Influence of surface modifications to titanium on antibacterial activity in vitro
Introduction
Microbial plaque accumulation surrounding dental implants may develop into peri-implantitis or peri-implantoclasia, which is defined as inflammation or infection around an implant, with accompanying bone loss. It is important to maintain plaque-free surfaces on both supra- and sub-gingival portions of dental implants to prevent peri-implantitis. There are at least two methods of inhibiting the formation of microbial plaque. The first method is to inhibit the initial adhesion of oral bacteria. The second method is to inhibit the colonization of oral bacteria, which involves surface antibacterial activity.
Microbial colonization and antibacterial activity on metallic and ceramic implant materials have been reported under in vitro and in vivo tests [1], [2], [3], [4], [5], [6]. Titanium itself has no antibacterial activity [7], but there is a probable risk of plaque formation on titanium implants [8]. Nevertheless, few experiments have been conducted on the surface modification of titanium implants to inhibit the colonization of oral bacteria [9].
The modified surfaces must resist wear, because these are the parts that are brushed as a means of plaque control. Surface modifications using a dry process have been utilized in the medical and dental fields as suitable methods for providing good resistance to wear as well as creating thin and adhesive fine ceramics [10], [11], [12], [13], [14].
In our previous study [8], the initial adherence of oral bacteria on cp-titanium and surface-modified titanium with a dry process was investigated. The results showed that comparatively large amounts of Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans, which are major periodontopathic bacteria, adhered to polished cp-titanium. These findings indicate that there is a probable risk of bacterial adhesion to titanium surfaces at the supra- and sub-gingival portions of implants, and surface modification to inhibit the adherence of oral bacteria is required. The data showed that some surface modification with a dry process is useful in controlling the initial adhesion of oral bacteria.
It is also required to provide antibacterial activity for maintaining plaque-free surfaces on titanium implants exposed to the oral cavity. The present study was therefore designed to investigate the influence of surface modification to titanium on the colonization of oral bacteria as an index of antibacterial activity in vitro. In addition, this study evaluated the release of fluorine ions and cytotoxicity of the L929 cells on F+-implanted titanium surfaces that exhibited remarkable antibacterial activity.
Section snippets
Preparation of specimens
Commercially pure wrought titanium (cp-Ti) plates (99.9 mass% Ti, 10×10×1 mm) were used as the substrate material for modification. They were ground down to 1200 grit, then polished using 0.3 μm alumina, and finally, ultrasonically cleaned with acetone and distilled water as the control material. The polished titanium surfaces were modified with ion implantation (Ca+, N+, F+), oxidation (anode oxidation, titania spraying), ion plating (TiN, alumina), and ion beam mixing (Ag, Sn, Zn, Pt) with Ar+,
Results
The percentage of CFUs relative to the control against P.g. and A.a. are shown in Fig. 2, Fig. 3, respectively. Analysis of the data via one-way ANOVA revealed significant differences (p<0.01). F+-implanted specimens significantly inhibited the growth of both P.g. and A.a. (p<0.01) than Ti-polished specimen. Other surface-modified specimens did not show any inhibition of the growth of either bacteria.
The concentration of fluorine ions released from F+-implanted specimens in 0.9% NaCl solution
Discussion
It is generally believed that rapid osseointegration with titanium compared with that of other metallic implants is due to the ease with which calcium phosphates and serum proteins are adsorbed on titanium surfaces. This implies, however, that the calcium and pellicle in saliva are adsorbed and form on titanium surfaces, and then, that oral bacteria adhere and colonize on titanium surfaces. This situation leads to the probable risk of plaque formation to titanium implants exposed to the oral
Acknowledgements
This study was supported in part by a Grant-in-Aid for Scientific Research No. 10085839 from The Ministry of Education, Science, Sports and Culture in Japan.
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