Some observations on the breakage of ultrasonic files driven piezoelectrically.
The incidence of breakage of Piezon-Master ultrasonic K files were evaluated. Three groups of unused files were subjected to three treatments, namely; free vibration in air without irrigation, free vibration in root canal while minimizing contact with the wall of canal in the presence of irrigation and light filing in root canal with free flow of irrigation. Cavitation produced by files in contact and free of contact with a glass surface was examined in order to observe the relationship between cavitation defects and breakage. In addition, the fractured and unfractured files were examined under a scanning electron microscope for the presence of cavitation pits. The results indicated that more files broke in air. In water, a higher incidence of breakage occurred when files were allowed to freely vibrate while no breakage occurred when the files were used in filing. All files generated cavitation which resulted in pitting of their surfaces. However, it was considered unlikely that the pits contributed to fracture. Fatigue cracks which could be the result of the manufacturing process were observed at some of the corners of the cross sections of the fractured files and could be the main contributory factor to fracture.
Optimizing the chemical aspect of root canal irrigation
Root canal treatment is aimed at the removal of inflamed and infected tissue present in the root canal system. It will prevent the entrance of new microorganisms or nutrients in order to maintain or create a healthy environment around the root. There is sufficient evidence that shows that traditional endodontic therapy cannot make the root canal system completely free of bacteria. Moreover, it may not always result in complete healing of apical periodontitis, highlighting the need of optimizing the cleaning procedures. In this thesis, new models and methodologies were examined to measure, to image and to compare the cleaning efficiency of various irrigation methods and solutions and to optimize the chemical aspect of root canal irrigation. Strategies for optimizing the chemical efficiency of NaOCl in contact with dentine were suggested by analyzing the effect of concentration, temperature, pH, laser and ultrasonic activated irrigation, irrigant refreshment and exposure time in the reaction rate of NaOCl. This work also brought new insight to the evolution of temperature and pH of irrigants during root canal therapy; on the occurrence of transient cavitation around sonic and ultrasonic activated endodontic instruments. Finally, the cleaning efficiency of different irrigation methods and solutions in confined accessory root canal anatomy was investigated with the introduction, in endodontic research, of a novel hydrogel model that mimics the biofilm viscoelastic properties. The results reported in this thesis, contribute to the scientific and clinical awareness of the mechanical and chemical aspects of irrigation, which may lead to a better clinical outcome.
Chromatographic analysis of elastomer antidegradants and accelerators
Summary The use of various chromatographic methods in the analysis of all classes of elastomer antidegradants and accelerators is reviewed. The review of extraction methods is also included.