Material removal and surface damage in high-speed grinding of enamel.

Although high-speed grinding of the enamel surface is often required in restorative dentistry, the knowledge of grinding mechanics, material removal, and fracture damage mechanism related to this process is still relatively limited; therefore, it is important to perform relevant scientific and theoretical research. As per the occlusal surface and the buccal/lingual surface of the teeth, the experimental scheme of high-speed grinding of the enamel surface using a diamond grinding bur was designed, and the grinding force, force ratio, grinding temperature, chips, surface morphology, surface damage, and other important characteristics were tested and analyzed. Furthermore, the grinding geometry model, grinding mechanics, material fracture, and removal mechanism associated with the high-speed grinding of an enamel surface were considered. The results show that the grinding force, friction coefficient, grinding temperature, and surface damage achieved through buccal/lingual surface grinding are considerably greater, and the grinding quality is worse than that obtained via occlusal surface grinding under the same grinding conditions. With the increase in the feed rate, grinding force, friction coefficient, grinding temperature, and surface damage obviously increase, and the surface quality decreases. The embrittlement effect and the ironing mechanism are present during the process of high-speed grinding of enamel. Regardless of the feed rate, the three types of material fracture modes of the buccal/lingual surface are more serious than those of the occlusal surface (making it more likely to produce unstable large chips or tearing chips); moreover, the brittle fracture and damage of the final machined surface are more obvious. The cutting mechanics and cutting mechanism identified in this study will provide scientific guidance for dental grinding operations.

Oxidative Dehydrogenation of Hydrazobenzenes toward Azo Compounds Catalyzed by tert-Butyl Nitrite in EtOH.

We describe a tert-butyl nitrite-catalyzed oxidative dehydrogenation of hydrazobenzenes for producing azobenzenes. This method proceeds at ambient temperature and under an atmospheric environment by employing eco-friendly EtOH as the medium, representing a mild, general route to the synthesis of various symmetrical and nonsymmetrical azobenzenes in excellent yields with broad functional group tolerance.

[Correlation analysis of color change and Maillard reaction during processing of Gardeniae Fructus Praeparatus].

The chromaticity space parameters of the samples during the processing of Gardeniae Fructus Praeparatus(Jiaozhizi in Chinese herbal name, JZZ) were measured by the visual analyzer to analyze the color variation rule during the processing of JZZ, and the content changes of total reducing sugar, total amino acid and 5-hydroxymethylfurfural(5-HMF) related to Maillard reaction were measured. Pearson correlation analysis and linear regression analysis of the data were carried out by SPSS 24.0 software. The experimental results showed that the objective coloration of the samples in the processing of JZZ was basically consistent with the traditional subjective color judgment; the contents of total reducing sugar and total amino acids showed a decreasing trend during the processing of JZZ, and the content of 5-HMF showed an increasing trend, which was in line with Maillard reaction law. Pearson correlation analysis results showed that there was a significant correlation between the chromaticity space parameters L~*(lightness value), a~*(red green value), b~*(yellow blue value), E~*ab(total color value) and the contents of total reducing sugar, total amino acid and 5-HMF(P<0.01), among which the values of L~*, a~*, b~*, E~*ab were positively correlated with the contents of total reducing sugar and total amino acid, and negatively correlated with the contents of 5-HMF. The results of linear regression analysis also showed that these two were highly correlated. In this study, by establishing the correspondence relationship between the color change of JZZ processing and Maillard reactants, wecan not only provide a basis for the objective digital expression of subjective color of JZZ, but also provide a reference for explaining the processing mechanism of JZZ from a new perspective.

[2 + 2 + 1] Heteroannulation of Alkenes with Enynyl Benziodoxolones and Silver Nitrite Involving C≡C bond Oxidative Cleavage: Entry to 3-Aryl-Δ2-isoxazolines.

A copper-catalyzed [2 + 2 + 1] heteroannulation of alkenes with enynyl benziodoxolones and AgNO2 involving oxidative cleavage of the C≡C bond promoted by cooperative Zn(OTf)2, KOAc, and 4 Å MS for producing 3-aryl Δ2-isoxazolines is reported. Mechanistic studies indicate that AgNO2 serves as the N/O two-atom unit source, enabling the formation of three bonds through NO2 addition across the C≡C bond, NO-transfer, C≡C bond cleavage, and annulation cascades.

Machinability of high-speed enamel cutting with carbide bur.

The cutting of tooth enamel using a high-speed air-turbine handpiece and carbide bur is a key procedure in oral surgeries, such as the minimally invasive extraction. However, presently little is known about the cutting mechanics and material removal mechanism related to tooth enamel machinability. In this study, the machinability of high-speed enamel cutting with carbide bur is studied by a computer-aided numerical control system. The dynamic cutting forces of enamel of the occlusal, buccal/lingual, and proximal surfaces were measured by the force measuring system. The force ratio, cutting torque, rotating speed, specific cutting energy, and bur wear were analyzed. The microstructure of enamel and carbide burs was observed by the scanning electron microscope, and the relationship between enamel microstructures and machinability was further analyzed. The results show that during the high-speed enamel cutting with carbide bur, the chip thickness is on the nano-scale, and the plastic deformation of the machined surface is obvious. With increased material removal rate, the cutting force, torque, specific cutting energy, and bur wear increases accordingly, whereas the rotating speed decelerates (p < 0.05). The different angles between the cutting direction and the axial direction of the enamel rods give rise to the large differences in the cutting mechanics and mechanism of the proximal, buccal/lingual, and occlusal surfaces of the teeth. When the cutting direction is parallel, vertical, and oblique 45° to the axial direction of the enamel rods, the force required for material fracture and crack propagation increases, and the cutting force increases as a consequence. Parallel and oblique 45° cutting are the main modes of tooth segmentation in the minimally invasive extraction. In comparison with the parallel cutting mode, the cutting force, torque, and cutting ratio of the oblique 45° cutting mode can be significantly increased, and the tool wear is obviously accelerated. This is the lowest priority in segmentation surgery, hence the problems of overload and temperature rise need to be considered. The cutting mechanics and cutting mechanism obtained in this study will provide scientific process guidance for dental cutting operations with the air-turbine handpiece driving bur.

Machinability of enamel under grinding process using diamond dental burrs.

Enamel grinding is a critical dental surgery process. However, tooth damage during the process remains a significant problem. Grinding forces, burr wear, and surface quality were characterised in relation to grinding speed, enamel orientation, grinding depth, and burr grit grain size. Results indicated that enamel rod orientation, grinding depth, and grinding speed critically affected enamel grinding. Occlusal surface grinding resulted in significantly higher normal forces, surface roughness, and marginally greater tangential forces than axial surface grinding. Damage to enamel machined surfaces indicated the significant impact of diamond grit size and rod orientation. Burr wear was primarily diamond grit peeling off and breakage. Surface roughness of axial and occlusal sections was largely influenced by grinding speed and diamond grit size. Improving the surface quality of machined enamel surfaces could be realised using fine burrs, reducing the grinding speed and grinding depth, and adjusting the feed direction vertical to the rod orientation. Enamel surface quality and roughness could be improved by reducing brittle failure and circular runout during the grinding process, respectively.

Iron-Catalyzed Intermolecular 1,2-Difunctionalization of Styrenes and Conjugated Alkenes with Silanes and Nucleophiles.

The first iron-catalyzed 1,2-difunctionalization of styrenes and conjugated alkenes with silanes and either N or C, using an oxidative radical strategy, is described. Employing FeCl2 and di-tert-butyl peroxide allows divergent alkene 1,2-difunctionalizations, including 1,2-aminosilylation, 1,2-arylsilylation, and 1,2-alkylsilylation, which rely on a wide range of nucleophiles, namely, amines, amides, indoles, pyrroles, and 1,3-dicarbonyls, thus providing a powerful platform for producing diverse silicon-containing alkanes.

Oxidative cyclization of 2-allenyl-1,1'-biphenyls with α-carbonyl alkyl bromides: facile access to functionalized phenanthrenes.

A new copper-facilitated oxidative cyclization of 2-allenyl-1,1'-biphenyls with α-carbonyl alkyl bromides for producing functionalized phenanthrenes is presented, which represents the first allene 2,3-dicarbofunctionalization triggered by oxidative radical-medicated C3-addition of the terminal allene moiety and C-Br/C-H functionalization.

Reciprocal regulation of miR-1254 and c-Myc in oral squamous cell carcinoma suppresses EMT-mediated metastasis and tumor-initiating properties through MAPK signaling.

AIM: This study aimed to determine the effect of miR-1254 on oral squamous cell carcinoma (OSCC) metastasis and the specific mechanism involved. METHODS: The metastatic properties of OSCC cells were analyzed by transwell assays. The tumor-initiating properties of OSCC cells were analyzed by tumor sphere formation assays. The mRNA and protein expressions of targeted genes were determined by quantitative polymerase chain reaction assays and western blot analyses, respectively. Xenograft experiments were employed to evaluate the anti-metastatic effects of miR-1254 and miR-1254-mediated cancer stem cell (CSC) properties in vivo. The gene targets of miR-1254 were investigated by luciferase reporter assays. Chromatin immunoprecipitation assays were performed to observe the transcriptional regulation of miR-1254 biogenesis by transcription factor. RESULTS: miR-1254 attenuated OSCC metastasis and tumor-initiating properties in vitro and in vivo. Consistent with the experimental observations, miR-1254 was decreased in late-stage OSCCs and strongly correlated with risk of OSCC metastasis. Moreover, miR-1254 was mechanistically shown to down-regulate MAP3K3, accompanied by inactivation of the MAPK signaling pathway and inhibition of epithelial-mesenchymal transition (EMT) in OSCC cells. miR-1254 was transcriptionally repressed by c-Myc to form a positive feed back loop through MAPK signaling. CONCLUSION: Our findings suggest that miR-1254 is a potential target for the treatment of OSCCs, and miR-1254 can be clinically utilized as a biomarker for the clinical prognosis or diagnosis of OSCCs.

Copper-promoted [2+2+2] annulation of 1,n-enynes through decomposition of azobis(alkyl nitrile)s.

A novel copper-promoted [2+2+2] annulation of 1,n-enynes with azobis(alkyl nitrile)s and H2O for the synthesis of diverse 7,8-dihydrophenanthridine-6,9(5H,6aH)-diones and fluorene is described. The reaction proceeds via the decomposition of azobis(alkyl nitrile)s into the cyanoalkyl radicals as the two-carbon units and offers a new efficient tool for the one-step formation of four new chemical bonds.

Metal-free carbonyl C(sp(2))-H oxidative alkynylation of aldehydes using hypervalent iodine reagents leading to ynones.

A new metal-free tert-butyl hydroperoxide (TBHP)-mediated carbonyl C(sp(2))-H oxidative alkynylation of aldehydes with ethynyl benziodoxolones (EBX) for the synthesis of ynones is described. This method is based on a carbonyl C(sp(2))-H oxidative radical coupling process according to mechanistic studies, and provides a general route to the assembly of diverse ynones with a broad substrate scope and excellent functional-group compatibility.

Copper-catalyzed oxidative coupling of acids with alkanes involving dehydrogenation: facile access to allylic esters and alkylalkenes.

We here describe a new copper-catalyzed oxidative coupling of acids with alkanes for the selective synthesis of allylic esters and alkylalkenes. This method achieves multiple dehydrogenation and esterification, representing a new unactivated C(sp(3))-H oxidative esterification of acids with common alkanes.

Oxidative 1,2-difunctionalization of activated alkenes with benzylic C(sp3)-H bonds and aryl C(sp2)-H bonds.

DTBP (di-tert-butyl peroxide) is utilized to mediate oxidative 1,2-difunctionalization of activated alkenes with an aryl C(sp(2))-H bond and a benzylic C(sp(3))-H bond for the synthesis of functionalized oxindoles. This reaction is a new organomediated strategy for alkene difunctionalization facilitated by Lewis acids.

[Influence of matrix on the optical limiting effect of metallophthalocyanine doped composite].

Nickle tetrasulfo-phthalocyanine (NiTSPc) and Lead phthalocyanine (PbPc) are introduced respectively into silica gel glass matrix by sol-gel technique. Homogeneously doped composites are produced, and optical limiting examination was carried out. The results show that the change in matrix composition, structure and sol-gel process will influence the chemical micro-environment and excited state physical process of doped metallo phthalocyanine, resulting in the change in composite's optical limiting behaviors.

[Study on the effect of extract of Chinese chive seed in warming kidney and enhancing yang].

OBJECTIVE: To explore the effect of extract from Chinese chive seed in warming kidney and enhancing yang. METHOD: The influence of extract from Chinese chive seed on the erection of penis of was investigated in adult male rats with experimental insufficiency of the kidney-yang produced by both removal of double spermaries and high dose of hydrocortisone. RESULT: The extract of Chinese chive seed enhanced the responsiveness of the penis of emasculate rats to outside stimulus, promoted the resistance of the emasculated rats to cold and tiredness and increased autonomous activity. CONCLUSION: The extract of Chinese chive seed has the effect of warming kidney and enhancing yang.