抄録
Purpose: Long-term implant patients often experience loose or fractured prosthetic screws. Our previous study using geometric analysis clarified the effects of occlusal load on prosthetic screws. However, the values obtained from geometric analysis are theoretical. For this study, implant superstructures were manufactured and the maximum loading at which the prosthetic screw actually fractured was measured to examine the correlation with the geometric analyses made in our previous study.
Method: The theoretical maximum loading was obtained using the formula and fracture resistance (1,104 ±10 N) of the prosthetic screws obtained in our previous study. To obtain the actual maximum loading, five superstructures were manufactured on an abutment replica using a CAD/CAM system, and tested with a universal testing machine at a crosshead speed of 1.0 mm/sec. The theoretical value was compared with the actual values from those tests.
Results: The actual maximum loading (236±10 N on average) was significantly lower (p<0.01) than the theoretical maximum loading (271±4 N on average) obtained by geometric analysis. While each specimen is under load, the platform's outermost part, which serves as the pivot point of rotation, undergoes a displacement of 0.15 mm due to the deformed edge of the superstructure. The theoretical value (250±3 N) obtained by taking into account the displacement of the pivot point was not significantly different from the actual value (p>0.01) .
Conclusion: It is suggested that when determining the maximum loading of prosthetic screws using geometric analysis, it is necessary to consider the displacement of the pivot point of rotation, which will also make the geometric analysis more relevant.