ABSTRACT
STATEMENT OF PROBLEM: Wear as a result of repeated closing/opening cycles may decrease the friction coefficient of screw head, threads, and other mating components and, consequently, resistance to opening gradually decreases. It may cause screw loosening, which is one of the most common failures in implant prosthesis. PURPOSE: The purpose of this study is to evaluate the changes on the head and thread surface of the abutment screws after repeated closing and opening through the examination of tested screws in SEM(scanning electron microscope). MATERIALS AND METHODS: Five species of abutments were selected (3i-three, Avana- two) respectively by two pieces. The implant fixtures were perpendicularly mounted in liquid unsaturated polyesther(Epovia, Cray Valley Inc.) with dental surveyor. Each abutment was secured to the implant fixture by each abutment screw with recommended torque value using a digital torque controller. The abutment screws were repeatedly tightened and removed 20 times with a digital controller. FESEM (field emission scanning electron microscope, Netherland, Phillips co., model:XL 30 SFEG) was used to observe changes of each part caused by repeatedly closing/opening expeiment. First, the Photomicrographs of pre-test screws provided by each manufacturer were taken. The changes of each screw were investigated after every fifth closing and opening experiment with FESEM. Scaning electron microscope photomicrographs of each screw were taken four times. RESULTS: As the number of closing and opening was increased, the wear or distortion of hexed or squared slot that contacted with the driver tip was more severely progressed. Wear or distortion of hexed slot was more severe than that of squared slot and it was more remarkable in the titanium screw than in the gold screw. All the tested screws showed that the width in the crest of their screw thread decreased gradually as the test was proceeded. CONCLUSIONS: Conclusively, we recommend the clinical use of gold screw, a periodic exchanges of abutment screws and avoiding repeated closing/opening unnecessarily. We also suggest a more careful manipulation of the abutment screw and screw-driver and using of abutment screw with an acute-angled slot design rather than an obtuse-angled one. Finally, it is suggested that the new slot design and the surface treatment for enduring wear or distortion should be devised.
Subject(s)
Friction , Head , Prostheses and Implants , Titanium , TorqueABSTRACT
STATEMENT OF PROBLEM: Regardless of any restoration, most of case, we used in screw connection between abutment and implant. For this reason, implant screw loosening has been remained problem in restorative practices. PURPOSE: The purpose of this study was to compare surface of coated/plated screw with titanium and gold alloy screw and to evaluate physical property of coated/plated material after scratch test in FESEM investigation. MATERIAL AND METHODS: GoldTite, titanium screw provided by 3i (Implant Innovation, USA) and TorqTite, titanium screw by Steri-Oss (Nobel Biocare, USA) and gold screw, titanium screw by AVANA (Osstem Implant, korea) - were selected for this study. Each abutment screw surface was observed at 100 times, and then screw crest, root, and slope were done more detailed numerical value, at 1000 times with FESEM. A micro-diamond needle was also prepared for the scratch test. Each abutment screw was fixed, micro-diamond scratch the surface of head region was made at constant load and then was observed central region and periphery of fine trace through 1000 times with FESEM. RESULTS: The surface of GoldTite was smoother than that of other kinds of screw and had abundant ductility and malleability compared with titanium and gold screw. The scratch test also showed that teflon particles were exfoliated easily in screw coated with teflon. Titanium screw had a rough surface and low ductility. CONCLUSION: It was recommended that the clinical use of gold-plated screw would prevent a screw from loosening.
Subject(s)
Alloys , Head , Needles , Polytetrafluoroethylene , TitaniumABSTRACT
STATEMETN OF PROBLEM: Surface alteration of the implant screws after function may be asso-ciated with mechanical failure. Theses metal fatigue appears to be the most common cause of structural failure. PURPOSE: The purpose of this study was to evaluate surface alteration of the implant screws after function through the examination of used and unused implant screws in SEM(scanningelectron microscope). MATERIAL AND METHODS: In this study, abutment screws(Steri-oss, 3i), gold retaining screw(3i) and titanium retaining screw(3i) were retrieved from patients. New, unused abutment and retain-ing screws were prepared for control group. Each of the old, used screws was retrieved with a screwdriver. And retrieved implant complex of Steri-oss system was prepared for this study. Then, SEM investigation and EDS analysis of abutment and retaining screws were per-formed. And SEM investigation of cross-sectioned sample of retrieved implant complex was performed. RESULTS: In the case of new, unused implant screws, as maunfactured circumferential grooves are regularly examined and screw thread are sharply remained. Before ultrasonic cleans-ing of old, used implant screw, a lot of accumulation and corrosion products were existed. After ultrasonic cleansing of old, used implant screws, circumferential grooves as examined before function were randomly deepened and scratches increased. Also, dull screw thread was examined. More surface alterations after function were examined in titanium screw than gold screw. And more surface alteration was examined when retrieved with driver than retrieved without driver. CONCLUSIONS: These surface alteration after function may result in the screw instability. Regularly cleansing and exchange of screws was recommended. We recommend the use of gold screw rather than titanium screw, and careful manipulation of the driver.