Examination of the implant-abutment interface after fatigue testing

Purpose. This study examined potential differences in detorque values of abutment screws after fatigue testing when the dimensions between external implant hexagon and internal abutment hexagon were altered or the implant external hexagonal shape was eliminated. Material and methods. Three subsets (N = 10) of NobelBiocare implants were assessed: (1) standard external hexagon (R), (2) modified hexagon (M), and (3) circular (C) platform geometry. Thirty Procera machined abutments with 25-degree angulated loading platforms were manufactured. Abutments were retained with gold Unigrip abutment screws tightened to 32 N/cm with an electronic torque controller. Vertical scribes across the implant-abutment interface allowed longitudinal displacement evaluation. A carousel-type fatigue testing device delivered dynamic loading forces between 20 and 200 N for 5,000,000 cycles, or the approximate equivalent of 5 years in vivo mastication, through a piston to the abutment platform. Macroscopic and radiographic examination of the implant/abutment specimens was performed. The abutment screws were removed and the detorque values recorded. Bearing surfaces were examined microscopically. Results. No abutment looseness or longitudinal displacements at the implant-abutment interface were noted. Radiographic examination demonstrated no indication of screw bending or displacement. The mean detorque values for R, M, and C were 14.40 ± 1.84 N/cm, 14.70 ± 1.89 N/cm, and 16.40 ± 2.17 N/cm, respectively. The analysis of variance demonstrated significant differences between only designs R and C (P=.031). Conclusion. Increasing the vertical height, or degree of fit tolerance, between the implant external hexagon and the abutment internal hexagon or completely eliminating the implant external hexagon did not produce a significant effect on the detorque values of the abutment screws after 5,000,000 cycles in fatigue testing, or the equivalent of 5 years' of mastication for the implant/abutment specimens evaluated. (J Prosthet Dent 2001;85:268-75.).