Changes in root canal morphology in simulated curved canals over-instrumented with a variety of stainless steel and nickel titanium files

How Does Intentional Apical Foraminal Enlargement Affect the Foramen and Root Canal Morphology?

INTRODUCTION

This study assessed the effect of intentional foraminal enlargement on the foramen and the apical root canal morphology.

METHOD

Sixty mesial roots of mandibular molars were scanned by micro-computed tomography. Their apical foramina were photographed with a stereomicroscope before and after preparation. Three groups were formed (n = 20) according to the working length (WL). G-1: foramen - 1 mm; G0: foramen; and G+1: foramen + 1 mm. Each group originated 2 subgroups (n = 10): G-1: Buchanan's patency (size 10 K-type file) and foraminal debridement (sizes 20, 25 and 30 K-type files); G0 and G+1: rotary foraminal enlargement (ProDesign S size 25/.08) or reciprocating foraminal enlargement (R25). The area, perimeter, transportation, and noninstrumented walls of the foramen were evaluated. The root canal transportation and the centering index of preparation at 1, 3 and 5 mm from the foramen were also assessed. Data were compared statistically (α = 5%).

RESULTS

The instruments used at the foramen and 1 mm beyond promoted foraminal enlargement and transportation. Regarding NIW, there was no difference between mechanized foraminal enlargements performed at the foramen or 1 mm beyond, similar to the manual foraminal debridement group (P > .05). There was no difference in transportation and centralization at 1-, 3-, and 5-mm apical levels, regardless of the instrumentation systems.

CONCLUSION

Mechanical preparation at the foramen, or 1 mm beyond, resulted in foraminal enlargement, transportation and were not able to touch all root canal walls that delimit the foramen.

Effectiveness of root canal instrumentation for the treatment of apical periodontitis: A systematic review and meta-analysis

BACKGROUND

The development of endodontic instruments has rapidly advanced, but their impact on endodontic outcome parameters remains unclear.

OBJECTIVES

This systematic review aimed to answer the following PICOT questions: In patients with apical periodontitis (P) what is the effectiveness of root canal instrumentation ([Q1] performed with contemporary techniques [I] in comparison with 'traditional' techniques [C]] and ([Q2] performed with contemporary engine-driven NiTi instruments [I] compared with other types of contemporary engine-driven NiTi instruments [with different design and/or technology] [C]) in terms of clinical and patient-related outcomes (O)?

METHODS

After PROSPERO protocol registration, a literature search was conducted using Clarivate Analytics' Web of Science, Scopus, PubMed and Cochrane Central Register of Controlled Trials. Grey literature and major journal contents were examined. Two independent reviewers performed the study selection, data extraction and appraisal of included studies. A quantitative meta-analysis was considered, and statistical heterogeneity and overall quality of evidence were assessed.

RESULTS

Nine studies were identified showing substantial methodological differences. Five studies addressed PICOT 1 and three PICOT 2, whereas one study aimed both. A random-effects meta-analysis model was considered for the outcome 'radiographic evidence of normal periodontal ligament space or reduction of apical lesion size' (PICOT 1) based on three studies with 332 evaluable participants and showed that contemporary instrumentation was associated with a more favourable outcome (p = .005) compared with root canal preparation with stainless steel instruments (odds ratio = 2.07 [95%-confidence interval = 1.25-3.44]) with no evidence of statistical heterogeneity (I2  = 0%) but low quality of evidence.

DISCUSSION

Albeit a few studies fulfilled eligible criteria, no study had a low risk of bias. Compelling evidence indicating significantly different outcome rates using different endodontic instruments when treating teeth with apical periodontitis is lacking.

CONCLUSIONS

In terms of healing, the results of the meta-analysis determined the higher effectiveness of root canal instrumentation performed with contemporary techniques in comparison with conventional stainless steel instruments in patients with apical periodontitis followed for a minimum of 1 year with low quality of evidence. No differences could be demonstrated between preparations with traditional stainless steel and contemporary NiTi instruments for other clinical and patient-related outcomes.

REGISTRATION

PROSPERO (CRD42021274642).

The effects of shape memory alloys’ tension–compression asymmetryon NiTi endodontic files’ fatigue life

Nowadays, NiTi rotary endodontic files are of great importance due to their flexibility which enables the device to cover all the portions of curved canal of tooth. Although this class of files are flexible, intracanal separation might happen during canal preparation due to bending or torsional loadings of the file. Since fabrication and characterization of such devices is challenging, time-consuming, and expensive, it is preferable to predict this failure before fabrication using numerical models. It is demonstrated that NiTi shape memory alloy shows asymmetric material response in tension and compression which can significantly affect the lifetime of the files fabricated from. In this article, the effects of this material asymmetry on the bending response of rotary files are assessed using finite element analysis. To do so, a constitutive model which takes material asymmetry into account is used in combination with the finite element model of a RaCe file. The results show that the material asymmetry can significantly affect the maximum von Mises equivalent stress as well as the force–displacement response of the tip of this file.

Comparison of dentine removal using V-taper and K-Flexofile instruments

AIM

To compare the dentine removal ability of V-Taper and K-Flexofile instruments in mesiobuccal canals of extracted mandibular first molar teeth.

METHODOLOGY

Preoperative images of 40 mesiobuccal canals of mandibular first molars (with a curvature between 20° and 35°) were obtained at 2, 4.5, and 7 mm from the root apices by CT-scan and divided into two groups. Group F was prepared with K-Flexofiles and Gates Glidden drills and Group V with V-Taper Ni-Ti rotary and stainless steel hand instruments. Post-instrumentation images were then obtained and compared with the preoperative images. The ratio of dentine removal based on pre- and postoperative images was calculated, and data was analysed by anova and Tukey post hoc test.

RESULTS

In group F in the coronal sections, the least ratio of the dentine removal to the initial root thickness was on the buccal aspect (15.14% ± 6.72), and the greatest ratio was found on the distolingual (29.38% ± 8.19). In group V in the coronal, the least ratio of the dentine removal to the initial root thickness was on the buccal aspect (9.81% ± 3.26); the greatest ratio was found on the distolingual surface in the coronal sections (34.38% ± 10.51). In the middle sections, the least ratio was on the buccal (10.51% ± 3.39) and the greatest on the distolingual aspects (27.46% ± 12.34) of the roots. In the apical sections, the amount of the dentine removed from the mesial and distal surfaces in group V was significantly more than group F (P < 0.01).

CONCLUSION

The distolingual aspect of the root canal is a danger zone for the mesiobuccal canal of the mesial root in mandibular molar teeth, and preparation of that area should be performed with caution. Except the apical part of the canal, no significant difference was found between the two preparation files or techniques used. Apart from the apical part of the canal, neither instrument maintained the original shape of the coronal and middle parts of the canal.

The principles of techniques for cleaning root canals

Chemomechanical preparation of the root canal includes both mechanical instrumentation and antibacterial irrigation, and is principally directed toward the elimination of micro-organisms from the root canal system. A variety of instruments and techniques have been developed and described for this critical stage of root canal treatment. Since their introduction in 1988, nickel-titanium (NiTi) rotary instruments have become a mainstay in clinical endodontics because of their exceptional ability to shape root canals with potentially fewer procedural complications. Safe clinical usage of NiTi instruments requires an understanding of basic metallurgy of the alloy including fracture mechanisms and their correlation to canal anatomy. This paper reviews the biologic principles of preparing root canals with an emphasis on correct use of current rotary NiTi instrumentation techniques and systems. The role and properties of contemporary root canal irrigants is also discussed.

Current Challenges and Concepts in the Preparation of Root Canal Systems: A Review

Nickel-titanium rotary instruments are important adjuncts in endodontic therapy. This review attempts to identify factors that influence shaping outcomes with these files, such as preoperative root-canal anatomy and instrument tip design. Other, less significant factors include operator experience, rotational speed, and specific instrument sequence. Implications of various working length definitions and desired apical widths are correlated with clinical results. Despite the existence of one ever-present risk factor, dental anatomy, shaping outcomes with nickel-titanium rotary instruments are mostly predictable. Current evidence indicates that wider apical preparations are feasible. Nickel-titanium rotary instruments require a preclinical training period to minimize separation risks and should be used to case-related working lengths and apical widths. However, and despite superior in vitro results, randomized, clinical trials are required to evaluate outcomes when using nickel-titanium instruments.