Significance of the periosteum in onlay craniofacial augmentation.

In the quest for bioinert, easily applicable, and individually adaptable alloplastic materials, hydroxyapatite (HA) has gained a new application in onlay craniofacial augmentation. On the basis of clinical and experimental proof that intraosseous translocation of HA occurs after HA onlay augmentation, we conducted an animal study on 16 adult Goettingen minipigs in which HA, as blocks or granular, was implanted for a maximum time of 72 weeks. Our aim was to study the difference between periosteal and subperiosteal onlay augmentation of two different HA forms by comparing HA-bone interface on the intact frontal bone treated with a block form of HA versus granular HA, with special emphasis on the periosteum. Within a few weeks after subperiosteal augmentation, subimplant changes in the grafted bone became evident to such an extent that within 72 weeks the granules migrated into the frontal sinus. In contrast, in epiperiosteal HA onlay augmentation, no intraosseous migration of HA particles was observed, regardless of the type of HA implants. The HA particles were integrated within the connective tissue, and the connective tissue infiltrated the interstitial spaces. For the most part, the location and the shape of the implant remained stable. The periosteum assumed the function of a limiting membrane. We recommend that epiperiosteal onlay augmentation with HA be performed only if previous studies have proven that shape and location are stable. The periosteum should be preserved because it functions as a limiting membrane, retaining the HA and preventing it from migrating into the subimplant bone.