Dental Materials Journal 25（4）：684－692, 2006 Plasma-based Fluorine Ion Implantation into Dental Materials for Inhibition of Bacterial Adhesion NURHAERANI, Kenji ARITA, Yukari SHINONAGA and Mizuho NISHINO Department of Pediatric Dentistry, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15, Kuramoto, Tokushima 770-8504, Japan Corresponding author, Kenji ARITA E-mail :[email protected] Received July 28, 2006/Accepted September 12, 2006 ―――――――――――――――――――――――――――――――――――――――――――――――――――――― The aims of this study were to evaluate the fluorine depth profiles of pure titanium （Ti）, stainless steel （SUS）, and polymethyl methacrylate（PMMA）modified by plasma-based fluorine ion implantation and the effects of fluorine ion im- plantation on contact angle, fluoride ion release, and S. mutans adhesion. Fluorine-based gases used were Ar＋F2 and CF4. By means of SIMS, it was found that the peak count of PMMA was the lowest while that of Ti was the highest. Then, up to one minute after Ar sputtering, the presence of fluorine and chromic fluoride could be detected by XPS in the surface and subsurface layer. As for the effects of using CF4 gas for fluorine ion implantation into SUS substrate, the results were: contact angle was significantly increased; no fluoride ion release was detected; antibacterial activity was significantly in- creased while initial adhesion was decreased. These findings thus indicated that plasma-based fluorine ion implantation into SUS with CF4 gas provided surface antibacterial activity which was useful in inhibiting bacterial adhesion. Key words : Ion implantation, Fluorine, Bacterial adhesion ―――――――――――――――――――――――――――――――――――――――――――――――――――――― analysis, no beam-transport optics, and no focusing INTRODUCTION or scanning of the beam14）. Therefore, compared to In a dental clinic, various kinds of appliances － such conventional ion implantation, the plasma-based ion as space maintainer and space regainer for occlusal implantation facility is smaller, less expensive, and guidance, and also as orthodontic appliances and den- simpler to maintain and operate13－17）. tures － are used frequently for children and adults. To date, some researchers have carried out sur- These appliances are susceptible to adhesion by oral face modification by fluorine ion implantation18－20） bacteria1－6）, and thus cause dental caries7,8）, periodon- and found it to be a useful means in inhibiting bacte- tal disease, or inflammation of oral soft tissue9,10）. rial adhesion. In this study, therefore, the surfaces Plasma surface modification, as an economical of Ti, SUS, and PMMA were modified by plasma- and effective material processing technique, is gain- based fluorine ion implantation to evaluate this ing popularity in the biomedical field. It is able to technique’s inhibitory effect against oral bacterial ad- change the surface chemical composition of the proc- hesion. It should be highlighted that bacterial adhe- essed material as well as improve the latter’s proper- sion to biomaterial surface is an important step dur- ties such as wettability, adhesion, dyeability, refrac- ing the initial stages of pathogenic infection. Two tive index, hardness, chemical inertness, lubricity, methods have been identified to inhibit the formation and biocompatibility11）. As such, in recent years, of microbial plaque. The first method is to inhibit there is an increasing trend to employ plasma-based the initial adhesion of oral bacteria, while the second ion implantation to modify the surface of method involves surface antibacterial activity to in- biomaterials12,13）. With plasma-based ion implanta- hibit the colonization of oral bacteria21,22）. tion, specimens are immersed in high-density plasma In view of the beneficial effects of fluorine ion and pulse-biased to a high negative potential relative implantation, the aims of this study were to evaluate to the chamber wall. Ions generated in the overlying the depth profiles and XPS spectra of fluorine con- plasma are accelerated across the sheath formed centration in the surface of dental materials, as well around the sample and implanted into the sample as evaluate the effects of fluorine ion implantation surface. However, in the event of ditch contours and on contact angle, fluoride ion release, and bacterial concave corners, it becomes difficult for the sheath to adhesion. follow the surface contour of the complex shape. Moreover, in the event of non-uniform plasma den- MATERIALS AND METHODS sity distribution around the matrix, it also becomes difficult to achieve uniform ion implantation on the Plasma-based fluorine ion implantation whole surface. Nonetheless, despite the aforemen- The principle of plasma-based ion implantation is tioned drawbacks, this technique features non-mass shown in Fig. 1 （modified from Okui et al.23））. NURHAERANI et al. 685 Plates of Ti（TP340C: 99.98 wt％ Ti, 0.003 wt％ H, X-ray photoelectron spectroscopy（XPS） 0.09 wt％ O, 0.01 wt％ N, 0.07 wt％ Fe; Kobe Steel After fluorine ion implantation using CF4 gas, the Ltd., Kobe, Japan）, SUS （SUS316L: 65.67 wt％ Fe, surface of SUS was analyzed by means of X-ray pho- 17.00 wt％ Cr, 13.00 wt％ Ni, 2.40 wt％ Mo, 1.40 wt％ toelectron spectroscopy （XPS）（ESCA-1000AX, Mn, 0.03 wt％ C, 0.50 wt％ Si; Daido Steel Co. Ltd., Shimadzu Co., Kyoto, Japan）. Measurements were Nagoya, Japan）, and PMMA （ACRYPET VH＃001, done using Mg Kα X-rays at 30 mA and 10 keV. Mitsubishi Rayon Co. Ltd., Tokyo, Japan）with size Depth profile analysis was performed using Ar gas of 10×10×1 mm were used. Before ion implantation, sputter method under these conditions: 20 mA cur- Ti and SUS plates were polished to a mirror-like sur- rent, 2 keV voltage, and gas pressure of 5×10－4 Pa. face and washed in an ultrasonic bath with 98％ alco- Sputtering speed was 20Å（SiO2）/min. Binding en- hol. PMMA plates were wiped with alcohol-soaked ergies were corrected against that of C 1s, an inter- cotton. Ti, SUS, and PMMA plates were then modi- nal standard with binding energy at 285.0 eV. fied by plasma-based ion implantation appliance at Ion Engineering Research Institute Co., Osaka, Contact angle Japan. Fluorine gas for plasma-based ion implanta- After fluorine ion implantation by CF4 gas, the sur- tion was 95％ argon and 5％ F2（Ar＋F2）or CF4 gas. face of SUS was washed in an ultrasonic bath（J.M. Conditions of plasma-based fluorine ion implantation Ultrasonic Cleaner SUW-50D, J. Morita Co., Tokyo, are shown in Table 1. For controls, non-fluorine-ion- Japan） containing distilled water for 10 minutes. implanted Ti, SUS, and PMMA were used. After the washing procedure, the sample was dried at room temperature. Secondary ion mass spectrometry（SIMS） A drop of distilled water was carefully placed on The peak count（count per second, CPS）and depth each slightly dried, prepared surface, and contact profile until 10 counts（nm）of fluorine in Ti, SUS, angle was measured using the sessile drop technique and PMMA samples were measured with a secondary with a contact angle meter （CA-DT, Kyowa ion mass spectrometer （SIMS）（ADEPT 1010, Kaimenkagaku Co. Ltd., Saitama, Japan）. Five ULVAC Inc., Kanagawa, Japan）. Measurements points per sample were measured. A total number of were carried out using 3.0 keV Cs＋. For each mate- 10 samples were prepared for fluorine ion implanta- rial, a total of eight samples were prepared for fluo- tion（i.e., N＝5）and to serve as controls with no ion rine ion implantation by Ar＋F2 gas（i.e., N＝4）and implantation（i.e., N＝5）. CF4 gas（i.e., N＝4）. Fluoride ion release Five SUS samples which were fluorine ion-implanted by CF4 gas were immersed in 10 ml of deionized water in a petri dish and shaken with a speed of 110 rpm （Double Shaker NR-3, Taitec Co., Saitama, Japan）at 37℃. The deionized water was changed every 24 hours and evaluated for fluoride ion concen- tration in ppm daily for a period of seven days. The immersion solution was kept at room temperature before fluoride ion concentration was measured. To provide a constant background ionic strength, 0.8 ml of total ionic strength adjustment buffer solution （TISABШ, Thermo Electron Co., Beverly, MA, USA） was added to 8 ml of immersion solution. Fluoride ion concentration（ppm）was then measured with an ion specific electrode （ionplus Sure-Flow Fluoride, 9609 BN, Orion Research Inc., Beverly, MA, USA） Fig. 1 Principle of plasma-based ion implantation（modi- connected to an expandable ion analyzer （model 23） fied from Okui et al. ）. 702A, Orion Research Inc., Beverly, MA, USA）. Table 1 Conditions of fluorine ion implantation into surface of dental materials Gas Ar＋F2 （95％ argon and 5％ fluorine） CF4 （100％ carbon tetrafluoride） Pressure of gas 1.0 Pa Negative electric charge 1000 Hz, 10μs Time 60 minutes Voltage 5 keV（Ti, SUS）, 3 keV（PMMA） 686 FLUORINE ION IMPLANTATION IN DENTAL MATERIALS Calibration of the analyzer was performed before the PMMA（p＜0.05 and p＜0.001, respectively）, and SUS test with standard solutions containing 0.1, 0.5, and to be higher than PMMA（p＜0.001）. Similarly, with 1.0 ppm of fluoride. CF4, the peak count of Ti was higher than that of SUS and PMMA （p＜0.001）, and SUS was higher Microbiological examination than PMMA（p＜0.001）. S. mutans（ATCC25175 type c, Summit Pharmaceuti- Fig. 3 shows the depth profiles until 10 counts of cals International Co., Tokyo, Japan）was used for fluorine after ion implantation（N＝4）. As shown, it the evaluation of bacterial adhesion and antibacterial was only in PMMA that CF4 led to a significantly activity. Substrate material was SUS which was higher depth profile than Ar＋F2 （p＜0.001）. With fluorine ion-implanted by CF4 gas. Ar＋F2 as a fluorine-based gas for ion implantation, Ti had a significantly higher depth profile than Antibacterial activity PMMA and SUS（p＜0.001 and p＜0.05, respectively）.