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Comparative analysis of cyclic fatigue of hyflex EDMtm instruments with and without sodium hypochlorite
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INTRODUCTION: Nickel-titanium files were introduced to overcome some undesirable features of stainless steel instruments. These flexible rotary instruments have enhanced endodontic practice. Shaping and cleaning with sodium hypochlorite are responsible for eliminating microorganisms in an infected root canal system. The aim of this study was to compare cyclic fatigue resistance between, as fabricated, files in presence and absence of sodium hypochlorite. MATERIAL AND METHODS: Twenty Hyflex EDMTM files were divided in 2 groups: 10 files were tested in presence of sodium hypochlorite and 10 files were tested in its absence. A mechanical device was used to simulate the root canal system, and, to compare our data with a previous study, the same experimental parameters were followed. The testing time was registered with a digital chronometer until fracture occurred. The temperature of the files (n=2) was measured at the beginning of the essays and after 5 and 10 minutes. The number of cycles to fracture (NCF) was calculated by multiplying time by rotational speed. The normality was tested with the Shapiro-Wilk and the Levene tests, differences between groups regarding NCF were analysed using a t-student test for unequal variances. A Mann-Whitney U test was used to analyse differences between groups regarding fracture length. Additionally, Spearman’s correlation coefficient was computed after plotting fracture length against NCF. The level of statistical significance was set at 0.05. RESULTS: There was no statistically difference related to NCF/time to fracture between groups. Length of the fractured fragments was also similar between groups. Both groups showed that the higher the NCF was, the smaller the length of fracture, presenting a statistically significant result. DISCUSSION AND CONCLUSION: Within the limitations of this study, results suggest that fatigue life is similar in both groups. A standardisation in cyclic fatigue tests is required to obtain consistent results and for a safer clinical use.
Descrição
Tese de mestrado, Medicina Dentária, Universidade de Lisboa, Faculdade de Medicina Dentária, 2017
Palavras-chave
Endodontia Materiais dentários Fadiga Teses de mestrado - 2017