Development of non-loosening abutment screw for implant

Objectives:

Screw loosening is one of major troubles on implant treatment. Therefore we developed non-loosening abutment screw “Spring-Bolt”. It seems that the Spring-Bolt is useful for fixing super-structure to implant. However there is a concern that the Spring-Bolt might have bad influences on internal thread in implant body because of its strong friction. In this study, the effects of Spring-Bolt for internal thread in implant body were investigated.

Methods:

New abutment screw with special designed thread (Spring-Bolt) was developed. Co-Cr and pure titanium Spring-Bolt were used for this study. Two types of pure titanium implant body (grade II and grade IV pure titanium, Japanese Industrial Standard) were prepared. Each Spring-Bolt was fastened to implant body once and removed. The surface of Spring-Bolt and internal thread in implant body was observed by scanning electron microscope.

Results:

The Co-Cr and titanium Spring-bolt were examined by scanning electron microscopy after the bolts were fastened to the implant bodies and removed. There were no changes in either type of Spring-Bolt after removed from implant body. However, there were obvious changes in internal thread of implant body which were fastened with Co-Cr Spring-Bolt. The scratch and deformation of thread were observed on internal thread. More remarkable influences were observed in grade II implants than grade IV implant. There are little scratches and deformation in the combination of titanium Spring-Bolt and grade IV titanium implant.

Conclusion:

The clinical use of Spring-Bolt must be careful, because it is possible that the deformation of internal thread in implant body causes severe trouble. However, It is suggested that the clinical application of titanium Spring-Bolt is possible on implant treatment as non-loosening abutment screw, because there are little scratch on internal thread with titanium Spring Bolt.