The behavior of a zirconia or metal abutment on the implant-abutment interface during cyclic loading

The effect of different abutment materials on the misfit and stability of the implant-abutment assembly under cyclic loading is unclear.

The purpose of this in vitro study was to evaluate the initial misfit, final misfit, and wear of external hexagon zirconia and metal implant abutments upon cyclic loading.

Forty 4.1-mm regular platform external connection implants were divided into 4 groups with 10 specimens in each group. The prosthetic abutments tested included Completely cast group (CC) (antirotational, castable burnout, custom abutment completely cast in nickel-chromium-titanium), Overcast group (OC) (Co-Cr premachined, antirotational, custom burnout abutment cast in nickel-chromium-titanium), Zirkonzahn group (Z) (antirotational castable, custom Y-TZP abutment produced; Zirkonzahn Prettau), and Neodent group (N) (antirotational castable, custom Y-TZP abutment; Neoshape). Abutments were fixed to the implants with 20-Ncm torque, and all specimens were cyclically loaded at 300 N with 9 Hz for 1 million cycles. The misfit on the implant-abutment interface was evaluated before and after cyclic loading by using an optical linear measuring microscope. Then, the wear of the external hexagon was analyzed by scanning electron microscopy (SEM) at a magnification of ×120. For a statistical analysis, a 1-way ANOVA was used for wear values. The data for the gaps were analyzed with a 2-way ANOVA. Any significant differences were resolved by using the Tukey HSD test (α=.05).

The CC (37 ±8 μm) and OC (35 ±5 μm) groups showed significantly larger initial misfit than the Z (4 ±5 μm) and the N (2 ±4 μm) groups (P<.05). After the mechanical cyclic loading, a statistically significant difference was found between the CC group (58 ±9 μm) and the other 3 groups (P<.05). The OC group (41 ±4 μm) showed significantly larger final misfit than the Z (19 ±7 μm) and the N groups (20 ±4 μm) (P<.05). Despite significantly increased misfit in all groups (P<.05), the OC group showed significantly less increased gap (6 μm) than the Z (15 μm) and the N (18 μm) groups, while CC showed the most increase in misfit (21 μm). Conversely, N (1313 ±315 μm²) and Z (735 ±126 μm²) groups showed significantly higher wear rate on the hexagon of external implants. The CC (231 ±182 μm²) and OC (201 ±125 μm²) groups were not statistically different.

Different materials and fabrication techniques resulted in different levels of misfit at the implant-abutment interface. The mechanical cyclic loading aggravated the misfit, regardless of material or fabrication technique. In addition, the difference in the hardness of the abutment materials may lead to different levels of wear on the external hexagon. Zirconia abutments had increased wear and misfit. Premachined, antirotational, castable custom dental implant abutments had the least amount of change in misfit, which may indicate long-term stability at the implant-abutment interface.