Incidence of dentinal defects after preparation of severely curved root canals using the Reciproc single-file system with and without prior creation of a glide path

Endodontic Dentistry: Analysis of Dentinal Stress and Strain Development during Shaping of Curved Root Canals

BACKGROUND

Endodontic shaping causes stress and strain in the root canal dentin. Dentin microcracks have the potential to be later followed by root fractures occurring under the occlusal load. The aim of our research was to theoretically determine the values of such dentinal states of stress and strain during the endodontic shaping of curved root canals using finite element analysis (FEA).

METHODS

To highlight the stress concentrations in dentin, two geometric models were created considering the volume of the curved dental root and the contact between the endodontic file and the root canal walls. The application of forces with different values was simulated both on a uniform curved root canal and on a root canal with an apical third curvature of 25° as they would be applied during the preparation of a root canal.

RESULTS

In the case of the first model, which was acted upon with a force of 5 N, the deformations of the root canal appeared along the entire working length, reaching the highest values in the apical third of the root, although there were no geometric changes in the shape of the root canal. Regarding the second root model, with an apical third curvature of 25°, although the applied force was 2 N, the deformations were accompanied by geometric changes in the shape of the root, especially in the upper part of the apical third. At a higher force of 7 N exerted on the endodontic file, the geometric shape changed, and the deformation reached extreme critical values. The resulting tensile stresses appearing in the experimental structure varied similarly to the deformations.

CONCLUSIONS

Significant stress and strain can develop, especially in the apical third of curved root canals during their shaping, and the risk of cracks is higher for endodontically treated teeth presenting severe curvatures in the apical third of the root.

Effectiveness of conservative instrumentation in root canal disinfection

OBJECTIVES

The impact of conservative instrumentation on the disinfection of root canals with different curvatures has not yet been determined. This ex vivo study aimed to evaluate and compare the effect of conservative instrumentation with TruNatomy (TN) and Rotate and a conventional rotary system, ProTaper Gold (PTG), on root canal disinfection during chemomechanical preparation of straight and curved canals.

MATERIALS AND METHODS

Ninety mandibular molars with straight (n = 45) and curved (n = 45) mesiobuccal root canals were contaminated with polymicrobial clinical samples. Teeth were divided into three subgroups (n = 14) according to the file systems and the curvature. Canals were instrumented with TN, Rotate, and PTG, respectively. Sodium hypochlorite and EDTA were used as irrigants. Intracanal samples were taken before (S1) and after (S2) instrumentation. Six uninfected teeth were used as negative controls. The bacterial reduction between S1 and S2 was measured by ATP assay, flow cytometry, and culture methods. Kruskal-Wallis and ANOVA tests were followed by the Duncan post hoc test (p < 0.05).

RESULTS

Bacterial reduction percentages were similar for the three file systems in straight canals (p > 0.05). However, PTG showed a lower reduction percentage of intact membrane cells in flow cytometry than TN and Rotate (p = 0.036). For the curved canals, no significant differences were obtained (p > 0.05).

CONCLUSION

Conservative instrumentation of straight and curved canals using TN and Rotate files resulted in similar bacterial reduction compared to PTG.

CLINICAL RELEVANCE

The disinfection efficacy of conservative instrumentation is similar to conventional instrumentation in straight and curved root canals.

Optimum shaping parameters of the middle mesial canal in mandibular first molars: A finite element analysis study

INTRODUCTION

This study investigated the effect of shaping parameters of two different configurations of middle mesial canals (MMC) on the biomechanical behavior and life span of a mandibular first molar using finite element analysis (FEA).

METHODS

A mandibular molar with an independent MMC and another with a confluent MMC were scanned via micro-CT, and FEA models were produced. For each tooth, an intact model and 5 experimental models were produced differed by parameters of how MMC was shaped: unshaped MMC, 25/.04, 25/.06, 30/.04, and 30/.06. Cyclic loading of 50 N was applied on the occlusal surface in vertical and oblique scenarios, and the number of cycles until failure (NCF) was compared to the intact models. In addition, mathematical analyses evaluated the stress distribution patterns and calculated maximum von Mises and maximum principal stresses.

RESULTS

For both the independent and confluent MMC models, shaping the MMC reduced the NCF. The lifelog percentage of models was inversely proportional with radicular shaping parameters during the vertical and oblique loading scenarios. The shaping size of 30/.06 resulted in lower lifelog percentage than the cases with shaping size of 25/.04 in both of the independent and confluent MMC models. For all models, oblique loading reduced NCF more than vertical loading.

CONCLUSION

Shaping the MMC should be kept as conservative as 25/.04. Also, whether the MMC is independent or confluent is a deciding factor in whether to increase the apical diameter or the root canal taper when larger shaping parameters are needed.

A single-file endodontic treatment: A promising endodontic concept

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Smear layer removal and sealer penetration with different tapers after using photon-initiated photoacoustic streaming technique

OBJECTIVE

To evaluate the effect of the photon-initiated photoacoustic streaming (PIPS) technique on irrigation performance with different instrumentation tapers in root canals regarding smear layer removal and subsequent sealer penetration.

MATERIALS AND METHODS

One hundred twenty human mandibular molars were divided into three equal groups according to the apical preparation taper (25/4%, 25/6%, and 25/8%). Each group was divided into two equal subgroups, one received passive irrigation (PI) while the other received PIPS activation of 2.5% sodium hypochlorite and 17% EDTA. Half the samples were evaluated using electron microscope images to assess smear layer removal. The other half was obturated using gutta-percha and rhodamine B-labeled AH Plus sealer before being sectioned horizontally at different root levels (coronal, middle, and apical) to evaluate the percentage of sealer penetration using CLSM. Mann-Whitney U and Friedman tests were used to analyze smear layer scores, while sealer penetration data were analyzed using the three-way analysis of variance (ANOVA) and Tukey's post hoc test.

RESULTS

Statistical analysis showed significantly better smear layer removal and better sealer penetration after PIPS activation when corresponding root thirds were compared (P<0.001). Only exception was sealer penetration in the apical third with root canal preparation of 25/4% where the difference between the irrigation methods was statistically insignificant (P>0.05).

CONCLUSIONS

The use of PIPS activation in the final irrigation protocol enhanced smear layer removal and sealer penetration into dentinal tubules if the taper of the prepared canal was at least 6%.

CLINICAL RELEVANCE

Increasing apical preparation taper significantly enhances PIPS performance in terms of irrigation activation thus enhancing smear layer removal and subsequent sealer penetration in dentinal tubules.

Influence of Negotiation, Glide Path, and Preflaring Procedures on Root Canal Shaping-Terminology, Basic Concepts, and a Systematic Review

INTRODUCTION

Negotiation, glide path, and preflaring are essential steps in root canal shaping procedures. This report aimed to discuss the terminology, basic concepts, and clinical considerations of negotiation, glide path, and preflaring procedures and the influence of these steps on root canal shaping.

METHODS

This systematic review was undertaken following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The protocol has been registered with the International Prospective Register of Systematic Reviews (number CRD42019127021). A comprehensive literature search was performed by 2 independent reviewers using a selected search strategy in 2 electronic databases (PubMed and Scopus) until January 28, 2019. A further search was performed manually in endodontic journals. Studies investigating or comparing at least 1 shaping property resulting from root canal instrumentation with a glide path or preflaring in human extracted teeth or clinical studies were included.

RESULTS

The literature shows that the definition of glide path and preflaring procedures remains controversial, which requires an elaboration in the American Association of Endodontists' Glossary of Endodontic Terms. After the removal of irrelevant and duplicated articles, 98 articles were included. The impact of glide path preparation and preflaring on working length determination, apical file size determination, canal transportation, separation of endodontic files, shaping time, dentinal microcrack formation, and extrusion of debris was discussed. Because of heterogeneity among the included studies, quantitative synthesis was not performed for most of the parameters.

CONCLUSIONS

An evidence-based guideline is needed to define and correlate the basic concepts and current applications of each step of contemporary advancements in root canal instruments. Glide path preparation reduces the risk of debris extrusion, has no influence on the incidence of dentinal crack formation, and improves the preservation of the original canal anatomy. The creation of a glide path may have no impact on Reciproc files (VDW, Munich, Germany) in reaching the full working length. Preflaring increases the accuracy of working length determination. Further randomized clinical trials are required to evaluate the effect of a glide path and preflaring on root canal treatment outcomes.

Root-originating dentinal defects: methodological aspects and clinical relevance

It was in the 1980s when the association between root-filling procedures and dentinal microcracks was made. Nowadays, root-originating microcracks, also known as dentinal defects, are recognized as a possible precursor that is part of the longitudinal process of root-originating fractures. The presence of dentinal defects has been shown to significantly decrease the outcome through a periapical microsurgery model. Several in vitro articles have been published in the past years in regards to dentinal defects, but most of them have serious methodology concerns that will be discussed in this review.

A total grasp of the development and the role dentinal defects play in endodontics is crucial to the specialty. This review aims to discuss dentinal defects and their causative factors and the research models that have been used and their clinical significance. Through a comprehensive critical review of the literature, this article will express the need for further in vivo clinical research and better ex vivo methods that can replicate the clinical setting to answer several remaining questions about the development of and the role dentinal defects play in endodontics.

A comparative study of cone-beam computed tomography and periapical radiographs in decision-making after endodontic instrument fractures

PURPOSE

This study aimed to compare the diagnostic efficacies of periapical radiographs (PRs) and cone-beam computed tomography (CBCT) scans on clinicians' decision-making in diagnosing and providing treatment of fractured instruments in root canals during glide path preparation.

METHODS

40 maxillary molar teeth were selected and randomly divided into 4 groups. In each experimental group (n = 10), Hedstroem stainless steel instruments were fractured in mesiobuccal (MB) or distobuccal (DB) root canals. In group 1 (#0.06), group 2 (#0.08), group 3 (#0.10), and group 4 (#0.15), instruments were forced to fracture. PRs and CBCT scans were evaluated and compared. Observers were asked to use the following scoring system to decide whether to: 1. remove the fragment; 2. leave the fragment in situ; 3. bypass the fragment; or 4. use a surgical approach for removing the fragment.

RESULTS

CBCT observers mostly decided on removing and bypassing the fractured fragment, while radiograph observers mostly decided to leave fragments in situ. However, there was no significant difference between these parameters when CBCT scans were compared to PRs for decision-making of the fractured instruments (p≥0.05) regarding different sizes of root canal instruments.

CONCLUSIONS

In decision-making regarding fractured instruments during glide path preparation, clinicians should strategize treatment options based on variables using high-resolution images that reflect accurate scenarios through PRs or CBCT scans that also take into account low radiation dosage in situ PRs have precedence for a diagnostic approach.

Light-emitting diode assessment of dentinal defects: the role of presumed extraction forces

Objectives

The evaluation of iatrogenic dentinal defects in extracted teeth may be influenced by extraction forces and prolonged dry times. The purpose of this study was to compare the presence of dentinal defects in freshly extracted, periodontally compromised teeth with those in a group of teeth with uncontrolled extraction forces and storage time.

Materials and Methods

The experimental group consisted of eighteen roots obtained from teeth extracted due to periodontal reasons with class II or III mobility. They were kept in saline and sectioned within 1 hour following extraction. The control group consisted of matched root types obtained from an anonymous tooth collection, consistent with previous dentinal defect studies. The slices were obtained at 3, 6, and 9 mm from the apex. The imaging process exposed all specimens to no more than 60 seconds of dry time. The × 12.8 magnification was used for the 9 mm slices and × 19.2 magnification for the 3 mm and 6 mm slices under light-emitting diode (LED) transillumination. The root canal spaces and periodontal tissues were masked to minimize extraneous factors that might influence the evaluators. Chi-square test was used for statistical analysis.

Results

Dentinal defects were detected in 17% of the experimental group teeth, compared to 61% of control teeth (p = 0.015).

Conclusions

LED transillumination assessment of freshly extracted roots with class II or III mobility showed smaller number of dentinal defects than roots with uncontrolled storage time and extraction forces. The use of freshly extracted roots with mobility should be considered for future dental defect assessment studies.

Evaluation of Dentin Defect Formation during Retreatment with Hand and Rotary Instruments: A Micro-CT Study

The purpose of this study was to compare the incidence and longitudinal propagation of dentin defects after gutta-percha removal with hand and rotary instruments using microcomputed tomography. Twenty mandibular incisors were prepared using the balanced-force technique and scanned in a 19.9 μm resolution. Following filling with the lateral compaction technique, gutta-percha was removed with ProTaper Universal Retreatment (PTUR) or hand instruments. After rescanning, a total of 24,120 cross-sectional images were analyzed. The numbers, types, and longitudinal length changes of defects were recorded. Defects were observed in 36.90% of the cross sections. A total of 73 defects were comprised of 87.67% craze lines, 2.73% partial cracks, and 9.58% fractures. No significant difference in terms of new defect formation was detected between the retreatment groups. The apical and middle portions of the roots had more dentin defects than the coronal portions. Defects in three roots of the PTUR instrument group increased in length. Under the conditions of this in vitro study, gutta-percha removal seemed to not increase the incidence of dentin defect formation, but the longitudinal defect propagation finding suggests possible cumulative dentinal damage due to additional endodontic procedures. Hand and rotary instrumentation techniques caused similar dentin defect formation during root canal retreatment.