Influência da velocidade de rotação na resistência à fadiga cíclica do sistema rotatório Logic / Influence of the rotational speed on the cyclic fatigue resistance of the Logic rotary system

O objetivo do presente trabalho foi avaliar a influência da velocidade de rotação na resistência à fadiga cíclica do instrumento rotatório Logic 25.06 (LOG 25.06; Easy Equipamentos Odontológicos, Belo Horizonte, Brasil). Métodos: Foram utilizados 20 instrumentos rotatórios Logic 25.06 (n=10). O teste de fadiga cíclica foi realizado em um aparato com um canal artificial de aço inoxidável com ângulo de curvatura de 60° e raio de 5 mm. Os instrumentos foram utilizados a 950 e 550 rotações por minuto (RPM), sendo mensurados o tempo e o número de ciclos para a fratura. Os dados foram analisados estatisticamente por meio do teste t de Student, sendo selecionado um nível de significância de 5%. Resultados: O teste de fadiga cíclica demonstrou que a velocidade de 550 RPM promoveu um aumento significativo no tempo e no número de ciclos para a fratura dos instrumentos LOG 25.06 (p<0,05). Houve um aumento de 95,9% no tempo e de 27,25% do número de ciclos para a fratura. Conclusão: Os resultados desse estudo demonstraram que a velocidade de rotação possui uma influência significativa na resistência à fadiga cíclica dos instrumentos rotatório Logic 25.06. A velocidade de 550 RPM é uma velocidade mais segura, aumentando significativamente a resistência à fadiga cíclica (AU).

Objective: The aim of this study was to evaluate the influence of rotational speed on the cyclic fatigue resistance of Logic 25.06 rotary instruments (LOG 25.06; Easy Equipamentos Odontológicos, Belo Horizonte, Brazil). Methods: 20 Logic 25.06 instruments were used (n=20). The cyclic fatigue test was performed in an artificial canal made of stainless steel with 60° of curvature and 5 mm of radius. The instruments were activated 950 and 550 rotations per minute (RPM) until the fracture occurred. The time (in seconds) and the number of cycles to fracture (NCF) were measured. The data were statistically analyzed using One-way ANOVA and Tukey Test, the level significance used was 5 %. Results: the 550 RPM promoted a significantly higher time and NCF of LOG 25.06 in comparison with 950 RPM (P>0.05). The time increased in 95.9% and the NCF 27.25%. Conclusion: The results of this study showed that the rotational speed had a significant influence on the cyclic fatigue resistance of the Logic 25.06 rotary instruments. The 550 RPM rotational speed seems to be safer than 950 RPM, increasing the cyclic fatigue resistance of Logic 25.06 (AU).

Ultrasonic tips as an auxiliary method for the instrumentation of oval-shaped root canals

Abstract To evaluate the influence of novel ultrasonic tips as an auxiliary method for the rotary preparation of flattened/oval-shaped canals. Forty-five mandibular incisors were selected and divided into one of three experimental groups (n = 15): Group PFCP - ProDesign Logic 25/.05 + Flatsonic + Clearsonic + Prodesign Logic 40/.01; Group FCP - Flatsonic + Clearsonic + ProDesign Logic 40/.01; and Group PP - Prodesign Logic 25/.05 + Prodesign Logic 40/.05. The teeth were scanned preoperatively and postoperatively using microcomputed tomography. The percentage values for increase in volume, non-instrumented surface area, dentin removal, degree of canal transportation, and centering ratio between the experimental groups were examined. Data were analyzed using the non-parametric Kruskal-Wallis and Dunn's tests (p < 0.05). Group PFCP showed the greatest volume increase in the total portion of the root canal and the lowest percentage of non-instrumented surface area. Regarding the degree of transportation in the buccolingual direction, statistically significant differences between groups PFCP and PP were observed at the coronal third of the canal. In the mesiodistal direction, no statistically significant differences were observed at the coronal, middle, and apical thirds. As for the centering ratio, statistically significant differences were found in the buccolingual direction. In the mesiodistal direction, no statistically significant differences were observed at the coronal, middle, and apical thirds. The use of novel ultrasonic tips combined with rotary instruments in group PFCP provided a significant increase in volume and reduced the percentage of non-instrumented areas during the preparation of flattened/oval-shaped canals.