The Anti-rotational Ability of Conical Implant-abutment Connections

Objectives: Conical connections are popular due to proper stability in implant-abutment connections. However, the shape of the cross-section of conical connections is round, and the anti-rotational ability is questionable because restorations in the oral cavity have to process twisting moments resulting from regular chewing patterns. The purpose of this study was to investigate the anti-rotational ability of conical implant-abutment connections under different loading conditions. Methods: Conical connection implant system (Cowell Medi, Busan, South Korea) was selected. All samples were divided into two groups (n=5) and respectively subjected to two kinds of cyclic loading, a 90-degree off-axis loading of 10~100 N (Group A) and a 30-degree off-axis loading of 20~200 N (Group B). Both were applied eccentrically 4mm right to the center of the crown and 10.5mm above the platform of the implant. Therefore, both generated the same bending and torsional moments, but the latter got an axial loading more. The loading rate was 10 Hz, and10⁶ cycles were applied. Then the number of cycles to fatigue was recorded and data were analyzed by t-test. Results: In Group A, all abutments generated rotation within 150 cycles. While, in Group B, all samples passed the fatigue test (10⁶ cycles). There was a statistically significant difference between these two groups (p<0.001). Conclusions: In Cowell implant system, there was no anti-rotational ability in purely conical connections under torsional and bending moments. However, adding an axial loading could improve their anti-rotational ability significantly. Therefore, an axial loading might plays an important role in the anti-rotational ability of conical connections.