Retrospective Evaluation of Variations in Root Canal Morphology of Permanent Maxillary Premolars Among the Emirate Population

Background: This research aims to identify the most common morphology of the upper premolars in a group of local and nonlocal people in the UAE using cone-beam computed tomography (CBCT). Methods: CBCT images of a total of 214 intact maxillary premolars were analysed with 3D reconstruction GALAXIS viewer software. The Pearson Chi squared test and the two samples t test were applied. Results: In all, 90% of the maxillary rst premolars had two roots (92% females, 88% males, 83% locals, 96% nonlocals). A total of 52% of maxillary second premolars had two roots (47% females, 56% males, 38% locals, 67% nonlocals). Two cases had three roots among local males. A signicant difference of one root in the maxillary second premolar was observed between locals (63%) and nonlocals (33%), while two roots were higher among nonlocals (67%) than locals (37%, p = 0.002). Three roots were discovered in two teeth of the local UAE rst premolar. The most common canal morphology in the maxillary rst premolar group among local UAE subjects was type V (52%), and among nonlocal UAE subjects was type V (59%). Additional types included 7 (13.2%) identi ﬁ ed and unrelated to the Vertucci classication. The dominant canal morphology in the maxillary second premolar among local UAE subjects was type II (32%), and among nonlocal UAE subjects was type V (25%); among the additional types, 12 (23.1%) were identi ﬁ ed and not related to the Vertucci classication. There was a signicant difference in the distance from the pulp chamber roof to the cementoenamel junction (CEJ) and the measurement between the single-rooted maxillary premolar CBCT for local UAE subjects was 1.36 mm (SD ±0.75) and for nonlocal subjects was 1 mm (SD ±0.27, p = 0.049). There were statistically signicant differences in all measurements between multiple rooted maxillary premolar CBCTs for local UAE and South Conclusions: The results suggest a more quantitative approach to maxillary rst and second premolar access cavity preparation in the UAE population to prevent errors and iatrogenic damage when identifying the canals; using CBCT measurements for more precise access preparations may be advantageous.

in two teeth of the local UAE rst premolar. The most common canal morphology in the maxillary rst premolar group among local UAE subjects was type V (52%), and among nonlocal UAE subjects was type V (59%). Additional types included 7 (13.2%) identified and unrelated to the Vertucci classi cation. The dominant canal morphology in the maxillary second premolar among local UAE subjects was type II (32%), and among nonlocal UAE subjects was type V (25%); among the additional types, 12 (23.1%) were identified and not related to the Vertucci classi cation. There was a signi cant difference in the distance from the pulp chamber roof to the cementoenamel junction (CEJ) and the measurement between the single-rooted maxillary premolar CBCT for local UAE subjects was 1.36 mm (SD ±0.75) and for nonlocal subjects was 1 mm (SD ±0.27, p = 0.049). There were statistically signi cant differences in all measurements between multiple rooted maxillary premolar CBCTs for local UAE and South Asian subjects (p < 0.05) Conclusions: The results suggest a more quantitative approach to maxillary rst and second premolar access cavity preparation in the UAE population to prevent errors and iatrogenic damage when identifying the canals; using CBCT measurements for more precise access preparations may be advantageous.

Background
Endodontology addresses the dental pulp and periradicular area in healthy, diseased, injured situations and encompasses how it functions, prevention and treatment [1]. The most frequent reason for endodontic treatment failure is a misunderstanding of tooth anatomy and technical competence [2]. As a result, a thorough knowledge of pulp canal anatomy is critical for a successful root canal treatment (RCT) [3,4]. Additionally, the dentist must be armed with the creative skills of reading an X-ray and must examine the dental pulp and periapical tissue to reach the correct diagnosis [5]. The initial stage in pulp canal therapy is to obtain access to hollow space preparation. The subsequent steps and the result will preserve the tooth structure as much as possible [6]. The tooth anatomy varies between populations, persons, and races; trouble is also faced when studying root canal morphology [7][8][9][10]. Most of the variation is seen in maxillary rst and second bicuspid teeth [11][12][13]. The anatomy of the premolar teeth is complex and is an enigma [3,14,15]. Even so, the bicuspid's maxillary tooth has an oval-shaped canal.
It has more than one canal, but the maxillary premolars generally have roots correlated with the number of root canals [3]. In most cases, many premolar teeth have extra roots and extra canals. Therefore, many modi cations have been made to classify root canal con guration systems in recent studies [16]. The most common one was the Vertucci classi cations. Vertucci has categorised root canal morphology into eight distinct categories [9,17]. Some research ndings in the literature are consistent with previous investigations by Vertucci et al. (2005). Other study ndings contradict previous research by Vertucci et al. (2005) [18]. Unfortunately, many investigations utilising various methods have shown signi cant differences in assessing the root canal anatomy of maxillary premolars across different cultures [13,17,19]. The success rate based on utilising the present technique to confront the challenge during root canal treatment lowers root canal treatment failure. A periapical radiograph has traditionally been used to visualise the dentition into 2D images for root canal treatment [20]. Recently, CBCT has made it possible to visualise the dentition and surrounding structures in the anatomical 3D space into 3D images [21]. CBCT is a basic image to demonstrate and assess root canal morphology for a given population [22]. This study further investigates the location of the canal ori ces, dimensions of the pulp chamber and variations in the number of roots and canals for the upper rst and second premolars due to their challenging morphology in clinical endodontics. The majority of research has found substantial differences in the root canal morphology of maxillary premolars among populations. However, there are no published studies with detailed data on the root canal anatomy of the maxillary rst and second premolars in the UAE population. Thus, the purpose of this research was to examine the root canal architecture of maxillary rst and second premolars in the UAE population and compare the results to previous studies in other populations.

Sample collection
From 2015 to December 2020, researchers from University Dental Hospital Sharjah performed a retrospective study. CBCT scans from patients who came to UDHS for different reasons were examined.
CBCT scans of maxillary rst and second premolars were examined for this research. The UDHS institutional review board granted ethical clearance (REC-20-03-03-01-S). The radiology archives of the hospital were used to acquire all of the scans. Sampling was performed at random, and the sample size was calculated using a previous study [23] with a con dence level of 95%. The sample size for maxillary rst premolars was 88, while the sample size for maxillary second premolars was 98. We needed 107 maxillary rst premolars and 108 maxillary second premolars to adjust for observational error.
CBCT images were obtained using the radiograph Sirona Galileos. 3D reconstruction was performed using Galaxix (Sirona Dental Systems, Bensheim Germany). All exposures were performed with 85 kV/10 mA, 14 S. Exposure protocol: Volume II to reduce image noise and patient dose. The xed FOV was 15 cm x 15 cm over the entire dentition with a voxel size of 0.075 mm. All images were collected according to the manufacturer's instructions by an experienced radiologist. On a 17-inch display, cross-sectional pictures were collected in the axial, coronal, and sagittal planes and reconstructed.

Inclusion criteria
The inclusion criteria were as follows: evaluation of maxillary bicuspids of males and females in the UAE aged 12-70 years who provided informed consent; patients were included in the current study if they required CBCT examination for treatment planning or dental diagnosis at University Dental Hospital Sharjah, had fully developed roots, were not treated endodontically, and had no resorbed roots or calci ed canals. The study excluded teeth with signi cant caries lesions, substantial metal restorations, fractures, orthodontic wires, veneers, teeth with immature root tips, endodontically treated teeth, and pictures with low image quality.

Radiographic evaluation
Two experienced endodontists performed all data measurements. Each investigator assessed the CBCT pictures twice and computed the average value with a two-week delay between assessments. When agreement could not be achieved, a senior oral radiologist assisted in decision-making. The following observational data were recorded during the examination of the teeth: (1) mesiodistal width of pulp chamber landmarks and morphologic measurements related to furcation, (2) number and con guration of roots, (3) number of root canals and canal con guration based on Vertucci's classi cation.
Teeth were radiographed in buccal and palatal views to allow direct morphological measurements related to furcation and to show cusp tips and furcation in one radiograph [24]. To reduce the possibility of perforating the furcation, the dentist should know where they are. Therefore, the most super cial landmark was selected for measurement [24][25][26]. A horizontal line was drawn parallel to each landmark, and six millimetre (mm) measurements were taken from these landmark lines. First, consider the midpoint of a line that connects the two cusp points. The ve measures were denoted by the letters A, B, C, D, and E. In detail, A is the space between the lowest point on the pulp chamber roof and the highest point on the pulp chamber oor. B is the space between the highest point at the pulp chamber's bottom and the highest at the root furcation. C is the distance obtained by adding A and B, i.e., the space between the lowest point on the pulp chamber ceiling and the highest position on the root furcation. D is the space between the midpoint of a line connecting the two cusp points and the lowest point on the pulp chamber's ceiling. E is the space between the midpoints of two cusp tips and the highest point on the root furcation ( Fig. 1).
While measurements for single-rooted maxillary premolars are obtained from the lines of these landmarks, in detail, A is the space between the midpoint of a line connecting the two cusp points and the lowest point on the pulp chamber's ceiling. B is the space between the pulp chamber's lowest point on the ceiling and the CEJ (Fig. 2).
According to Krasner and Rankow (2004), the dental pulp chamber's mesiodistal width in an axial view of CBCT scans was measured in an area showing the centricity of the pulp chamber at the CEJ along the horizontal plane running from mesial to distal of the pulp chamber for each upper premolar [27].

Statistical analysis
Analysis was performed using SPSS, version 26 (IBM, Armonk, NY, USA). Means (standard deviations, SD) were reported for numerical variables. Frequencies with percentages were reported for categorical variables. Pearson's Chi squared test was used to examine the association between categorical variables. Independent-sample t tests were used to compare the means of different numerical variables. Statistical signi cance was set at p < 0.05.

Results
A total of 107 bilateral MFPPs with 108 bilateral MSPPs were examined. Table 1 shows that there were 52% male cases, and there were 51% cases from a local ethnic group. Table 2 shows the distribution of maxillary rst and second premolar roots by gender and ethnicity. The majority of the maxillary rst premolars (90%) had two roots; this was observed in 92% of females, 88% of males, 83% of locals, and 96% of nonlocals. Similarly, most of the maxillary second (52%) premolars were two roots, in 47% of females, 56% of males, 38% of locals, and 67% of nonlocals. There were only 2 cases of three roots among local males. The prevalence of one root in the maxillary second premolar was signi cantly higher among locals (63%) than nonlocals (33%). In comparison, the prevalence of two roots was higher among nonlocals (67%) than locals (37%, p = 0.002).     A total of 54 maxillary rst premolars and 56 maxillary second premolars in the local UAE population and 53 maxillary rst premolars and 52 maxillary second premolars in the nonlocal UAE population were analysed, and the number of roots, root canals, and type of canal con gurations were evaluated. The results are presented in Tables 4 & 5. Table 4 shows that one root in a maxillary rst premolar was detected in 17% of local UAE subjects and 11% of nonlocal UAE subjects and two roots maxillary rst premolar in 68% of local UAE and 59% of nonlocal UAE (p < 0.0001). Found three roots only in 2 teeth in the rst premolar. Almost all local and nonlocal groups had two canals for both the rst and second maxillary premolars.
Found one root of maxillary second premolar in 83% of local UAE subjects and 90% of nonlocal UAE subjects, and two roots of the maxillary second premolar were found in 32% of local UAE subjects and 41% of nonlocal UAE subjects (Table 4). Table 5 shows the distribution of different canal morphologies in maxillary premolars. Based on the Vertucci classi cation, the most common canal morphology in the maxillary rst premolar group among local UAE, was type V (52%), followed by type IV (26%) and type II (6%). An additional type, 2 (3.7%), was also identi ed and is not related to the Vertucci classi cation.
The dominant canal morphology in the maxillary second premolar group among local UAE subjects was type II (32%), followed by type III (27%) and type V (20%).
Based on the Vertucci classi cation, the most common canal morphology in the maxillary rst premolar group among nonlocal UAE subjects was type V (59%), followed by type IV (9%) and type VI (8%). An additional type, 7 (13.2%), was also identi ed and unrelated to the Vertucci classi cation.
In the maxillary second premolar group among nonlocal UAE subjects, the dominant canal morphology was type V (25%), followed by type III (15.4%) and type VII (13.5%). Based on the Vertucci classi cation, an additional type, 12 (23.1%), was also identi ed and not related to the Vertucci classi cation. Table 6 shows a comparison of various morphological measurements recorded from single-rooted maxillary premolar CBCT. There was a statistically signi cant difference in the distance from the mesial to the distal pulp chamber in the single-rooted maxillary premolar CBCTs between the local UAE (1.26 ± 0.27 mm) and South Asian population (1.10 ± 0.32 mm, p = 0.037).
There was no statistically signi cant difference in the distance from the midpoint of a line connecting the two cusp tips to the lowest point on the roof of the pulp chamber in single-rooted maxillary premolar CBCTs for the local UAE population (5.58 ± 0.72 mm) and South Asian population (5.31 ± 1.08 mm, p = 0.252).
There was a signi cant difference between the distance from the lowest point on the pulp chamber roof to the CEJ in the single-rooted maxillary premolar CBCT for local UAE subjects (1.36 ± 0.75 mm) and South Asian subjects (1 ± 0.27 mm, p = 0.049). Table 7 shows a comparison of various morphological measurements recorded from multiple rooted maxillary premolars in CBCTs. There were statistically signi cant differences in all measurements in multiple rooted maxillary premolar CBCT between the local UAE and South Asian population (p value <0.05).

Discussion
Endodontic procedures are standard challenging procedures in daily dental practice. Therefore, an understanding of root canal anatomy is required for a successful RCT. However, tooth anatomy varies between persons and between populations. The most variation in anatomical structures was seen in maxillary rst and second bicuspid teeth [11].
The majority of the problems encountered while treating the root canal were seen in maxillary premolars owing to variations in the architecture of the root canal systems; thus, maxillary premolars were selected for the current research.
To our knowledge, this is the rst study to investigate the root and canal morphologies and symmetry of each maxillary rst and second premolar simultaneously in a UAE population using a pattern of CBCT images. We hoped that our research would assist in improving effective root canal treatment in the UAE and contribute to the literature on root canal morphology and symmetry of permanent teeth in the South Asian population.
According to Ingle, most anatomic investigations have shown that the most common type of maxillary second premolar is the single-rooted form, with the frequency of three-rooted forms ranging from 0-1%.
Most of the teeth studied in this research (52%) had two roots, whereas the remaining teeth (48%) had a single root. The proportion of two-rooted teeth was greater than in prior research with other groups [7,18,31,32,38]. These differences emphasise the impact of ethnic background, evaluation techniques, and sample sizes on root morphology studies in maxillary premolars.
Root canal con gurations vary from teeth to teeth and from population to population. In our study, almost all local and nonlocal populations had two canals in both the rst and second maxillary premolars (Table 4). This share lies within the range mentioned in research on the usage of CBCT or clearing techniques [7,8,19,23,29,36,[38][39][40]. Only two maxillary rst premolars (0.2%) had the threecanal morphology within the previously described range of 0.4-3.3%. [4,7,23,35,41,42]. Vertucci (1984) found that the maxillary rst premolar was the only tooth with all eight kinds of canal morphology [9].
Similar to this research, several published investigations have identi ed these kinds of canals in maxillary bicuspids. Yi-Han Li, Mutasim, and Jayasimha reported type XIX canal con gurations [14,23,38].
Mutasim and Senan reported type 1-2-3, type 3-2-1, type 2-3-2 and type 3-2 canal con gurations [19,38]. The current study's most interesting ndings were the new root canal types discovered in 3.7% of local UAE subjects and 36.3% of nonlocal UAE subjects. These canal types account for a sizable proportion of the total. As a result, it is necessary to assume that therapy will be di cult. Type V (52%) was the most common canal con guration in maxillary rst premolars among local UAE subjects, whereas type II (32%) was the most common canal con guration in second premolars. Moreover, type V (59%) was the most common canal con guration in maxillary rst premolars among nonlocal UAE residents, and type V (25%) was the most common canal con guration in second premolars. This nding is consistent with previous ndings [3,14,29,37,38,44,45].
Understanding pulp chamber morphological measurements is important for proper access for successful endodontic treatment and the avoidance of errors such as perforation while locating the canals.
The anatomical landmark associated with the pulp chamber of maxillary furcated bicuspids was measured for the rst time in Deutsch's study [24]. Then, in 2007, Venkateshbabu et al. observed that the morphological measurement of maxillary rst premolars in the Indian population was equivalent to a previous study [25]. In the Nagpur population, however, these furcated bicuspid teeth were observed to be signi cantly longer. In maxillary rst premolars, the author observed that the CEJ corresponds to the ceiling of the pulp chamber, which is identical to the pulp chamber discovered by Deutsch [24,26].
The distance between the midpoint of a line connecting the two cusp points and the furcation, according to Deutsch and Musikant (2005), is 11.55 mm [24]. The height of the pulp chamber is 2.76 mm, and the average distance between the midpoint of a line joining the two cusp suggestions and the roof of the pulp chamber is 6.94 mm. The authors found that the CEJ was constantly near the pulp chamber ceiling of the top furcated bicuspids.
The distance between the midpoint of a line connecting the two cusp points and the closest point to the furcation was 10.83 ± 1.33 mm in the local UAE population and 9.77 ± 1.24 mm in the nonlocal UAE population in our research. For maxillary second premolars, the average distance between the midpoint of a line connecting the two cusps and the ceiling of the pulp chamber was 6.11 ± 0.99 mm for local UAE subjects and 5.75 ± 0.90 mm for nonlocal UAE subjects. For maxillary rst premolars, the mean distance between the midpoint of a line connecting the two cusps and the ceiling of the pulp chamber was 5.58 ± 0.72 mm for the local UAE population and 5.31 ± 1.08 mm for the nonlocal UAE population. The height of the pulp chamber was 2.57 ± 0.88 mm for local UAE subjects and 2.24 mm ± 0.78 mm for nonlocal UAE subjects.
Clinically, approximately 4.6 mm is available to perforate after reaching the pulp chamber's roof (at the level of the CEJ). The addition of this distance to the 6.1 mm distance between the cusp tip and the pulp chamber ceiling for bicuspids yields 10.7 mm, approximately 11 mm. A drill should be marked at 11 mm, so the dentist understands where it is in the furcation to decrease the possibility of perforation in the furcation. These results were similar to those of Deutsch's study.
As each year of life progressed, the size of the pulp chamber decreased due to calci cation. Therefore, these measurements differed in ways that were either directly or indirectly related to the height of the pulp chamber.

Conclusions
Our study is the rst to analyse the most common morphology of the upper premolars in a group of Emirati subpopulations. The results in the current study serve as a guide that can offer a more quantitative approach to maxillary rst and second premolars to access cavity preparation in the UAE population to prevent errors and iatrogenic damage when identifying the canals; CBCT measurements can be advantageous for more precise access preparations.

Consent for publication
Not applicable Availability of data and materials The datasets used and analysed during the current study are available from the corresponding author on reasonable request.