The purpose of this study was to evaluate the effect of the pitch of thread on single-tooth implant abutment screw loosening.
First, the dimension of four implant abutment screws(Branemark, Steri-Oss, 1W, 31) was
measured. On the basis of these measurements, experimental models were fabricated by means of milling pure titanium Abutment screws were designed with M 4 X P 03(metric coarse thread screw) and M 4 X P 05(metric fine thread spew) resnectively. Fixtures were mounted in the epoxy resin block and superstructures were constructed.
Implant-superstructure combinations were tightened to the torque of 20 Ncm and 30 Ncm respectively, and then the torque required to loosen the abutment screw was measured with the torque gauge(Model 9 B)G, Tohnichi Mfg. Co., Japan).
To test screw stability under the condition of loading, implant-superstructure combinations were tightened to the torque of 20 Ncm and the load of 6 kgf and 1,000. cycles was applied, and then the torque required to loosen the abutment screw was measured with the torque gauge.
The obtained results were as follows =
1. The dimension of abutment screws of four implant systems was M 2 X P 0.4, that was metric coarse thread screw by KS.
2. When the implant-superstructure combinations were tightened to the torque of 20 Ncm and 30 Ncm respectively, significantly more torque was required to loosen the abutment screw in the metric fine thread screw, in case of 20 Ncm(p<0.05) and 30 Ncm(p<0.01).
3. When the implant-superstructure combinations were tightened to the torque of 20 Ncm and the load of 6 kgf and 1,000 cycles was applied, significantly more torque was required to loosen the abutment screw in the metric fine thread screw(p<0.01).
As a result of this study, significantly more torque was required to loosen the abutment screw in the metric fine thread screw. It seems to mean that the pitch of abutment screw was the effective parameter in the prevention of abutment screw loosening.
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