Transmission electron microscopy. The various stages of bone formation adjacent to the Ep surface could be observed at 12 weeks of healing. (a–c) At the bone-implant interface, osteoblasts (Ob) produce an unmineralised extracellular matrix, the osteoid, which undergoes progressive mineralisation. (d) Collagen fibrils are aligned parallel to the osteoblast surface. (e) Early mineralisation stage with patchy distribution of bone apatite (dark areas). (f) In high-resolution, the characteristic 67 nm cross-striated pattern of collagen fibrils (white arrows) can be observed, with accumulation of intra- and interfibrillar mineral. (g) Late mineralisation stage with diffuse distribution of bone apatite (dark areas). (h) An osteocyte (Ot) embedded within the mineralised matrix lies in close proximity to the implant surface with several dendritic processes residing within canaliculi (white arrows), sectioned longitudinally as well as transversally, extending towards the implant surface.