Long-term ingrowth and apposition of porous hydroxylapatite implants

Bone implant materials are often used to fill in bone gaps that frequently result from orthognathic and craniofacial reconstruction. The substrate hydroxylapatite (HA) is commonly implanted into the bone voids, resulting from these conditions due to its established biocompatibility and osteoconductive properties. The porous structure of HA provides a three-dimensional guideline for fibrovascular ingrowth, facilitating the process that ultimately results in the deposition of new bone. Porous HA (Interpore, 200) implants were implanted in the mandible or maxilla of nine humans and removed after 14-30 months (19.1-month mean). There was no evidence of an inflammatory response. The sample composition and apposition against the implant were determined using point counting and a digitizing tablet and software. Percent ingrowth in available space (%IAS) was defined as %Bone/(%Bone + %Void). A new measure of implant saturation (%IAS-%Apposition of bone) was established to help determine the fundamental manner in which long-term HA implants incorporate bone. In the mean, the samples were composed of 27% bone, 21% void, and 53% implant. The apposition percentages averaged 60% bone, 16% void, and 24% soft tissue. The %IAS averaged 58%, and implant saturation averaged -3%, indicating that a near-balance between the implant and surrounding bone has been established.