Stability of implant-abutment interface with a hexagon-mediated butt joint: failure mode and bending resistance.

BACKGROUND Clinical data showed that the external hexagon implant system with a gold abutment screw has reduced the problem of screw loosening or fracture. However, the behavior of the implant-abutment joint components with respect to unfavorable bending force is still unclear. PURPOSE This study investigated the joint instability and bending resistance of a single-tooth external hexagon implant system after lateral cyclic loading. MATERIALS AND METHODS Fifteen implant assemblies (Nobel Biocare, Göteborg, Sweden) were divided equally into three groups: A, B, and C. Each assembly consisted of a Brånemark System Mk IV implant (4 x 10 mm) mounted in a brass block, a CeraOne abutment (3 mm), and an experimental cement-retained superstructure. For group A, a centric lateral cyclic load of 50 N was applied for 1.0 x 10(6), whereas for group B, the same load was eccentrically applied for 1.0 x 10(6) cycles. Group C, the control, was not loaded. After cyclic loading, specimens were mounted in a universal testing machine, and the yield and bending strengths were measured (kg). The external hexagon surface texture was examined using a secondary electron microscope. The data were analyzed with one-way analysis of variance and compared by the Tukey test (alpha = .05). RESULTS For all test specimens, the abutment screw was plastically bent in the unthreaded portion. Group B had a significantly lower mean yield and bending strengths than group C (p = .005 and .010, respectively). Post-cyclic loading photographs showed that group B implants had marked burnishing around the hexagon corners. The bending force abraded both corner areas of the hexagon surface but left the middle area nearly intact for all tested groups. However, group B had the significantly lowest mean abraded area. CONCLUSION Within the limits of this study, eccentric rather than centric lateral cyclic loading negatively affected the resistance of the implant-abutment joint to static bending.

[1]  J I Nicholls,et al.  Implant-abutment screw joint preload of 7 hex-top abutment systems. , 2001, The International journal of oral & maxillofacial implants.

[2]  I Herrmann,et al.  Osseointegrated implants for single-tooth replacement: a prospective 5-year multicenter study. , 1996, The International journal of oral & maxillofacial implants.

[3]  P. Krogh,et al.  Osseointegrated implants for single-tooth replacement: progress report from a multicenter prospective study after 3 years. , 1994, The International journal of oral & maxillofacial implants.

[4]  I Herrmann,et al.  Osseointegrated implants for single tooth replacement: a 1-year report from a multicenter prospective study. , 1991, The International journal of oral & maxillofacial implants.

[5]  T Jemt,et al.  3-year followup study of early single implant restorations ad modum Brånemark. , 1990, The International journal of periodontics & restorative dentistry.

[6]  P P Binon,et al.  The effect of eliminating implant/abutment rotational misfit on screw joint stability. , 1996, The International journal of prosthodontics.

[7]  Akihiko Hashimoto,et al.  Effect of lateral cyclic loading on abutment screw loosening of an external hexagon implant system. , 2004, The Journal of prosthetic dentistry.

[8]  Ameen Khraisat,et al.  Fatigue resistance of two implant/abutment joint designs. , 2002, The Journal of prosthetic dentistry.

[9]  A. Khraisat,et al.  Abutment screw loosening and bending resistance of external hexagon implant system after lateral cyclic loading. , 2004, Clinical implant dentistry and related research.

[10]  P Lockowandt,et al.  Comparison of strength and failure mode of seven implant systems: an in vitro test. , 1997, The Journal of prosthetic dentistry.

[11]  S Toreskog,et al.  A 5-year multicenter study on implant-supported single crown restorations. , 1998, The International journal of oral & maxillofacial implants.

[12]  P. Branemark,et al.  Cemented single crowns on osseointegrated implants after 5 years: results from a prospective study on CeraOne. , 1998, The International journal of prosthodontics.

[13]  U. Belser,et al.  Mechanics of the implant-abutment connection: an 8-degree taper compared to a butt joint connection. , 2000, The International journal of oral & maxillofacial implants.

[14]  D L Dixon,et al.  Comparison of screw loosening, rotation, and deflection among three implant designs. , 1995, The Journal of prosthetic dentistry.

[15]  D L Dixon,et al.  Torque required to loosen single-tooth implant abutment screws before and after simulated function. , 1993, The International journal of prosthodontics.

[16]  T Jemt,et al.  A 3-year follow-up study on single implant treatment. , 1993, Journal of dentistry.

[17]  J. Kaukinen,et al.  The influence of occlusal design on simulated masticatory forces transferred to implant-retained prostheses and supporting bone. , 1996, The Journal of prosthetic dentistry.

[18]  T Jemt,et al.  Loads and designs of screw joints for single crowns supported by osseointegrated implants. , 1992, The International journal of oral & maxillofacial implants.