The impact of clinical use on the torsional behavior of Reciproc and WaveOne instruments

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.

Influência do movimento recíproco na resistência à torção dos instrumentos de NiTi: reciproc, waveone e protaper universal / Influence of the reciprocal movement on the torsion resistance of NiTi instruments: reciproc, waveone and universal protaper

As propriedades mecânicas dos instrumentos endodônticos são afetadas por fatores como diâmetro, design, composição química, e tratamentos termomecânicos aplicados durante o processo de fabricação. O objetivo deste trabalho foi avaliar a flexibilidade e a resistência torcional de instrumentos de NiTi Reciproc (RC), Wave One (WO) e ProTaper Universal (PTU), novos e após o uso clínico. A composição química dos instrumentos foi analisada por espectroscopia de energia de raios X (EDS), as fases presentes identificadas por difração de raios X (DRX) e as temperaturas de transformação determinadas por calorimetria exploratória diferencial (DSC). Imagens das seções longitudinal e transversal foram empregadas para determinar o diâmetro e a área a 3 mm da ponta (D3 e A3), posição onde as solicitações mecânicas se concentram durante o uso clínico e os instrumentos são apreendidos nos testes. O comportamento mecânico foi avaliado através de ensaios de flexão e torção até a ruptura, de acordo com a especificação ISO 3630-1. Os instrumentos RC, WO e PTU apresentaram composição química semelhante e fase ß como principal constituinte à temperatura ambiente. No entanto, os instrumentos Reciproc e WaveOne apresentaram um aumento relevante nas temperaturas de transformação, sugerindo a presença da fase B19', coexistindo com a fase austenítica. Apesar de apresentarem D3 semelhantes, a análise estatística dos valores de A3 entre os pares de instrumentos analisados mostrou diferença significativamente menor para os instrumentos RC. Os instrumentos RC foram significativamente mais flexíveis, possivelmente devido ao tratamento termomecânico a que foram submetidos os fios utilizados na fabricação dos mesmos (MWire), além da morfologia de sua sessão tranversal, seguidos por WO, que também são fabricados a partir do fio M-Wire, e PTU, nesta ordem. Dentre os instrumentos novos, os PTU apresentaram valores de torque máximo, quando ensaiados em torção, significativamente menores. Os instrumentos PTU apresentaram os maiores valores de deflexão angular, seguidos pelos instrumentos RC e WO, nesta ordem. Todos os sistemas após serem utilizados na prática clínica apresentaram redução da resistência torcional. Entretanto, a comparação estatística entre os valores de torque máximo para os instrumentos novos e após uso clínico, não apresentou diferença estatisticamente significativa para nenhum dos sistemas avaliados. Com relação à deflexão angular, a comparação entre instrumentos novos e após uso clínico, mostra uma redução dos valores desse parâmetro após o uso clínico, com exceção dos instrumentos RC. Entretanto, as análises estatísticas mostraram não haver diferenças significativas entre os pares de instrumentos analisados.(AU)

The mechanical properties of the endodontic instruments are affected by factors such as diameter, design, chemical composition and thermo-mechanical treatments applied during the manufacturing process. The main goal of this study was to assess the flexibility and torsional resistance of the NiTi Reciproc (RC), Wave One (WO) and ProTaper Universal (PTU) instruments, new and after clinical use. The instruments chemical composition was analyzed with X-Ray energy spectroscopy (EDS), the present phases were determined by X-Ray Diffractions (DRX) and the transformation temperatures were obtained with differential scanning calorimeter (DSC). Images from the longitudinal and transversal sections were used for determining the diameter and the area at 3mm from the tip (D3 and A3), the position where the mechanical requests are focused in clinical use and where the instruments are apprehended during the tests. The mechanical behavior has been evaluated through simulation of bending and torsion until rupture according to ISO 3630-1. The RC, WO and PTU instruments have presented a similar chemical composition with the predominance of ß phase at room temperature. However, Reciproc and Waveone instruments showed a significant increase in transformation temperatures, suggesting the presence of B19 phase, coexisting with the austenitic phase Despite showing similar D3, statistical analysis of the values of A3 between pairs of instruments analyzed showed significantly lower difference for RC instruments. The RC instruments were significantly more flexible, possibly due to the thermomechanical treatment applied to the wire (M-Wire) used in their manufacture process in addition to their cross section design, followed by WO instruments, which are also made of M-Wire, and PTU instruments, in that order. Among the new instruments, PTU showed significantly lower maximum torque values in torsion tests. PTU instruments presented the highest angular deflection values, followed by RC and WO instruments, in that order. All systems reduced their torsional strength after clinical use. However, statistical comparison between the maximum torque values for new and after clinical use instruments, showed no statistically significant difference for any of the evaluated systems. Regarding the angular deflection, the comparison between new and after clinical use instruments demonstrated a reduction of the values of this parameter after clinical use, with the exception of RC instruments. However, statistical analysis showed no significant differences between the pairs of instruments analyzed.(AU)