Effect of Aging and Porcelain Sintering on Rotational Freedom of Internal-Hex One-Piece Zirconia Abutments

Purpose: The purpose of this study was to assess the variation of rotational freedom at the implant interface of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic abutments with internal-hexagon connections before and after artificial aging and after porcelain sintering. Materials and Methods: Thirty Y-TZP ceramic abutments with internal-hex connections were used in this study. Three groups of 10 abutments each were created. Group C was made up of abutments in the as-received condition, group A abutments went through 1 hour of autoclaving at 134°C to simulate the effect of 3 to 4 years of aging in vivo, and group P abutments went through porcelain sintering procedures. Measurements of rotational freedom were compared between groups. The quantitative differences between groups were assessed using multivariate analysis of variance. Statistical testing was carried out at the 5% significance level. Results: A mean rotational freedom of 115.34 ± 1.42 minutes was found for group C abutments; the values for group A and group P abutments were 115.35 ± 1.73 minutes and 115.37 ± 1.54 minutes, respectively. None of these differences were statistically significant between the three groups. Conclusion: Misfit of the Y-TZP ceramic abutment on the internal-hex connection of implants may be implicated in screw joint loosening. The results of this report suggested that, if all laboratory steps are followed carefully, changes will not occur at the implant/Y-TZP ceramic abutment interface. Maintenance of the original features of the abutment may reduce the risk of screw loosening. Keywords: aging, implant abutment, implant/abutment connection, internal-hexagon connection, zirconia