Regulation of Pre-Osteoblast Osteogenic Transcription Factors by Different Titanium Surface Topography

Recent topic of discussion on dental implants revolves around differences in titanium surface topography. According to previous studies, different chemical or mechanical processing of titanium surface would elicit diverse cell or tissue reactions. Processes such as sandblasting, acid etching, or the even newer titanium oxide surface, render to excite more osteoblasts than the previous machined surface or plasma spray technique. Of all the parameters of surface processing, roughness and porosity are the two variables of relative importance. Macroscopically, the structure of processed surface increases the contact area per unit; and its bonding strength with bone tissue is strengthened from the mechanical undercut formed. Related animal study has revealed that once rabbit femur has achieved osteointegration with experimental implants, the torque removal would show obvious increase, achieving four times the value compared to the control implants with machined surface [1]. Microscopically, the importance of surface architecture on the mechanism of osteointegration can be observed. When an implant is placed, hydration takes place between water molecules and titanium implant surface in a fraction of a second. At the same time, bonding occurs between calcium ion, phosphate ion and micromolecules, changing the electric charge on the titanium surface. Organic molecules such as amino acids, proteins, ester and peptide thus tightly attach to the hydrated interface, which is an important layer [2]. Early in 1987, Williams proposed that unique surface structure of implants can provide adherence for protein molecules. These protein molecules, when adhered to an implant surface, would form an organized structure to attract specific cells to bind and differentiate [3]. In the process of bone formation and osteointegration, osteoblast differentiation is a key factor [4]. Cell culturing and animal studies have discovered that different implant surface treatments would result in varied osteoblastic differentiation [5-9]. Micro-arc oxidation (MAO) technique applies increasing voltage on metal compartments in an aqueous solution. As the oxidation rate increases on the metal, the surface structure recrystallizes, creating a local tunneling ionization reaction. Under the high temperature plasmatic effect, MAO-treated surface forms a layered structure. The outmost layer being porous and oxidized as the residue resulted from high temperature outburst of the treated metal. As the inner surface continues to be heated, it gradually acquires the properties of highly durable ceramics with high wear-resistance. With a dense oxidized layer and a outer porous structure to increase the route of ion diffusion, the metal of concern is more resistant to acid etching [10]. In recent years, micro-arc oxidation technology has brought recognition in the surface oxidation of light metals such as aluminum, magnesium and titanium alloys [11], providing a simple and efficient way to process light metal surfaces. This porous structure significantly enhances the bonding of bone tissue and the titanium alloy surface [12]. According to Boyan’s study, culturing of osteoblasts on sandblasted and acid etched pure titanium surface would increase the formation of alkaline phosphatase (ALP) and type I collagen. ALP is a secreted enzyme in early stage of osteoblast differentiation. Type I collagen is the main protein secreted by osteoblasts, taking up to 90% of the bone matrix. Hence ALP and type I collagen are the two major detectors for osteoblast differentiation.