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research | Properties Grade 1 Grade 2 Grade 3 Grade 4 Grade 5 Ti-13Nb-13Zr (Ti-6Al-4V) Tensile strength (MPa) 240 Yield strength (0.2 % offset; MPa) 170 Elongation (%) Reduction of area (%) 24 30 345 275 20 30 450 380 18 30 550 485 15 25 860 795 10 25 1,030 900 15 45 Table 1 spite of Ti’s excellent biocompatibility, allergy to this metal can still be observed in dental implant pa- tients, although its prevalence is very low (0.6 %).14 Some authors still recommend a metal allergy test for patients with previous hypersensitivity of any kind.15, 16 While we have no gold standard test for detecting Ti allergy, dermal patch tests or in vitro blood tests such as the lymphocyte transformation test or the memory lymphocyte immunostimulation assay (MELISA®) are frequently used methods, even if the results are often ambiguous.17 It must be added that Ti exposure from personal care products and biomedical implants is common, and still there is no reliable evidence for actual toxicity or true allergic reactions. Furthermore, according to a review by Javed et al., Ti per se cannot be identified as a cause of allergic reactions in patients with dental implants.18 In their opinion, it is the occasional and otherwise negligible impurities (i.e. additional elements besides Ti) that trigger hypersensitivity reactions.18 Harloff et al. ex- amined common dental implant materials (Grade 1 Ti and Ti alloys, including Grade 5) by spectral analy- sis.19 Their results showed that all the investigated materials contained low but detectable amounts of various other elements (nickel, chromium, copper, palladium, manganese) that may induce allergic reactions, especially in people with existing metal sensitivity. Since it is quite rare for a patient’s metal allergy to be diagnosed first upon implant placement, failure due to hypersensitivity can be avoided by careful his- tory taking. However, it can happen that the patient denies knowledge of any metal allergy and an allergic reaction occurs nevertheless. The appearance of a rash, urticaria, oedema, mucosal erythema, swelling, or hyperplastic lesions of the soft tissue after implant placement indicates an allergic reaction.20 In these cases, a corrosion process is occurring in which ions released from the surface form active complexes with proteins and trigger the characteristic reactions.21 Such cases, however, are rare, and Ti implants for prosthodontic purposes can be considered safe and reliable for the general population. Dental implant surface modifications Tab. 1: Mechanical properties of titanium and its alloys.5 Bulk properties, such as corrosion resistance and modulus of elasticity, which determine the selection of the appropriate biomaterial for the relevant biomedi- cal application, are important for implant success. However, surface properties also play a significant role. First of all, the geometric configuration of the im- plant should be designed to achieve an extensive bone–implant contact area for faster osseointegra- tion. This in itself, however, is not sufficient. During osseointegration, the outermost layers of the implant interact with the host tissues and cells. Therefore, de- veloping surfaces that enable a shorter healing time and optimal connection between the biomaterial and the surrounding bone is a major focus of research. In order to achieve that goal, various surface treat- ments have been developed, generally classified into two major categories: physicochemical and bio- chemical. A common feature of these treatments is that they leave the bulk properties unchanged and modify only certain target properties of the surface, such as its roughness or chemical composition.22–24 Here, we give a brief summary of these methods and their resulting surfaces and discuss the sandblasted, large-grit, acid-etched (SLA) method that combines two physicochemical methods. Physicochemical methods Physicochemical methods are usually used to in- crease the implant’s surface roughness. Rougher surfaces yield better bone response and higher bone quality than machined/turned surfaces, as demon- strated by histomorphometric studies.25–27 Wenner- berg and Albrektsson classified surfaces according to their roughness (Sa) as follows: smooth (Sa < 0.5 µm), minimally rough (Sa = 0.5–1 µm), moderately rough (Sa > 1–2 µm) and rough (Sa > 2 µm); and concluded that moderately rough surfaces (such as SLA, de- tailed later) show the most favourable bone re- sponses.28 The most widely used physicochemical surface treatments are sandblasting, ion implanta- tion, laser ablation, covering with inorganic calcium phosphates and purely chemical methods, like oxida- tion and acid etching.24 implants 4 2017 07