ABSTRACT
O objetivo deste trabalho foi comparar a deflexão angular até a fratura e o torque máximo em torção de instrumentos endodônticos de NiTi mecanizados de um mesmo número, de um mesmo fabricante de diferentes conicidades. Os instrumentos foram submetidos ao ensaio mecânico de torção à direita. Os valores obtidos foram submetidos à análise estatística e os resultados revelaram que a conicidade das hastes helicoidais dos instrumentos ensaiados influenciaram na deflexão angular até a fratura e no torque máximo suportado pelo instrumento antes da fratura. A deflexão angular aumentou com a redução da conicidade, enquanto o torque máximo diminuiu com a redução desta.
The aim of this work was to compare the angular deflection at failure and the maximum torque of NiTi rotatory instruments with the same size, same trademark and different tapers. The instruments were submitted to clockwise torsional mechanical tests. The values were submitted to statistical analisys and the results showed that the taper of helical shaft influenced theangular deflection and the maximum torque at failure. The angular deflection increased with the taper reduction,although the maximum torque at failure decreased with the taper reduction.
Subject(s)
Biomechanical Phenomena , Dental Instruments/standards , Nickel , Titanium , Torque , Torsion, MechanicalABSTRACT
The specific tension index (STI) estimates the ratio of maximum torque (TQ) to muscle volume (MV) for a specific task and includes muscle thickness as a parameter, which can be directly evaluated by ultrasound. The objective of the present study was to compare TQ, MV and STI of the elbow flexors between strength-trained and untrained subjects. Forty men, including 11 subjects strength trained for at least two years [trained group (TG): 23.5 ± 3.1 years; 182.1 ± 4.9 cm; 88.1 ± 8.4 kg] and 29 untrained subjects [untrained group (UG): 29.8 ± 1.6 years; 172.4 ± 6.6 cm; 76.4 ± 8.1 kg], participated in the study. The STI of the elbow flexors, expressed as the TQ/MV ratio, was calculated for both groups. Muscle thickness measured by ultrasound was used to estimate MV. TQ of the elbow flexors was estimated using maximum isometric voluntary contractions. The Mann-Whitney test was used to determine possible differences in TQ, STI and MV between groups. MV and TQ were significantly higher in TG (526.07 ± 86.13 cm3; 112.04 ± 24.18 Nm) than UG (385.40 ± 80.89 cm3; 88.46 ± 13.77 Nm). There was no significant difference in the STI between TG (0.213 ± 0.03 Nm.cm3-) and UG (0.233 ± 0.02 Nm.cm3-). Although stronger, trained subjects presented elbow flexor STI values similar to those of the untrained group, a finding suggesting the maintenance of the linearity of the force-volume ratio. TQ and MV estimates were found to be reliable parameters for the distinction between groups. The STI may contribute to a more applied analysis in clinical practice and in the prescription of physical activity as an indicator of inadequate levels of overload and of the risk of injury.
The specific tension index (STI) estimates the ratio of maximum torque (TQ) to muscle volume (MV) for a specific task and includes muscle thickness as a parameter, which can be directly evaluated by ultrasound. The objective of the present study was to compare TQ, MV and STI of the elbow flexors between strength-trained and untrained subjects. Forty men, including 11 subjects strength trained for at least two years [trained group (TG): 23.5 ± 3.1 years; 182.1 ± 4.9 cm; 88.1 ± 8.4 kg] and 29 untrained subjects [untrained group (UG): 29.8 ± 1.6 years; 172.4 ± 6.6 cm; 76.4 ± 8.1 kg], participated in the study. The STI of the elbow flexors, expressed as the TQ/MV ratio, was calculated for both groups. Muscle thickness measured by ultrasound was used to estimate MV. TQ of the elbow flexors was estimated using maximum isometric voluntary contractions. The Mann-Whitney test was used to determine possible differences in TQ, STI and MV between groups. MV and TQ were significantly higher in TG (526.07 ± 86.13 cm3; 112.04 ± 24.18 Nm) than UG (385.40 ± 80.89 cm3; 88.46 ± 13.77 Nm). There was no significant difference in the STI between TG (0.213 ± 0.03 Nm.cm3-) and UG (0.233 ± 0.02 Nm.cm3-). Although stronger, trained subjects presented elbow flexor STI values similar to those of the untrained group, a finding suggesting the maintenance of the linearity of the force-volume ratio. TQ and MV estimates were found to be reliable parameters for the distinction between groups. The STI may contribute to a more applied analysis in clinical practice and in the prescription of physical activity as an indicator of inadequate levels of overload and of the risk of injury.