Unveiling the Performance of Nickel-Titanium Endodontic Instruments through Multimethod Research: A Review

Abstract

This article aims to explore the importance of multimethod research in assessing the performance of nickel-titanium (NiTi) endodontic instruments. The review highlights the limitations of relying solely on measurements obtained through a narrow set of mechanical tests and acknowledges the challenge of replicating real-world working conditions in controlled laboratory settings. While achieving a perfect simulation may be difficult, the focus should be on developing research strategies that provide a superior understanding of outcomes. The multimethod research, which combines qualitative and quantitative methodologies, offers a promising solution to address this challenge effectively. By integrating nonquantifiable data with quantitative measurements, researchers may overcome the limitations of individual methodologies and gain deeper and more comprehensive insights into instrument performance. This multimethod approach enables a more accurate interpretation of results, enhancing the validity of the methodology. Therefore, conducting a comprehensive analysis of various competencies displayed by NiTi systems is essential for a comprehensive understanding of their characteristics, including cyclic fatigue, torsional and bending resistance, cutting efficiency, microhardness, design analysis, element composition, phase transformation temperatures, shaping ability, and additional methodologies that can address specific inquiries. By combining qualitative and quantitative methodologies in a multimethod approach, researchers can enhance their ability to answer research questions and provide valuable insights for clinical practice.

1. Introduction

The development of nickel-titanium (NiTi) systems for root canal preparation has provided clinicians with instruments that exhibit exceptional performance [1]. Nevertheless, concerns regarding the potential occurrence of unexpected fractures during clinical use have arisen. To address this concern, manufacturers have focused on improving the mechanical performance of these instruments by changing their characteristics. A significant advancement has been the production of heat-treated instruments, resulting in markedly improved fatigue strength and flexibility [2]. Furthermore, the mechanical performance of NiTi instruments can be also significantly impacted by various aspects of their design, including cross-sectional geometries, helical angle, and the number of spirals [3]. The impact of surface finishing [4] and the crystallographic arrangement of the metal alloy [5] further validate the significance of these design factors. However, despite these significant advancements, the issue of instrument fracture still poses a challenge that requires attention.

The occurrence of instrument fracture can be attributed to two mechanisms: cyclic fatigue and torsional failure [6]. Cyclic fatigue happens when the instrument experiences repetitive cycles of compressive and tensile stress within a curved root canal [3]. This hampers its functionality, overloads stress levels, and ultimately prevents the sustained strain of NiTi at 8%, causing premature failure without unwinding or plastic deformation [7]. Conversely, torsional failure occurs when intense twisting stress is applied over a brief duration, surpassing the NiTi’s 8% strain limit. This can result in initial plastic deformation followed by fracture [7]. But the presence of surface irregularities, such as machining marks, can result in localized stress concentration, potentially causing the instrument to fail prematurely during torsional tests. Another concern regarding the use of NiTi instruments is the preservation of the anatomical integrity of the root canal and the minimization of deviations from the original pathway during the preparation procedures, which can be addressed by their enhanced flexibility.

Testing protocols for materials commonly follow standardized procedures aiming to ensure reproducibility and simulate applicable working conditions that correspond to the specific stresses encountered in their intended applications. The American National Standards Institute (ANSI), the American Dental Association (ADA), and the International Organization for Standardization (ISO) have established comprehensive standards for testing dental materials, including endodontic instruments. They provide researchers with standardized methodologies, protocols, and criteria, ensuring consistent and reliable data collection, analysis, and reporting. These standards enable reproducibility and comparability of research findings, allowing for the validation and verification of experimental results across different laboratories and research groups. This helps clinicians and researchers to make informed decisions when selecting materials for specific applications. However, while they provide valuable guidelines, they may not address the specific nuances and complexities of every research discipline or study design and, therefore, researchers need to critically evaluate and adapt these standards to suit their specific research goals and context.

One of the significant challenges in dental material testing is the replication of complex working conditions. This issue poses a major hurdle in achieving accurate and reliable test results that can directly correlate with real-world clinical situations. By recognizing these limitations, researchers and manufacturers have been working towards developing innovative testing approaches that strike a balance between scientific rigor and clinical relevance. However, due to the intricate nature of clinical environments and the numerous variables involved, it is often difficult or impossible to fully replicate these conditions in laboratory settings. This is particularly evident when it comes to certain mechanical tests used to characterize endodontic instruments, such as the cyclic fatigue test. This test presents challenging aspects in achieving standardized and comprehensive methodologies for endodontic instruments, as outlined: (a) establishing a universally recognized standard for canal geometry in testing is exceedingly challenging due to the intricate nature of root canals; (b) reproducing instrument-canal contact during fatigue testing is complicated by the presence of dentin on the inner walls of the root canal, unless a real tooth is used. However, in such cases, the validity of test results would be constrained to the specific canal geometry of that particular tooth [5]; (c) choosing the type of irrigation conditions can impact the chemical interactions between liquids and the instrument surface, as well as create a thermal environment that affects the behavior of the metal alloy [3]. As a result, the thermal/chemical environment becomes an additional variable of interest that should be considered. Moreover, the duration of exposure of the instrument to the irrigant can differ significantly, whether it is in a typical clinical intervention (which may take a few seconds) or in a fatigue test (which may take several minutes); (d) the surface finishing of different instruments undeniably plays a significant role in the initiation and propagation of cracks, making it a crucial factor to consider.

Given these limitations, reporting test results that focus on a single variable, as is often the case in fatigue tests, may have limited relevance for clinical practitioners and researchers [8,9]. A recent editorial published in the International Endodontic Journal [9] emphasized the redundancy of manuscripts focusing on the fracture susceptibility of NiTi instruments, primarily through torsion or cyclic fatigue tests, as these publications lacked standardized methodologies and comprehensive information. Darvell [10] emphasized the researcher’s responsibility to ensure that methodologies are current, robust, relevant, and fully justified, stressing the importance of investigating assumptions and validity conditions. To overcome these challenges, a promising approach entails the thoughtful selection of a combination of methodologies. This comprehensive approach enables a deeper understanding of the mechanical, structural, and geometrical characteristics of various instruments, ultimately facilitating the identification of their optimal overall profile. Considering the limited space available in journals for instrument testing studies, it is crucial to consider the types of methodologies that are truly needed. These efforts aim to provide dental professionals with valuable insights into the performance and suitability of dental materials in real-world scenarios, ultimately improving the quality of patient care and treatment outcomes. Therefore, the aim of this review is to comprehensively explore the multimethod approach as a research design capable of generating solid, reliable, and clinically oriented knowledge in the testing of NiTi endodontic instruments.

2. The Characteristics of Endodontic Instruments

2.1. Mechanical Testing

The cyclic fatigue test is the most employed method to evaluate the fracture resistance of NiTi instruments [11]. Numerous models have been employed in research to conduct cyclic fatigue tests, including the tube model [12], block model with machined grooves [13], cylindrical pins [14], concave and convex assembly [15], and sloped metal plane models [16] (Figure 1). Each model has its proponents, but there is insufficient reliable information available to definitively classify one model as superior to the others. The absence of a consensus is likely due to the fact that all these models reliably provide a curved trajectory for the instrument during rotation.

Regardless of the specific model employed, the cyclic fatigue test has proven valuable in identifying various testing conditions that can potentially impact the outcomes of cyclic fatigue resistance assessments. These conditions encompass factors such as the radius and angle of curvature [12], the presence of double curvatures [17], static versus dynamic motions of the handpiece [18], temperature variations [19], rotations per minute and kinematics [20], instrument condition (new versus used) [21], immersion solutions [22], sterilization methods [23], and instrument-related aspects like electropolishing [24], size [12], design [4], and metal alloy composition [25]. The examination of these specific variables during cyclic fatigue testing has contributed to a deeper understanding of their potential influence on the mechanical performance and has shaped the practical approach to root canal instrumentation in real-world scenarios. However, when the cyclic fatigue test is conducted with the instruments as independent variables, the resulting outcomes are influenced by numerous complex factors [9].

The principle that applies to the cyclic fatigue test also extends to the torsion test, which evaluates the capacity of an instrument to withstand high levels of twisting stress, particularly in scenarios such as tip lock in narrow root canals. However, due to the existence of an international standard for torsional resistance (ISO 36303631:2008. Dentistry–root canal instruments–part 1: general requirements and test methods), there is less variation in test models compared to the cyclic fatigue method. Nevertheless, aside from the static torsion test outlined in this standard, a few modifications have been proposed. For instance, there have been suggestions to introduce different rotations per minute during the test [26], as well as the development of a dynamic torsion model [27]. The torsional test has also played a crucial role in identifying different testing conditions that can potentially influence the outcomes of torsional strength. These conditions include rotations per minute [26], static versus dynamic torsion [27], temperature variations [28], the use of new versus cyclic flexural preloaded instruments [29], new versus torsional preloaded instruments [30], instrument condition (new versus used) [31], sterilization methods [32], instrument size, and metal alloy composition [33]. By exploring these conditions as independent variables, torsional studies have significantly influenced the development of technical procedures in the clinical setting. However, similar to the cyclic fatigue test, considering the instruments as independent variables reveals that multiple conditions can influence their strength.

The bending test operates on a similar principle as the aforementioned tests, but aims to assess the flexibility of an instrument. Flexibility plays a pivotal role, particularly in achieving a more conservative approach when shaping curved canals. Despite the existence of an international specification for this test (ISO 36303631:2008. Dentistry–root canal instruments–part 1: general requirements and test methods), researchers have proposed alternative models, including the cantilever [34] and the three-point [35] models. These alternative models offer the opportunity to investigate potential confounding factors, such as deflection distance and temperature [34], instrument size [36], and metal alloy composition [37]. This principle can be extrapolated to various other mechanical tests, such as buckling, microhardness, or cutting efficiency (Figure 2).

In summary, although extensive research has influenced current practices in technical procedures, there is a need for methodological improvements in testing NiTi systems to attain a comprehensive understanding of the underlying factors that influence the response of specific endodontic instruments. Consequently, relying solely on one of the previously mentioned mechanical test to interpret or explain instrument outcomes is inadequate for reliably assessing the clinical strength and performance of instruments in real working situations.

2.2. Limitations of Standardizing Endodontic Instrument Testing to Simulate Clinical Conditions

Several experimental setups have been proposed for instrument testing to better replicate real-world working conditions. These endeavors aim to investigate the impact of specific conditions on the resistance of endodontic instruments while also intended to enhance the simulation of real-world working scenarios and improve the reliability of the results obtained. The cyclic fatigue test, in particular, has been the subject of various protocols and standardization efforts [11]. The implementation of a vertical handpiece movement, which aims to simulate the dynamic in-and-out motion, exemplifies the challenges associated with standardization in instrument testing. While there have been a few contradictory findings concerning the Reciproc Blue instrument [18,38], the majority of studies indicate that the time to fracture can vary under different testing conditions, potentially resulting in an overextension of cyclic fatigue life in dynamic models [18,39,40,41,42]. However, it is important to note that, with few exceptions [38], this variable does not significantly impact the direct comparison between different instruments [18,40,41,42]. Therefore, notwithstanding it has been recognized that conducting root canal instrumentation through a continuous pecking motion is crucial [16], the significance of this feature becomes less pronounced when considering endodontic instruments as independent variables [18].

The impact of different artificial canal taper conditions is expected to follow a similar pattern. The use of a tapered canal in cyclic fatigue testing is motivated by its ability to better follow a specific and predefined artificial canal curvature (in terms of radius and angle of curvature). This occurs because the far apical end of the tapered artificial canal provides less compensation for the instrument’s tip outside the curve once it surpasses the inner point of maximum curvature. In contrast, non-tapered canals are less effective in accommodating such deviations from the original pathway. However, unless the objective of the test is to compare specific curvatures or to analyze the differences between endodontic instruments as independent variables, this argument loses relevance. Regardless of the radius or angle of curvature, the overall differences between tested instruments are comparable [12,43]. Therefore, the selection of a specific test setting should be guided by the research question, and both tapered and non-tapered settings are valid options depending on the study objective.

The test temperature is a highly debated parameter in endodontic instrument testing. Some researchers argue that a temperature close to body temperature (~36 °C) more accurately replicates real working conditions [44,45,46]. However, it is important to acknowledge that the specificities of a cyclic fatigue test do not align entirely with a real working situation. Several arguments support this notion:

(1)

Different outcomes can be observed when exposing the instrument to temperature changes, leading to a uniform phase transformation throughout the entire instrument. It is unreliable to assume that the short duration (usually seconds) in which the instrument is within the root canal space during shaping procedures would have an equivalent effect on its crystallographic arrangement as several minutes of continuous rotation in a laboratory-based heated bath [47];

(2)

The surface temperature of an instrument, right after its removal from the root canal, is lower than the body temperature, ranging from 30.8 °C to 32.5 °C [44];

(3)

Due to thermal conductivity, the metal alloy does not uniformly and simultaneously increase in temperature throughout its entire structure when subjected to temperature elevation. Therefore, assuming that the core temperature is equivalent to the surface temperature would be inaccurate [48];

(4)

Intracanal temperatures in in vivo conditions do not reach body temperature and instead range from 31 °C to 33.5 °C [49];

(5)

An irrigating solution at room temperature introduced into the root canal system in a clinical setting takes approximately 4 min to reach 35 °C, which is considered body temperature under healthy conditions. Similarly, pre-heated solutions (66 °C) decrease in temperature to 35.7 °C after the same time period [50];

(6)

During root canal preparation, the in-and-out motions further reduce the instrument’s contact with the root canal wall, thereby minimizing its exposure to the canal temperature [51].

There is compelling evidence indicating that the testing temperature can influence the outcomes of cyclic fatigue, although the extent of this impact may vary depending on the specific instruments being tested [18,45,51,52,53]. However, determining the optimal temperature for conducting the mechanical tests remains a challenge due to the temperature fluctuations and cycles experienced by the instrument during the shaping procedures. Consequently, the recommendation to perform tests at body temperature raises significant concerns [45,46]. Taken together, these factors emphasize that while the test temperature in cyclic fatigue testing can be a subject of discussion, it does not fully replicate the complexities of a real working environment. Therefore, careful consideration should be given to the interpretation and applicability of results obtained under specific temperature conditions. Similar to cyclic fatigue tests, adjustments have been also made to the international specification for torsion tests in an effort to better simulate real working conditions. Once again, studies have consistently reported comparable results across various tested models when comparing different instruments [26,54]. But this finding is expected considering that endodontic instruments adhere to fundamental metallurgical principles.

In summary, the choice of test settings depends on whether the independent variable is a specific testing condition or the instruments themselves. It is essential to recognize that all mechanical tests for instruments adhere to fundamental physical and metallurgical principles. Given the multitude of variables that can influence clinical outcomes, it becomes questionable to determine a specific laboratory setting that precisely mimics real working conditions. Instead, these tests should be viewed as laboratory experiments designed to measure specific parameters under controlled conditions. Therefore, the examples highlighted earlier, such as the handpiece movement, the taper of the artificial canal, and the use of different testing temperatures, should not be used as sole criteria for assessing the reliability of a study. Although mechanical tests have inherent limitations in simulating clinical conditions, they offer a valuable approach to compare and rank various instruments by assessing their response to specific types of stress. By recognizing these limitations and understanding their intended purpose, researchers can utilize these tests effectively in their studies.

2.3. Evaluation of Instrument Performance in Ex Vivo Settings

Several ex vivo tests have been developed to investigate parameters that closely resemble those encountered in clinical practice. These tests aim to evaluate the shaping ability of various instrumentation systems in canals with specific shapes and dimensions, such as oval or curved canals. In the last decade, the use of micro-CT imaging technology has emerged as the gold standard for evaluating the shaping ability of NiTi systems. By employing micro-CT analysis, a precise three-dimensional assessment of the root canal is performed before and after mechanical preparation [5]. The assessment follows a systematic procedure: extracted teeth are carefully selected and subjected to micro-CT scanning to obtain an accurate three-dimensional image of the root canal prior to instrumentation. The teeth are then categorized into groups based on specific anatomical parameters, aiming to achieve optimal homogeneity and balanced group pairing. This approach enhances the validity of the method and minimizes potential anatomical bias, which could otherwise result in erroneous outcomes. The selected instruments are then used to prepare the root canals. After instrumentation, the teeth undergo another scanning process to obtain a three-dimensional image of the root canal post-preparation. The data from pre- and post-preparation scans are meticulously co-registered and compared to assess several parameters including changes in root canal geometry, volume, surface area, untouched walls, transportation, accumulated hard tissue debris, and dentin thickness [5,55]. This assessment method offers several advantages, notably providing an accurate and objective means of comparing different instruments. Consequently, it aids clinicians in selecting the most suitable instrumentation system or specific instrument for each clinical scenario [55] (Figure 3).

2.4. Application of 3D Optical Scanning for Evaluating Instrument Design and Dimensions

Historically, researchers have faced challenges in accurately determining the dimensions of endodontic instruments. Recently, the 3D optical scanning method has emerged as a promising approach to assess instrument dimensions and geometries independently [56]. This method eliminates the need to rely solely on manufacturer-provided information, allowing for more accurate and objective evaluations. This method utilizes a high-resolution optical scanner in a laboratory setting to capture detailed surface images of NiTi instruments, enabling the creation of reliable virtual models. Through this non-destructive process, the 3D scanning method offers precise measurements of various parameters, including perimeter, area, long axis length, and core diameter, at any cross-section level (Figure 4). Moreover, it provides valuable information on the instrument’s overall volume and surface area. The utilization of this approach can be considered a valuable auxiliary methodology as it quantifies parameters that have significant relevance to the performance of the instrument.

2.5. Finite Elements Method: An in Silico Approach

The Finite Element Method is another valuable approach for evaluating the mechanical behavior of instruments, as it offers a computational solution to differential equations in engineering and mathematical modeling [11]. This in silico assessment enables testing of virtual instruments at various levels and under different stress conditions, providing non-destructive insights into their performance.

2.6. Qualitative Assessment of Endodontic Instruments

Several variables associated with NiTi instruments, such as their geometry, surface finishing, and metal alloy characteristics, have been identified as factors that directly influence the outcomes of mechanical tests. By incorporating the evaluation of qualitative data alongside quantitative results, the inclusion of nonquantifiable information becomes a valuable approach. This cross-referencing of data facilitates a deeper understanding of the outcomes and enhances the overall validity of the methodology [57,58]. Although qualitative assessment relies on description and interpretation rather than numerical counts or measurements, rendering it unsuitable for comparative statistical analysis, it should not be considered as secondary information.

3. A Multimethod Approach for Investigating Endodontic Instruments

3.1. Enhancing Study Design: Addressing the Need for Improvement

A recent editorial published in the Dental Materials journal presented a distinction between the terms ‘test’ and ‘research’ [59]. According to the editorial, a ‘test’ aims to observe specific behaviors or effects and characterize dental materials or products by comparing them directly with others or with predefined criteria. On the other hand, ‘research’ refers to a thorough and diligent inquiry and investigation with the aim of discovering and interpreting facts. The editorial also noted that some individuals consider tests merely as a means to report mechanical properties without considering them as genuine research endeavors [59]. The conclusion drawn was that while both tests and research have their place, greater emphasis should be placed on research as it plays a pivotal role in improving the methods employed. Although the differentiation presented in the editorial may be subject to questioning, it underscores the importance of comprehensively addressing the outcomes.

3.2. The Multimethod Research

The multimethod approach is a research methodology that involves the use of multiple methods and techniques to investigate a particular phenomenon or research question. It combines different data collection and analysis methods, allowing researchers to gather a more comprehensive and nuanced understanding of the topic under investigation. This approach acknowledges that no single method can capture the complexity and richness of real-world phenomena, and therefore, multiple methods are employed to enhance the validity and reliability of the findings [57].

One of the key advantages of the multimethod approach is its ability to triangulate data. By using multiple methods, researchers can cross-validate and corroborate findings, increasing the robustness of the conclusions drawn. Triangulation helps mitigate the limitations of individual methods and provides a more holistic view of the research topic. Another advantage of the multimethod approach is its flexibility and adaptability. Researchers can tailor the combination of methods to suit the specific research question, context, and available resources. This allows for a more tailored and contextually appropriate investigation, enhancing the validity and generalizability of the findings. The multimethod approach is particularly useful when studying complex phenomena that cannot be fully understood using a single method alone. It allows researchers to capture different aspects, perspectives, and dimensions of the phenomenon, leading to a more comprehensive understanding. Additionally, the use of multiple methods can help overcome the limitations and biases inherent in individual methods, leading to a more objective and comprehensive analysis. However, the multimethod approach also has some limitations. It can be time-consuming and resource-intensive, as it requires expertise in multiple research methods and data collection techniques. Researchers need to carefully plan and coordinate the different methods to ensure their integration and complementarity. Furthermore, analyzing and synthesizing data from multiple sources can be challenging and may require specialized skills in data integration and interpretation [58].

In summary, the multimethod approach is a powerful research methodology that offers several advantages in terms of triangulation, flexibility, and comprehensiveness. By combining multiple methods, researchers can overcome the limitations of individual methods and gain a deeper understanding of the research topic. While it may present challenges in terms of time, resources, and data analysis, the benefits of the multimethod approach make it a valuable tool for conducting rigorous and insightful scientific research.

3.3. Enhancing Endodontic Instrument Testing through Multimethod Research

Multimethod research involves the utilization of multiple qualitative or quantitative methodologies within a study design [58]. When both qualitative and quantitative methodologies are concurrently employed, it assumes a mixed methods characteristic [57], which offers a notable advantage by mitigating the limitations associated with each individual approach. While quantitative assessments may unveil differences, it is often through the integration and contextualization of nonquantifiable data that these differences can be fully understood and explained [57,58]. The symbiotic relationship between qualitative and quantitative approaches equips researchers with robust tools to address research questions and problems comprehensively, providing enhanced validation from both perspectives [57,58,60,61].

The discussion surrounding the appropriate temperature for instrument testing serves as an illustrative example of the advantages offered by multimethod research. To fully comprehend the complex interplay of the involved factors, it is imperative to approach temperature from a materials engineering standpoint. Merely assuming body temperature as the ideal testing model without considering the broader implications may oversimplify the issue [45,46]. Neglecting temperature-related nuances, such as the instrument’s crystallographic arrangement at specific temperatures, the patient’s physiological temperature range (ranging from 35 °C [hypothermia] to 42 °C [fever]), or the manufacturer’s guidelines specifying storage away from direct sunlight at ambient temperature (ProTaper Gold Treatment—Directions for use) [62], would be a missed opportunity for comprehensive investigation. A more insightful approach entails delving deeper into the topic, acknowledging the dynamic nature of the service temperature, which could range from room temperature (as recommended for storage) to an unspecified temperature more closely aligned with body temperature. In this multidimensional inquiry, researchers can design tests under controlled conditions to establish baseline quantitative results. This can be complemented by a qualitative analysis of phase transformation temperatures, which have been validated as effective predictors of endodontic instrument behavior in response to temperature changes [51]. By integrating these quantitative and qualitative outcomes, researchers gain a more nuanced understanding of the underlying facts (Figure 5), surpassing the limitations of singular approaches and providing a robust foundation for evidence-based interpretations.

It is paramount to recognize that the primary objective of root canal therapy is to facilitate effective debridement and disinfection of the root canal system [63]. The achievement of this goal is closely tied to the extent of prepared root canal surface area. While many studies comparing mechanized endodontic instruments primarily focus on their mechanical performance, a thorough understanding of an instrument’s behavior encompasses more than just the time or torque required for fracture. The mechanical performance is intricately linked to the instrument’s design and the characteristics of its metal alloy. Even minor variations in these aspects can yield significant changes in the instrument’s performance. Given the multifaceted nature of the factors contributing to the performance of an instrument, studies should employ a comprehensive analysis encompassing various competencies of NiTi mechanized systems. This includes employing multiple assessment methods such as cyclic fatigue, torsional, and bending resistance tests, cutting efficiency, microhardness measurements, instrument design analysis through stereomicroscopy and scanning electron microscopy, evaluation of alloy characteristics based on element composition using energy dispersive X-ray spectroscopy, determination of phase transformation temperatures using differential scanning calorimetry technology, and shaping ability through micro-CT evaluation—aligning with the advocated multimethod research concept [64,65,66,67,68,69,70,71,72]. Performing the cross-section analyses of NiTi instruments through non-destructive 3D surface scanning at various levels can be valuable for comprehensively interpreting the mechanical outcomes [56].

Therefore, it is recommended to adopt a mixed methods research approach in the form of a multimethod methodology, as it offers a comprehensive analysis that surpasses the limitations of single-method assessments. This approach enables a more comprehensive evaluation of the assessed instruments and provides a higher level of ability to address the primary research question at hand. In fact, the multimethod research not only enhances the validity and reliability of the findings but also provides valuable insights for clinical practice, aiding in the selection of the most appropriate instruments for specific clinical scenarios. By embracing this multimethod research paradigm, we can further advance our understanding and enhance the overall effectiveness of root canal therapy. In summary, multimethod research is a powerful tool for investigating the performance of endodontic instruments. By combining qualitative and quantitative methodologies, researchers can unlock a deeper understanding of instrument behavior, leading to advancements in the field of endodontics and ultimately improving patient outcomes.

4. Final Remarks: A Multimethod Approach for Investigating Endodontic Instruments

The investigation of the mechanical properties of endodontic instruments demands a research-oriented perspective that extends beyond the mere reporting of test outcomes. A comprehensive assessment of multiple facets is essential to elucidate the underlying facts. It is crucial to recognize that surface quality finishing can hinder the analysis of individual tests. The presence of surface irregularities, for instance, may induce premature torsional rupture, leading to a misleading perception of increased torsional flexibility. However, by employing a multimethod perspective strategy that also integrates the bending test, a clearer understanding of the true performance of a specific instrument can be achieved.

Future research endeavors should embrace a holistic design that incorporates essential mechanical performance parameters such as time to fracture, maximum torque, angle of rotation, and maximum bending load. Furthermore, the quantitative variable of the percentage of unprepared surface area should be considered, along with its correlation to qualitative descriptions of instrument design, encompassing geometric cross-sections, surface finishing, and the crystallographic arrangement of the metal alloy. Supplementing these investigations with additional tests such as microhardness assessment, buckling strength evaluation, cutting efficiency analysis, or even finite element analysis can provide supplementary insights in those future studies. Moreover, it is pertinent to delve into the fine design characteristics of the instruments, encompassing accurate measurements of their dimensions and tapers. By integrating these multifaceted elements into the research design, a more comprehensive evaluation of the mechanical properties of endodontic instruments can be achieved, advancing our understanding of their performance. This comprehensive approach will enable researchers to gain deeper insights into the intricate dynamics that influence instrument behavior, fostering advancements in endodontic instrument design and optimization.