Transcriptional profiling of osseointegration in humans S. Ivanovski S. Hamlet G.E. Salvi G. Huynh-Ba D.D. Bosshardt N.P. Lang N. Donos Authors’ affiliations: S. Ivanovski, S. Hamlet, Griffith University, Southport, Queensland, Australia G.E. Salvi, G. Huynh-Ba, D.D. Bosshardt, University of Berne, Berne, Switzerland N.P. Lang, The University of Hong Kong, Hong Kong SAR, China N. Donos, UCL Eastman Dental Institute, Periodontology Unit, London, UK Corresponding author: Prof. Saso Ivanovski School of Dentistry and Oral Health, Griffith University, Gold Coast Campus, QLD 4222, Australia Tel.: +61 75 678 0741 fax: +61 75 678 0708 e-mail: s.ivanovski@griffith.edu.au Key words: gene expression, human, hydrophilic surface, oral implants, osseointegration, transcriptome Abstract Objective: To determine the temporal gene expression profile associated with the early healing events during osseointegration in a human model. Material and methods: Nine solid screw-type cylindrical titanium implants, 4 mm long and 2.8 mm wide, with a chemically modified surface (SLActive) were surgically inserted in the retromolar area of nine human volunteers. The devices were removed using a trephine following 4, 7 and 14 days of healing. The tissue surrounding the implant was harvested, total RNA was extracted and microarray analysis was carried out to identify the differences in the transcriptome between days 4, 7 and 14. Results: Gene ontology (GO) analysis of the temporal transcriptional changes was characteristic of a maturing, osteogenic process over the course of the study (4–14 days). At day 4, a gene expression profile associated with proliferation and immuno-inflammatory processes was predominant. However, by day 14, by far the most predominant mechanisms were associated with skeletogenesis, with the GO categories of skeletal system development, bone development and ossification being predominant, with the majority of changes occurring between days 7 and 14. Furthermore, the biological processes of angiogenesis and neurogenesis were also predominant by day 14. In terms of signal transduction, I- kB kinase/NF-kB cascade was predominant at day 4, whereas TGF-b/BMP, Wnt and Notch signalling were all associated with the osteogenic process over the duration of the study. Furthermore, Ras and Rho protein signal transduction was regulated throughout the osseointegration process. Conclusion: The temporal transcriptional changes during osseointegration involve the expression of proliferation and immuno-inflammatory response associated genes during the early stages of osseointegration, which are ultimately replaced by genes associated with the biological processes of skeletogenesis, angiogenesis and neurogenesis. The early immuno-inflammatory changes appear to be regulated via the I-kB kinase/NF-kB cascade, whereas the later osteogenesis-related mechanisms are regulated by TGF-b/BMP, Notch and Wnt signaling. The high clinical success of titanium dental implants results from the process of osseointegra- tion, whereby there is direct apposition of bone onto the surface of the implant. This process requires the complex interaction of a number of biological mechanisms. The temporal sequence of wound healing associated with osseointegra- tion has been histologically analysed in some detail in a dog model (Berglundh et al. 2003). Following implant placement and the establish- ment of a blood clot, an initial immuno-in- flammatory response is followed by neo-vascu- larization and the recruitment of mesenchymal progenitor cells. Differentiation of these progeni- tor cells into osteoblasts and the deposition of collagen matrix are subsequently followed by ossification (Berglundh et al. 2003; Chang et al. 2010). Animal studies of wound healing have demon- strated that the differentiation of osteoblasts occurs earlier in sites with a bone–implant inter- face compared with osteotomy sites alone (Col- not et al. 2007). Importantly, on microrough surface implants, it was shown that osteogenesis not only occurs from the margins of the osteot- omy (distance osteogenesis) as is the case with relatively smooth machined surfaces but also at the implant surface itself (contact osteogenesis) Date: Accepted 5 November 2010 To cite this article: Ivanovski S, Hamlet S, Salvi GE, Huynh-Ba G, Bosshardt DD, Lang NP, Donos N. Transcriptional profiling of osseointegration in humans. Clin. Oral Impl. Res. 22, 2011; 373–381. doi: 10.1111/j.1600-0501.2010.02112.x c  2011 John Wiley & Sons A/S 373