ABSTRACT
Abstract This study aimed to evaluate the influence of temperature on torsional strength and angular deflection of two experimental NiTi rotary instruments manufactured from Blue and Gold thermal treatments and with identical cross-sections. A total of 40 experimental NiTi instruments 25.06 and with a triangular cross-section and manufactured from Blue and Gold thermal treatments were used (n=20). The torsional test was performed in the 3 mm from the tip of the instrument according to ISO 3630-1. The torsional test evaluated the torsional strength and angular deflection to failure at room temperature (21°C ± 1° C) and body temperature (36°C ±1°C). The fractured surface of each fragment was observed by using scanning electron microscopy (SEM). Data were analyzed using an unpaired t test for inter and intra-group comparison and the level of significance was set at 5%. The results showed that the body temperature did not affect the torsional strength and angular deflection of the instruments when compared with room temperature (P>0.05). However, at body temperature, the Blue NiTi instruments presented significantly lower angular deflection in comparison with Gold NiTi instruments (P<0.05). There was no significant difference regarding the torsional strength of the instruments at body temperature (P>0.05). The temperature did not affect the torsional strength of the instruments manufactured from Blue and Gold technology. However, the Blue NiTi instruments presented significantly lower angular deflection than Gold instruments at 36°C temperature.
Resumo O objetivo deste estudo foi avaliar a influência da temperatura nas propriedades de torção (resistência à torção e deflexão angular) de dois instrumentos rotatórios experimentais de NiTi fabricados com secção triangu.ar e tratamentos térmicos Blue e Gold. Quarenta instrumentos experimentais de NiTi 25.06 com tratamento térmico Blue e Gold foram usados (n= 20). Foi avaliada a resistência torcional e a deflexão angular até a fratura na temperatura ambiente (21°C ± 1°C) e corporal (36°C ± 1°C). O teste torcional foi realizado nos 3 mm da ponta dos instrumentos de acordo com a ISO 3630-1. A superfície fraturada de cada instrumento foi observada pelo microscópio eletrônico de varredura (MEV). Os dados foram analisados por meio do teste t não pareado para a comparação inter e intragrupos e o nível de significância à 5%. Os resultados demonstraram que a temperatura corporal não afetou a resistência a torção e deflexão angular quando comparada com a temperatura ambiente (P>0.05). No entanto, na temperatura de 36°C o instrumento com tratamento térmico Blue apresentou menor deflexão angular quando comparado com o Gold (P<0.05). Não houve diferença significante entre os dois instrumentos em relação a resistência à torção. A temperatura corporal não modificou a resistência torcional dos instrumentos fabricados com tecnologia Blue e Gold. No entanto, os instrumentos com NiTi Blue apresentaram menor deflexão angular do que o Gold a 36°C.
ABSTRACT
Aim: The purpose of this study was to evaluate the effect of multiple root canal usage on the surface topography and fracture of Twisted File (TF) and ProTaper (PT) rotary Ni-Ti file systems, using scanning electron microscope (SEM). Materials and Methods: Ten sets of PT and TF instruments were used to prepare the mesial canals of mandibular first molars. TF 25, 0.06 taper and PT F1 instruments were analyzed by SEM when new and thereafter every three root canal usages. This sequence was repeated for both the TF and PT groups until 12 uses. Two images of the instrument were recorded, one of the instrument tip and the other 5 mm from the tip, both at ×100 magnification. The sequential use was continued till the instrument fractured and the number of root canal usages for the file to fracture was noted. All fracture surfaces were examined under the SEM. Results: Fresh TF instruments showed no surface wear when compared to PT instruments (P < 0.05). Spiral distortion scores remained the same for both the groups till the 6 th usage (P > 0.05), while at the 9 th usage TF showed a steep increase in the spiral distortion score when compared to PT (P < 0.05). PT instruments fractured at a mean root canal usage of 17.4, while TF instruments showed a mean root canal usage of 11.8. Fractographically, all the TF instruments failed due to torsion, while all the PT instruments failed because of cyclic fatigue. Conclusion: PT instruments showed more resistance to fracture than TF instruments.