Gianluca Gambarini

Fatigue Resistance of Engine-driven Rotary Nickel-Titanium Instruments Produced by New Manufacturing Methods

The aim of the present study was to investigate whether cyclic fatigue resistance is increased for nickel-titanium instruments manufactured by using new processes. This was evaluated by comparing instruments produced by using the twisted method (TF; SybronEndo, Orange, CA) and those using the M-wire alloy (GTX; Dentsply Tulsa-Dental Specialties, Tulsa, OK) with instruments produced by a traditional NiTi grinding process (K3, SybronEndo). Tests were performed with a specific cyclic fatigue device that evaluated cycles to failure of rotary instruments inside curved artificial canals. Results indicated that size 06-25 TF instruments showed a significant increase (p < 0.05) in the mean number of cycles to failure when compared with size 06-25 K3 files. Size 06-20 K3 instruments showed no significant increase (p > 0.05) in the mean number of cycles to failure when compared with size 06-20 GT series X instruments. The new manufacturing process produced nickel-titanium rotary files (TF) significantly more resistant to fatigue than instruments produced with the traditional NiTi grinding process. Instruments produced with M-wire (GTX) were not found to be more resistant to fatigue than instruments produced with the traditional NiTi grinding process.

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 instruments 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 Students 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 of Nickel-Titanium Rotary Instruments after Clinical Use with Low-and High-Torque Endodontic Motors

This study investigated the cyclic fatigue resistance of used nickel-titanium rotary instruments, clinically operated by a traditional high-torque motor and a new low-torque electric motor. Fifty instruments (ProFile, Maillefer, Baillagues, Switzerland) for each of the following sizes were used: .06-25, .06-20, and .04-25. They were divided into three groups: A = 10 new instruments (control), B = 20 used instruments operated by a high-torque motor, and C = 20 used instruments operated by a low-torque motor. Each instrument was used in 10 clinical cases (at least six molars). Cyclic fatigue testing of new and used instruments was performed with a device that allowed the instruments to rotate freely inside a stainless-steel artificial canal at 350 rpm. Data were recorded and statistically analyzed. Mean (and SD) numbers of rotation-to-breakage cycles for .06-25, .06-20, and .04-25 instruments were, respectively: group A 463 (85), 535 (101), and 613 (105); group B 229 (64), 343 (92), and 233 (84); and group C 352 (77), 454 (89), and 466 (86). Results showed that group A instruments exhibited significantly higher values of rotation-to-breakage cycles (two-sample t test, p < 0.01), when compared with groups B and C, respectively. Statistically higher resistance to cyclic fatigue was noted for group C in all sizes compared with group B (two-sample t test, p < 0.01), showing that the use of endodontic motor with lower torque values reduced cyclic fatigue of nickel-titanium rotary 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 Tukeys 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 Students 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.

Bending Properties of a New Nickel-Titanium Alloy with a Lower Percent by Weight of Nickel

INTRODUCTION The aim of the present study was to evaluate the bending properties of Hyflex instruments, which exhibit a lower percent in weight of nickel (52 Ni %wt) and compare them with other commercially available nickel-titanium (NiTi) rotary instruments. METHODS Ten instruments with tip size 25, 0.06 taper of each of the following NiTi rotary instrumentation techniques were selected for the study: Hyflex, EndoSequence, ProFile, Hero, and Flexmasters. All instruments from each group were tested for stiffness by comparing their bending moment when they attained a 45-degree bend. Experimental procedures strictly followed testing methodology described in ISO 3630-1. All data were recorded and subjected to statistical evaluation by using analysis of variance test. Statistical significance was set at P < .05). RESULTS Statistical analysis of the data revealed that Hyflex files were found to be the most flexible instruments, with a significant difference (P < .05) in comparison with the other instruments. Among the other files, a significant difference has been reported for EndoSequence instruments compared with ProFile, Hero, and FlexMaster (P < .05), whereas no significant differences have been reported among those 3 files (P > .05). CONCLUSIONS Results of the present study have illustrated an increased flexibility of the new NiTi alloy over conventional NiTi alloy, and they highlight the potential of the new manufacturing process.

Shaping and cleaning the root canal system: a scanning electron microscopic evaluation of a new instrumentation and irrigation technique.

The purpose of the present scanning electron microscopic study was to investigate the efficacy of a combination of EDTA, NaOCl, and surface-active irrigating solutions during and after root canal preparation with ProFile nickel-titanium rotary instruments. Thirty canals were divided into three groups, instrumented and irrigated as follows: 5% NaOCl and a final flush with 17% EDTA were used for group A; group B specimens were irrigated using 17% EDTA, followed 15 s later by 1% TRITON X-100 (tensioactive agent) and then by 5% NaOCl; and group C specimens were irrigated with the same combination, but once shaping procedures were completed the irrigating sequence was repeated three times. After scanning electron microscopic evaluation, group C specimens exhibited the most effective debridement of the root canals. Results showed that tensioactive agent contributed to enhanced debridement. Cleaning was significantly improved once shaping procedures were completed.

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.

Mechanical properties of a new and improved nickel-titanium alloy for endodontic use: an evaluation of file flexibility

OBJECTIVE A new manufacturing method to produce more flexible and resistant NiTi endodontic instruments has been recently developed. The purpose of the study was to determine whether this new manufacturing method produces NiTi instruments (TF) of superior flexibility. STUDY DESIGN Ten .06 size 25 prototype (TF) instruments (Sybron Endo) and ten 06.25 ProFile instruments (Dentsply-Maillefer) were evaluated for stiffness on bending. Test procedures strictly followed ANSI/ADA Specification No.28. Bending moment was measured when the instrument attained a 45 degrees bend. All data obtained were recorded and statistically analyzed using an ANOVA test. RESULTS Statistical analysis of data showed that bending moments were significantly greater (P < .05) for ProFile instruments (mean value 59.06 g/cm), compared to the prototype instruments (mean value 35.60 g/cm), thereby confirming the increased flexibility of TF instruments. CONCLUSION Results of the present study demonstrate the ability of the new manufacturing process to produce more flexible NiTi rotary instruments.

Blue treatment enhances cyclic fatigue resistance of vortex nickel-titanium rotary files.

INTRODUCTION The aim of the present study was to evaluate the difference in cyclic fatigue resistance between Vortex Blue (Dentsply Tulsa Dental, Tulsa, OK) and Profile Vortex nickel-titanium (Dentsply Tulsa Dental) rotary instruments. METHODS Two groups of nickel-titanium endodontic instruments, ProFile Vortex and Vortex Blue, consisting of identical instruments in tip size and taper (15/.04, 20/.06, 25/.04, 25/.06, 30/.06, 35/.06, and 40/.04) were tested. Ten instruments from each system and size were tested for cyclic fatigue resistance, resulting in a total of 140 new instruments. All instruments were rotated in a simulated root canal with a 60° angle of curvature and a 5-mm radius of curvature of a specific cyclic fatigue testing device until fracture occurred. The number of cycles to failure and the length of the fractured tip were recorded for each instrument in each group. The mean values and standard deviation were calculated, and data were subjected to 1-way analysis of variance and a Bonferroni t test. Significance was set at the 95% confidence level. RESULTS When comparing the same size of the 2 different instruments, a statistically significant difference (P < .05) was noted between all sizes of Vortex Blue and Profile Vortex instruments except for tip size 15 and .04 taper (P = 1.000). No statistically significant difference (P > .05) was noted among all groups tested in terms of fragment length. CONCLUSIONS Vortex Blue showed a significant increase in cyclic fatigue resistance when compared with the same sizes of ProFile Vortex.