**4. Discussion**

Micro-CT analysis has proven useful in a wide variety of applications in dental research. It can provide high-resolution images, as well as qualitative and quantitative analysis of teeth [83,84]. To achieve long-term treatment success, endodontic anatomical knowledge is required. As a result, a detailed description of the apical region is required [85]. Until now, there was a scarcity of detailed information on the anatomy of the RCS; therefore, 3-D, high-resolution techniques dominated. Compact commercial systems are now available and are quickly becoming vital in many academic and corporate research laboratories. It is possible to study a wide range of specimens using Micro-CT to examine mineralized tissue, teeth, bone, and materials such as ceramics, polymers, and biomaterial scaffolds [86–89]. Micro-CT provides a repeatable, nondestructive, and noninvasive technique for nonclinical ex vivo evaluation with this goal in mind, enabling measured values of the structures investigated and providing critical info regarding minimal structures such as the end part of the apical portion of teeth [49,50,90,91].

Even though data is challenging to come by, it appears that a large group of researchers agree that Micro-CT gives more objective information than traditional 2-D optical techniques [92], the clearing procedure, or scanning microscopy [44]. As a result, in the present study, a substantial number of sufficiently recognized teeth were evaluated using Micro-CT, allowing for a thorough statistical analysis of the sample. Compared with other investigating techniques, the advantages of Micro-CT produce extraordinary resolution 3-D and 2-D figures, with possibilities of rescanning the sample and volumetric analysis of external and internal structures. The Micro-CT system using a microfocal spot X-ray source and a high-resolution detector is projected in several directions to obtain a three-dimensional reconstructed image of the sample. Since the imaging process is nondestructive, the unique properties of the same sample can be tested multiple times, and the sample can still be used after scanning for further biological and mechanical testing [89]. Some of the recent applications of Micro-CT in dental research includes enamel thickness and tooth measurement [93], analysis of root canal morphology and evaluation of root canal preparation [94], craniofacial skeletal development and structure [95], biomechanics, tissue engineering, determination of mineral concentrations of teeth [96], and the measurement of implant stability and osseointegration [97]. The main disadvantage of Micro-CT is that it cannot be utilized in medical practices due to elevated radiation heights, the operating cost, time taken to process data, cost-effectiveness, and safety [98,99].

The current study provides an overview of the Micro-CT studies for root canal morphology. The data included in this systematic review are secondary information collected from various past research studies. Secondary data are prone to flaws or biases present in the original data, which might eventually appear in the study's findings. For example, it may appear in the analysis technique, or the smallest number of teeth examined in the research. However, the goal was to give the dentistry and endodontic communities a Micro-CT-based analysis of the massive data on the root canal morphology.

Endodontic therapy, both nonsurgical and surgical, needs a thorough understanding of tooth anatomy and morphology [100,101]. Because it is used to instrument and fill root canals to a considerable extent, the morphological interpretation of the apical region should be accurate. Understanding the apical region and the configuration of the root canals is an essential and challenging condition that the clinician must have to make judgments about during endodontic therapy [102].

Despite the fact that the permanent anterior maxillary and mandibular teeth are typically single-rooted, studies sugges<sup>t</sup> that an auxiliary root might be present [103]. Earlier studies in other ethnicities, comprising Turkish, American, Brazilian, and Indian communities, found that all maxillary incisor teeth were single-rooted [104–106]. This suggests that the number of roots in maxillary incisors does not differ structurally throughout all populations. Nevertheless, it is important to note that the presence of a double-rooted maxillary anterior has only been confirmed in a few case studies [103]. However, studies revealed a double-rooted mandibular anterior [4]. Numerous root canal morphology dif-

ferences in mandibular incisors were documented [37,43,47]. The current review showed that the most common type of root canal morphology classified using the four-digit system was 1-1-1, Type I using Vertucci's classification system, and Type 1-1 using Weine's classification. According to previous research, Vertucci type I in mandibular incisors can range between 55% and 87% [107]. In two earlier investigations of Turkish populations, type I in the mandibular incisors was lower [108,109]. The most common type of root canal configuration identified in this study was type I (75 percent), similar to Vertucci's results [16]. Both mandibular incisors had 88% of type 1 configuration, according to Madeira and Hetem [110]. Furthermore, De Almeida, MM et al. revealed that the most common was type III from the Vertucci classification (16%) [47].

The mandibular first molar is not only the most treated endodontically, but it also presents several anatomic difficulties. The diversity includes isthmuses, several canals, apical ramifications, and lateral canals [3]. Additionally, the distal surface of the mesial root has a thin patch of dentin referred to as a danger zone because there is a higher chance of perforation of dentin in this region during mechanical instrumentation. Hence, orthograde and retrograde endodontic treatment in this tooth may be difficult because of its unusual form [40,102]. The anatomy of the mandibular second molar has been widely investigated, notably using the cleaning procedure [102]. According to previous research, the frequency of C-shaped canals is between 31 and 45% (mostly of Asian people) [52,111–113]. Various classifications of the tridimensional distributions of RCS and the transverse sections have also been published subsequently [114,115].

The canal shape of posterior maxillary teeth varies significantly between races and geographical locations. As per Mohara et al., Brazilians have a 64.2 percent frequency of MB2 in the foremost permanent molar and a 33.5 percent incidence in the subsequent permanent maxillary molar, respectively [116]. In South Africa, type IV root canals are widespread in maxillary primary molar and type I root canals are the most familiar in a maxillary second molar, according to the Vertucci classification of the root canal [117]. According to Li et al., the most common maxillary first premolar anatomy in the Chinese population is one root with two canals (58.0 percent), and the most common canal morphology is type IV (42.7 percent) [118]. Guo et al., on the other hand, examined the maxillary first molars' morphology amongs<sup>t</sup> the North American population and discovered that Asians had a higher occurrence of type I (35.0 percent) and type IV (45.0 percent) configurations than whites (type IV: 36.3 percent, type I: 23.4 percent) [119]. As a result, root canal shape varies depending on where you live. Relevant studies in native communities can help dentists better analyze and understand root canal therapy while also adding to the body of information about root and canal morphology in humans.

The current work uses Micro-CT imaging of many samples to provide a detailed assessment of root canal morphology of the mandibular and maxillary teeth. This knowledge will help practitioners comprehend and anticipate the challenges of 3-D endodontic therapy, particularly during root canal shaping and cleaning. This study revealed that the maxillary first molar and mandibular first premolars had a higher incidence of morphological endodontic variables than the other maxillary and mandibular molars and incisors, indicating that they are more complicated.

#### **5. Study Limitations**

We searched data from a small number of significant websites for our systematic review. Articles that have appeared in other publications not indexed in the indices searched may have been ignored. We have also only included items published in English; as a result, publications in other languages may have been overlooked. A limited number of studies have been performed using Micro-CT.
