Scanning electron microscope for the titanium fixture retrieved from the 4 week specimen at the experimental side. (a) Overall view for the retrieved titanium fixture (SEM ×25). (b) Area between serrations 2 and 3 showing part of the peri-implant tissue attached to the surface of the serration covered with densely packed collagen fibers similar to natural cementum; typical perforated-like bone structure appears at the outer layer of the peri-implant tissue (SEM ×140). (c and d) Area between serrations 3 and 4 showing periodontal-like tissue with numerous bundles of collagen fibers attached, while many were cut during fixture removal (SEM: [c] ×170, [d] with larger magnification for 1 bundle; original magnification ×1500). (e and f) Area between serrations 4 and 5 showing serrations covered with cementum-like structure and periodontal-like tissue with obvious numerous collagen bundles of fibers attached to the cementum-like structure covering the fixture serration. Although the densely packed collagen fibers of the cementum are running parallel to the implant, the collagen bundles of periodontal tissue are attached to the cementum and are growing perpendicular (SEM: [e] ×250, [f] ×1500).