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Reciprocation of OTR motion improved significantly cyclic fatigue resistance of all instruments tested compared with continuous rotation. Mtwo and TF had significantly higher cyclic fatigue than the other instruments, in both continuous rotation and reciprocation of OTR motion.

Purpose:The aim of the present study was to evaluate the sealing performance, expressed as microleakage (ML), of two root-end filling materials when used at different retro-preparation lengths. Methods: Fifty single-rooted human teeth were collected for the study. The teeth were cut at the cement-enamel junction and endodontic treatment was performed. Each root was cut at 3 mm from the apex and then stored in wet condition. The teeth were divided into three groups according to the retro-preparation length: control group (no retro-preparation); group 1 (retro-preparation of 3 mm); group 2 (retro-preparation of 9 mm). The teeth were equally allocated to either Biodentine or Super EBA treatment group. The teeth were immersed in 3% methylene blue dye solution for 24 h. The samples were split longitudinally and the depth of dye penetration was examined through light microscopy. Results: No significant statistical differences were found at different retropreparation lengths (P > 0.05). Differences were found between materials (P > 0.05). Conclusion: Biodentine showed significantly lower ML when compared to Super-EBA and no statistical significative differences were observed when samples were retro-prepared at 3 mm or 9 mm.

Aim The aim of the present study was to evaluate the immediate and residual antimicrobial activity of cordless sonic or ultrasonic devices on Enterococcus faecalis (E faecalis)‐infected teeth. Methods A total of 140 single‐rooted extracted teeth with E faecalis were grouped as follows (N = 15): conventional syringe irrigation with 3% sodium hypochlorite activated by ultrasonic device (group 1) or cordless ultrasonic device (group 2), EndoActivator (group 3) or without activation (group 4), conventional syringe irrigation with sterile bi‐distilled water and ultrasonic device (group 5), EndoUltra (group 6), EndoActivator (group 7), or without activation (group 8). The remaining 20 teeth were used for positive and negative controls. Colony‐forming units (CFU) and turbidity were recorded from bacteriological samples taken before and after irrigation and after 24 hours of re‐incubation. Data were statistically analyzed using Student's t test, Mann‐Whitney test, Kruskal‐Wallis test, and Dunn's multiple comparison tests (P < .05). Results Groups 1 and 2 showed higher antimicrobial efficacy than groups 3 and 4 (P < .05). No bacteria reduction was found in groups 5‐8 (P > .05). After 24 hours, regrowth of bacteria was not significantly different for all groups (P > .05). Conclusions Ultrasound produced lower CFU and turbidity after treatment and after re‐incubation of 24 hours than sonic or no activation.

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Nickel-titanium (NiTi) rotary instruments are commonly used for endodontic practice today. These instruments offer many advantages, including flexibility over conventional stainless steel files. 1 Despite their undeniably favorable qualities, there is a potential risk of unexpected fracture. Many variables might contribute to file separation, but the two main causes are cyclic fatigue and torsional stress. 2 Recent attempts have used thermal treatments to modify the phase transition temperatures, and thereby enhance the mechanical properties of the files. 3 In addition to this, file manufacturers have tried to develop new designs, manufacturing processes, and kinematics to minimize fracture occurrence. 1 Moreover, the use of reciprocating motion was shown to extend the lifespan of NiTi instruments, and thus resistance to fatigue, compared with continuous rotation. 4 Reciproc R25 (Rec) (VDW, Munich, Germany) and WaveOne Primary (WO) Sirona Maillefer, Ballaigues, Switzerland) are two well-known reciprocating single-file instruments. 5 Rec and WO have the same nominal size (tip size of 25 with a 0.08 taper). The taper is constant in the apical 3 mm of the instruments, Abstract Aim: The aim of the present study was to evaluate the resistance to cyclic fatigue of heat-treated single files used in proper or in reciprocating optimum torque reverse motions. Methods: Ninety-six HyFlex electrical discharge machining (EDM), Reciproc R25 (Rec), WaveOne Primary (WO), and WaveOne Gold (WOG) Primary were used.Resistance to cyclic fatigue was determined by recording time to fracture in a stainless steel artificial canal. Differential scanning calorimetric analysis was performed.Data were analyzed by two-way analysis of variance and Bonferroni post-hoc tests at 0.05. Results:In both movements, HyFlex EDM showed higher time to fracture than other files (P < 0.0001). Rec showed higher time to fracture than WO (P < 0.0001), while WOG showed higher cyclic fatigue resistance than Rec and WO with both movements (P < 0.005). Conclusions:Reciprocating optimum torque reverse motion improved significantly cyclic fatigue resistance of gold and controlled memory wire single files. K E Y W O R D S differential scanning calorimetric analysis, fatigue resistance, nickel-titanium, optimum torque reverse, reciprocation 2 of 7 | PEDULLÀ Et aL. but it is reduced in the middle and coronal portion of the working part of the instrument. Rec instruments have a constant S-shaped cross-section with two cutting blades; WO instruments have a modified convex triangular cross-section at the tip and a convex triangular cross-section in the middle and coronal portion of the instrument. 5 Additionally, Rec and WO are manufactured using M-wire NiTi, which increases their flexibility and resistance to cyclic fatigue. 6 Recently, WO was upgraded to WaveOne Gold (WOG) (Sirona Maillefer, Switzerland). The kinematics of this system was unchanged, but the design of the files has been modified, and the heat treatment has been changed in the gold treatment, which allows...

ment is locked in root canal, while the remaining part continues to rotate over the alloy torsion elastic limit [3]; cyclic fatigue, when an instrument rotates inside of a curved root canal and it is subject to an excessive number of deformation cycles tension-compression in the region of maximum curvature of the root canal [2,4].

This in vitro study assessed morphological changes and efficiency of reciprocating files after multiple uses. Sixty standardized Endo Training Blocks and 10 ReciprocR25 files were selected (six blocks for each file). Each file was its own control (before use vs. after each instrumentation). The instruments were used according to the manufacturer's instructions, and scanning electron microscopy was used to observe fatigue cracks, metal strips/metal flash, pitting, fretting, debris, disruption of the cutting edge, and plastic deformations after each instrumentation. The presence of seven wear variables was scored semiquantitatively by viewing micrographs collected before and after use. The prepared areas in resin blocks were calculated and compared by using AutoCAD software. The control group had significantly lower values for all wear variables except fretting and plastic deformation. The presence of fatigue cracks and metal strips/metal flash significantly differed between unused instruments and instruments used four or five times, in all observed sections. The area of instrumented Endo Training Blocks significantly differed in relation to the number of instrument uses. The Reciproc files wore progressively, and repeated use affected their shaping efficiency in simulated canals.