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This study involved histometry of the healed tissues around submerged and nonsubmerged dental implants in beagle dogs. In a split-mouth design, 19 submerged and 19 nonsubmerged commercially pure titanium implants, titanium plasma-sprayed in the bone anchoring part and smooth in the transmucosal portion, were placed in the mandibles of 6 dogs. Oral hygiene was performed 3 times weekly. After 3 months of healing, transmucosal abutments were inserted in the submerged implants. Six weeks after second stage surgery, the dogs were sacrificed and specimens obtained and processed for histology and histometry. Using a light microscope and a digitizing pad, the distance from implant top to mucosa border (DIM), the extent of epithelial downgrowth (ED), the attachment level, (AL), the length of connective tissue contact (CTC) and the distance of the first coronal alveolar bone contact from the implant top (DIB) were measured at the mesial and distal aspects. Means +/- standard deviations for submerged and nonsubmerged implants were calculated, with the dog being the unit of measure. No statistically significant differences between submerged and nonsubmerged implants were found for DIM, CTC and DIB. However, significant differences were observed for ED and AL. This study in beagle dogs indicates that the apical extension of the peri-implant epithelium is significantly greater and the attachment level significantly lower adjacent to submerged implants with second-stage transmucosal abutments than in nonsubmerged, one-stage implants.

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A possible complication associated with the use of hydroxyapatite (HA) or HA/tricalcium phosphate (HA/TCP) coating on the surfaces of prosthetic devices used for dental and orthopedic implants is their potential to fragment and thus exist as wear debris. In contrast to the so-called osteoconductive properties of HA or HA/TCP coatings, in particulate form these materials may lead to an adverse pattern of cellular and tissue responses at the bone-implant interface. We have established an in vitro cell culture system to characterize the biologic and biochemical effects of various particulate materials. The present study demonstrates that the HA/TCP particles derived from different sintering temperatures exhibit differential effects on cultured human monocyte/macrophages (M/M). The HA/TCP particles dried at 110 degrees C were the most biologically active, stimulating significant release of interleukin 1 beta (IL-1 beta), IL-6, tumor necrosis factor alpha, and prostaglandin E2 (PGE2), products implicated as important mediators of inflammation in diverse pathologic conditions. Other particles, sintered at either 900 or 1200 degrees C, did not stimulate production of cytokines or PGE2. HA/TCP particles from plasma-spray coatings also failed to release proinflammatory products. These results suggest that the biochemical and crystalline structural properties of particles markedly affects their capacity to modulate M/M function. This in vitro culture system should be useful in characterizing the specific physical and chemical properties of HA or HA/TCP particulates that are responsible for stimulating proinflammatory cell responses.

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