Evaluation of the frequency and temperature dependence of the dynamic mechanical properties of acetal resins

Preparation of hexamethylol melamine resin with low crystallization water and low viscosity for hexamethylol melamine/polyvinyl alcohol composite membrane

Hexamethylol melamine resins (HMM) with low crystallization water content and low viscosity were prepared by inhibiting the condensation polymerization of low hexamethylol melamine. The effects of catalyst, pH, formalde-hyde/melamine ratio, reaction temperature and time on the synthesis parameters of HMM were investigated. The results showed that the sample (HMM8) synthesized with Na2CO3-NaHCO3 as catalyst had the crystallization water content lower than 10%, being with a viscosity of about 0.26 Pa·s. The melting temperature of HMM8/polyvinyl alcohol (PVA) curing system was about 164.3 °C. It was found that the higher the amount of formaldehyde, the greater the hydroxyl methyl bounded to each triazine ring. Compared with the traditional melamine formaldehyde resin which had the crystallization water content of about 20–30%, the production of this resin was expected to reduce the energy consumption of industrial reaction, while the resin with 10% crystallization water content was more conducive to the development of alloying HMM/PVA composite membrane.

CAD/CAM Diagnostic Esthetic Functional Splint (DEFS) as a Removable Prototype to Evaluate the Final Prosthetic Rehabilitation: A Narrative Review

The main objective of this narrative review was to provide an overview of DEFS (Diagnostic Esthetic Functional Splint), namely CAD/CAM manufactured, “snap-retained”, tooth-colored splints available by materials exhibiting a certain degree of elasticity (like polycarbonates or acetal resins) for restoring function, esthetics and occlusion in several clinical situations, before or as an intermediate alternative to undergoing the final treatment. The search strategy included all papers dealing with snap-retained prosthetic systems and was based on a literature review of papers available in electronic databases (Pubmed/Medline, Evidence-Based Dentistry, BMJ Evidence-Based Medicine, Dynamed, Embase, BMJ Clinical Evidence, Web of Science, Scientific reports); eligible papers were researched on Opengreyand a manual search was performed, as well. From the electronic databases emerged 13,199 records, many of which were duplicates. The grey literature and the manual research did not produce any eligible article. After duplicates removal, 7690 records were obtained. Titles, abstracts and keywords were analyzed. The studies concerning the topic of interest were examined by the reviewers and discussed. Although no evidence-based data were found in the literature, according to the authors’ clinical experience, the DEFS (Diagnostic Esthetic Functional Splint) is a very promising solution in multiple clinical situations, due to its diagnostic, therapeutical, functional and esthetic versatility.

Fabrication and Characterization of Isotropic and Anisotropic Magnetorheological Elastomers, Based on Silicone Rubber and Carbonyl Iron Microparticles

This article focuses on studying the rheological behavior of isotropic and anisotropic magnetorheological elastomers (MREs), made of carbonyl iron microparticles dispersed into a silicone⁻rubber matrix by considering 20 and 30 wt % of microparticles. Sample sets were prepared for each composition, with and without the application of an external magnetic field. Experimental measurements of the material rheology behavior were carried out by a shear oscillatory rheometer at constant temperature, to determine both the shear storage modulus (G') and shear loss modulus (G'') for all characterized samples. Then, experimental data collected from the isotropic and the anisotropic material samples were used to plot the Cole-Cole diagrams to quantify the interfacial adhesion between carbonyl iron microparticles and the silicone-rubber matrix. Furthermore, the Fractional Zener Model (FZM) with two spring-pots in series is used for quantitative analysis of collected experimental data.