Additive Technology Provides Implant-Supported Frameworks with Improved Dimensional Precision

Objectives: The aim of this in vitro study was to verify whether the SLM additive manufacturing technology provides superior dimensional precision for partial implant-supported framework fabrication when compared to the subtractive manufacturing soft metal block (SMB) milling.
Methods: Implant-supported FPDs Co-Cr frameworks were fabricated by casting (control group), SMB (experimental group), and SLM methods (experimental group) (n=10/group). The marginal fit between the implant abutment and framework was analyzed according to the single-screw test protocol on the photoelastic (PH) and strain gauge (SG) models. The stress and strain were evaluated by quantitative photoelastic and strain gauge analyses after the tightening of frameworks for the models with standardized 10-Ncm torque.
Results: The results were subjected to Kruskal-Wallis test, Mann-Whitney U test, and Spearman correlation test (α=.05). The framework manufacturing method affected the marginal fit (P<.001), stress, and strain values (P<.05). Best mean ±standard deviation marginal fit (μm) was found for the SLM group (PH model: 8.4 ±3.2; SG model: 6.9 ±2.1) in comparison with SMB (PH model: 42.3 ±15.7; SG model: 41.3 ±15.3) and cast (PH model: 43.5 ±27.8; SG model: 41.3 ±24.6) (P<.05). Lower mean ±standard deviation stress and strain values was found for SLM group (60.3 ±11.6 MPa; 91.4 ±11.1 µstrain) when compared with SMB (218.6 ±101.7 MPa; 289.7 ±89.3 µstrain) and cast (225.5 ±142.8 MPa; 226.95 ±55.4 µstrain) (P<.05). Positive correlation between fit and stress or strain was observed for all groups (P<.05).
Conclusions: SLM technology provides partial implant-supported frameworks with superior dimensional precision to that obtained with the SMB or casting methods.