**1. Introduction**

Endodontic therapy aims to thoroughly clean and obturate the whole system of the root canal. However, to prevent endodontic failure and execute successful root canal therapy, specific determinants play an essential role [1,2]. Precise shaping, cleaning, and filling of all spaces previously filled by the radicular pulp tissues or pulp capping/pulpotomy

**Citation:** Karobari, M.I.; Arshad, S.; Noorani, T.Y.; Ahmed, N.; Basheer, S.N.; Peeran, S.W.; Marya, A.; Marya, C.M.; Messina, P.; Scardina, G.A. Root and Root Canal Configuration Characterization Using Microcomputed Tomography: A Systematic Review. *J. Clin. Med.* **2022**, *11*, 2287. https://doi.org/10.3390/ jcm11092287

Academic Editors: Gianrico Spagnuolo, Edgar Schäfer, Massimo Amato, Giuseppe Pantaleo and Alfredo Iandolo

Received: 21 February 2022 Accepted: 18 April 2022 Published: 20 April 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

to maintain healthy dental pulp is required. The morphologic uniqueness of each root necessitates a comprehensive knowledge of variations in the root canal system, which should be reflected during the diagnostic and treatment process [3]. Research upon the root canal morphology in lasting teeth has revealed that the root canal's amount and classification can differ by ethnicity, gender, and in different populations, within the same population, and uniquely in each person [4,5]. Furthermore, it is possible that a variety of morphologic root canal system configurations exist; as a result, each tooth should be evaluated separately using a proper classification system [6].

The investigation of external and internal anatomy of different teeth using many in vitro and in vivo techniques were performed in the beginning of 20th century [7]. Various in vitro techniques were used to identify root and canal morphology which includes root sectioning, staining, tooth clearing, microscopic investigation, radiographic investigations using conventional radiographs, and three-dimensional techniques such as CBCT and microcomputed tomography (MCT) [8]. The in vivo techniques include conventional radiographic examinations, retrospective evaluation of patients' data, clinical evaluation during root canal treatment, digital radiography, and advanced radiographic techniques such as CBCT [8]. An investigation showed a technique by using longitudinal sectioning to produce a sagittal view of pulp space from pulp chamber to the root apex [9]. Opaque wax was used to fill the exposed canals, but this method showed lateral canals very rarely [10]. Rosenstiel (1957) introduced a technique using a Radio opaque material to reproduce the root canals. A study demonstrated a simple in vitro technique to evaluate both endodontically treated and untreated root canal systems. The following steps were used in the technique to make teeth transparent. Firstly, teeth were decalcified using nitric acid, then dehydrated using alcohol, and finally cleared with methyl salicylate [11].

Digital radiography, magnetic resonance imaging (MRI), densitometry, ultrasound, and computed tomography (CT) are just a few of the noninvasive dental imaging technologies that have been developed in recent years. However, most of these approaches are restricted since they only provide a 2-dimensional (2-D) examination of the root canal system (RCS) and cannot be easily compared subjectively or quantitatively with other samples [12]. Furthermore, these methods do not allow for synchronized 3-dimensional (3-D) examination of teeth surface and interior anatomy [13]. In endodontic research, microcomputed tomography (Micro-CT) has acquired much interest since it displays high-resolution (10 μm) tooth morphological structures and has proven to be an essential information source for dentists, as shown in Figure 1 [14]. Microcomputed tomography is a nondestructive and reproducible ex vivo research method and is considered as the research method that offers the foremost possibility for an accurate examination of the morphology of the root canal system.

**Figure 1.** Micro-CT in endodontics.

The ex vivo investigation is used in Micro-CT imaging, which is widely accepted because of its accuracy, repeatability, and noninvasiveness, all of which are superior to other commonly used research methods [15]. Maxillary central incisors have one root and

one main canal. Rarely, at a 6% rate, one canal of central maxillary teeth splits into two parts at the apical foramina which can be classified as Vertucci type V [16]. Apical root canal morphology should be considered because of its main effect on the success of root canal treatment. In the study of Adorno et al. [17], accessory canals in the apical 3 mm in the Japanese population were found among 46% of the specimens. Over the years, different studies have been conducted to understand the root canal morphology of premolars using different research methods [18] and different populations [19–21]. The frequency of a single canal is 54–88.5%. However, multiple canals were reported in 11.5–46% of cases [21,22]. In the study of Pan et al. [23], the prevalence of maxillary first premolar teeth with one main root canal was 67.8%, with two roots at 31.9%, and with two canals at 88.2%. In the Malaysian population, according to Vertucci's classification, the second premolar was detected as single-root type I with the rate of 58.2% [16]. In posterior teeth, mandibular first molars are recognized to exhibit various complex and distinct morphological variations of the root canal system [24,25]. This tooth usually has two roots, but sometimes it has three, with two or three canals in the mesial root and one, two, or three canals in the distal root [26,27]. When only one distal root canal is present, it is often buccolingually oval, and untreated surface areas were shown to be as high as 59–79% when rotary instruments were used for the shaping procedure [28].

Similarly, a study on the Burmese population showed that the prevalence of two canals in mesiobuccal roots of the upper first molar teeth decrease gradually towards the upper third molars. About 85.2% of the 270 roots of the maxillary teeth had one root canal at the apex, 14% had two apical canals, and 0.8% had three apical canals [25,29]. Moreover, the morphology of root canals was explored, white spot lesions on enamel were identified, and enamel demineralization with therapy were assessed using Micro-CT [30,31]. The latest evidence demonstrated the ability to scan isthmuses successfully, while another claimed to detect inorganic material within a tooth root [32,33]. The nondestructive Micro-CT imaging method allows for multiple exposures and data collection. As a result, this imaging method is beneficial for evaluating experimental endodontics [34]. The goal of this systematic review was to carry out a thorough examination of the literature on root canal physiology using sophisticated microcomputed tomography.
