Cleaning efficacy of two kinds of mechanical nickel-titanium instruments in preparation of severely curved root canals: A scanning electron microscopic study / 中国组织工程研究

BACKGROUND: The preparation and cleaning of severely curved root canal is the difficult point of root canal treatment. A large number of smear layer will be produced in the process of root canal preparation. Removing effectively these debris and smear layer will be conducive to improving the success rate and longterm effect of severely curved root canal treatment. OBJECTIVE: To explore the cleaning efficacy of Twisted File and ProTaper file combined with chemical preparation on smear layer of severely curved root canal by scanning electron microscope. METHODS: Twenty clinically extracted mandibular molars with severely curved root canals were collected and randomly divided into two groups: Twisted File group and ProTaper group. The root canals were prepared by Twisted file and ProTaper Ni-Ti file, respectively. They were prepared by chemical method with 3% NaClO and 17% EDTA. After preparation, the root canals were split longitudinally and the cleaning efficacy of smear layer of coronal, middle and apical thirds was observed by scanning electron microscope. RESULTS AND CONCLUSION: (1) The images of scanning electron microscope showed that the dentinal tubules of root canal coronal thirds in the ProTaper group and Twisted file group were completely open, almost without smear layer. Dentinal tubules of middle thirds were also open, and simply part of them were covered by smear layer. However, dentinal tubules of apical thirds had few and no obvious opening, and was covered by a large number of smear layer. (2) In Twisted file group, the scores of smear layer at root canal apical thirds were higher than coronal and middle thirds (P 0.05). (3) The results showed that the chemo-mechanical preparation with Twisted File and ProTaper could remove effectively the debris and smear layer in the root canal walls of coronal and middle thirds of the severely curved crown, but the removal effect on apical thirds and dentin tubules was not good.

Metallurgic behavior and mechanical property of nickel-titanium endodontic files made by 3 heat treatment techniques / 中华口腔医学杂志

Objective@#To compare the phase transformation behavior, bending property and cyclic fatigue resistance of CM-wire, R-phase and M-wire nickel-titanium endodontic files treated by 3 heat treatment techniques.@*Methods@#Hyflex CM (25 mm, 25#/0.06) made from CM wire, TF (25 mm, 25#/0.06) made from R-phase heat treatment, ProTaper Next X2 (25 mm, tip size 25#/0.06) made from M-wire, Mtwo (25 mm, 25#/0.06) and ProTaper F2 (25 mm, tip size 25#/0.08) made from conventional nickel-titanium wire were chosen. Five of each files were chosen for differential scanning calorimetric (DSC) evaluation (n=5). The specimens were prepared from adjacent portions of the shaft. The weight and length were typically (20±1) mg and 2-3 mm. Another eight of the 5 nickel-titanium files were undergone cantilever-bending test, respectively (n=8). Further ten of the 5 instruments were submitted to the cyclic fatigue test by using a simulated metal root canal (n=10). The data of Ms, Mf, As, Af, ΔH, bending load, number of cyclic fatigue (NCF), fragment length were analyzed using one-way analysis of variance at a significance level of P<0.05.@*Results@#The Af of Hyflex CM [(60.27±0.94) ℃] and ProTaper Next [(51.40±0.32) ℃] were higher than body temperature of 37 ℃. The bending load values at 3.0 mm deflection of Hyflex CM [(0.867±0.074) N], TF [(1.275±0.146) N], Mtwo [(2.281±0.426) N], ProTaper Next [(3.104±0.252) N] and ProTaper [(4.227±0.483) N] increased gradually and significantly. The NCF of Hyflex CM (582±99), TF (427±85), ProTaper Next (158±22), Mtwo (129±32) and ProTaper (65±20) decreased gradually.@*Conclusions@#The 3 heat treatment techniques exert tremendous influence on the phase transformation behavior and mechanical characteristics of the files, which demonstrate improved bending property and cyclic fatigue resistance than the conventional ones.

Effect of surface treatment on the mechanical properties of nickel-titanium files with a similar cross-section

OBJECTIVES: The aim of this study was to compare the mechanical properties of various nickel-titanium (NiTi) files with similar tapers and cross-sectional areas depending on whether they were surface-treated. MATERIALS AND METHODS: Three NiTi file systems with a similar convex triangular cross-section and the same ISO #25 tip size were selected for this study: G6 (G6), ProTaper Universal (PTU), and Dia-PT (DPT). To test torsional resistance, 5 mm of the straightened file's tip was fixed between polycarbonate blocks (n = 15/group) and continuous clockwise rotation until fracture was conducted using a customized device. To evaluate cyclic fatigue resistance, files were rotated in an artificial curved canal until fracture in a dynamic mode (n = 15/group). The torsional data were analyzed using 1-way analysis of variance and the Tukey post-hoc comparison test, while the cyclic fatigue data were analyzed using the Mann-Whitney U test at a significance level of 95%. RESULTS: PTU showed significantly greater toughness, followed by DPT and G6 (p < 0.05). G6 showed the lowest resistance in ultimate torsional strength, while it showed a higher fracture angle than the other files (p < 0.05). In the cyclic fatigue test, DPT showed a significantly higher number of cycles to failure than PTU or G6 (p < 0.05). CONCLUSIONS: Within the limitations of this study, it can be concluded that the torsional resistance of NiTi files was affected by the cross-sectional area, while the cyclic fatigue resistance of NiTi files was influenced by the surface treatment.

Preference of undergraduate students after first experience on nickel-titanium endodontic instruments

OBJECTIVES: This study aimed to compare two nickel-titanium systems (rotary vs. reciprocating) for their acceptance by undergraduate students who experienced nickel-titanium (NiTi) instruments for the first time. MATERIALS AND METHODS: Eighty-one sophomore dental students were first taught on manual root canal preparation with stainless-steel files. After that, they were instructed on the use of ProTaper Universal system (PTU, Dentsply Maillefer), then the WaveOne (WO, Dentsply Maillefer). They practiced with each system on 2 extracted molars, before using those files to shape the buccal or mesial canals of additional first molars. A questionnaire was completed after using each file system, seeking students' perception about 'Ease of use', 'Flexibility', 'Cutting-efficiency', 'Screwing-effect', 'Feeling-safety', and 'Instrumentation-time' of the NiTi files, relative to stainless-steel instrumentation, on a 5-point Likert-type scale. They were also requested to indicate their preference between the two systems. Data was compared between groups using t-test, and with Chi-square test for correlation of each perception value with the preferred choice (p = 0.05). RESULTS: Among the 81 students, 55 indicated their preferred file system as WO and 22 as PTU. All scores were greater than 4 (better) for both systems, compared with stainless-steel files, except for 'Screwing-effect' for PTU. The scores for WO in the categories of 'Flexibility', 'Screwing-effect', and 'Feeling-safety' were significantly higher scores than those of PTU. A significant association between the 'Screwing-effect' and students' preference for WO was observed. CONCLUSIONS: Novice operators preferred nickel-titanium instruments to stainless-steel, and majority of them opted for reciprocating file instead of continuous rotating system.

Screw-in forces during instrumentation by various file systems

OBJECTIVES: The purpose of this study was to compare the maximum screw-in forces generated during the movement of various Nickel-Titanium (NiTi) file systems. MATERIALS AND METHODS: Forty simulated canals in resin blocks were randomly divided into 4 groups for the following instruments: Mtwo size 25/0.07 (MTW, VDW GmbH), Reciproc R25 (RPR, VDW GmbH), ProTaper Universal F2 (PTU, Dentsply Maillefer), and ProTaper Next X2 (PTN, Dentsply Maillefer, n = 10). All the artificial canals were prepared to obtain a standardized lumen by using ProTaper Universal F1. Screw-in forces were measured using a custom-made experimental device (AEndoS-k, DMJ system) during instrumentation with each NiTi file system using the designated movement. The rotation speed was set at 350 rpm with an automatic 4 mm pecking motion at a speed of 1 mm/sec. The pecking depth was increased by 1 mm for each pecking motion until the file reach the working length. Forces were recorded during file movement, and the maximum force was extracted from the data. Maximum screw-in forces were analyzed by one-way ANOVA and Tukey's post hoc comparison at a significance level of 95%. RESULTS: Reciproc and ProTaper Universal files generated the highest maximum screw-in forces among all the instruments while M-two and ProTaper Next showed the lowest (p < 0.05). CONCLUSIONS: Geometrical differences rather than shaping motion and alloys may affect the screw-in force during canal instrumentation. To reduce screw-in forces, the use of NiTi files with smaller cross-sectional area for higher flexibility is recommended.

Surface Characteristics of Reciprocating Instruments Before and After Use - A SEM Analysis

The presence of debris, defects and deformations of endodontic reciprocating instruments before and after chemical-mechanical preparation (MCP) was analyzed using scanning electron microscopy (SEM). The following 26 instruments were divided into 2 groups: Waveone (n=13) and Reciproc (n=13) and examined by SEM (150 x magnification) prior to canal preparation at 2 and 4 mm from the tip. The instruments were used in the preparation of mesial root canals of 26 extracted human permanent mandibular molars. The instruments were then washed in ultrasonic bath and subjected to new microscopic analysis of debris and deformation by a score that used the presence or absence of irregular edges, grooves, microcavities and burrs as criteria. After the SEM analysis and with the scores of the examiners, the collected data were subjected to descriptive statistical analysis using the Kruskall-Walis and Mann Whitney test at a 5% significance level. All instruments examined presented debris before and after use. A statistically significant difference was found for defects and deformation between the groups (p<0.05). The presence of defects and deformities was higher in the WaveOne instruments, and Reciproc instruments presented a lower rate.

Analisou-se por meio de microscopia eletrônica de varredura) MEV, a presença de debris, defeitos e deformações dos instrumentos endodônticos reciprocantes antes e após o preparo químico-mecânico (PQM). Vinte e seis instrumentos foram divididos em 2 grupos: WaveOne (n=13) e Reciproc (n=13), eletromicrografados previamente ao PQM com aumento de 150×, a 2 e 4 mm da ponta. Os instrumentos foram utilizados no preparo de canais radiculares mesiais de 26 molares permanentes inferiores humanos extraídos. Após, foram lavados em cuba ultrassônica e submetidos a nova análise microscópica para visualizar detritos e deformações tendo como critérios um escore que avaliou a presença ou não de borda irregular, ranhura, microcavidade e rebarba. Após análise em MEV e de posse dos escores dos avaliadores, os dados coletados foram submetidos à analise estatística descritiva pelos testes de Kruskall-Walis e Mann Whitney, ao nível de significância de 5%. Todos os instrumentos analisados apresentaram detritos antes e após o uso. Houve diferença estatisticamente significante quanto a defeitos e deformações entre os grupos (p<0,05). A presença de defeitos e deformações foi maior nos instrumentos WaveOne, enquanto que para os instrumentos Reciproc tal índice foi menor.

Refinement influence in the cleaning efficacy of rotary nickel-titanium Mtwo ® instruments in oval-shaped canals by means of optical microscopy.

Objective: This study evaluated the cleaning efficacy of the rotary nickel–titanium Mtwo® by means of optical microscopy in oval‑shaped root canals and compared refinement influence using ultrasonic files or Hedströem files. Materials and Methods: Twenty mandibular incisors were accessed, included in epoxy resin blocks, and cut transversely at 3, 6, and 9 mm from the apex. Teeth were instrumented using rotary nickel–titanium Mtwo. Digital images of the root cross sections were obtained before and after instrumentation with a digital camera attached to an optical microscope. Subsequently, samples were randomly divided into two groups for refinement. Group I was refined using ultrasonic files #30 and group II with Hedströem files #30. Final digital images of cross sections after refinement were captured and analyzed. The boundaries for the uninstrumented perimeter were measured by the software ImageTool 3.0. The data obtained were statistically analyzed by analysis of variance (ANOVA) and t‑test. Results: Mtwo instrumentation produced 41.48% of the uninstrumented perimeter. The final refinement using Hedströem and ultrasonic files decreased the uninstrumented perimeter. Significant differences (t‑test, P = 0.00) were found at the three thirds after the final refinement, except for the apical third that was enhanced by Hedströem file. However, there was no statistical difference between the two refinement techniques used (P > 0.05). Mtwo instrumentation was not capable of cleaning and shaping the entire perimeter of the root canals walls. Conclusions: The final refinement, either with ultrasonic files or with Hedströem files, resulted in significantly less uninstrumented perimeter.

Curative effect observation of two kinds of root canal preparation for root canal filling on posterior teeth / 重庆医学

Objective To evaluate the influence of ProTaper rotary nickel-titanium files root preparation on root canal filling . Methods 30 cases of molars pulpitis and 20 cases of premolars pulpitis or periapical periodontitis were equally divided into two groups .The group A(30 cases) used the ProTaper rotary nickel-titanium files in root canal preparation and the group B (30 cases) adopted the common K files modified step-back technique for root canal preparation .The influence of the root preparation by 2 sets of apparatus on the effect of root canal filling ,and the several aspects of the root canal filling time ,the matching degree of main root canal file and master gutta-percha ,proper filling rate ,postoperative reaction of root canal filling were compared for conducting the e-valuation .Results In the mean root canal filling time of the group A ,average premolar time was 4 min 25 s and molar was 1 min 30 s ,however in the group B ,average premolar was 5 min 30 s and molar was 11 min 41 s ,the time in the group A was greatly short-ened with statistical difference(P0 .05);the postoperative pain reaction of root canal filling in both groups were very low and weak without statistical difference .Conclusion The ProTaper rotary nickel-titanium files root preparation can accelerate the root canal filling speed ,improve the matching degree of main root canal files and master gutta-percha and simplify the root-filling therapy procedure .

Influence of glide path on the screw-in effect and torque of nickel-titanium rotary files in simulated resin root canals

OBJECTIVES: The purpose of this study was to investigate the screw-in effect and torque generation depending on the size of glide path during root canal preparation. MATERIALS AND METHODS: Forty Endo-Training Blocks (REF A 0177, Dentsply Maillefer) were used. They were divided into 4 groups. For groups 1, 2, 3, and 4, the glide path was established with ISO #13 Path File (Dentsply Maillefer), #15 NiTi K-file NITIFLEX (Dentsply Maillefer), modified #16 Path File (equivalent to #18), and #20 NiTi K-file NITIFLEX, respectively. The screw-in force and resultant torque were measured using a custom-made experimental apparatus while canals were instrumented with ProTaper S1 (Dentsply Maillefer) at a constant speed of 300 rpm with an automated pecking motion. A statistical analysis was performed using one-way analysis of variance and the Duncan post hoc comparison test. RESULTS: Group 4 showed lowest screw-in effect (2.796 +/- 0.134) among the groups (p < 0.05). Torque was inversely proportional to the glide path of each group. In #20 glide path group, the screw-in effect and torque decreased at the last 1 mm from the apical terminus. However, in the other groups, the decrease of the screw-in effect and torque did not occur in the last 1 mm from the apical terminus. CONCLUSIONS: The establishment of a larger glide path before NiTi rotary instrumentation appears to be appropriate for safely shaping the canal. It is recommended to establish #20 glide path with NiTi file when using ProTaper NiTi rotary instruments system safely.

A clinical evaluation of new type of rotary nickel-titanium instrument Mtwo for seniles in root canal therapy / 实用口腔医学杂志

To evaluate the clinical effects of rotary nickel-titanium instruments Mtwo in root canal therapy in the aged patients. Using step-back technique,80 teeth with pulpal and periapical involvement were instrumented by Mtwo in the M group, and by K file in the K group. Mtwo could keep the original curvature and flow of the root canals. No transportation, apical blockage, ledge or perforation was found in the M group. There was more complications in the K group than in the M group.The operative time was shorter and posttreatment pain seldom occurred in the M group. With rotary NiTi instruments Mtwo for seniles' root canals treatment, root canals can be prepared effectively and quickly,and is worth of clinical application.

Stress distribution for NiTi files of triangular based and rectangular based cross-sections using 3-dimensional finite element analysis / 대한치과보존학회지

The purpose of this study was to compare the stress distributions of NiTi rotary instruments based on their cross-sectional geometries of triangular shape-based cross-sectional design, S-shaped cross-sectional design and modified rectangular shape-based one using 3D FE models. NiTi rotary files of S-shaped and modified rectangular design of cross-section such as Mtwo or NRT showed larger stress change while file rotation during simulated shaping. The stress of files with rectangular cross-section design such as Mtwo, NRT was distributed as an intermittent pattern along the long axis of file. On the other hand, the stress of files with triangular cross-section design was distributed continuously. When the residual stresses which could increase the risk of file fatigue fracture were analyzed after their withdrawal, the NRT and Mtwo model also presented higher residual stresses. From this result, it can be inferred that S-shaped and modified rectangular shape-based files were more susceptible to file fracture than the files having triangular shape-based one.