# Micro-Raman Spectroscopy of Dental Implants Subjected to Different Surface Treatments
## 1 Introduction  
From [PERSON]'s initial studies, titanium represents the most-used material, although not the only one, for the production of endosseous dental implants [1; 2; 3]. Success rates with titanium implants are high in both the short and long term; moreover, they are indicated in many particular situations [4; 5; 6; 7; 8; 9; 10]. The native very thin (\(<\)10 nm) oxide layer of TiO\({}_{2}\) gives features of exceptional biocompatibility to titanium [11; 12; 13; 14]. Moreover, Ti and its alloys possess mechanical and chemical properties that make them ideal implant materials [15]. Commercially, pure titanium is classified into four grades by its stoichiometric composition, with grade one having the least (0.18%) and grade four having the most (0.4%); in addition, grade five titanium alloy (Ti-6 Al-4V) is also used for commercially available dental implants [16; 17]. Due to the presence of minimal quantities of contaminants, mechanical features of resistance increase from grade one to grade five [16; 18]. Amorphous titanium oxide forms during normal ambient conditions on Ti; moreover, in nature, three crystalline phases of titanium dioxide exist, namely anatase, rutile and brookite; the latter is rarely found because of its metastable crystal structure [19; 20]. Through the application of an appropriate heat treatment, amorphous TiO\({}_{2}\) transforms to the anatase, thanks to its lower surface free energy compared to rutile, and then to the rutile phases. The anatase phase completely transforms into the rutile phase at 680 \({}^{\circ}\)C [20]. To obtain rutile at low temperatures, precipitation of crystalline TiO\({}_{2}\) and hydrothermal methods are needed [21]. The biological effects of the morphological characteristics of the implant surfaces have been thoroughly investigated [17; 22], while little information concerns the influence of the different polymorphic crystalline phases of TiO\({}_{2}\) on osseointegration. The crystalline phase of TiO\({}_{2}\) can influence bioactivity. Crystalline TiO\({}_{2}\) appears to favor apatite deposition [13; 23; 24; 25]. Anatase coating enhanced osseointegration in in-vivo studies in rabbits [26; 27] and reduced marginal bone loss in humans [28]. Moreover, the anatase-coated surfaces proved to be more sensitive to UV light and showed a greater photocatalytic effect [29]. Recent studies have also shown that bacterial flora can be influenced by the titanium surface structure. Anatase exposed to near-UV light demonstrated a strong bactericidal effect [30; 31]. Anatase-coated titanium surfaces significantly reduced the presence of bacteria on the subgingival and screw-threaded portion of healing screws in humans [32], but, recently, in a small-sample-size and short-term study in humans, antibacterial features of anatase-coated implant collars were only partially confirmed [28]. Literature on the relation between surface treatment and superficial oxide layer structure is scarce. Most clinical titanium implants have thin surface oxides and can therefore be expected to have essentially amorphous surface oxides. As the oxides' thickness increases, a crystalline structure becomes possible [12]. Anodic oxidation (anodization) and thermal treatment demonstrated the ability to form a crystalline layer of TiO\({}_{2}\) on commercial pure and alloy titanium surface [27; 33; 34; 35]. Recently, anatase was clearly identified in two commercially available implants, with an anodizing surface treatment. The remaining surfaces (machined, acid-etched, blasted or plasma-sprayed) presented spectra that can be fitted only weakly or moderately to the rutile and/or amorphous TiO\({}_{2}\) spectra. Moreover, this study does not disclose the alloy composition of each implant analyzed [36]. Another study on commercially available implants evaluated the structure of TiO\({}_{2}\) by TEM. This study identified anatase on anodized and on blasted and acid-etched surfaces and rutile on machined surfaces [37].