Abstract
Titanium and titanium alloys are currently accepted as the gold standard in dental applications. Their excellent biocompatibility has been attributed to the inert titanium surface through the formation of a thin native oxide which has been correlated to the excellent corrosion resistance of this material in body fluids. Whether this titanium oxide layer is essential to the outstanding biocompatibility of titanium surfaces in orthopedic biomaterial applications is still a moot point. To study this critical aspect further, human fetal osteoblasts were cultured on thermally oxidized and microarc oxidized (MAO) surfaces and cell differentiation, a key indicator in bone tissue growth, was quantified by measuring the expression of alkaline phosphatase (ALP) using a commercial assay kit. Cell attachment was similar on all the oxidized surfaces although ALP expression was highest on the oxidized titanium alloy surfaces. Untreated titanium alloy surfaces showed a distinctly lower degree of ALP activity. This indicates that titanium oxide clearly upregulates ALP expression in human fetal osteoblasts and may be a key bioactive factor that causes the excellent biocompatibility of titanium alloys. This result may make it imperative to incorporate titanium oxide in all hard tissue applications involving titanium and other alloys.
Highlights
Titanium alloys have become the most popular metallic biomaterials in dental applications because of their excellent biocompatibility [1]
Col 1 and alkaline phosphatase (ALP) are detected earlier on followed by the secretion of RGD containing proteins such as bone sialoproteins (BSP) and osteopontin (OP) and culminating in the synthesis of OC in the last stage of differentiation
Bone morphogenetic proteins (BMPs) and various members of TGF-β family are secreted by the osteoblast cells and, once sequestered in the extracellular matrix (ECM), these have been reported to be critical for osteoblast differentiation [25]
Summary
Titanium alloys have become the most popular metallic biomaterials in dental applications because of their excellent biocompatibility [1]. This is attributed to the inert nature of the titanium surface due to the formation of a thin native titanium oxide layer [2] which provides excellent corrosion resistance. Titanium alloys have virtually replaced other metallic biomaterials in dental implant applications, currently there is little insight into the reasons for this excellent biocompatibility of titanium surfaces. A number of studies have pointed out various factors that contribute to the biocompatibility of titanium or of modified titanium surfaces [3,4,5,6]. Despite having a good understanding of the signaling pathways in osteoblast differentiation [4], the effect of titanium oxide on osteoblast differentiation has not been fully researched even though the fact that a thin native titanium oxide layer forms on all titanium alloys is well known and a large amount of research has been conducted on these popular biomaterials
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