Trueness of removable partial denture frameworks additively manufactured with selective laser melting.

STATEMENT OF PROBLEM: Although studies have reported on selective laser melting (SLM)-fabricated removable partial dentures (RPDs), research addressing the trueness of SLM-fabricated RPD metal frameworks is sparse. PURPOSE: The purpose of this in vitro study was to evaluate the trueness of powdered cobalt-chromium (Co-Cr) or titanium-6 aluminum-4 vanadium (Ti-6Al-4V) alloy frameworks for RPDs fabricated by SLM. MATERIAL AND METHODS: A digital scan of a Kennedy class II mandible typodont was obtained to design an RPD framework by using a computer-aided design (CAD) software program (denoted as CRF). Two experimental groups of frameworks were fabricated from the CRF by using SLM in alloys of Co-Cr (SLM-Co-Cr, n=6) and in Ti-6Al-4V (SLM-Ti-6Al-4V, n=6) while a control group was fabricated by using traditional lost-wax casting following stereolithography (CA-Co-Cr, n=6). In total, 18 RPD frameworks were digitally scanned (denoted as CRF), with each scan then superimposed on the CRF and evaluated for discrepancies by using a 3D analysis software program. A nonparametric Kruskal-Wallis test was performed to determine differences in trueness among groups (α=.05). RESULTS: The CA-Co-Cr group showed the highest discrepancy between CEF and CRF. Statistically significant differences were found between the CA-Co-Cr and SLM-fabricated groups (P=.03 for Co-Cr, and P=.016 for Ti-6Al-4V). However, no significant difference was found between the SLM-Co-Cr and SLM-Ti-6Al-4V groups (P=.787). CONCLUSIONS: SLM-fabricated RPD frameworks exhibited higher trueness than CA-Co-Cr fabricated ones, indicating the potential of selective laser melting to produce the geometric shapes required for accurate dental restorations.

Environmental Risk Perception and Preventive Behavior during the COVID-19 Pandemic in Central Taiwan.

Due to traffic and industrial and seasonal air pollution, wearing masks outside the home has long been a daily habit for many people in Taiwan. After the emergence of the novel coronavirus (COVID-19), which has an incubation period of up to 14 days, wearing masks and maintaining social distancing was advised to reduce exposure to this new environmental risk. This study investigates open and semi-open spaces in three districts in central Taiwan, using a non-participant observation method, with the aim of understanding people's mask-wearing behavior. The results indicate that mask-wearing rates were higher in urban areas than in rural ones and among females than males. By age cohort, mask-wearing was most prevalent among young adults and middle-aged people and least prevalent among minors, with the elderly occupying a middle position. Masks were also more likely to be worn in semi-open spaces than in open ones. This study enriches our understanding of environmental risk perception of the pandemic and of public perceptions, which are vital to increasing the adoption of preventative measures.