Comparison of splinted and non-splinted superstructures of three implants placed in a mandibular distal extension...

This study evaluated the effects of two types of superstructures (splinted crown and non-splinted crown) on four vibration characteristics (natural frequency, damping ratio (DAR), vectors in antiphase, maximum displacement (MDP)) by using modal analysis. These structures were fabricated on three implants placed in the mandibular free-end defect model. After placing three implants on a mandibular distal extension model with missing teeth, the three-unit splinted and non-splinted crowns were designed on the CAD software. Subsequently, the zirconia disc was milled using a milling machine to produce the superstructures (n = 5). After establishing four measurement points on each crown of the prostheses, a vibration was applied to the mandible model with an impact hammer, and the transfer function of each measurement point was identified. Using the modal analysis software, the natural frequency and damping ratios were calculated from the transfer function, modal shapes at each natural frequency were observed, and maximum displacement that takes into account the lateral force during mastication was simulated. The t-test was performed for each of the averaged values of natural frequency, maximum displacement, and damping ratio (p < 0.05). Mann-Whitney U test was performed on the average of the number of vectors in antiphase (p < 0.05). The mean natural frequency was significantly higher in the splinted crown (758.2 ± 2.8 Hz) than that in the non-splinted crown (752.8 ± 3.7 Hz) (P = 0.047). The mean damping ratio was not significantly different for the splinted (3.3 ± 0.2%) and non-splinted crowns (3.2 ± 0.3%) (P = 0.535). The average number of vectors in antiphase was significantly smaller in the non-splinted crown (4.4 ± 0.9) than in the splinted crown (10 ± 2.5) (P = 0.008). The mean value of the maximum displacement was significantly smaller in the splinted crown (6.7 ± 1.1 μm) than that in the non-splinted crown (7.3 ± 0.6 μm) (P = 0.048). Within the limitations of this study, the vibration characteristics of the superstructures differed between designs with splinted and non-splinted crowns. Crown splinting increased the rigidity and natural frequency and decreased the MDP. However, the higher number of vectors in antiphase indicated more twists in the superstructures during vibration. The non-splinted crowns showed a lower natural frequency and a greater maximum displacement; however, they comprised fewer vectors in antiphase, indicating that the twist during vibration was less than that observed with the splinted crowns. Thus, our results suggest that crown splinting reduces the deformation of the superstructure, implants, and the surrounding tissues in comparison to the deformation observed when no splinting is performed.