European Society of Endodontology position statement: Surgical extrusion, intentional replantation and tooth autotransplantation: European Society of Endodontology developed by.

This European Society of Endodontology (ESE) position statement on surgical extrusion, intentional replantation and tooth autotransplantation represents the consensus of an expert committee, convened by the ESE. A narrative review in the International Endodontic Journal (Plotino et al. 2020, international Endodontic Journal, 53, 1636-52) formed the basis for the position statement. The review provided detailed information on the background, clinical procedures and the outcome of surgical extrusion, intentional replantation and tooth autotransplantation techniques. The aim of the current statement is to summarize the best available evidence on these clinical techniques to provide appropriate clinical guidance to undergraduate and postgraduate students, dental practitioners, clinical teachers and researchers. The current position statement will be updated by the ESE periodically to reflect new evidence as it becomes available to provide the most current treatment guidance for clinical practice.

Clinical procedures and outcome of surgical extrusion, intentional replantation and tooth autotransplantation - a narrative review.

Surgical extrusion is defined as the procedure in which the remaining tooth structure is repositioned at a more coronal/supragingival position in the same socket in which the tooth was located originally. Intentional replantation is defined as the deliberate extraction of a tooth and after evaluation of root surfaces, endodontic manipulation and repair, placement of the tooth back into its original position. Tooth autotransplantation is defined as the transplantation of an unerupted or erupted tooth in the same individual, from one site to another extraction site or a new surgically prepared socket. The advent of titanium implant rehabilitation has reduced the use of these treatments in day-by-day clinical practice; however, the re-emerging trend to conserve and preserve natural sound tissues has led to a rediscovery of these treatments. All three distinct surgical methods are closely related, as they act to treat teeth that cannot be predictably treated using other more conventional procedures in endodontics, periodontics and restorative dentistry. Furthermore, these procedures share the same treatment approach and include the atraumatic extraction of a tooth, visual inspection of the tooth/root and its subsequent replantation. The clinical procedures for surgical extrusion, intentional replantation and tooth autotransplantation treatment have undergone several changes in recent years, and currently, there are no clear clinical treatment protocols/guidelines available. The clinician should be aware of the outcome of these treatments. Hence, the aim of this narrative review is to provide the background, clinical procedures and outcomes of surgical extrusion, intentional replantation and tooth autotransplantation.

C-shaped canal configuration in mandibular premolars and molars: Prevalence, correlation, and differences: An In Vivo study using cone-beam computed tomography.

AIMS: To evaluate the prevalence, correlation, and differences of C-shaped canal morphology in mandibular premolars and molars by means of cone-beam computed tomography (CBCT). MATERIALS AND METHODS: A total of 1433 mandibular premolars and molars CBCT scans from the Saudi population were evaluated. Axial sections of the roots were acquired at coronal, middle, and apical levels to evaluate C-shaped canals types. The prevalence, correlation, differences of C-shaped canals, bilateral/unilateral presence, gender differences, and location of external grooves on roots were assessed. RESULTS: The prevalence of C-shaped canals in the first premolars was 1.5%, 0.80% in second premolars and 7.9% in second molars, whereas C-shaped canals were absent in first molars. No correlation was found between the presence of C-shaped canals within premolars and molars and between the two groups in the same individual. Both premolars and molars exhibited different types of C-shaped canals, C2 being predominant in premolars and C3 in second molars. Longitudinal external grooves were mostly located on mesiolingual (ML) surface in premolars and lingual in molars. Females showed more prevalence of C-shaped canals in second molars and no differences in premolars. Bilateral symmetry and unilateral presence in premolars and second molars were not significant. CONCLUSIONS: Although the prevalence of C-shaped canals is significantly higher in mandibular second molars, they are also found in mandibular premolars but in small percentages. No significant differences were found between both genders and both sides. Since they exhibit unpredictable morphology and differences across the root length, the use of small field CBCT is recommended when such anatomy is presented in a tooth indicated for root canal treatment for better management.

Measurement of torque generated during intracanal instrumentation in vivo.

AIM: To compare two different clinical techniques when using endodontic rotary instruments by monitoring the torque in vivo. METHODOLOGY: Ten single-rooted maxillary anterior teeth were prepared by an endodontist using size 25, .06 taper TF rotary instruments (KerrEndo, Orange, CA, USA). All instruments were rotated at 500 rpm with maximum torque set at 2.5 N cm using an endodontic motor (Kavo, Biberach, Germany), which automatically recorded the torque values every 1/10 of a second. Instruments were used with two modi operandi: (i) Inward action: short-length intermittent progression with slight apical pressure aiming to reach the working length (also known as pecking motion), followed by (ii) Outward action: lateral brushing action selectively directed to address the canal circumference whilst removing instruments in the coronal direction. The mean, maximum and accumulated torque values were recorded and analysed statistically (t-test and Wilcoxon test) with a significance level set at 5%. None of the recorded values exceeded the selected torque limit. RESULTS: A significant difference between inward and outward actions was found regarding the evaluated parameters (P < 0.05). The outward action (brushing) was significantly safer (requiring less torque) compared to the inward action (pecking). CONCLUSIONS: Torque measurements during in vivo instrumentation provided useful information regarding the techniques evaluated. Although the torque limit was not reached by any of the two actions, the technique impacted significantly on the torque applied to the instrument.

A preliminary assessment of a new dedicated endodontic software for use with CBCT images to evaluate the canal complexity of mandibular molars.

AIM: To investigate in vivo the complexity of canals within mesial roots of mandibular molars using 3D Endo™ software linked to CBCT images. METHODOLOGY: The CBCT images of 100 mandibular first molars were analysed using the 3D Endo™ software. The number of canals in the mesial roots, the presence of apical confluences, the canal lengths and the canal configurations using Vertucci's classification were evaluated in buccolingual (BL) and mesiodistal (MD) views. The software allowed the visualization of canal trajectories in three dimensions using a coloured outline, which was used to develop a new objective scoring system to provide an overall assessment of canal complexity. Data were analysed statistically using anova and t-tests with the significance set at P < 0.05. RESULTS: Vertucci type IV canals were found in 44% of the cases, whilst 54% were type II. The mean distance from the apical foramen to the orifice was 13.15 mm (±1.21) and that between a confluence and the foramen, 2.81 mm (±1.13). The number of curvatures and the canal complexity scores in the MD view were significantly higher than in the BL view (P < 0.05). The scores were not directly correlated to the canal (MB versus ML), to the canal length or to the presence of confluences. CONCLUSIONS: 3D Endo software features the automatic detection and measurement of several anatomical canal parameters, and is a promising tool for the study of canal complexity in vivo. The unpredictable anatomy of the mesial roots of mandibular molars highlights the value of a three-dimensional preoperative evaluation of each case. The proposed scoring system aims to provide the clinician with an overall assessment of canal complexity.

Shaping ability of two nickel-titanium instruments activated by continuous rotation or adaptive motion: a micro-computed tomography study.

OBJECTIVES: The objective of the study was to evaluate the shaping ability of curved root canals using Twisted File Adaptive (TFA) files (SybronEndo, Orange, CA) and Mtwo (Sweden & Martina, Padova, Italy) activated by continuous rotation or adaptive motion. MATERIALS AND METHODS: Thirty-two mandibular molars with two separate mesial canals and severe angles of curvature were selected. Each canal was randomly assigned to one of the four experimental groups (n = 16): TFA and Mtwo files used in continuous rotation (groups 1 and 3) or in adaptive motion (groups 2 and 4). Root canals before and after preparation were assessed by micro-computed tomography. Volume, surface area, canal transportation, and centering ability were recorded and analyzed using two-way analyses of variance. RESULTS: Volume and surface area increased less with TFA files in continuous rotation than in other groups (P < 0.001 and P < 0.01, respectively, for each comparison) that were not different (P > 0.05). TFA files had significantly less transportation and higher centering ability than Mtwo both in continuous and adaptive motion (P < 0.0001). Centering ratio, but not canal transportation, was improved by adaptive motion compared with continuous rotation for both instruments (P < 0.01). However, no differences were found in canal transportation and centering ability in the apical third for both instruments and motions (P > 0.05). CONCLUSIONS: No difference between the devices and kinematics was found in the apical third; TFA performed significantly better in the middle and coronal parts of the root canal. CLINICAL RELEVANCE: The use of NiTi files made by heat-treated alloy and/or adaptive motion could improve the qualities of root canal shaping rather than the use of conventional NiTi instruments and/or continuous rotation in the coronal and middle thirds of the root canals, but not in the apical one. Moreover, these findings encourage the use of adaptive motion with conventional NiTi files to improve centering ability without affecting other preparation qualities of root canals.

Cyclic fatigue resistance of two reciprocating nickel-titanium instruments after immersion in sodium hypochlorite.

AIM: To assess resistance to cyclic fatigue of reciprocating nickel-titanium ( NiTi ) files (Reciproc and WaveOne) after immersion in NaOCl solution over several time periods. METHODOLOGY: A total of 90 new Reciproc R25 and WaveOne Primary were tested. The 45 files of the same brand were randomly assigned to three groups (n = 15) and submitted to the following immersion protocol in 5% NaOCl at 37 °C for 16 mm: no immersion (control), 1 or 5 min dynamically. The dynamic immersion and the following cyclic fatigue tests were performed using the appropriate preset reciprocation modes ('RECIPROC ALL' or 'WAVEONE ALL') in a specially designed endodontic motor. Resistance to cyclic fatigue was determined by recording time to fracture (TtF) in a stainless steel artificial canal with a 60° angle of curvature and 5 mm radius of curvature. The artificial canal was manufactured reproducing the instrument's size and taper. Data were analysed by 2-way analyses of variance. RESULTS: Resistance to cyclic fatigue of the same NiTi file was not significantly affected by immersion in NaOCl . Reciproc R25 was associated with a higher cyclic fatigue resistance in all groups compared to WaveOne Primary (P < 0.0001). CONCLUSIONS: Reciprocating dynamic immersion in NaOCl for 1 or 5 min did not reduce the cyclic fatigue resistance of NiTi files significantly. However, the type of reciprocating instrument influenced cyclic fatigue resistance with Reciproc R25 being more resistant than WaveOne Primary.

Cyclic fatigue of Reciproc and WaveOne reciprocating instruments.

AIM: To evaluate the cyclic fatigue resistance of Reciproc(®) and WaveOne(®) instruments in simulated root canals. METHODOLOGY: Two groups of 15 NiTi endodontic instruments of identical tip size of 0.25 mm were tested, group A; Reciproc(®) R25 and group B: WaveOne(®) primary. Cyclic fatigue testing was performed in a stainless steel artificial canal manufactured by reproducing the instrument's size and taper. A simulated root canal with a 60° angle of curvature and 5-mm radius of curvature was constructed for both the instruments tested. The centre of the curvature was 5 mm from the tip of the instrument and the curved segment of the canal was approximately 5 mm in length. The Reciproc(®) instruments were activated using the preset programme specific for the Reciproc(®) instruments, whilst the WaveOne(®) instruments were activated using the preset programme specific for the WaveOne(®) instruments. All instruments were rotated until fracture occurred and the time to fracture (TtF) and the length of the fractured tip were recorded and registered. Means and standard deviations of TtF and fragment length were calculated for each system and data were subjected to Student's t-test (P < 0.05). RESULTS: A statistically significant difference (P < 0.05) was noted between Reciproc(®) and WaveOne(®) instruments. Reciproc(®) R25 instruments were associated with a significant increase in the mean time to fracture when compared with primary WaveOne(®) instruments (130.8 ± 18.4 vs. 97.8 ± 15.9 s). There was no significant difference (P > 0.05) in the mean length of the fractured fragments between the instruments. CONCLUSIONS: Reciproc(®) instruments were associated with a significantly higher cyclic fatigue resistance than WaveOne(®) instruments.

Cyclic fatigue analysis of twisted file rotary NiTi instruments used in reciprocating motion.

AIM: To evaluate the cyclic fatigue fracture resistance of engine-driven twisted file (TF) instruments under reciprocating movement. METHODOLOGY: A sample of 30 size 25, 0.08 taper NiTi TF instruments was tested in a simulated canal with 60˚ angle of curvature and a 3 mm radius. During mechanical testing, different movement kinematics were used at a constant speed, which resulted in three experimental groups (each group n = 10). The instruments from the first group (G1) were rotated until fracture occurred. The instruments in the second (G2) and third group (G3) were driven under reciprocating movement with different angles of reciprocation. The time of fracture for each instrument was measured, and statistical analysis was performed using one-way analysis of variance followed by Tukey's Honestly Significant Different test. RESULTS: Reciprocating movement resulted in a significantly longer cyclic fatigue life (P < 0.0001) when compared with continuous rotation. No difference was found between reciprocation 150° clockwise/30° counterclockwise (CW/CCW) and 30° CW/150° CCW. CONCLUSIONS: The reciprocating movement was associated with an extended cyclic fatigue life of the TF size 0.25, 0.08 taper instruments in comparison with conventional rotation.

Mechanical properties of nickel-titanium rotary instruments produced with a new manufacturing technique.

AIM: To investigate whether flexibility and cyclic fatigue resistance was increased for nickel-titanium instruments produced by a new manufacturing technique. METHODOLOGY: Forty K3 tip size 25, 0.06 taper (SybronEndo) nickel-titanium rotary instruments were randomly selected and divided into two groups (n = 20). One group served as control, being the commercially available instruments produced with a traditional grinding process (K3). The second group of instruments (K4 prototypes) were then subjected to a proprietary thermal treatment after the grinding process. Finally, each group was randomly divided into two subgroups of 10 instruments each, to perform the stiffness test and the cyclic fatigue test. All data were recorded and subjected to statistical evaluation using Student's t-test. Significance was set at the 95% confidence level. RESULTS: For the stiffness test, a statistically significant difference (P < 0.05) was noted between K3 and K4 prototype instruments. K4 prototype instruments were significantly more flexible when compared to K3 instruments (59.3 ± 4.3 vs. 98.1 ± 6.4 g cm(-1) ). For the cyclic fatigue test, a significant difference (P < 0.05) was noted between K3 and K4 prototype instruments. K4 prototype instruments demonstrated a significant increase in the mean number of cycles to failure (NCF) when compared to K3 instruments (1198 ± 279 vs. 542 ± 81 NCF). CONCLUSIONS: The new manufacturing technique resulted in the K4 prototype instruments having enhanced mechanical properties, compared to K3 instruments, manufactured with a traditional grinding process.

Differential diagnosis of endodontic-related inferior alveolar nerve paraesthesia with cone beam computed tomography: a case report.

AIM: To discuss the use of cone-beam computed tomography (CBCT) in the differential diagnosis of a case of labiomandibular paraesthesia caused by extrusion of endodontic sealer into the mandibular canal. SUMMARY: A 59-year-old woman suffering from a paraesthesia on the left posterior mandible and numbness on the left side of the lower lip was referred to an endodontic specialist 1 month after multiple root canal treatments. A panoramic radiograph revealed the presence of extruded root filling material beyond the apex of the mesial root of the mandibular left second molar and also beyond the apex of the first premolar. A cone beam computed tomography examination was undertaken, which confirmed the presence of radiopaque root canal filling material in the periapical area of the second molar, and revealed that the material was inside the mandibular canal. No extruded filling material was found inside the mental foramen beyond the apex of the first premolar tooth. KEY LEARNING POINTS: Small field of view CBCT (where possible) can be considered an effective radiographic diagnostic device when endodontic-related inferior alveolar nerve or mental foramen paraesthesia are suspected. CBCT is able to provide detailed three-dimensional images of the tooth, the root canal system and the surrounding tissue.

Influence of the shape of artificial canals on the fatigue resistance of NiTi rotary instruments.

AIM: To investigate the influence of the trajectory of NiTi rotary instruments on the outcome of cyclic fatigue tests. METHODOLOGY: Ten ProFile and Mtwo instruments tip size 20, taper 0.06 and tip size 25, taper 0.06 were tested in two simulated root canals with an angle of curvature of 60 degrees and radius of curvature of 5 mm but with different shape. Geometrical analysis of the angle and radius of the curvature that each instrument followed inside the two different artificial canals was performed on digital images. The instruments were then rotated until fracture at a constant speed of 300 rpm to calculate the number of cycles to failure (NCF) and the length of the fractured fragment. Mean values were calculated and analysed using two different multivariate linear regression models and an independent sample t-test. RESULTS: The shape of the artificial root canal used in cyclic fatigue studies influenced the trajectory of the instrument. This difference is reflected by the NCF measured for the same instrument in the different artificial root canals and by the impact of the type of canal on both the NCF (St.beta = 0.514) and fragment length (St.beta = -0.920). CONCLUSIONS: Small variations in the geometrical parameters of the curvature of an instrument subjected to flexural fatigue could have a significant influence on the results of fatigue tests.

Cyclic fatigue of NiTi rotary instruments in a simulated apical abrupt curvature.

AIM: To evaluate the cyclic fatigue resistance of five NiTi rotary systems in an abrupt apical curvature. METHODOLOGY: Cyclic fatigue testing was performed in stainless-steel artificial canals with a 2-mm radius of curvature and an angle of curvature of 90 degrees constructed to the dimensions of the instruments tested. The middle of the simulated curvature was 2.5 mm from the tip of the instrument that was placed at full working length. All instruments were new and 25 mm in length. Ten ProTaper Universal F2 (Dentsply Maillefer, Ballaigues, Switzerland); FlexMaster (VDW, Munich, Germany) tip size 25, taper 0.06; Mtwo (Sweden & Martina, Padova, Italy) tip size 25, taper 0.06; ProFile tip size 25, taper 0.06 from Dentsply Maillefer (Ballaigues, Switzerland); and ProFile tip size 25, taper 0.06 from Dentsply Tulsa (Tulsa, OK, USA) were rotated passively at 300 rpm until fracture occurred, and the number of cycles to failure (NCF) recorded. Length of the fractured tip was measured. Data were analysed by one-way anova and Tukey HSD test to determine any statistical difference amongst groups. RESULTS: Mtwo had the highest fatigue resistance compared to the other instruments (NCF 124 +/- 25) (P < 0.001); there was no statistical difference between ProFile from the two different brands, although ProFile from Maillefer had the higher fatigue life (NCF 75 +/- 10) compared to ProFile from Tulsa (NCF 66 +/- 10). No difference was registered between FlexMaster (NCF 53 +/- 5) and ProFile from Tulsa; ProTaper F2 had a significantly (P < 0.001) lower fatigue life compared to the other instruments tested (NCF 29 +/- 5). CONCLUSIONS: Lifespan registered for the instruments tested in an apical abrupt curvature was Mtwo > ProFile from Maillefer > ProFile from Tulsa > FlexMaster > ProTaper.

The effect of a new finishing process on the torsional resistance of twisted nickel-titanium rotary instruments.

AIM: The process of twisting has been used for decades to fabricate stainless steel instruments, but it was previously thought to be an impractical method for nickel-titanium (Ni-Ti) instrument manufacture A manufacturing method of twisting Nickel-Titanium wire to produce Ni-Ti files has been recently developed: the twisted files (TF). Theoretically, this new manufacturing process should overcome the problems associated with a grinding process, which previously limited instrument strength. Since TF manufacturing process is new and different from grinding, the aim of the present study was to evaluate the effects of a final deoxidation process (Deox) on torsional resistance of TF instruments. METHODS: Testing was performed in accordance with the International Standard (ISO 3630-1) by comparing 20 TF instruments versus 20 TF prototype instruments produced without the final deoxidation process. Data were collected and statistically analyzed (t-test). RESULTS: Results show that TF instruments withstood 90% more torque (max. torque) than TF prototype instruments manufactured without the deoxidation process (88.7 vs. 53.3 g/cm). This difference was found to be statistically significant at the 0.05 level of significance. CONCLUSION: Since design and dimensions of tested instruments were the same, the deoxidation process could be the only explanation of the improvement in torsional resistance.

Sealing ability of a new carrier-based obturating material.

AIM: The aim of the present study was to investigate the in vitro sealing ability of a new obturating material (Real Seal 1, SybronEndo, Orange, CA, USA) and compare it with the Thermafil (Dentsply Maillefer, Baillargues, Switzerland) and One-Step systems (CMS Dental, Copenhagen, Denmark). METHODS: Forty-four freshly extracted lower premolars teeth were selected and a root canal treatment was performed using a crown-down Nickel-Titanium rotary preparation technique. Teeth were randomized into three groups (N.=14): 1) Thermafil group; 2) One/step group; 3) Real Seal 1 (RS1) group. The remaining two teeth served as controls. A fluid filtration system device was utilized to assess quantitatively the microleakage. Statistical analyses were performed by ANOVA and significance was set at 95%. RESULTS: Data clearly showed that the RS1 provided the best results, showing a minimal leakage after 24 hours. Statystical analysis showed a significant difference about the RS1 group, the Thermafil and One/Step group, while no significant differences were noted between these last two groups. Results show that the number of teeth that had no (=0) leakage was higher in the RS1 group (8 specimens) than in the remaining ones (1 and 1 specimen, respectively). CONCLUSIONS: Under the conditions of the present experimental test, the new RS1 material (carrier-based Resilon) provided excellent preliminary results showing sealing ability at 24 hours significantly better that traditional carrier-based gutta-percha systems.

Microbial contamination of brand new nickel-titanium endodontic instruments.

AIMS: This study aims to estimate the microbial presence on the surface of different brand new NiTi endodontic instruments for clinical use. MATERIAL AND METHODS: Eleven different types of NiTi rotary endodontic instruments, obtained from their fresh opened original packages, were assigned to three different groups, according to packaging type and sterilization and tested for bacterial contamination. Isolated bacteria were identified by using standard microbiological methods and then counted. Differences observed in groups were analyzed statistically by using the one-way analysis of variance (ANOVA) for dependent samples and the Tukey HSD post hoc test. RESULTS: Statistical differences were found between instruments delivered in plastic boxes which bacterial count resulted higher than those obtained from instruments delivered in blisters (p<0.01). CONCLUSIONS: Some brand new endodontic instruments showed degrees of bacterial contamination that both quantitatively and qualitatively deserve to be considered in clinical procedures.

Mandibular ameloblastic fibroma in 6-years-old girl: a case report.

Ameloblastic fibroma (AF) is defined in WHO classification as a ''neoplasm composed of proliferating odontogenic epithelium embedded in a cellular ectomesenchymal tissue that resembles dental papilla, and with varying degrees of inductive change and dental hard tissue formation''. AF is a rather uncommon tumor, accounting for only 2.5% of all odontogenic tumors. AF is a true mixed tumor, in which the epithelial and ectomesenchymal elements are neoplastic. AF raises at any age, ranging from 6 months to 42 years (mean 14.6 to 15.5 years); it does not show sex predilection. The lesion occurs in nearly 70% of cases in posterior areas of the mandible. Patients exhibit swelling of the jaw; pain is not usually described. Authors present a clinical and surgical management of an early onset of a large mandibular ameloblastic fibroma in a 6-year-old girsl.

Bending properties of nickel-titanium instruments: a comparative study.

AIM: The aim of the present study was to evaluate the bending properties of twisted file instruments, and compare them with other commercially available nickel-titanium (NiTi) instruments (Mtwo and Hero) manufactured with traditional methods. METHODS: Despite NiTi superelastic properties, flexibility of NiTi instruments is limited by size and taper. A new manufacturing process involving twisting of a ground blank combined with heat treatment has been developed by SybronEndo, aiming to produce a NiTI rotary file with superior flexibility: the Twisted File (TF). Experimental procedures strictly followed the testing methodology described in ISO 3630-1. Bending moment was measured when the instrument attained a 45 degrees bend. Data were collected and statistically analyzed. RESULTS: Results showed that TF were the most flexible instruments, with a significant improvement in flexibility (P< 0.05). ranging from 100% to 250% over the other tested instruments. Even if flexibility is also influenced by instruments design, such a great improvement is mainly related to the new TF manufacturing process. CONCLUSION: The flexibility is influenced by instruments design, such a great improvement is mainly related to the new manufacturing process developed by SybronEndo, which seems to play a major role in increasing the flexibility of TF instruments.

Fatigue Resistance of New and Used Nickel-Titanium Rotary Instruments: a Comparative Study.

OBJECTIVES: Aim of the present study was twofold. First, to evaluate in vitro, the performance of two different NiTi rotary instruments in one molar case; then, to evaluate their resistance to cyclic fatigue, compared to new ones. MATERIAL AND METHODS: 25 ProTaper Next (PTN) nickel-titanium (NiTi) instruments (Maillefer-Dentsply, Baillagues, CH) for each of the following two sizes: X1 (17.04 ) and X2 (25.06) were randomly divided into two groups. The first group (n = 10) immediately under- went to a cyclic fatigue test. The second group (n = 15) was initially used to prepare 15 extracted molar teeth and then subjected to a cyclic fatigue test. Same was done for 25 Horizen (HZ) instruments (Kerr Endodontics, Orange, Ca) for each of the following two sizes: 20.04 and 25.06. Instruments were rotated in curved artificial canal until fracture occurred and times to fracture were recorded. All data were collected and statistically analyzed using a variance test (confidence interval CI = 95%). RESULTS: HZ reached working length more rapidly than PTN, and with less deformations. For the fatigue tests, all the new instruments were significantly more resistant than the used ones. The HZ instru- ments were significantly more resistant in all sizes than PTN, both when new and used instruments were tested. CONCLUSIONS: Since in previous studies ProTaper Next demonstra- ted a better resistance to cyclic fatigue than most of nickel-titanium instruments, Horizen's performance put them in a high rank amongst the most resistant nickel-titanium rotary instruments.