Effect of print layer height on the assessment of 3D-printed models.

INTRODUCTION: Many variables can affect the accuracy of 3D-printed orthodontic models, and the effects of different printing parameters on the clinical utility of the printed models are just beginning to be understood. The objective of this study was to investigate the effect of print layer height on the assessment of 3D-printed orthodontic models with the use of the American Board of Orthodontics Cast-Radiograph Evaluation grading system. METHODS: Twelve cases were scanned using a desktop model scanner and 3D-printed using a stereolithography-based printer at three different layer heights (25, 50, and 100-µm; n = 12 per group). All models were scored by eleven graders using the Cast-Radiograph Evaluation grading system. All models were scored a second time, at least two weeks later. RESULTS: No statistically significant effects of print layer height were found on the scoring of the models for any of the grading metrics or total score. 3D-printed models of each layer height were highly positively correlated with stone models for the total score, with the strongest correlation found with models printed at 100-µm. CONCLUSIONS: 100-µm layer height 3D-printed models are potentially clinically acceptable for the purposes of evaluation of treatment outcomes, diagnosis and treatment planning, and residency training.

Morphology and connectivity of parabrachial and cortical inputs to gustatory thalamus in rats.

The ventroposterior medialis parvocellularis (VPMpc) nucleus of the thalamus, the thalamic relay nucleus for gustatory sensation, receives primary input from the parabrachial nucleus, and projects to the insular cortex. To reveal the unique properties of the gustatory thalamus in comparison with archetypical sensory relay nuclei, this study examines the morphology of synaptic circuitry in the VPMpc, focusing on parabrachiothalamic driver input and corticothalamic feedback. Anterogradely visualized parabrachiothalamic fibers in the VPMpc bear large swellings. At electron microscope resolution, parabrachiothalamic axons are myelinated and make large boutons, forming multiple asymmetric, adherent, and perforated synapses onto large-caliber dendrites and dendrite initial segments. Labeled boutons contain dense-core vesicles, and they resemble a population of terminals within the VPMpc containing calcitonin gene-related peptide. As is typical of primary inputs to other thalamic nuclei, parabrachiothalamic terminals are over five times larger than other inputs, while constituting only 2% of all synapses. Glomeruli and triadic arrangements, characteristic features of other sensory thalamic nuclei, are not encountered. As revealed by anterograde tracer injections into the insular cortex, corticothalamic projections in the VPMpc form a dense network of fine fibers bearing small boutons. Corticothalamic terminals within the VPMpc were also observed to synapse on cells that were retrogradely filled from the same injections. The results constitute an initial survey describing unique anatomical properties of the rodent gustatory thalamus.