Histologic Evaluation of Guided Vertical Ridge Augmentation Around Implants in Humans

Histologic Evaluation of Guided Vertical Ridge Augmentation Around Implants in Humans S. Parma-Benfenati, C. Tinti, T. Albrektsson, et al., Int J Periodontics Restorative Dent. 1999;5: 425–437 Studies in recent years have demonstrated predictable success in obtaining vertical ridge augmentation around dental implants. Most of these studies reported clinical success, with one report by Simion demonstrating histologic evidence of direct bone contact to miniscrews. To date, there is a lack of human histologic data evaluating new bone formation around commercially available endosseous implants. The present report qualitatively and quantitatively evaluates the bone response to exposed implant surfaces after treatment with GBR in human subjects. Six patients treatment planned for fixed partial dentures with insufficient vertical bone height for implant placement were included in the study. Study implants were placed protruding 5 to 7 mm above the crest of bone. Autogenous bone dust or bone chips with titanium-reinforced e-PTFE membranes were adapted over underlying bone and implants. After 12 months of healing, the experimental implants were removed with a trephine bur, with undecalcified histologic sections made. Qualitative and computer-based histomorphometrics were performed. Clinically, the space underneath the intact membranes was filled with bone with two exceptions. One implant had a 1 mm or less layer of soft tissue overlying bone; a second case, in which the membrane was dislodged, demonstrated soft tissue in the exposed area. Histologic evaluation demonstrated new bone formation, with the crest in some cases covering the upper, unthreaded portion of the implant; in other cases, poor bone contact was seen on the uppermost threads. Bone morphology was “shell-like” with a thin cortical-type external layer and underlying nondense bone with thin trabeculae. Percent of bone-to-metal contact over the nonexposed implant threads (44%) was significantly higher than the exposed threads (22%). Similarly, the bone volume was higher in the nonexposed areas (60%) than the exposed areas (25%). This study demonstrates that bone-to-metal contact is present at 1 year with this implant system in humans. Although the amount of bone contact and bone formation is less in the exposed sections, than in the unexposed, this study design does determine whether this is sufficient bone formation to withstand functional loading. Although it is assumed that more bone-to-metal contact is better, no studies exist that have definitively demonstrated this, or determined what percent contact is critical for success. The implant type used in this study was a machined surface; current knowledge suggests that more rapid bone contact and higher percentages of bone formation occur on the surface of rough surfaced implants. A comparison of this type between different surfaces would be interesting. Additionally, the implants were evaluated at 12 months; a usual loading time for implants is 6 months or less. An evaluation of implants at the 6 month time point, or earlier, would be useful.