WooCheol Lee

Cyclic fatigue and torsional resistance of two new nickel-titanium instruments used in reciprocation motion: Reciproc versus WaveOne.

INTRODUCTION The use of reciprocating movement was claimed to increase the resistance of nickel-titanium (NiTi) file to fatigue in comparison with continuous rotation. Recently 2 new brands of NiTi files have been marketed for use in a RM mode. The purpose of this study was to compare the cyclic fatigue resistance and torsional resistance of these 2 files, Reciproc and WaveOne. METHODS Cyclic fatigue test with a simultaneous pecking motion was performed with the instrument (n = 10 each) operating in the recommended reciprocation motion until fracture for the Reciproc R25 and WaveOne Primary files. ProTaper F2 was tested in continuous rotation to serve as a control for comparison. The number of cycles to fracture (NCF) was determined by measuring the time to fracture. The length of the fragment was measured and the fracture surface was examined by using scanning electron microscopy. Torsional strength was measured by using a torsiometer after fixing the apical 5 mm of the instrument rigidly. Statistical analysis was performed by using one-way analysis of variance. RESULTS The results showed that Reciproc had a higher NCF and WaveOne had a higher torsional resistance than the others. Both reciprocating files demonstrated significantly higher cyclic fatigue and torsional resistances than ProTaper (P < .05). The fractographic analysis showed typical features of cyclic fatigue and torsional failure for all instruments. CONCLUSIONS The 2 brands of NiTi file for use with a reciprocation motion seem to have superior mechanical properties.

Lifespan of One Nickel-Titanium Rotary File with Reciprocating Motion in Curved Root Canals

INTRODUCTION The purpose of this study was to examine the lifespan of one nickel-titanium (NiTi) rotary file when used in reciprocating motion and to compare the time required for its preparation of a curved root canal using both reciprocating and continuous motion. METHODS One hundred twenty curved canals from 60 extracted maxillary and mandibular molars were selected for measuring the mean number of uses. Each canal was prepared with reciprocating motion until the ProTaper F2 single file (Dentsply Maillefer, Ballaigues, Switzerland) reached the working length. One file was used until it was fractured. Another 60 canals were divided into two groups. 30 canals in the continuous rotation motion (CM) group were prepared using continuous rotation following the sequence of ProTaper files, whereas the canals in the reciprocating motion (RM) group (n = 30) were prepared with reciprocating motion with the sole use of the ProTaper F2. The total root canal preparation time was measured until the F2 file finally reached the working length in both groups. RESULTS A total of 11 files were used in the preparation of 120 curved root canals. The average lifespan of one F2 file was 10.60 ± 4.35 canals with the longest lifespan of 21 canals. The total time for canal preparation was 46.42 ± 18.12 seconds and 21.15 ± 6.70 seconds in the CM and RM groups, respectively. There was a statistically significant difference between the groups (p < 0.01). CONCLUSION Within the limitation of this study, one F2 file can be safely used to the working length of curved canals at least six times under reciprocating motion. Reciprocating preparation with only one F2 file was much faster than root canal instrumentation with continuous rotation.

Shaping Ability of Reciprocating Motion in Curved Root Canals: A Comparative Study with Micro–Computed Tomography

INTRODUCTION Recently, root canal shaping with reciprocating motion has been postulated to reduce the possibility of unexpected file fractures. However, there has been little information on the shaping capability of this reciprocating motion preparation technique. Therefore, the purpose of this study was to evaluate the shaping ability of reciprocating motion when compared with continuous rotation motion in curved root canals. METHODS The mesiobuccal and distobuccal canals of 20 extracted maxillary molars with curvatures of 20-45 degrees were instrumented with a series of ProTaper rotary files. The canals in the continuous rotation motion (CM) group (n = 20) were prepared by using continuous rotation with pecking motion, whereas the canals in the reciprocating motion (RM) group (n = 20) were prepared with reciprocating motion (clockwise 140 degrees and counterclockwise 45 degrees). Basic geometric parameters such as curvature, root canal volume, surface area, and structure model index (SMI) before and after canal shaping were evaluated by using micro-computed tomography. The degrees and directions of transportation were also measured, and statistical analysis was carried out with one-way analysis of variance and Tukey post hoc tests. RESULTS There were no significant differences between the 2 groups in canal curvature, volume, surface area, and SMI categories measured before preparation (P > .05). Changes in curvature, root canal volume, surface area, and SMI were not affected by the instrumentation technique used (P > .05). There were no significant differences in the degrees and directions of transportation between CM and RM groups (P > .05). CONCLUSIONS The application of reciprocating motion during instrumentation did not result in increased apical transportation when compared with continuous rotation motion, even in the apical part of curved canals. Reciprocating motion might be an attractive alternative method to prevent procedural errors during root canal shaping.

Carbon nanotube reservoirs for self-healing materials

A novel nanoreservoir made of carbon nanotubes (CNTs) is proposed for realizing tougher and automated self-healing materials. The advantages of the approach are that CNTs have the potential to play the role of reinforcing elements prior to and after sealing a crack and that the number of voids is reduced after the material and the CNTs themselves are healed. The focus of this paper is on investigating the feasibility of using CNTs as a nanoreservoir by analyzing the dynamics of a fluid flowing out of a ruptured single-walled CNT (SWNT), where the fluid resembles an organic healing agent. With this in mind the escaping mechanism of organic molecules stored inside a cracked SWNT was investigated through a molecular dynamics study. The study shows that, when a SWNT wall suffers the formation of a crack, a certain amount of organic molecules, stored inside the SWNT, escape into space in a few picoseconds. This phenomenon is found to depend on the temperature and on the size of the cracks. The results of this study indicate that CNTs have the potential to be successfully used to realize the next generation of stronger, lighter and self-healing materials.

Heavy Metal Analysis of Ortho MTA and ProRoot MTA

INTRODUCTION Recently, several kinds of mineral trioxide aggregate (MTA)-based products have been introduced in endodontics. Ortho MTA (BioMTA, Seoul, Republic of Korea) is one of those products, which was developed for retrograde filling, perforation repair, orthograde root canal obturation, and direct pulp capping. The inclusion of heavy metals in MTA-based materials is of concern because they come into direct contact with hard and soft tissues. The aim of this study was to investigate and compare the levels of arsenic (As), chromium (Cr), hexavalent chromium (Cr(6+)), and lead (Pb) in Ortho MTA and ProRoot MTA. METHODS One gram of each MTA was digested using a mixture of hydrochloric and nitric acids and filtered. The As, Cr, and Pb in the resulting filtrates were analyzed by inductively coupled plasma-optical emission spectrometry. The level of Cr(6+) was measured by the methods suggested in the Korean Standard L 5221. The results were statistically analyzed using the Mann-Whitney U test. RESULTS The concentration of As in ProRoot MTA was 1.16 ppm, but As was not detected in Ortho MTA. Cr(6+) and Pb were not detected in either MTA. Ortho MTA contained significantly less Cr than ProRoot MTA (P < .05). CONCLUSIONS Ortho MTA and ProRoot MTA meet the ISO specification 9917-1 regarding the safety limits of As and Pb and are safe biomaterials when the purity of As, Cr(6+), and Pb is considered.

Analysis of the cause of failure in nonsurgical endodontic treatment by microscopic inspection during endodontic microsurgery.

INTRODUCTION This study examined the clinical causes of failure and the limitation of a previous endodontic treatment by an inspection of the root apex and resected root surface at 26× magnification during endodontic microsurgery. METHODS The data were collected from patients in the Department of Conservative Dentistry at the Dental College, Yonsei University in Seoul, Korea between March 2001 and January 2011. All root-filled cases with symptomatic or asymptomatic apical periodontitis were enrolled in this study. All surgical procedures were performed by using an operating microscope. The surface of the apical root to be resected or the resected root surface after methylene blue staining was examined during the surgical procedure and recorded carefully with 26× magnification to determine the state of the previous endodontic treatment by using an operating microscope. RESULTS Among the 557 cases with periapical surgery, 493 teeth were included in this study. With the exclusion of unknown cases, the most common possible cause of failure was perceived leakage around the canal filling material (30.4%), followed by a missing canal (19.7%), underfilling (14.2%), anatomical complexity (8.7%), overfilling (3.0%), iatrogenic problems (2.8%), apical calculus (1.8%), and cracks (1.2%). The frequency of possible failure causes differed according to the tooth position (P < .001). CONCLUSIONS An appreciation of the root canal anatomy by using an operating microscope in nonsurgical endodontic treatment can make the prognosis more predictable and favorable.

Mesiobuccal root canal anatomy of Korean maxillary first and second molars by cone-beam computed tomography

OBJECTIVE The aim of this study was to investigate the types of canal configurations and the incidence of a second mesiobuccal (MB2) canal in Korean maxillary molar mesiobuccal (MB) roots by analyzing cone-beam computed tomographic (CBCT) images. STUDY DESIGN Three-dimensional CBCT images of 458 maxillary first molars and 467 second molars from 276 Korean patients were analyzed to determine the incidence of an MB2 canal, the types of canal configurations, and the correlations between the incidence of an MB2 canal and age, gender, and tooth position. RESULTS The incidence of 2-canaled MB roots was 71.8% in first molars and 42.2% in second molars, with the most common configurations being Weine types III and II. The frequency of an MB2 canal decreased with age in both molars (P < .05). CONCLUSIONS Types III and II canal configurations were the most prevalent in the 2-canaled MB roots of Korean maxillary molars.

A comparison of nickel-titanium rotary instruments manufactured using different methods and cross-sectional areas: ability to resist cyclic fatigue

OBJECTIVE This study examined the effect of the manufacturing methods (ground, electropolished, and twisted) and the cross-sectional area (CSA) of nickel-titanium (NiTi) rotary instruments on their cyclic fatigue resistance. STUDY DESIGN A total of 80 NiTi rotary instruments (ISO 25/.06 taper) from 4 brands (K3, ProFile, RaCe, and TF) were rotated in a simulated root canal with pecking motion until fracture. The number of cycles to failure (NCF) was calculated. The CSA at 3 mm from the tip of new instruments of each brand was calculated. The correlation between the CSA and NCF was evaluated. All fractured surfaces were analyzed using a scanning electron microscope to determine the fracture mode. RESULTS The TF instruments were the most resistant to fatigue failure. The resistance to cyclic failure increased with decreasing CSA. All fractured surfaces showed the coexistence of ductile and brittle properties. CONCLUSION The CSA had a significant effect on the fatigue resistance of NiTi rotary instruments.

Effect of final irrigation regimen on sealer penetration in curved root canals.

INTRODUCTION The purpose of this study was to evaluate the effect of different final irrigation regimens on the sealer penetration into dentinal tubules of curved root canals. METHODS The mesiobuccal canals from 45 extracted maxillary and mandibular molars were instrumented with sodium hypochlorite (NaOCl) irrigation. The samples were divided into 3 groups according to the final irrigation used: group N (control), 3.5% NaOCl; group E, 17% ethylenediaminetetraacetic acid (EDTA); and group EN, 17% EDTA followed by 3.5% NaOCl. All teeth were obturated with gutta-percha and AH Plus sealer labeled with fluorescent dye. Transverse sections at 2 mm (apical) and 5 mm (coronal) from root apex were examined by using confocal laser scanning microscopy. Then, total percentage and maximum depth of sealer penetration were measured. RESULTS The apical sections in each group showed significantly lower percentage and maximum depth of sealer penetration than the coronal sections (P < .05). In apical levels, group E and EN resulted in a higher percentage of sealer penetration than the control group (P < .05), but there was no significant difference of maximum depth between group E and the control group (P > .05). CONCLUSIONS In curved canal, final rinse with NaOCl after the use of EDTA had no additional effect on sealer penetration. Complete debridement with a 1-minute application of EDTA remains a challenge in the apical area of curved canals.

Flexural Stiffness and Stresses in Nickel-Titanium Rotary Files for Various Pitch and Cross-sectional Geometries

INTRODUCTION Shape is the main determinant of mechanical performance for nickel-titanium rotary instruments. This study evaluated how pitch and cross-sectional geometry affected flexural stiffness and stresses. METHODS Finite element models of rotary instruments with 4 cross-sectional geometries (triangle, slender-rectangle, rectangle, square) and 3 pitches (5-, 10-, 15-threads) were created, featuring superelastic nickel-titanium properties. All models had the same length, taper, and external peripheral radius; cross-sectional area and/or center-core area varied. The clamped shaft was rotated axially, while the tip was deflected 5 mm. Flexural stiffness and maximum von Mises stresses were calculated. RESULTS Stiffness and maximum stress decreased with decreasing pitch (increasing threads). Doubling or tripling the threads for the triangular or rectangular cross sections decreased the stiffness and stress 6% and 12%, respectively; square cross sections were less affected (1% and 3% decrease, respectively). Square cross sections (higher cross-sectional and center-core areas) had higher stiffness and stresses than other models with same deflection. Rectangular and triangular models with the same center-core areas had similar stresses, but the rectangular model was 30%-40% stiffer. The slender-rectangle had the smallest center-core area and the lowest stiffness and stresses. Both rectangular cross sections caused stiffness and stress variations with rotation angle (13% for slender-rectangle); larger pitch caused more variation. CONCLUSIONS Under the same tip deflection (simulating canal curvature), flexural stiffness and stress correlated with center-core area. Increasing pitch increased flexural stiffness and stresses.