Additive Manufacturing of Metallic Frameworks Supported by the All-on-Six Implant Concept: Dimensional Precision After Veneer Layering and Spark Erosion

Purpose: To compare frameworks manufactured by selective laser melting (SLM) and electron beam melting (EBM) with frameworks manufactured by milling, regarding dimensional precision after veneer layering and spark erosion for the all-on-six implant concept.
Materials and methods: Frameworks (n = 5/group) were manufactured by milling, SLM, and EBM. Dimensional precision of the frameworks was evaluated by marginal fit, screw loosening torque, and strain. Marginal fit was assessed by the single screw protocol. The screw-loosening torque was measured for the evaluation of screw stability. Tension distribution was analyzed with strain gauges. All frameworks received veneer layering followed by the marginal fit, screw-loosening torque, and strain gauge tests. Subsequently, the frameworks were subjected to the spark erosion process. The analyses were repeated after each stage (baseline, veneer layering, and spark erosion). Data was explored by two-way repeated-measures analysis of variance (ANOVA) with the Bonferroni test (α = .05).
Results: At baseline, the highest (worst) marginal fit values were displayed by SLM frameworks (mean ± standard deviation [SD]: 186.13 ± 21.27 μm), while the milling group (83.30 ± 12.03 μm) showed the lowest (best) values (P < .05). After veneer layering, EBM presented the worst marginal fit values (222.55 ± 52.56 μm; P < .05) among the groups. Over time (from the baseline to veneer layering), the marginal fit values increased (became worse) for milling (P = .002) and EBM (P < .001), while for SLM (P = .002) the values decreased (improved). Compared with veneer layering data, spark erosion improved the marginal fit values only for EBM (P = .005). Irrespective of time, the screw-loosening torque for the milling group showed higher values. The lowest strain was found for the SLM at baseline (P < .05), but it increased after veneer layering (P = .015) and after spark erosion (P = .028).
Conclusion: Additive technologies are promising for dental applications. In addition, all technologies demonstrated accuracy in the manufacturing of implant-supported frameworks, especially the EBM technology, which demonstrated biomechanical behavior similar to the milling technology after the intervals (baseline, veneer layering, and spark erosion) assessed in the study.