**2.3 Anodic oxidization**

Another type of surface treatment reported in the past is anodic oxidization of titanium implants [39]. It is an electrochemical process wherein an oxide film is produced on a metallic substrate. Anodic oxidization of titanium orthodontic miniscrews produces a titanium dioxide (TiO2) layer on the implant surface with a thickness ranging from 10 to 25 μm increasing from the neck of the implant to the apex (**Figure 5**). Ivanoff et al. conducted some of the first clinical studies to evaluate the effects of anodic oxidization on micro-implant osseointegration [40, 41]. With the help of an optical confocal laser profilometer and histomorphometric analysis, they showed that anodized micro-implants had an increased surface roughness and BSC value as compared to machined micro-implants. Omar et al. investigated the gene expression and cellular reaction around machined and anodized miniscrews in rabbit tibiae at 1, 3 and 6 days [42]. The quantitative polymerase chain reaction (qPCR) and immunohistochemistry results concluded that (i) the rapid recruitment of mesenchymal cells, (ii) the rapid triggering of gene expression crucial for bone remodeling and (iii) the transient nature of inflammation, probably constitute the biological mechanisms for osseointegration and high implant stability associated with anodically oxidized miniscrews. Karmarker et al. reported higher RT values for anodized miniscrews indicating their improved stability [43]. Choi et al. carefully studied the changes in surface roughness and characteristics of anodically oxidized miniscrews [44, 45]. Atomic force microscopy (AFM) revealed that anodized miniscrews had nanotubular open pores and increased roughness on the middle thread edges. Nonetheless, there were no differences in IT or RT

#### **Figure 5.**

*Surface modification by anodic oxidization. (A) Machined surface miniscrew; (B) Anodic oxidized miniscrew. (Taken from: Choi et al. [44].)*

values as well as BSC values of anodized miniscrews when compared to machined miniscrews. Conflicting results from the aforementioned studies suggest that the role of anodic oxidization in enhancing the biomechanical stability of orthodontic miniscrews might yet be questionable.
