The study was undertaken to evaluate the biaxial flexural strength, biaxial flexural strength after etching with 9 % HF acid and fracture toughness of three commonly used pressable all ceramic core materials. Ninety glass ceramic specimens were fabricated from three commercially available leucite based core ceramic material (1) Esthetic Empress, (2) Cergo, and (3) Performance Plus. Thirty discs of each material were divided into three groups of 10 discs each. Biaxial flexural strength (30 discs,) Biaxial flexural strength for samples treated with 9 % HF acid (30 discs) and fracture toughness (30 discs) were evaluated. Core material Performance Plus had the lowest biaxial strength of 124.89 MPa, Cergo had strength of 152.22 MPa and the highest value of 163.95 was reported for Esthetic Empress. For samples treated 9 % HF, Performance Plus had the lowest biaxial strength of 98.37 MPa, Cergo had strength of 117.42 MPa and the highest value of 143.74 was reported for Esthetic Empress. Core material Performance Plus had the lowest fracture toughness of 1.063 MPa, Cergo had strength of 1.112 MPa and the highest value of 1.225 was reported for Esthetic Empress. The results shows that Esthetic Empress had better mechanical properties compared to Cergo had Performance Plus in relation to the parameters tested.

Metrics & MoreArticle Recommendations * sı Supporting InformationABSTRACT: [4 + 2] oxidative Diels−Alder reaction of readily available alkynols with maleimide is achieved for the rapid access of pthalimidefused multicyclic compounds. The reaction is proposed to go through a sequence of Sc(OTf) 3 -catalyzed electrophilic cyclization, ligand exchange with Cp*-free cobalt, and C−H activation followed by maleimide insertion.

Background: A stereoselective synthetic strategy towards (+)-paecilomycin F is reported. The approach utilizes readily available commercial 2,4,6-trihydroxybenzoic acid and easily accessible chiral R(+)-propylene oxide as starting materials. Methods: The synthesis involves regioselective Grignard reaction, Wittig reaction, Sharpless asymmetric dihydroxylation, Barbier-type allylation, Stille coupling and ring closing metathesis as key reactions. Results: The target molecule is produced in a 7-step linear sequence with an overall yield of 20% starting from 2,4,6-trihydroxy benzoic acid or 12-step sequence with an overall yield of 12.95% starting from R(+)-propylene oxide. Conclusion: The aromatic fragment synthesis was achieved using earlier known protocols starting from 2,4,6-trihydroxybenzoic acid (vide infra).

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