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IMPLANT TRIBUNE Dental Tribune Middle East & Africa Edition | 2/2018 Microparticles released by titanium on the immunological mechanism of the body could possibly initiate peri-implantitis. 4 ◊Page D3 of implants. The prevalence of peri- implantitis according to the review of Zitzmann and Berglund (2008) varies between 12 and 43 per cent of implant sites.26 Many aetiological factors have been implicated, bacte- rial contamination among them. In peri-implantitis, the lesion extended apical to the pocket epithelium con- tains large proportions of plasma cells and lymphocytes but also PMN cells and macrophages in high num- bers.27,28 Peri-implantitis though has hardly been reported on zirconia implants. Zirconia demonstrates a low affi nity to bacterial plaque, small amounts of infl ammatory infi ltrate and good soft tissue integration. These properties might lower the risk for peri-implant diseases.1–3 This hypothesis is strengthened by the re- sults of the study conducted by Nas- cimento et al. (2014), where cast and polished titanium were presented with the highest incidence and to- tal count of bacteria, while zirconia showed the lowest.29 help of ozone and autologous plas- ma. Nutrition and food supplements could also be helpful, too. Intolerance to titanium and genetic predisposition to infl ammation has been introduced as an additional and independent risk factor (Odds Ratio 12 and Odds Ratio 6 respec- tively) for peri-implantitis.33 The au- thors propose a direct effect of the released microparticles of titanium on the immunological mechanism of the body that could possibly ini- tiate peri-implantitis. Zirconia parti- cles on the other hand have no effect on the release of TNF-a.34 Titanium microparticles are released as a re- sult either of friction, electrochemi- cal corrosion, or the synergistic effect of both and can either be taken up by macrophages, remain in the intercel- lular space near the releasing site, or systemically migrate in organs such as liver, spleen and lung, as Olmedo et al. (2003 and 2002) found.35,36 Same group of authors made a long- term evaluation of the distribution, destination, and potential risk of both TiO2 and ZrO2 microparticles, in an animal study.37 They evaluated: (a) the presence of particles in blood cells and liver and lung tissue, (b) Ti and Zr deposit quantitation, (c) oxidant-antioxidant balance in tissues, and (d) O2– generation in alveolar mac- rophages. Ti and Zr particles were detected in blood mononuclear cells and in organ parenchyma. At equal doses and times post administration, Ti content in organs was consistently higher than Zr content. Ti elicited a signifi cant increase in O2– genera- tion in the lung compared to Zr. The consumption of antioxidant en- zymes was greater in the Ti than in the Zr group. Conclusion Scientifi c studies are promptly needed to fulfi l gaps like long-term clinical evaluations of all existing zirconia implant systems. Protocols used to design, manufacture and test titanium implants cannot simply apply to produce and evaluate the zirconia ones. Every step, from pro- duction to surgery and prosthetic reconstruction needs to be carefully planned, with respect to the proper- ties of the new material. Accordingly, the advantages of zirconia would be fully benefi cial and the risk of failure could be minimised. Dr Sofi a Karapataki Implant and Periodontal Clinic Adrianeiou 42 11525 Athens, Greece Tel.: +30 210 671138-0 info@skarapataki.gr www.leadingimplantcenters.com Rosenberg et al. (1991) claimed dis- tinct differences between bacterial profi les of infected and overloaded titanium implants.30 The latter were characterised by the absence of mo- tile rods, spirochetes and classical periodontopathogens, along with a predominance of Gram-positive organisms, similar to what is ob- served in periodontal health. These observations were supported by Quirynen and Listgarten in 1990.31 Failures of zirconia implants due to bacteria, should be differentiated against those of technical reasons and the microbiota should be inves- tigated. It should be kept in mind that bacterial cells have a net nega- tive charge on the cell wall, although the magnitude of this charge varies from strain to strain. Especially on the Gram-negative bacteria, LPS as a major component of their cell mem- brane increases even more the nega- tive charge.32 Titanium is also negatively charged, thus acting repulsively to bacteria. This could be one of the reasons of success of titanium implantation in a contaminated environment. Zir- conia though has no electric charge. Depending on the roughness and the hydrophilic surface of every zirconia implant system, contami- nation may be easier to occur and this could be a reason of early fail- ure when zirconia is implanted in a contaminated environment. Studies are needed to clarify whether the lat- ter could affect the osseointegration result and what is the relative danger comparing to titanium. 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