This study aimed to investigate the root and root canal morphology of the maxillary and mandibular premolars in a sample of Lebanese patients using in vivo CBCT imaging for clinical approach purposes. To date, no comparable data have been published in Lebanon. In our sample, the two-root root anatomy was predominant (85.3%) for the maxillary first premolars, consistent with previous reports [7, 14]. Indeed, single-rooted first premolars are commonly thought to be a Mongoloid characteristic , which may explain the frequency differences regarding single-rooted first premolars between our study and previous results . These variations in the number of roots illustrate the impact of ethnicity on the root morphology of the maxillary premolars. The frequency of three-rooted teeth (0.4%) was similar to that reported by Li et al.  and Neelakantan et al. . In general, three-rooted maxillary first premolars, also known as small molars, are uncommon and thought to be a Caucasian feature . The percentages of maxillary first premolars with different numbers of root canals were similar in earlier investigations [17, 18]. In the current study, two-root canals were the most common, followed by one-root canals and three-root canals, with 11.2% having a complex root canal system (types II, III, V, VI, and VIII). Knowledge about the prevalence of this complex anatomy is essential for achieving better root canal treatment outcomes.
Most maxillary second premolars (79.8%) had only one root, while 17.9% had two roots and 2.3% had three roots. In previous reports, the percentages of one-, two-, and three-rooted teeth varied from 69–90%, 13–30%, and 0–1%, respectively [17, 19]. Changes in demographics, evaluation methods, and/or sample size may account for the variance in anatomy between the previous and present results. Two-root canals were more common than one-rooted canals, which agrees with Vertucci’s findings ; these two-canal variations are relatively easy to identify, manage and treat. It should be pointed out that some of the maxillary second premolars in this study had three canals or presented with a complex root canal system (types II, III, V, VI, VII, and VIII) that is difficult to detect with periapical radiographs and magnification, thus minimizing the endodontic treatment outcome. The presence of this morphology is another essential parameter that should be considered during endodontic treatment.
Similar to the literature [20, 21], the majority (99.2%) of mandibular first premolars had only one root. However, no three-root teeth were detected, contrary to previous reports showing a frequency of 0.2% . In our study, 84.5% of mandibular first premolars had a one-root canal, consistent with previous findings [20, 23]. The frequency of two-root canals (15.5%) is critical information that should be accounted for during endodontic treatment, as it requires proper management. Regarding the internal root canal configuration of the mandibular first premolars, the Vertucci type I configuration was the most prevalent, followed by type II. Previous studies reported the Vertucci type I configuration to be more prevalent than type II [20, 24].
In our study, all mandibular second premolars (100%) had one root, similar to previous reports [20–21]. Additionally, most mandibular second premolars (88.6%) had one canal, in line with previous findings reporting frequencies of 74%-95% for the single-canal configuration [23, 25]. Our results also showed a two-canal morphology in 11.4% of the cases, as previously obtained in the literature . Clinicians should focus on this feature, for which additional efforts are needed. The prevalence of the type I root canal configuration among mandibular second premolars is consistent with literature findings, indicating that type I is the most common [25, 27]. Complex Vertucci classifications (II, III, IV, V) were also found in this group of premolars, making root canal treatment very challenging for these teeth.
Our results showed bilateral symmetry for the maxillary and mandibular premolars with no significant difference regarding the number of roots, the number of canals, and the canal configuration, consistent with previous observations [11, 16]. A micro-CT study  reported symmetry in the linear measurements of root canal configurations and orifice forms between the contralateral premolars. However, discrepancies were found between these teeth in the apical part. Research among 59 patients with bilateral maxillary first premolars found that only 64% of maxillary first premolars had similarities in root number and canal configuration . Another study identified few symmetrical premolar pairs  when using CBCT to provide well-balanced experimental groups. Disagreements in results regarding the symmetry in the contralateral premolars could be due to the different methodologies used to record the morphology and the different anatomic characteristics evaluated. Bilateral symmetry in contralateral anatomic structures is widespread . In this context, it should also be expected in the Lebanese population. Bilateral symmetry would be helpful in comparative endodontic research in Lebanon when evaluating instrumentation systems, irrigation protocols, and obturation techniques. Overall, studies have revealed symmetry in the root canal morphology in the maxillary and mandibular contralateral premolars regarding the number of roots, the number of canals, and the canal configuration, all of which are of notable clinical significance. Practitioners could use the root and canal anatomy of the contralateral treated premolar as a guide to perform endodontic treatment on the homologous premolar for the same patient.
Regarding sex distributions, men had remarkably more roots and root canals in their maxillary first premolars than women, which aligns with previous results [1, 3]. Our study revealed that more women had the Vertucci type I configuration, and more men presented with the Vertucci type IV configuration in the maxillary first premolars, but no differences related to sex were found in the mandibular premolars, also in accordance with previous observations  in mandibular premolars (types II–VIII). These results may help practitioners during preoperative assessments and improve endodontic treatment success in the Lebanese population. However, more studies with larger samples are necessary to analyze a potential sex difference.
Effective nonsurgical and surgical endodontic treatments require a thorough understanding of root and root canal morphology. Practitioners should anticipate anatomic variations in the maxillary and mandibular premolars and use their knowledge, expertise, and new tools to recognize and treat these teeth. Despite the low prevalence of three-rooted maxillary premolars in our study, physicians must make sure not to leave a probable third canal untreated. A rigorous clinical and radiographic evaluation is needed. A third root or root canal may be present if the mesiodistal diameter of the crown is larger than the buccolingual dimension or when the mesiodistal width of the midroot region on preliminary radiography is equal to or larger than the mesiodistal diameter of the crown . The frequency of two-root canals in the mandibular premolars in this study presents critical information for physicians due to missed canals, which have been associated with postendodontic diseases . A sudden narrowing of the canal system in the mandibular premolars on a parallel radiograph supports the presence of extra canals . Angulated radiography is required to estimate the number of canals and roots. Consequently, physicians should be aware of this issue during shaping and filling procedures so as not to miss treating a canal. This study detected premolars with complex root canal systems (types II, III, V, VI, and VIII) that are challenging to identify and treat. The results from a recent study  revealed that the prevalence of endodontic technical errors, such as underfilling and the presence of periapical lesions, increased in patients with teeth with a complex root canal anatomy. Nonfilled canals were frequent errors associated with type V configurations. A thorough clinical and radiographic examination and appropriate access cavity may help locate and negotiate root canals. CBCT imaging can be used before endodontic treatment to evaluate the complexity of the root canal system when the clinician suspects an abnormal or complicated anatomy on periapical radiography . These data and the shift toward new magnification techniques aim at improving root canal outcomes.
Regarding methodology, the voxel size in this study (0.2 mm) may not be optimal, given that smaller voxel sizes (0.075 mm) are available in some CBCT systems and are commonly used in root canal morphology assessments [7–16]. However, several previous studies have employed voxel sizes comparable to or higher than ours, ranging from 0.125 to 0.3 mm, to assess the morphology of the root canal system [1, 9, 20, 21]. Although CBCT is a reliable screening tool for examining root and root canal morphology, it may not show anatomic features as in high-resolution scans, such as micro-CT , which is one of the limitations of this study.