The Potential Risk of Conical Implant-Abutment Connections: The Antirotational Ability of Cowell Implant System

Background: Conical implant-abutment connections are popular because of good antibending performance. However, the cross section is round, and the antirotational ability is questionable because restorations in the oral cavity also have to bear torsional moments resulting from chewing patterns. Purpose: The purpose of this study was to investigate the antirotational ability of conical implant-abutment connections with and without an index. Materials and Methods: Conical connection implant system (Cowell Medi, Busan, South Korea) was selected. Two kinds of cyclic loading, a bending moment with (C) and without (L) a torsional moment, were respectively applied to two kinds of abutments, pure cone (N-Octa) and cone with an octagonal index (Octa). The number of cycles to fatigue and the failure modes was recorded. Morphologies of the abutments were examined with scanning electron microscopy. Results: Only group C(N-Octa) passed the fatigue test, whereas the other three groups failed because of different failure modes. In group L(N-Octa), all abutments generated rotation within 150 cycles. In groups C(Octa) and L(Octa), all abutments fractured but in different areas. Conclusions: In Cowell implant system (taper angle=7°), there was no antirotational ability in purely conical connections. Adding an octagonal index could provide an antirotational function but could compromise the antibending strength of the abutment.