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Manufacturing of Metal Frameworks for Full-Arch Dental Restoration on Implants: A Comparison between Milling and a Novel Hybrid Technology.

PURPOSE
To determine the trueness and precision of frameworks manufactured with a selective laser melting/milling hybrid technique (SLM/m) and conventional milling by comparing the implant-platform/framework interface with those of the original computer-aided design (CAD).


MATERIALS AND METHODS
Using a virtual 6-implant-supported full-arch framework CAD drawing, 27 titanium replicas were manufactured by 3 independent manufacturing centers (n = 9/center) using a hybrid SLM/m technology (labs 1 and 2) or the conventional milling technique (lab 3). Using an opto-mechanical coordinate measuring machine, the frameworks' misfit distribution and patterns were analyzed, and the position error between paired platform positions within each framework was evaluated to calculate the misfit tendency for each group. A multilevel analysis using a mixed-effects model was conducted (α = 0.05). The trueness was evaluated as the dimensional difference from the original, while the precision as the dimensional difference from a repeated scan.


RESULTS
The 3 dimensional misfits differed significantly among the 3 groups, with the milled group exhibiting the least accurate outcome (p = 0.005). The mean 3D positioning errors ranged from 8 to 16 µm and from 9 to 22 µm for the SLM/m technique (labs 1 and 2, respectively), and from 20 to 35 µm for conventional milling (lab 3). Regarding the misfit distribution pattern, the misfit increased with the distance between paired platform positions in all groups.


CONCLUSIONS
All groups had 3D misfits well within the error limits reported in the literature. The 3D misfits of new hybrid (SLM/milling) and conventional (milling) procedures differed significantly among them, with the milling technique the less accurate and precise. The largest errors in all groups were found between the most distant implants, resulting in a correlation between the framework span and the inaccuracies.