The Role of Pecking Motion Depths in Dynamic Cyclic Fatigue Resistance: In Vitro Study

OBJECTIVE

This is the first study evaluating the impact of different pecking motion depths on dynamic cyclic fatigue resistance of different endodontic instruments.

METHODS

Four nickel-titanium systems (Hyflex EDM OneFile 25/. ∼; Rotate 25/0.6; Mtwo 25/0.6; Reciproc Blue R25) were tested. Forty instruments from each group were subjected to 4 different pecking movements to evaluate their cyclic fatigue resistance. The distances for the pecking motion were 3-mm forward and backward, 1-mm (3-mm forward and 2-mm backward), 2-mm (4-mm forward and 2-mm backward), and 3-mm (5-mm forward and 2-mm backward). Speeds were 100 and 200 mm/min for the descending and ascending motion, respectively. The times to fracture (TtF) in seconds were recorded for each instrument. Data were statistically analysed by using 2-way ANOVA and Bonferroni multiple comparison post hoc test (P < .05).

RESULTS

All instruments had a significant increase in cyclic fatigue resistance during the forward dynamic motion compared with the axial continuous. Overall, the heat-treated instruments reported higher fatigue strength than the untreated files (P < .05). Reciproc Blue and Hyflex EDM showed higher TtF in the forward movements of 1-/2-mm and 2-mm (P < .05), respectively while Mtwo 25.06 and Rotate 25.06 in the forward movement of 3-mm (P < .05).

CONCLUSIONS

Within the limits of this in vitro study, the pecking motion depths had varying impacts on the cyclic fatigue resistance of instruments. Reciproc Blue and Hyflex EDM performed significantly better with pecking motions of 1-and 2-mm. Improving endodontic instrument durability through specific pecking depths has the potential for improving clinical performance and reducing instrument failures.

Effect of number of uses and sterilization on the instrumented area and resistance of reciprocating instruments

Objectives

This study evaluated the effect of repeated uses and autoclaving in the instrumented area, fracture resistance, and time of instrumentation of thermally treated nickel-titanium reciprocating systems.

Materials and Methods

Two hundred simulated canals were instrumented using Reciproc Blue and WaveOne Gold. Each file was used up to 10 times or until fracture. The instrumented area was measured in pre- and post-operative images, using ImageJ software. Kaplan-Meier survival analysis evaluated the number of uses of instruments before fracture. Instrumented area and time of instrumentation were analyzed by Mann-Whitney U test and Kruskal-Wallis. Correlations among the number of uses and instrumented area were measured. The level of statistical significance was set at p < 0.05.

Results

Reciproc Blue presented a higher estimated number of uses in comparison with WaveOne Gold (p = 0.026), but autoclaving did not affect the resistance to fracture of instruments (p > 0.05). The instrumented area was different among the evaluated groups (p = 0.039), and the instrumented area along the uses of both tested instruments was reduced. With the time of instrumentation, there was also a significant difference among the evaluated groups; the groups without sterilization cycles were faster, in comparison to those submitted to autoclaving (p = 0.010).

Conclusions

Reciproc Blue was more resistant than WaveOne Gold, suffering later fracture. Additionally, the sterilization cycles did not influence the estimated number of uses of thermally treated reciprocating instruments, but the instrumented area of root canals was reduced along with the repeated uses of both instruments.

Surgical Management of a Separated Endodontic Instrument using Second Generation Platelet Concentrate and Hydroxyapatite

Fractured endodontic instrument is an unfortunate endodontic mishap which may obstruct thorough cleaning and shaping of the root canals with potential impact on the endodontic prognosis and treatment outcome. When the fractured segment lies apical to canal curvature, overzealous removal of tooth structure is required to gain access to the separated segment which in turn increases the likelihood of root fracture. In infected cases, the stage at which instrument separation occurs is crucial as root canal disinfection is jeopardized. This case report describes the surgical retrieval of a fractured endodontic file from the mesiobuccal canal of mandibular first molar by limited resection of mesial root. Second generation platelet concentrate called Platelet Rich Fibrin (PRF) and nanocrystalline hydroxyapatite and β-tricalcium phosphate bone graft was placed to fill the surgical defect as the combination enhances the regenerative effect of PRF by exerting an osteoconductive effect in the bony defect area. The clinical and radiographic examination after eighteen months revealed complete periapical healing.

Fracture Incidence of WaveOne and Reciproc Files during Root Canal Preparation of up to 3 Posterior Teeth: A Prospective Clinical Study

INTRODUCTION

Reciprocating instruments were developed to improve and simplify the preparation of the root canal system by allowing greater centralization of the canal and requiring a shorter learning curve. Despite the risk of instrument separation, using a reciprocating instrument in more than 1 case is a relatively common clinical practice. The aim of this study was to evaluate the fracture resistance of Reciproc (R25; VDW, Munich, Germany) and WaveOne (Primary; Dentsply Maillefer, Ballaigues, Switzerland) instruments according to the number of uses during the preparation of root canals in up to 3 posterior teeth.

METHODS

A prospective clinical study was conducted by 3 experienced specialists who performed treatment of 358 posterior teeth (1130 canals) over a period of 12 months using 120 reciprocating instruments, 60 of which were Reciproc R25 and 60 were WaveOne Primary. The motion used during instrumentation followed the recommendations of the respective manufacturers. After each use, the instruments were observed under a dental operating microscope at 8× magnification. In the case of fracture or deformation, the instrument was discarded.

RESULTS

None of the instruments showed any signs of deformation, but 3 instruments fractured (0.26% of the number of canals and 0.84% of the number of teeth). All fractures occurred in mandibular molars (1 WaveOne Primary file during the third use and 2 Reciproc R25 files, 1 during the first use and the other during the third use).

CONCLUSIONS

There was a low incidence of fracture when reciprocating files were used in up to 3 cases of endodontic treatment in posterior teeth.

Prevention and management of fractured instruments in endodontic treatment

Intracanal instrument fracture is an unpredictable and problematic occurrence that can prevent adequate cleaning and shaping procedures and influence the prognosis of endodontic treatment. The prevalence of instrument fracture is reported to range between 0.28% and 16.2%. This article presents an overview of the prevention and management of instruments fractured during endodontic therapy on the basis of literature retrieved from PubMed and selected journal searches. Instrument fracture occurs because of reduced metal fatigue and/or torsional resistance. The reasons include canal morphology and curvature, manufacturing processes and instrument design, instrument use times and technique, rotational speeds and operator experience. With the development of various equipment and techniques, most of the retained instrument separations can be removed safely. However, in canals without associated periapical disease not every fractured separation should be removed from difficult locations because of the increased risk for root perforation and fracture. In difficult cases, either retain or bypass the fragment in the root canal and ensure regular follow-up reviews. Fractured instruments retained in the presence of periapical disease reduce significantly the prognosis of endodontically treated teeth, indicating a greater need to attempt the removal or bypass of the file separations. Apical surgery might be required in some instances, emphasizing the importance of preventing instrument fracture.