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Three-dimensional finite element simulation of intrusion of the maxillary central incisor

Ryniewicz W., Ryniewicz A. M., Bojko Ł., Pełka P., Filipek J., Williams S., Loster B. W.

Biocybernetics and Biomedical Engineering

2016

Vol. 36, no. 2

385--390

Purpose: The aim of this study is to generate a global digital model of treatment, analysis of stress distribution and displacements: in a construction of the bracket, in the incisor with bonded bracket, in tissues of the incisor, in a periodontal membrane and in an alveolus. Methods: An orthodontic therapy was provided with a three-dimensional model of a unique Cannon Ultra bracket. The placement of the bracket to the incisor was provided according to clinical standards. Composite material was placed between the rough surface of the bracket's base and labial incisor surface – which, in a digital model, resulted in contact without displacement. The bracket was loaded. An orthodontic arch wire was free to move in a wing slot of the bracket. For simplification, a force vector was parallel to the longitudinal axis of the incisor. A clamper was set on the surface of the cortical bone of the alveolus. The model was divided into a finite number of tetrahedral elements. To calculate the distribution of stress Ansys Workbench software was used. Results: The stress values indicate that there were no tissue overloaded areas. The stress distribution was regular in the periodontal ligament. Slight movements were observed with maximal values in the area of apex. Conclusions: This study simulation proves that tissues surrounding the tooth were influ-enced mechanically by the force loaded on the bracket. [...]

Spectroscopy and Photophysics of 6,8-Dimethylalloxazine. Experimental and Theoretical Study

Sikorska E., Khmelinskii I., Bednarek A., Williams S., Worrall D., Herance J., Bourdelande J., Nowacka G., Koput J., Sikorski M.

Polish Journal of Chemistry

2004

Vol.78 /nr 11-12

2163-2173

Photophysics of 6,8-dimethylalloxazine was studied experimentally in function of solvent properties and theoretically by using time-dependent density functional theory (TD-DFT) calculations. The absorption spectrum of 6,8-dimethylalloxazine in the near-UV region shows one broad maximum at approximately 350 nm (ca. 28600 cm-1), which is a superposition of the two lowest-energy bands, and a fluorescence emission band varying from about 462 nm (21600 cm-1) in dioxane and acetonitrile to 475 nm (21000 cm-1) in methanol solution. In aprotic solvents neither band shows a significant dependence on the solvent polarity. The fluorescence lifetime increases in protic relative to aprotic solvents, and increases with increasing solvent polarity, due to reduction of the non-radiative rate constant. TD-DFT calculations provide details of the electronic structure of the molecule in its excited states and allow the interpretation of the observed photophysics in terms of the proximity effect.