Effect of canal curvature location on the cyclic fatigue resistance of reciprocating files

Comparative analysis of methods for measuring root canal curvature based on periapical radiography: A laboratory study

AIM

To evaluate the agreement between six currently available periapical radiography-based methods for measuring the root canal curvatures in mesial roots of mandibular first molars, assessed by two examiners with different proficiency levels.

METHODOLOGY

Non-endodontically treated mesial roots of 41 human mandibular first molars were radiographed using the parallelling technique. Two independent observers (a specialist in endodontics and radiology and a final-year dental student) assessed their root canal curvature using the methodologies described by Schneider (1971, Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology, 32, 271), Weine (1982, Endodontic therapy), Berbert and Nishiyama (1994, Revista Gaúcha de Odontología, 356), Luiten et al. (1995, Journal of Endodontics, 21, 26), Hankins and ElDeeb (1996, Journal of Endodontics, 22, 123) and Pettiette et al. (1999, Journal of Endodontics, 25, 230). Intra- and inter-examiner reliability was assessed using the intraclass correlation coefficient. The differences in curvature angle measured by the different methods were compared using the one-way anova for repeated measures test, followed by Tukey's post hoc analysis. The effect was calculated using the Cohen's d method. To determine the agreement between methods, the Bland-Altman analysis was used. The significance level was set at 5%.

RESULTS

Agreement for the observers was excellent (>0.81) for the six methods considered. For the angle comparisons between methods, the maximum differences were for Schneider versus Weine (35.77°) and Luiten versus Hankins (35.14°), whilst the highest percentage of angles with a difference >10° were Weine versus Luiten and Berbert versus Pettiette (90%) and the comparison Weine versus Hankins presented with the lowest frequency (15%). Excellent agreement was found for five comparisons: Weine versus Luiten (0.940), Berbert versus Pettiette (0.917), Weine versus Pettiette (0.907), Luiten versus Pettiette (0.904) and Berbert versus Luiten (0.812). Compared to Schneider's method, the other methods showed a tendency of increasing difference as the angles became more acute. The other methods exhibited linear differences, remaining constant for smaller and larger angles.

CONCLUSIONS

Reliability was excellent for all methods assessed separately. Maximum differences in curvature angles were found when comparing Schneider versus Weine and Luiten versus Hankins. Excellent agreement was found for Weine versus Luiten, Berbert versus Pettiette, Weine versus Pettiette, Luiten versus Pettiette and Berbert versus Luiten. In the presence of dilacerations, the method by Schneider was less sensitive.

Screw-in force, torque generation, and performance of glide-path files with three rotation kinetics

We aimed to evaluate the screw-in force, torque generation, and performance of three nickel-titanium (NiTi) glide-path files with different rotational kinetics. ProTaper Ultimate Slider (PULS) and HyFlex EDM Glide-path (HEDG) files were used for canal shaping with constant rotation (CON) or the alternative rotation technique (ART). In the ART mode, the NiTi file was periodically rotated at a speed of 1.5 times faster than that in the CON mode. WaveOne Gold Glider was used with reciprocating motion (WOGG_RCP). Sixty J-shaped resin blocks were assigned to five groups: PULS_CON, PULS_ART, HEDG_CON, HEDG_ART, and WOGG_RCP (n = 12). Glide-path preparation was performed using an automated pecking device. During glide-path preparation, the screw-in force and clockwise and counterclockwise torques were recorded and the number of pecking motions required to reach the working length was determined. The centering ratio was calculated after glide-path preparation using stereomicroscopic images. Data were analyzed using one-way analysis of variance with the Games-Howell post hoc test and the Kruskal-Wallis test with Bonferroni correction. PULS_ART generated a lower maximum screw-in force than PULS_CON. The average number of pecking motions required to reach the working length by HEDG_ART was lower than that by HEDG_CON. The mean centering ratios of PULS_CON and HEDG_CON were - 0.04 and - 0.06, respectively, while those of PULS_ART, HEDG_ART, and WOGG_RCP were 0.09, 0.01, and 0.08, respectively. The ART mode reduced the screw-in force of PULS and enabled faster glide-path preparation with the HEDG file.

A novel model to evaluate the fatigue resistance of NiTi instruments: Rotational and axial movement at body temperature

To develop a model to test cyclic fatigue resistance of TruNatomy instruments undergoing rotational and axial movement at body temperature. A total of 288 Prime and Medium instruments were subjected to cyclic fatigue testing in simulated canals (at 37°C) using a model with either rotational movement only or rotational and axial movement simultaneously. Two different sized canals and three different types of curvatures were tested for each instrument (30/0.04 and 30/0.06 for Prime; 38/0.04 and 40/0.06 for Medium). The number of cycles to failure (fatigue resistance) was recorded. Rotational and axial movement of instruments led to greater fatigue resistance compared with rotational movement alone. Apical curvatures led to greater fatigue resistance than curvatures in the coronal and middle third. The developed dynamic model at body temperature to evaluate fatigue resistance of instrument closer simulates clinical scenarios.

An Appraisal on Newer Endodontic File Systems: A Narrative Review

AIM

This narrative review aims to explore and elicit the newer endodontic file systems used for root canal treatments.

BACKGROUND

The primary goals of endodontic therapy continue to be the mechanical enlargement and shaping of the intricate endodontic root canal systems to aid in disinfection. Nowadays endodontists have access to a wide range of endodontic file systems for root canal preparations with various design characteristics and benefits.

REVIEW RESULTS

ProTaper Ultimate (PTU) files' tip have a triangular convex cross-section, an offset mass of rotating design, a maximum flute diameter of 1.0 mm, and are constructed of gold wire, hence, commonly applied in conditions with restricted accessibility or an extremely curved canal. TruNatomyhas advantages over other cutting-edge file systems like maximum flute diameter of the corona, reduced distance between active cutting flutes, and shorter handles in comparison to SX instruments. In comparison to PTU files, ProTaper Gold (PTG) files are noticeably more elastic and fatigue-resistant. Compared to files in the F1-F3 range, size S1 and S2 files have a significantly longer fatigue life. MicroMega One RECI is more resistant to cyclic fatigue because of its heat treatment and reciprocating action and the C-wire heat treatment of the former gives it flexibility and controlled memory, enabling the prebending of the file. The RECIPROC blue demonstrated enhanced flexibility, increased fatigue resistance, and lower microhardness while maintaining the same surface qualities.

CONCLUSION

As per the necessity and requirement on case to case basis, every endodontic file system has advantages and disadvantages as mentioned in this narrative review. According to the need, an endodontist can select the file system which is required specifically. Although several studies are comparing these various systems in the literature, this narrative review aims to give the clinician a summary of some recently launched endodontic rotary file systems available in the market and their clinical uses.

CLINICAL SIGNIFICANCE

As per the priority and need of the case, whether removal and extrusion of debris, reduction of micro-organisms, keeping canal anatomy, and cutting efficiency, a specific required file system can be utilized.

Influence of needle working length and root canal curvature on irrigation: a computational fluid dynamics analysis based on a real tooth

Backgrounds

To compare the irrigation efficiency with different needle working length and different root canal curvature based on a real unshaped root canal using computational fluid dynamics (CFD) method.

Methods

Images of the root canal of the maxillary first molar after being prepared to .04/15 were scanned using micro-CT, and then imported into the software for three-dimensional reconstruction. A palatal root canal with a curvature of 23.4° was selected as the experiment canal. The needle working length of the 30-G flat needle was 4.75 mm, 5 mm, 5.25 mm and 5.5 mm short of apical foramen respectively, the flow pattern, irrigation velocity, shear stress were compared. The modified curved canals with a curvature of 0°, 5°, 10°, 20° and 30°were reconstructed via software. The flat needle was replaced at the optical inserted depth, and key parameters of irrigation efficiency were analyzed.

Results

Decreased needle working length had a positive impact on irrigation efficiency. With the optimal needle working length, the replacement of the apical irrigation fluid, the effective velocity, and wall shear stress were significantly improved in more severely curved root canals. With the same needle working depth and analogous canal curvature, irrigation efficiency is higher in real canal than that of modified canal.

Conclusions

Short needle working depth, large curvature and the anomalous inner wall of canals help to improve irrigation efficiency.

A critical analysis of research methods and experimental models to study the physical properties of NiTi instruments and their fracture characteristics

The aim of this review is to provide a critical overview of the physical properties (surface hardness, cutting efficiency, bending properties, flexibility and cyclic fatigue resistance) of NiTi instruments. Frequently used experimental models regarding these aspects will be presented and discussed with regard to their strengths and weaknesses. For all these aspects, a plethora of experimental models have been described. Based on a critical appraisal and especially taking the appropriate translation of experimental findings to clinical endodontics into account, suggestions for future research based on clearly defined and valid experimental methodologies will be provided. Up to now, very few attempts have been made to assess which particular physical properties of NiTi instruments exert an impact on the clinical outcome of root canal treatment. Departure from merely focusing on physical properties and fracture characteristics towards more biological aspects in terms of treatment outcome is essential.