Research Spotlight

Revilla-León, M., Mostafavi, D., Methani, M.M. and Zandinejad, A. (2021). “Manufacturing accuracy and volumetric changes of stereolithography additively manufactured zirconia with different porosities.” J Prosthet Dent Feb 8;S0022-3913(20)30504-7. [Epub ahead of print].

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STATEMENT OF PROBLEM: When compared with subtractive fabricating methods, additive manufacturing (AM) technologies are capable of fabricating complex geometries with different material porosities. However, the manufacturing accuracy and shrinkage of the stereolithography (SLA) AM zirconia with different porosities are unclear. PURPOSE: The purpose of this in vitro study was to measure the manufacturing accuracy and volumetric changes of AM zirconia specimens with porosities of 0%, 20%, and 40%. MATERIAL AND METHODS: A digital design of a bar (25×4×3 mm) was obtained by using an open-source software program (Blender, version 2.77a; The Blender Foundation). The standard tessellation language (STL) file was exported. Three groups were created based on the material porosity: 0% porosity (0% group), 20% porosity (20% group), and 40% porosity (40% group). The STL was used to manufacture all the specimens by using an SLA ceramic printer (CeraMaker 900; 3DCeram Co) and zirconia material (3DMix ZrO(2) paste; 3DCeram Co) (n=20). After manufacturing, the specimens were cleaned of the green parts by using a semiautomated cleaning station. Subsequently, debinding procedures was completed in a furnace at 600 °C. The sintering procedures varied among the groups to achieve different porosities. For the 0% group, the ZrO(2) was sintered in a furnace at 1450 °C, and for the 20% and 40% groups, the sintering temperature varied between 1450 °C and 1225 °C. The specimen dimensions (length, width, and height) were measured 3 times with digital calipers, and the mean value was determined. The manufacturing volume shrinkage (%) was calculated by using the digital design of the bar and the achieved AM dimensions of the specimens. The Shapiro-Wilk test revealed that the data were not normally distributed. Therefore, the data were analyzed by using the Kruskal-Wallis followed by pairwise Mann-Whitney U tests (α=.05). RESULTS: The Kruskal-Wallis test demonstrated significant differences among the groups in length, width, and height (P<.001). The Mann-Whitney U test indicated significant differences in pairwise comparisons of length, width, and height among the 3 groups (P<.001). The 0% group obtained a median ±interquartile range values of 20.92 ±0.14 mm in length, 3.43 ±0.07 mm in width, and 2.39 ±0.03 mm in height; the 20% group obtained 22.81 ±0.29 mm in length, 3.74 ±0.07 mm in width, and 2.62 ±0.05 mm in height; and the 40% group presented 25.11 ±0.13 mm in length, 4.14 ±0.08 mm in width, and 2.96 ±0.02 mm in height. Significant differences in manufacturing volumetric changes were encountered among the 3 groups (P<.001). In all groups, volumetric changes in the length, width, and height were not uniform, being higher in the z-axis direction compared with the x- and y-axis. The manufacturing volumetric changes varied from -20.33 ±1.00% to +3.5 ±2.00%. CONCLUSIONS: The 40%-porosity group obtained the highest manufacturing accuracy and the lowest manufacturing volume change, followed by the 20%-porosity and the 0%-porosity groups. An uneven manufacturing volume change in the x-, y-, and z-axis was observed. However, none of the groups tested were able to perfectly match the virtual design of the specimens.

Hinsdale, T.A., Malik, B.H., Cheng, S., Benavides, O.R., Giger, M.L., Wright, J.M., Patel, P.B., Jo, J.A. and Maitland, K.C. (2021). “Enhanced detection of oral dysplasia by structured illumination fluorescence lifetime imaging microscopy.” Sci Rep 11(1): 4984.

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We demonstrate that structured illumination microscopy has the potential to enhance fluorescence lifetime imaging microscopy (FLIM) as an early detection method for oral squamous cell carcinoma. FLIM can be used to monitor or detect changes in the fluorescence lifetime of metabolic cofactors (e.g. NADH and FAD) associated with the onset of carcinogenesis. However, out of focus fluorescence often interferes with this lifetime measurement. Structured illumination fluorescence lifetime imaging (SI-FLIM) addresses this by providing depth-resolved lifetime measurements, and applied to oral mucosa, can localize the collected signal to the epithelium. In this study, the hamster model of oral carcinogenesis was used to evaluate SI-FLIM in premalignant and malignant oral mucosa. Cheek pouches were imaged in vivo and correlated to histopathological diagnoses. The potential of NADH fluorescence signal and lifetime, as measured by widefield FLIM and SI-FLIM, to differentiate dysplasia (pre-malignancy) from normal tissue was evaluated. ROC analysis was carried out with the task of discriminating between normal tissue and mild dysplasia, when changes in fluorescence characteristics are localized to the epithelium only. The results demonstrate that SI-FLIM (AUC = 0.83) is a significantly better (p-value = 0.031) marker for mild dysplasia when compared to widefield FLIM (AUC = 0.63).

DeSantis-Rodrigues, A., Hahn, R.A., Zhou, P., Babin, M., Svoboda, K.K.H., Chang, Y.C., Gerecke, D.R. and Gordon, M.K. (2021). “SM1997 Downregulates Mustard Induced Enzymes that Disrupt Corneal Epithelial Attachment.” Anat Rec (Hoboken) Feb 7. [Epub ahead of print].

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Amino-Plex (SM1997) is a spray or liquid cosmeceutical that has been used for skin dryness, aging, or sun exposure. Its formulation includes electrolytes, trace minerals, amino acids, peptides, nucleosides and nucleotides, all substances that are less than 10 kDa. It is designed to increase oxygen levels in cells, improve glucose transport, stimulate ATP synthesis, and stimulate collagen formation, actions that can help facilitate repair of damaged cells. It also supports collagen synthesis and formation of healthy granulation tissue, accelerating re-epithelization of damaged skin. Here, SM1997 has been tested as an agent to improve the healing of mustard injury to the cornea. The results indicate that SM1997 facilitates the retention of corneal epithelial attachment when applied to corneal organ cultures after nitrogen mustard exposure. In addition, it reduces the activation of enzymes that lead to epithelial-stromal separation, namely, ADAM17 and MMP-9. Therefore, SM1997 should be further investigated as a potential therapy sulfur mustard and nitrogen mustard exposure.

Piedra-Cascón, W., Krishnamurthy, V.R., Att, W. and Revilla-León, M. (2021). “3D printing parameters, supporting structures, slicing, and post-processing procedures of vat-polymerization additive manufacturing technologies: A narrative review.” J Dent Mar 5;103630. [Epub ahead of print]. 103630.

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OBJECTIVE: To review the elements of the vat-polymerization workflow, including the 3D printing parameters, support structures, slicing, and post-processing procedures, as well as how these elements affect the characteristics of the manufactured dental devices. DATA: Collection of published articles related to vat-polymerization technologies including manufacturing workflow description, and printing parameters definition and evaluation of its influence on the mechanical properties of vat-polymerized dental devices was performed. SOURCES: Three search engines were selected namely Medline/PubMed, EBSCO, and Cochrane. A manual search was also conducted. STUDY SELECTION: The selection of the optimal printing and supporting parameters, slicing, and post-processing procedures based on dental application is in continuous improvement. As well as their influence on the characteristics of the additively manufactured (AM) devices such as surface roughness, printing accuracy, and mechanical properties of the dental device. RESULTS: The accuracy and properties of the AM dental devices are influenced by the manufacturing trinomial namely technology, printer, and material selected. The printing parameters, printing structures, slicing methods, and the post-processing techniques significantly influence on the surface roughness, printing accuracy, and mechanical properties of the manufactured dental device; however, the optimization of each one may vary depending on the clinical application of the additively manufactured device. CONCLUSIONS: The printing parameters, supporting structures, slicing, and post-processing procedures have been identified, but further studies are required to determine the optimal manufacturing protocol and enhance the properties of the AM polymer dental devices. CLINICAL SIGNIFICANCE: The understanding of the factors involved in the additive manufacturing workflow leads to a printing success and better outcome of the additively manufactured dental device.

Pérez-Giugovaz, M.G., Mostafavi, D. and Revilla-León, M. (2021). “Additively Manufactured Ingot For Interim Dental Restorations Fabrication Using A Chairside Milling Machine.” J Prosthodont Feb 27. [Epub ahead of print].

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This manuscript describes a technique to fabricate additively manufactured ingots for producing tooth- and implant-supported interim dental restorations using a chairside milling machine. The technique aimed to ease the additively manufactured interim restoration’s manufacturing by using a chairside milling machine, optimize the manufacturing workflow time, and eliminate the surface roughness of additively manufactured restorations.