임플란트 시스템에서 반복풀림조임 후 전기화학적 침식이 파절거동에 미치는 영향

Abstract

Titanium (Ti) and Ti-6Al-4V have been intensively used for dental implant system applications because of excellent mechanical properties, corrosion resistance, and biocompatibility. Dental implant system consists of abutment, abutment screw and implant fixture. The fracture of this implant system can cause significant problems for both clinicians and patients, although it is fortunately rare. Major cause of fractured implant may be a loosening/tightening and stability of abutment screw. The problems of loosening/tightening and stability of abutment screw mainly depend on surface characteristics, like a surface roughness, coating materials and friction resistance and so on. The purpose of this study was to investigate the effects of electrochemical attack on the fracture behavior of implant system after repeated loosening and tightening. In this sturdy, abutment screw, abutment and fixture were used respectively for the experiment. TiN and WC film coating were carried out on the abutment screw using EB-PVD and sputtering, respectively. In order to observe the coating surface of abutment screw after loosening/tightening, each coated abutment was secured to the implant fixture by each abutment screw with recommended torque value using a digital torque controller and was repeatedly delivered and removed by 1 time and 20 times, respectively. The surfaces of specimens were observed by field emission scanning electron microscope(FE-SEM) and energy dispersive x-ray spectroscopy(EDS) at the abutment screw. The electrochemical characteristics of TiN and WC coated abutment screw in implant system was tested by using potentiodynamic and AC impedance tests in 0.9% NaCl solution at 36.5 ± 1℃. After corrosion test of implant system, fracture test was carried out using tensile tester and then the fractured morphology of each sample was investigated by FE-SEM.

1. In the case of TiN and WC coated abutment surface, surface roughness predominantly was improved and machined defects were decreased. After 20 times loosening/tightening, abutment screw surface showed the debris like TiN and WC particles.

2. After corrosion test of loosening/tightening implant system with 20 times, corrosion potential(-350 mV) of implant system used with TiN coated abutment screw showed higher than that of implant system used with non-coated abutment screw(-380 mV) and used with WC coated implant system(- 400 mV).

3. From impedance tests of loosening/tightening implant system with 20 times, the polarization resistance(Rp: 4.01×105 Ω㎠) of implant system used with TiN coated abutment screw showed higher than those of implant system used with non-coated abutment screw(Rp; 3.81×105 Ω㎠) and used with WC coated implant system(Rp; 3.56×105 Ω㎠).

4. From load-displacement test of loosening/tightening implant system with 20 times, compressive force(213 kgf) of implant system used with TiN coated abutment screw showed higher than that of implant system used with non-coated abutment screw(197 kgf) and used with WC coated implant system(196 kgf).

The electrochemical characteristics and mechanical fracture strength of implant system after loosening/tightening depend on surface phenomena and coated materials on the abutment screw surface like a TiN and WC film. Therefore, we can recommend the use of coating materials with low friction coefficient.