular one. Granulation tissue with fibroblastic and angioblastic proliferation is followed by proliferation of immature osteoid tissue at periphery of graft. After the osteoid is replaced by mature bone there is no evidence of grafted avascular bone graft.

Classification of grafts

Bone grafts can be classified according to the structure, source and immune response and embryological origin. Bone grafts classified according to structure include :

• Cortical skull, chin and body of mandible
• Cancellous - Inner tibia or iliac crest
• Cortico- cancellous or composite- Blocks from iliac crest

Bone grafts classified according to source and immune response include:

• Autograft or autologous
• Autograft- from a different human
• Xenograft- from another living being
• Alloplast or Synthetic

Bone grafts classified according to embryological origin include:

• Membranous: originated from mesenchymal cells (for instance, all the bone located in the craniofacial skeleton)
• Endochondral- originated from ectomesenchymal cells (for instance, iliac crest, tibia)

Cortical Bone This type of bone is highly osteoconductive due to Haversian system and thus more resistant to resorption, which is useful when structural rigidity is an issue. It is, however, deficient in osteogenic cells. Cortical bone can be harvested in large quantities from the parietal bones. The problem of medium-sized defects can be solved with blocks from chin, body and ramus of mandible. The zygomatic buttress is more suitable for small defects or dehiscence. The gold standard for bone reconstruction is fresh autograft. Among different autologous sources, cancellous bone from iliac crest has been considered the reference source, due to its enhanced osteogenic properties.

General Principles of Bone Grafting

Preservation:

One of the main goals when harvesting bone grafting is preservation of highest possible number of living osteoblasts.