The Effect of WC Tungsten Carbide Coating for Abutment Screw on

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					                                                                                      The Effect of WC(Tungsten-Carbide) Coating for     Thesis
                                                                                          Abutment Screw on Reliability of Connection




12         The Effect of WC(Tungsten-Carbide) Coating for
           Abutment Screw on Reliability of Connection


   Kwang-Hoon Kim1, Chang-Mo Jeong2, Ji-Hoon Yoon3

   1,3
        Osstem R&D Center, Busan, Korea
   2
       The Department of Prosthodontics ,Pusan National University Hospital, Busan, Korea




Introduction
   A common problem associated with dental implant restorations is screw loosening by loss of preload. Many efforts to reduce
screw loosening have been made by clinicians and implant manufacturers. Recently, it has been introduced that abutment screws
with treated surfaces to increase preload by reducing the fiction coefficient.
   The aim of this study is to evaluate the influence of WC coating Ti abutment screw on joint stability compare to non-coating Ti
abutment screw.


Material & Methods
   In this study, we used Osstem(Korea) GS assembly with 11             internal conical joint design. Tightening Torque of each assembly
(n=5) was 30Ncm. Preload was measured by angle rotation method and compressive force sensor.


                                                    [Fig. 1] Measurement of Rotation Angle




                 WC coating screw         Rotation Angle test System (Rotary encoder: Autonics, Korea)            Ti screw



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      Chapter 6   Clinical and Experimental Thesis




                                                       [Fig. 2] Measurement of Preload




                                Schematic Diagram                             Preload Test System
                                  of Test System                  (Force Sensor 9132B21: KISTER, Switzerland)




         To confirm the influence of                                                     [Fig. 3] Cyclic fatigue loading

    reliability of connection according to a
    preload increase, each assembly (n=5)
    was loaded by step loading
    device(205N, 30             , 1Hz, 1.0E6
    Cycles). Removal Torque(RT) was
    recorded before and after loading. The
    data was verified by T-Test.                          Schematic Diagram of Testing Condition                       Cyclic Loading System
                                                                                                                      (8516, Instron corp, USA)




    Results

         WC coating screw showed higher preload than
    non-coating screw. (P<0.05),                                         [Table 1] Rotation Angle & Preload under TT of 30Ncm

                                                                                                          Non-Coating Screw         WC Coating Screw

                                                                           Rotation Angle [degree]              28     1.8               39       1.5
                                                                                 Preload [N]                    267     27               350      21




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                                                                              The Effect of WC(Tungsten-Carbide) Coating for               Thesis
                                                                                  Abutment Screw on Reliability of Connection




   WC coating screw showed smaller change rate                     [Table 2] Comparison of Removal Torque after Cyclic loading

of RT than that of non-coating Screw on                                                         Non-Coating Screw      WC Coating Screw

reliability of connection. (P<0.05),                                Tightening Torque [Ncm]            28   1.8                39       1.5
                                                                     Removal Torque [Ncm]         Initial    After        Initial          After
                                                                                               24.7 1.8 19.8 2.1       24.9 1.5 22.7 1.9




Conclusion

   This study indicated that the WC coating screw produced greater value of rotation angles and preload than that of non-coating
screw. As a result, WC coating screw showed smaller change rate of RT value than non-coating screw after cyclic fatigue loading.
Conclusively, WC coating screw seems to be very useful for reducing the coefficient of friction and contribute to the prevention of
screw loosening.




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posted:3/23/2011
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