ABSTRACT Torsional overload is a fracture representative parameter for instruments in single-file techniques. Objective The aim of this study was to assess the influence of clinical use, in vivo, on the torsional behavior of Reciproc and WaveOne instruments considering the possibility that they degraded with use. Material and Methods Diameter at each millimeter, pitch length, and area at 3 mm from the tip were determined for both types of instruments. Twenty-four instruments, size 25, 0.08 taper, of each system were divided into two groups (n=12 each): Control Group (CG), in which new Reciproc (RC) and WaveOne Primary (WO) instruments were tested in torsion until rupture based on ISO 3630-1; and Experimental Group (EG), in which each new instrument was clinically used to clean and shape the root canals of one molar. After clinical use, the instruments were analyzed using optical and scanning electron microscopy and subsequently tested in torsion until fracture. Data were analyzed using one-way analysis of variance at a=.05. Results WO instruments showed significantly higher mean values of cross-sectional area A3 (P=0.000) and smaller pitch lengths than RC instruments with no statistically significant differences in the diameter at D3 (P=0.521). No significant differences in torsional resistance between the RC and WO new instruments (P=0.134) were found. The clinical use resulted in a tendency of reduction in the maximum torque of the analyzed instruments but no statistically significant difference was observed between them (P=0.327). During the preparation of the root canals, two fractured RC instruments and longitudinal and transversal cracks in RC and WO instruments were observed through SEM analysis. Conclusion After clinical use, no statistically significant reduction in the torsional resistance was observed.

Este estudo avaliou protocolos de irrigação sônica e a vácuo em relação à capacidade de remoção de debris do sistema de canais radiculares. Trinta primeiros molares mandibulares tiveram seus canais radiculares preparados pela utilização do Sistema ProTaper Universal. Os dentes foram divididos em dois grupos experimentais (n=15): Grupo 1: protocolo de irrigação sônica, e Grupo 2: protocolo de irrigação a vácuo. Posteriormente, as raízes mesiais foram seccionadas e observadas em lupa estereoscópica e microscopia eletrônica de varredura. Três examinadores independentes avaliaram as imagens do terço apical de acordo com as seguintes pontuações: 1. pequena presença de debris; 2: moderada presença de debris; e 3. densa presença de debris. Os dados foram analisados pelos testes estatísticos ANOVA e Kruskal-Wallis (α=0,05). A comparação entre os grupos revelou que, no terço apical, as hemissecções radiculares do Grupo 1 apresentaram debris remanescentes de forma significativamente menor (p=0,002) do que as do Grupo 2. No entanto, a 2 mm do comprimento de trabalho, as amostras do Grupo 2 mostraram menos debris remanescentes em aproximadamente 75% dos canais radiculares analisados. Considerando todo o terço apical, o protocolo de irrigação sônica removeu significativamente mais debris do que o protocolo de irrigação a vácuo. No entanto, na região a 2 mm do comprimento de trabalho, o segundo método de irrigação demonstrou um melhor desempenho

This study evaluated the protocols of sonic and vacuum irrigation regarding the capacity of debris removal from root canal systems. Canal preparations were carried out on 30 mandibular first molars using the ProTaper Universal System. Teeth were divided into two experimental groups (n=15): Group 1: sonic irrigation and Group 2: vacuum irrigation protocol. Subsequently, the mesial roots were sectioned and observed by stereomicroscopy and scanning electron microscopy. Three independent examiners evaluated images of the apical thirds according to the following scores: 1= small presence of debris, 2= moderate presence of debris, and 3= dense presence of debris. Data were analyzed with ANOVA and Kruskal-Wallis tests (α=0.05). Comparison among the groups revealed that at the apical third, the root halves of Group 1 had significantly less surface debris (p=0.002) than those of Group 2. However, at 2 mm from the working length, Group 2's specimens showed less remaining debris in approximately 75% of the analyzed root canals. At the whole apical third, the sonic irrigation protocol removed significantly more debris than the vacuum protocol. However, in the region at 2 mm from the working length, the second irrigation method demonstrated a better performance.

OBJECTIVE: This study identified which regions of ProTaper instruments work during curved root canal instrumentation. MATERIAL AND METHODS: Twelve ProTaper instruments of each type, S1, S2, F1, and F2, were assessed morphometrically by measuring tip angle, tip length, tip diameter, length of each pitch along the cutting blades, and instrument diameter at each millimeter from the tip. Curved canals in resin blocks were explored with manual stainless steel files and prepared with ProTaper instruments until the apical end following four distinct sequences of instrumentation: S1; S1 and S2; S1, S2, and F1; S1, S2, F1, and F2. Image analysis was employed for measuring canal diameters. The diameters of the canals and diameters of the instruments were compared. Data were analyzed by one-way ANOVA and Tukey's test. RESULTS: No statistically significant difference was found between the canals and instrument diameters (p>0.05). The largest diameters in the end-point of the instrumented canals were obtained with F1 and F2 instruments and in the initial and middle thirds with S1 and S2 instruments. CONCLUSIONS: All instruments worked at the tip and along their cutting blades, being susceptible to fail by torsion, fatigue, or the combination of these two mechanisms.