A Structural Analysis of 3D Printed Pediatric Space Maintainers.

Purpose: To design, fabricate, and evaluate in vitro 3D printed space maintainers (SMs) and compare their retentive capabilities to tradi- tional stainless-steel (SS) space maintainers. Methods: E-Guard was selected as the printing material based on flexural strength and elastic modulus. SMs with a claw design were printed, cemented to testing blocks, and vertically loaded to determine failure strength and flexure (n equals 10). The intaglio surfaces of SM bands, printed with plain, crosshatched, or horizontal ridges, were cemented to extracted primary teeth. The force needed to dislodge the bands was compared to cemented traditional SS bands (n equals 14). Results: Flexural strength (mean±standard deviation [SD]) of E-Guide, E-Dent, and E-Guard materials was 65±12, 90±13, 134±25 MPa, respectively. Elastic modulus (mean±SD) was 1.54±0.40, 2.49±0.14, 2.65±0.89 GPa, respectively. When subjected to vertical loading, the mean failure load of 3D printed SMs (E-Guard) was 124 N and the mean deflection at fracture was 1.73 mm. Retention strengths (mean±SD) of 3D printed bands were 32±13, 43±13, 43±16 N for the plain printed, cross- hatched, and horizontal ridges designs, respectively. The retention strength of traditional SS bands was 126±27 N. Conclusions: E-Guard had superior mechanical properties among tested printing resins. Strength and deflection under the vertical load of claw-design 3D printed space maintainers may be adequate as a viable alternative to traditional SMs. Retention of 3D printed SMs was significantly lower than for traditional SS bands. Textured intaglio surfaces did not significantly improve the retention of 3D printed bands.

Disrupted propionate metabolism evokes transcriptional changes in the heart by increasing histone acetylation and propionylation.

Propiogenic substrates and gut bacteria produce propionate, a post-translational protein modifier. In this study, we used a mouse model of propionic acidaemia (PA) to study how disturbances to propionate metabolism result in histone modifications and changes to gene expression that affect cardiac function. Plasma propionate surrogates were raised in PA mice, but female hearts manifested more profound changes in acyl-CoAs, histone propionylation and acetylation, and transcription. These resulted in moderate diastolic dysfunction with raised diastolic Ca2+, expanded end-systolic ventricular volume and reduced stroke volume. Propionate was traced to histone H3 propionylation and caused increased acetylation genome-wide, including at promoters of Pde9a and Mme, genes related to contractile dysfunction through downscaled cGMP signaling. The less severe phenotype in male hearts correlated with ß-alanine buildup. Raising ß-alanine in cultured myocytes treated with propionate reduced propionyl-CoA levels, indicating a mechanistic relationship. Thus, we linked perturbed propionate metabolism to epigenetic changes that impact cardiac function.

Elastic Modulus Maturation Effect on Shrinkage Stress in a Primary Molar Restored with Tooth-Colored Materials.

Purpose: Polymerization shrinkage stress is determined by shrinkage as well as elastic modulus. Elastic modulus develops during polymerization. This study evaluated how elastic modulus affects shrinkage stresses in a primary molar for three types of restorative materials. Methods: Elastic modulus of resin composite, compomers, and resin-modified glass ionomer (RMGI) were determined using four-point bending of rectangular beams at 10 minutes, 24 hours, and after one to four weeks storage in water (n equals 10). Results were analyzed using twoway analysis of variance and pairwise comparisons (α equals 0.05). The elastic moduli were used with published shrinkage data to calculate stresses at the tooth-restoration interface in finite element models of a cross-sectioned restored primary molar. Results: The elastic modulus ranged between 5.6 to 19.9 gigapascal. Elastic modulus values were lowest at 10 minutes, regardless of material, and increased significantly (43 to 95 percent) in 24 hours; RMGI continued to increase (64 percent) for one week. Shrinkage stresses increased nonproportionally (resin composite 31 percent, compomer 35 percent, RMGI 52 percent) with increasing elastic modulus for sustained volumetric shrinkage. Conclusions: Elastic modulus development is material dependent and an important factor in polymerization shrinkage stress. Maturation of restorative materials can cause long-lasting stress increases if shrinkage is not alleviated by hygroscopic expansion.