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Figure 1. Implant design and placement, histomorphometric study area, and histology. (A) At the time of initial surgery, implants were positioned so that the implant-abutment interface was either supracrestal, crestal, or subcrestal to the alveolar bone, i.e., 1 mm coronal to, at, or 1 mm apical to the alveolar bone crest, respectively. Three months later, abutments (outlined in a dashed line) were connected to implants. After 3 additional mos, specimens were derived for histomorphometric analyses. (B) Sequential histological (test) fields of apico-coronal peri-implant soft tissue were digitally captured; morphometric assessment of peri-implant tissue was confined to connective tissue immediately adjacent to the implant surface from gingival epithelium to alveolar bone. All non-vascular interstitial cells were assessed and designated as either neutrophils or mononuclear cells. For the latter, lymphocytes, plasma cells, monocytes, and macrophages were collectively considered as a single population of cells. (C) Photomicrographs of representative soft tissues immediately adjacent to the implant-abutment interface. Although neutrophils are abundant in the specimen with crestal or subcrestal placement, these cells were infrequent in the supracrestal specimen. Toluidine blue, basic fuchsin stain. A = abutment; AB = alveolar bone; BC = bone crest; CT = connective tissue; GE = gingival epithelium; IAI = implant-abutment interface; R = rough portion of implant (SLA surface); S = smooth-machined collar of implant.
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