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.

Can ceramic veneer spark erosion and mechanical cycling affect the accuracy of milled complete-arch frameworks supported by 6 implants?

STATEMENT OF PROBLEM: Milling is a well-established method for manufacturing prosthetic frameworks. However, information about the influence of ceramic veneer and spark erosion on the accuracy of the all-on-six complete-arch fixed frameworks manufactured from different materials is lacking. PURPOSE: The purpose of this in vitro study was to compare the accuracy of milled complete-arch fixed frameworks with zirconia, cobalt-chromium, and titanium at different steps of their manufacturing process and the influence of mechanical cycling. MATERIAL AND METHODS: Fifteen milled complete-arch fixed frameworks, supported by 6 implants, were made in zirconia, cobalt-chromium, and titanium (n=5). The fit was measured by the single-screw test protocol. Stress was measured by photoelastic analysis. The loosening torque was evaluated by tightening the screws, retightening them after 10 minutes, and then evaluating the loosening torque 24 hours later. Thereafter, all frameworks received ceramic veneer, and the previous tests were repeated. Cobalt-chromium and titanium frameworks received spark erosion after ceramic veneer, and all analyses were repeated. Before and after mechanical cycling, loosening torque was evaluated. The results were subjected to 2-way repeated-measures ANOVA and the Bonferroni test (α=.05). RESULTS: Titanium presented higher fit values than zirconia (P=.037) and similar to cobalt-chromium frameworks (P>.05) at baseline. After ceramic veneer, higher fit levels were observed for zirconia (P=.001) and cobalt-chromium (P=.008). Titanium showed higher stress values (P<.05) regardless of time. Baseline for all materials presented lower stress values (P<.05). Higher loosening torque values were found for the titanium group at baseline (P<.001) and after ceramic veneer (P<.001). Spark erosion improved fit and loosening torque values only for cobalt-chromium (P<.05). Mechanical cycling did not influence the loosening torque (P>.05). CONCLUSIONS: Titanium milled complete-arch fixed frameworks presented poorer fit values than zirconia, although the loosening torque at baseline was higher. Ceramic veneer increased the fit levels for zirconia and cobalt-chromium, decreased the loosening torque values for cobalt-chromium, and enhanced stress levels. Spark erosion can be a reliable technique to improve fit and loosening torque for cobalt-chromium frameworks. Mechanical cycling did not decrease loosening torque.

3D metal printing in dentistry: An in vitro biomechanical comparative study of two additive manufacturing technologies for full-arch implant-supported prostheses.

The use of 3D technologies is progressing in the dental field. However, little is known about the biomechanical behavior of the additive manufacturing of full-arch fixed dental prostheses (FAFDPs) for the establishment of clinical protocols. We investigated the influence of three CAD/CAM technologies: milling (control), Selective Laser Melting (SLM) and Electron Beam Melting (EBM) for FAFDP manufacturing. Also, the effects of ceramic veneer and spark erosion on marginal misfits of FAFDPs, the stability of prosthetic screws, strain and stress on the implant-supported system, as well as the effect of chewing simulation on screw stability were evaluated. Fifteen Ti-6Al-4V alloy FAFDPs were obtained by means of CAD/CAM systems: milling, SLM and EBM (n = 5/group). The marginal misfit was analyzed according to the single-screw test protocol. Screw stability was analyzed by screw-loosening torque. Strain-gauge analysis investigated the strain on the mini-abutment analog, and photoelastic analysis investigated the stress on the peri-implant region. Subsequently, all frameworks underwent ceramic veneer and spark erosion procedures. Marginal misfit, screw-loosening and strain and stress analyses were assessed after each evaluation time: initial, ceramic veneer and spark erosion. Finally, all prostheses were subjected to 106 mechanical cycles (2 Hz/150 N), and screw-loosening was re-evaluated. Data were subjected to two-way ANOVA for repeated measures, and the Bonferroni test as a post hoc technique (α = 0.05). At the initial time, the milling group presented the lowest marginal misfit (p < 0.001). Ceramic veneer did not alter marginal misfit for all groups (p > 0.05); spark erosion decreased the misfit values for the SLM and EBM groups (p < 0.05). Evaluation time did not alter screw-loosening values for all groups (p = 0.191), although the milling group presented the highest screw-loosening values (p < 0.05). Ceramic veneer and spark erosion reduced strain in the components regardless of the manufacturing technology used (p < 0.05). The milling group presented the lowest stress values regardless of evaluation time (p = 0.001), and lower stress values were found after spark erosion regardless of the manufacturing group (p = 0.016). In conclusion, although milled frameworks exhibited the best biomechanical behavior, frameworks manufactured by additive technologies presented acceptable values of screw-loosening torque, strain and stress. Ceramic veneer did not negatively interfere in the biomechanical tests of the study, and clinically acceptable marginal misfit was achieved after spark erosion. Therefore, such 3D printing technologies seem to be feasible for the manufacturing of full-arch implant-supported frameworks.

Biomechanical behavior of CAD/CAM cobalt-chromium and zirconia full-arch fixed prostheses.

PURPOSE: To verify the influence of computer-aided design/computer-aided manufacturing (CAD/CAM) implant-supported prostheses manufactured with cobalt-chromium (Co-Cr) and zirconia (Zr), and whether ceramic application, spark erosion, and simulation of masticatory cycles modify biomechanical parameters (marginal fit, screw-loosening torque, and strain) on the implant-supported system. MATERIALS AND METHODS: Ten full-arch fixed frameworks were manufactured by a CAD/CAM milling system with Co-Cr and Zr (n=5/group). The marginal fit between the abutment and frameworks was measured as stated by single-screw test. Screw-loosening torque evaluated screw stability, and strain analysis was explored on the implant-supported system. All analyses were performed at 3 distinct times: after framework manufacturing; after ceramic application in both materials' frameworks; and after the spark erosion in Co-Cr frameworks. Afterward, stability analysis was re-evaluated after 106 mechanical cycles (2 Hz/150-N) for both materials. Statistical analyses were performed by Kruskal-Wallis and Dunn tests (α=.05). RESULTS: No difference between the two materials was found for marginal fit, screw-loosening torque, and strain after framework manufacturing (P>.05). Ceramic application did not affect the variables (P>.05). Spark erosion optimized marginal fit and strain medians for Co-Cr frameworks (P<.05). Screw-loosening torque was significantly reduced by masticatory simulation (P<.05) regardless of the framework materials. CONCLUSION: Co-Cr and Zr frameworks presented similar biomechanical behavior. Ceramic application had no effect on the biomechanical behavior of either material. Spark erosion was an effective technique to improve Co-Cr biomechanical behavior on the implant-supported system. Screw-loosening torque was reduced for both materials after masticatory simulation.

Biomechanical behavior of overdentures supported by different implant position and angulation using Micro ERA® system: a finite element analysis study

Aim: The aim of this study was to investigate the biomechanical behavior of implant-retained mandibular overdentures using Micro ERA® system with different implant position and angulation by finite element analysis (FEA). Methods: Four 3D finite element models of simplified mandibular overdentures were constructed, using one Bränemark implant with a Micro ERA® attachment. The implant was positioned on the canine or lateral incisor area with an angulation of either 0º (C-0º; LI-0º) or 17º (C-17º, LI-17º) to the vertical axis. A 100 N axial load was applied in one side simultaneously, from first premolar to second molar. In all models it was analyzed the overdenture displacement, compressive/tensile stress in the bone-implant interface, and also the von Mises equivalent stress for the nylon component of the housing. The stresses were obtained (numerically and color-coded) for further comparison among all the groups. Results: The displacement on the overdenture was higher at the posterior surface for all groups, especially in the C-17º group. When comparing the compressive/tensile stress in the bone-implant interface, the lateral-incisor groups (LI-0º and LI-17º) had the highest compressive and lowest tensile stress compared to the canine groups (C-0º and C-17º). The von Mises stress on the nylon component generated higher stress value for the LI-0º among all groups. Conclusions: The inclination and positioning of the implant in mandibular overdenture interferes directly in the stress distribution. The results showed that angulated implants had the highest displacement. While the implants placed in the lateral incisor position presented lower compressive and higher tensile stress respectively. For the attachment the canine groups had the lowest stress