ABSTRACT
Radical-polar crossover reactions were studied for the intramolecular cyclopropanation of active methylene derivatives. In the presence of FeCl3 as a stoichiometric oxidant and K2HPO4 as a base, the dehydrogenative cyclopropanation of active methylenes proceeded through the FeCl3-promoted oxidative radical cyclization followed by the ionic cyclization to give the bicyclic cyclopropanes. The use of α-chloro-active methylenes leads the subcatalytic cyclopropanation involving two redox pathways. In the presence of K2HPO4, the redox cyclopropanation proceeded by using FeCl2 (20â mol%) in combination with ligand (20â mol%).
ABSTRACT
PURPOSE: This study aimed to analyze the effects of core materials, remaining tooth structures, and interfacial bonding on stress distribution in endodontically treated teeth using finite element analysis (FEA). MATERIALS AND METHODS: Three-dimensional FEA was conducted using a reverse engineering technique based on maxillary premolars scanned by micro-computed tomography. Six models were generated with or without ferrules and with one of the following three abutment systems: metal core, resin core, or resin core with fiber posts. In each model, bonding and debonding were assumed in the dentin and surrounding structures: bonded and debonded models. The maximum principal stress values were recorded, and stress distribution of the entire restored teeth and dentin was generated. Furthermore, the distribution of the displacement vector of the debonded models was generated. RESULTS: In comparing the bonded and debonded models, the debonded models showed larger values for tensile stresses than those in bonded models for all abutment models. The models without ferrules rotated around the center of the abutment, whereas those with ferrules did not show remarkable displacement in the analysis. CONCLUSION: FEA assuming fracture of adhesive interface proved to be an effective method to clarify the significance of ferrules. It prevents stress concentration in dentin by reducing the rotation of the abutment, even when the adhesive fails.
ABSTRACT
The prevention of root fractures of pulpless teeth is an important clinical issue to maintain healthy teeth through lifetime. The aim of this study was to examine a clinically effective treatment method for strengthening vulnerable pulpless teeth using CAD/CAM (computer-aided design/computer-aided manufacturing) fiber-reinforced post-core by conducting a fracture resistance test. A post-core made with a fiber-reinforced resin disk TRINIA (TR, SHOFU, Kyoto, Japan) was fabricated using a CAD/CAM system. The fiber-layer orientation of the CAD/CAM post-core was parallel to the axis of the restored tooth. A post-core using a conventional composite and a fiber post (CF) was also prepared. A fracture resistance test of teeth restored with the post-cores and zirconia crowns was conducted using a universal testing machine, and fracture patterns were identified by micro-CT observation. The fracture load of the roots restored with TR was 1555.9 ± 231.8 N, whereas that of CF was 1082.1 ± 226.7 N. The fracture load of TR was 43.8% that was significantly higher than that of CF (Student's t-test, p < 0.05). The restored teeth with CAD/CAM resin post-core were found to be repairable even after fracture. These results suggest that the CAD/CAM indirect fiber post-core has the potential to strengthen the vulnerable pulpless teeth.
ABSTRACT
OBJECTIVES: This study aimed to investigate physical properties of a fiber-reinforced CAD/CAM resin disc, which included woven layers of multi-directional glass fibers. METHODS: Fiber orientations of CAD/CAM specimens (TRINIA, SHOFU) were specified as longitudinal (L), longitudinal-rotated (LR), and anti-longitudinal (AL). A fiber-reinforced composite (everX posterior, GC (E)) and a conventional composite (Beauti core flow paste, SHOFU (B)) were also tested. A three-point bending test and a tensile test with notchless prism-shaped specimens were conducted using a universal testing machine (AUTOGRAPH AG-IS, Shimadzu). A water absorption test was also carried out after the specimens were stored in water for 24h or 1 week. Flexural strength and fracture toughness were obtained by conducting a three-point bending test. RESULTS: TRINIA L and LR groups showed significantly high flexural strength (254.2±22.3 and 248.8±16.7MPa, respectively). Those were approximately 2.5 times higher than those in AL, E, and B groups (96.8-98.0MPa) (p<0.05, ANOVA and Tukey HSD test). No significant difference was shown in flexural modulus among the experimental groups. The fracture toughness in L group (9.1±0.4MPa/m1/2) was found to be significantly higher than those in other groups (1.9-3.0MPa/m1/2; p<0.05). TRINIA group demonstrated significantly lower water absorption (4.7±1.9µg/mm3) than did E (16.1±3.1µg/mm3) and B (17.3±3.7µg/mm3) groups (p<0.05). SIGNIFICANCE: TRINIA demonstrated distinct anisotropy. TRINIA can be used as a superior restorative material when specifying directions of its fiber mesh layers.