Comparison Between Conventional Milling and a Novel Hybrid Manufacturing Technology

Objectives: Poor fit at the framework-implant interface increases the strain and stress within both the framework and the surrounding tissues. The primary aim of this study was to compare the accuracy and precision (repeatability) of the selective laser melting/milling hybrid technology (SLM/m) with that of conventional milling to manufacture implant-supported frameworks for full-arch oral rehabilitation on implants. Methods: A computer model of a six-implant-supported full-arch framework was used to manufacture a total of 27 titanium clones by three independent manufacturing centres (9 specimens for each lab) using hybrid SLM/m technology (Lab 1 and Lab 2), or the conventional milling technique (Lab 3). Measurements of the accuracy, precision and inter-distance error were performed using a metrological approach with an opto-mechanical coordinate-measuring machine (OCMM). Results: The accuracy analysis of 3D error among framework connecting platform (FCP) position showed significant differences (Multilevel analysis) between Lab 3 and both Lab 1 (p=0.007) and Lab 2 (p=0.039); no significant difference was detected between Lab 1 and 2 (hybrid technology). The precision (repeatability) analysis of variance within each laboratory showed no significant differences within laboratories (Multilevel analysis, p > 0.05), suggesting good within-laboratory repeatability. However, significant differences in repeatability were observed among laboratories (p<0.01). The effect of FCP inter-distance magnitude on framework accuracy confirmed that the absolute distance error within paired FCP increases when the distance increases. Conclusions: All labs showed 3D misfits well within the error limits reported in the literature. Regarding accuracy, a significant difference was seen between the SLM/m and milling technologies. Regarding precision, repeatability was consistent within each lab, but a significant difference was detected among laboratories. Moreover, the absolute error increased as the inter-distance of paired FCP increased