a comparison between desktop model scanners, an intraoral scanner, a CBCT model scan, and stereolithographic 3D printing

Zielsetzung: Ziel dieser Studie ist es, die Genauigkeit von Ganzkieferscans zu untersuchen, die mithilfe unterschiedlicher direkter und indirekter Digitalisierungsverfahren gewonnen werden. Diese soll mit der Genauigkeit von gedruckten Modellen verglichen werden, um eine Aussage darüber treffen zu können, wann ein direkter oder indirekter Workflow in der Kieferorthopädie zu bevorzugen ist. Methodik: Ein modifiziertes Mastermodell wurde mithilfe eines Koordinatenmessgeräts vermessen. Die untersuchten Strecken waren die Intercanineweite, die Intermolarenweite und die Zahnbogenlänge. Sechs Intraoralscanner, elf Desktop-Scanner und fünf digitale Volumentomographen (DVT) wurden einbezogen. Es wurden jeweils 37 Scans durchgeführt und mithilfe einer Messsoftware analysiert. Für den Vergleich mit der Genauigkeit von 3D- gedruckten Modellen wurde das digitale Mastermodell 37-mal mithilfe eines Stereolithografie-Druckers gedruckt. Die gedruckten Modelle wurden anschließend mit einem Koordinatenmessgerät vermessen. Ergebnisse: Zwischen den Digitalisierungsverfahren und innerhalb einer Gerätegruppe konnten signifikante Unterschiede festgestellt werde. Die geringsten Abweichungen wurden mit den Desktop-Scannern erzielt. Die untersuchten intraoralen Scans zeigen annähernd vierfach höhere mittlere Abweichungen und vierfach größere Standardabweichungen gegenüber den untersuchten Desktop-Scannern. Zwischen den DVT-Geräten herrschten große Unterschiede hinsichtlich der Genauigkeit. Die gedruckten Modelle zeigten vergleichbare Abweichungen zu den Intraoralscannern. Schlussfolgerung: Die zusätzlichen Fehlerpotenziale Abformung und Modellherstellung bei indirekter Digitalisierung relativieren die geringeren Abweichungen. Im klinischen Workflow bestehen daher keine Unterschiede zwischen einer direkten Digitalisierung mit Intraoralscannern und einer indirekten mit Desktop-Scannern hinsichtlich der Genauigkeit. Wird neben dem digitalen Modell ein physisches Modell benötigt, sollte ein indirekter Workflow bevorzugt werden. Ein intraoraler Scan und anschließender Modelldruck stellt einen alternativen Weg dar, kann jedoch nicht als Goldstandart angesehen werden. Eine indirekte Modelldigitalisierung mittels DVT scheint großes Potenzial zu besitzen und sollte in weiteren Studien verifiziert werden.Objective: The primary objective of this study is to compare the accuracy of full-arch scans obtained by different indirect and direct digitalization workflows with that of three-dimensional (3D) printed models in order to identify the most suitable method for orthodontic use. Method: A modified master model was measured with a coordinate measuring instrument. The distances measured were the intercanine width, the intermolar width, and the dental arch length. Six intraoral scanners, eleven desktop scanners and five cone beam computed tomography (CBCT) units were included. Thirty-seven scans were taken with each device and analyzed with a measuring software. One scan was selected and printed thirty-seven times on a stereolithographic 3D printer. The printed models were measured again using the coordinate measuring instrument. Results: Significant differences between the devices and digitalization workflows were found. The desktop scanners obtained the most accurate results. The mean deviations and standard deviations of the intraoral scanners were approximately four times higher than the deviations of the desktop scanners. With regard to the accuracy of digitalization great differences between the CBCT units were found. The printed models showed a level of accuracy that is comparable to that of to the intraoral scanners. Conclusion: The additional potential for deviations including impression taking and model casting when using desktop scanners relativizes the higher accuracy. Therefore, there is no clinically relevant difference between direct digitalization with intraoral scanners and indirect digitalization with desktop scanners. If a physical model beside the digital model is needed, an indirect digitalization workflow is recommended. An intraoral scan and printing of the model afterward is a possible alternative, but cannot be considered a new gold standard. An indirect digitalization with a CBCT unit seems to have high potential and should be verified in further studies

3-D Printed Protective Equipment during COVID-19 Pandemic

While the number of coronavirus cases from 2019 continues to grow, hospitals are reporting shortages of personal protective equipment (PPE) for frontline healthcare workers. Furthermore, PPE for the eyes and mouth, such as face shields, allow for additional protection when working with aerosols. 3-D printing enables the easy and rapid production of lightweight plastic frameworks based on open-source data. The practicality and clinical suitability of four face shields printed using a fused deposition modeling printer were examined. The weight, printing time, and required tools for assembly were evaluated. To assess the clinical suitability, each face shield was worn for one hour by 10 clinicians and rated using a visual analogue scale. The filament weight (21-42 g) and printing time (1:40-3:17 h) differed significantly between the four frames. Likewise, the fit, wearing comfort, space for additional PPE, and protection varied between the designs. For clinical suitability, a chosen design should allow sufficient space for goggles and N95 respirators as well as maximum coverage of the facial area. Consequently, two datasets are recommended. For the final selection of the ideal dataset to be used for printing, scalability and economic efficiency need to be carefully balanced with an acceptable degree of protection

Clinical Outcomes of Root-Analogue Implants Restored with Single Crowns or Fixed Dental Prostheses: A Retrospective Case Series

The objective was to investigate clinical and radiological outcomes of rehabilitations with root-analogue implants (RAIs). Patients restored with RAIs, supporting single crowns or fixed dental prostheses, were recruited for follow-up examinations. Besides clinical and esthetical evaluations, X-rays were taken and compared with the records. Patients were asked to evaluate the treatment using Visual Analogue Scales (VAS). For statistical analyses, mixed linear models were used. A total of 107 RAIs were installed in one dental office. Of these, 31 were available for follow-up examinations. For those remaining, survival has been verified via phone. RAIs were loaded after a mean healing time of 6.6 ± 2.5 months. 12.1 ± 6.9 months after loading, a mean marginal bone loss (MBL) of 1.20 ± 0.73 mm was measured. Progression of MBL significantly decreased after loading (p = 0.013). The mean pink and white esthetic score (PES/WES) was 15.35 ± 2.33 at follow-up. A survival rate of 94.4% was calculated after a mean follow-up of 18.9 ± 2.4 months after surgery. Immediate installation of RAIs does not seem to reduce MBL, as known from the literature regarding screw-type implants, and might not be recommended for daily routine. Nevertheless, they deliver esthetically satisfying results

A nitrogen-base catalyzed generation of organotin(II) hydride from an organotin trihydride under reductive dihydrogen elimination

CPS thanks the Fonds der chemischen Industrie and the Studienstiftung des deutschen Volkes for PhD research scholarshipsSince their first description over a decade ago, organotin(II) hydrides have been an iconic class of compounds in molecular main group chemistry. Among other approaches they have been accessed from the hydrogenation of distannynes. We herein report their accessibility from the other direction by dehydrogenation of organotin trihydride. On reacting pyridine and amine bases with the bulky substituted organotin trihydride Ar*SnH3 (Ar* = 2,6-trip2(C6H3)–, trip = 2,4,6-triisopropylphenyl) hydrogen evolution was observed. In case of catalytic amounts of base the dehydro-coupling product diorganodistannane Ar*H2SnSnH2Ar* was obtained quantitatively whilst for excessive amounts (>4 eq.) the monomeric base adduct to known Ar*SnH was obtained almost exclusively. The base adducts were found to be remarkably thermally robust. They readily react with polar fulvenic CC-bonds in hydro-stannylenylation reactions. The resulting half-sandwich complex Ar*SnCp* was structurally characterized. Moreover, on application of less nucleophilic amine bases, the uncoordinated, in solution dimeric [Ar*SnH]2 is formed. NMR spectroscopic studies on the kinetics of the DMAP-catalysed reductive elimination of dihydrogen were performed. The activation energy was approximated to be 13.7 kcal mol−1. Solvent dependencies and a kinetic isotope effect KIE of kH/kD = 1.65 in benzene and 2.04 in THF were found and along with DFT calculations support a polar mechanism for this dehydrogenation.Publisher PDFPeer reviewe