An ultrastructural study of the bone-titanium interface using pure titanium-coated plastic and pure titanium rod implants

The present study was designed to examine the bone-titanium interface of the titanium-coated or titanium rod implants inserted for 28 days in the tibiae of 6-week-old rats. Basically, there were hardly differences in the interfaces between the titanium-coated and titanium rod implants. Light microscopically, titanium layer appeared to make direct contact with the mature bone or poorly mineralized layer, and one or a few layers of slender cells were localized contacting the titanium. Ultrastructurally, titanium came in direct contact with either the bone, the poorly mineralized layer consisting of delicate fibril-like structures or the slender cell layer through a thin amorphous zone (2040 nm). This amorphous zone was positive for ruthenium red which has a high affinity for proteoglycans. Part of the interfacial slender cells had abundant rough-ER and glycogen granules as osteoblasts, while some slender cells had well-developed rough-ER but no glycogen, and often endocytosed the titanium fragments, as shown in the fibroblasts. These findings suggest that an amorphous zone consisting of proteoglycans is thus essential for attachment between the slender cell layer, poorly mineralized layer or mature bone and titanium. Furthermore, slender cells close to the implant may also be considered to function as either osteoblasts for bone production adjacent to the implant or as scavengers for the removal of interfacial debris at the bone-titanium interface.