The effect of hydrofluoric acid treatment of TiO2 grit blasted titanium implants on adherent osteoblast gene expression in vitro and in vivo
Introduction
Endosseous implants are of growing importance in medicine and dentistry. The expanding use of titanium implants as anchorage for orthopedic and dental prostheses is supported by favorable clinical responses. In the field of dental implants, long-term endosseous implant success is dependent on the phenomenon of osseointegration, defined as the formation of a direct bone-to-implant interface observed at the light microscopic level [1]. The required formation of bone on the endosseous surface of the cpTitanium implant is due to the activity of adherent and adjacent mesenchymal cells [2], [3]. Recent histological evaluation of this process in the canine model demonstrated that the formation of osteoid and its mineralization occurs within weeks of implant placement [4]. Implied is a functional relationship between the adherence of cells to the cpTitanium surface and their bone forming activity. In fact, the endosseous implant surface is one of the principal factors affecting the process of osseointegration [5]. The effect of surface topography and surface chemistry on osteogenesis is demonstrable at the cellular level in cell culture studies [6].
Osseointegration at endosseous implants requires activation of the key regulatory pathways affecting osteoblastogenesis, promotion of osteoblastic differentiation from uncommitted mesenchymal stem cells. The bone morphogenetic proteins (BMPs) are prominent signaling molecules of osteogenesis [7]. The main intracellular switch for osteogenic pathway in the mesenchymal stem cell is RUNX-2, a transcription factor necessary for osseous skeletal development and bone repair [8]. A second intracellular switch controlling osteoinduction is Osterix, another transcription factor required for osseous skeletal development [9]. In mouse studies, knockout of RUNX-2 [10] or Osterix [11] expression precluded osseous skeletal development and osteoblastogenesis. While many other signaling molecules and intracellular signaling pathways are important for regulation of bone formation, RUNX-2 and Osterix are clearly essential to the process of osteogenesis.
Recently, the regulation of RUNX-2 and Osterix expression in titanium surface-adherent osteoprogenitor cells was reported to be influenced by adherent surface parameters [12]. The aim of the present study was to determine the effect of a specific endosseous titanium surface modification on RUNX-2 and Osterix expression in adherent osteoprogenitor cells in vitro and in vivo.
Section snippets
Implant preparation and scanning electron microscopy (SEM) analysis
About 8 mm cpTitanium (grade IV) disks were prepared by machining. Other disks were subsequently treated by TiO2 grit blasting using 75 μm titanium dioxide (TiO2) particles or by identical TiO2 grit blasting with treatment by hydrofluoric acid immersion (AstraTech AB). The threaded implants (1.5 mm×1.0 mm; 0.2 mm pitch) were machined from cpTitanium and TiO2 grit blasted using 75 μm TiO2 particles. All implants and disks were manufactured for AstraTech AB and subsequently cleaned and sterilized
Results
The machined, TiO2 grit blasted (TiO2), and TiO2 grit blasted and HF treated (TiO2/HF) implants were examined by SEM (Fig. 1b–d). At 5000× magnification, the moderately rough surface of the TiO2 grit blasted surface was readily apparent (Fig. 1c). The HF treatment imparted nanofeatures to the surface with dimensions of approximately 100 nm in diameter (Fig. 1d). Comparison of the chemical composition of the TiO2 versus TiO2/HF surfaces by X-ray photoelectron spectroscopy (XPS) analysis revealed
Discussion
The interaction of cells and tissues with the endosseous implant surface has been the focus of experimental scrutiny for several decades. In vitro investigations at the cellular and molecular level [3], [6] and histological interpretation of these events [19] suggest that implant surface properties influence interfacial bone formation by modulating the adherent cell phenotype. This study provides cell culture-derived data and novel in vivo evidence corroborating the observations that
Conclusions
Scanning electron micrographs revealed that the HF treatment TiO2 grit blasted cpTitanium surfaces provided the treated surface with nanometer scale surface features. Both cell culture and in vivo comparison of the implant surface adherent cell phenotype at the level of bone-specific mRNA expression indicated that the treatment of TiO2 grit blasted cpTitanium surfaces using HF results in a surface that enhanced the adherent cell osteoinductive and bone-specific mRNA expression. Ongoing analysis
Acknowledgment
The authors wish to thank AstraTech AB for providing the disks and the associated analyses of the prepared surfaces.
References (35)
Biologic determinants of bone formation for osseointegration: clues for future clinical improvements
J Prosthet Dent
(1998)- et al.
Targeted disruption of Cbfa1 results in a complete lack of bone formation owing to maturational arrest of osteoblasts
Cell
(1997) - et al.
The novel zinc finger-containing transcription factor osterix is required for osteoblast differentiation and bone formation
Cell
(2002) - et al.
Fluoride modification effects on osteoblast behavior and bone formation at TiO2 grit-blasted cp. titanium endosseous implants
Biomaterials
(2006) - et al.
Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method
Methods
(2001) - et al.
Evaluation of a predictive model for implant surface topography effects on early osseointegration in the rat tibia model
J Prosthet Dent
(2001) - et al.
Critical molecular switches involved in BMP-2-induced osteogenic differentiation of mesenchymal cells
Gene
(2006) - et al.
Ovariectomy hinders the early stage of bone-implant integration: histomorphometric, biomechanical, and molecular analyses
Bone
(2002) - et al.
Cbfa1 isoforms exert functional differences in osteoblast differentiation
J Biol Chem
(1999) - et al.
Altered Cbfa1 expression and biomineralization in an osteosarcoma cell line
J Orthop Res
(2004)