Physiology of onlay bone healing

Abstract

Onlay bone grafting represents one strategy for locally increasing bone stock. This may be due to the need to restore bone in a large defect site such as the use of either autologous bone, or other products, in cranial reconstruction; or the need to provide load-bearing bone for the placement of implants as witnessed in “J” grafts and wedge grafts in the alveolar bone. Clearly, the basic phenomena of host bone healing, comprising the response to surgical intervention, will be common to all cases. However, where inlay grafts are surrounded by host bone tissue, onlay grafts are placed onto the bone surface where the recipient bed may be poorly vascularized cortical bone with a paucity of osteogenic precursors to initiate new bone matrix formation. For this reason, various strategies are available to enhance the wound healing dynamics of onlay grafts. These include the addition of autogenous (platelet products) and/or purified (growth factors) stimulants to healing, the use of membranes in an attempt to control the cellular composition at the wound site, or the augmentation of the host bone with artificial materials. The latter, in the tissue-engineering context, may be combined with both cells and/or growth factors to optimize healing. The long-term response to the graft will be dependent upon the type of graft employed and, importantly, on the biomechanical constraints of the anatomical placement site. Thus, an onlay graft employed in the reconstruction of the zygoma will need to provide long-term mechanical tissue support while on onlay graft in the maxillary sinus may function almost as an inlay graft which can become completely remodeled in time to only that bone which supports an endosseous implant.