Additive manufacturing of CAD-CAM complete arch fixed implant restorations supported by six implants: Prosthetic screw stability and marginal precision under masticatory simulation.

STATEMENT OF PROBLEM

Titanium frameworks for implant-supported fixed prostheses can be fabricated through subtractive or additive manufacturing using computer-aided design and computer-aided manufacturing (CAD-CAM) systems. However, the accuracy achieved by these technologies remains uncertain.

PURPOSE

The purpose of this in vitro study was to evaluate complete arch maxillary fixed prostheses supported by 6 implants using CAD-CAM frameworks manufactured by milling and 3D printing technologies, selective laser melting (SLM), and electron beam melting (EBM) on the marginal fit and screw loosening torque before and after masticatory simulation.

MATERIAL AND METHODS

Ti-6Al-4V frameworks were manufactured by milling, SLM, and EBM technologies (n=5) and were subsequently ceramic veneered. The surface topography of the framework was assessed by scanning electron microscopy and laser scanning confocal microscopy. One-way analysis of variance (ANOVA) was used to evaluate surface area. The specimens were further evaluated for the dependent variables (marginal fit and screw loosening torque) before and after masticatory simulation. Two-way repeated measures ANOVA and the Pearson correlation were performed (α=.05).

RESULTS

Topographical analysis demonstrated that the milling group had a smooth surface (surface area: 1.17 ±0.02 µm) with regular regions, while additive manufacturing groups showed a dendritic profile with higher surface area (SLM: 1.23 ±0.05 µm; EBM: 1.21 ±0.03 µm; P<.05). A 2-way ANOVA found no interaction between technology and time (P>.05) for both dependent variables. Marginal fit showed no further significant differences regarding either the manufacturing technology or the evaluation time. Masticatory simulation reduced screw loosening torque (P=.032). Regarding manufacturing technology, milling resulted in a higher screw loosening torque compared with SLM (P=.01); however, no difference was observed between EBM and either SLM or milling (P>.05). A moderate correlation (P=.02) between marginal fit and screw loosening torque was observed only at baseline for the pooled CAD-CAM (milling, SLM, and EBM) specimens.

CONCLUSIONS

CAD-CAM complete arch fixed prostheses on 6 implants made by milling, SLM, and EBM exhibited marginal fit values below the acceptable error limits. Regarding prosthetic screw loosening torque, the pooled milled frameworks showed better values compared with SLM. After masticatory simulation, prosthetic screw stability decreased in all prostheses.