Measurement of the Rotational Misfit and Implant-Abutment Gap of All-Ceramic Abutments

Purpose: The specific aims of this study were to measure the implant and abutment hexagonal dimensions, to measure the rotational misfit between implant and abutments, and to correlate the dimension of the gap present between the abutment and implant hexagons with the rotational misfit of 5 abutment-implant combinations from 2 manufacturers. Materials and Methods: Twenty new externally hexed implants (n = 10 for Nobel Biocare; n = 10 for Biomet/3i) and 50 new abutments were used (n = 10; Procera Zirconia; Procera Alumina; Esthetic Ceramic Abutment; ZiReal; and GingiHue post ZR Zero Rotation abutments). The mating surfaces of all implants and abutments were imaged with a scanning electron microscope before and after rotational misfit measurements. The distances between the corners and center of the implant and abutment hexagon were calculated by entering their x and y coordinates, measured on a measuring microscope, into Pythagoras' theorem. The dimensional difference between abutment and implant hexagons was calculated and correlated with the rotational misfit, which was recorded using a precision optical encoder. Each abutment was rotated (3 times/session) clockwise and counterclockwise until binding. Analysis of variance and Student-Newman-Keuls tests were used to compare rotational misfit among groups (a = .05). Results: With respect to rotational misfit, the abutment groups were significantly different from one another (P .001), with the exception of the Procera Zirconia and Esthetic Ceramic groups (P = .4). The mean rotational misfits in degrees were 4.13 ± 0.68 for the Procera Zirconia group, 3.92 ± 0.62 for the Procera Alumina group, 4.10 ± 0.67 for the Esthetic Ceramic group, 3.48 ± 0.40 for the ZiReal group, and 1.61 ± 0.24 for the GingiHue post ZR group. There was no correlation between the mean implant-abutment gap and rotational misfit. Conclusions: Within the limits of this study, machining inconsistencies of the hexagons were found for all implants and abutments tested. The GingiHue Post showed the smallest rotational misfit. All-ceramic abutments without a metal collar showed a greater rotational misfit than those with a metal collar. Keywords: ceramic abutment, metal abutment, misfit, rotational freedom, screw