Introduction

The primary objective of endodontic therapy is to preserve tooth function while eliminating pain through comprehensive disinfection and three-dimensional obturation of the root canal system [1]. A leading cause of endodontic failure is inadequate debridement of the root canal space [2, 3], as residual pulp tissue and subsequent microbial colonization have been shown to compromise treatment outcomes [4–6]. In some cases, organic tissue remnants persist due to the clinician’s inability to identify additional root canals.

The mandibular first molar, being the first permanent posterior tooth to erupt, is the most commonly treated tooth in endodontics [7]. Given its frequent need for endodontic intervention, clinicians must be prepared to address variations in its internal anatomy. Extensive in vitro and in vivo studies have documented morphological variations in this tooth, including extra roots, additional canals, lateral canals, and anastomoses within the mesial root [3, 8–12].

Despite these well-documented anatomical complexities, few clinical case reports have described the presence of four canals in the mesial root of mandibular first molars [13–18]. Accurate identification and localization of such additional canals are critical for achieving clinical success—a task greatly enhanced by the use of a dental operating microscope.

This case report demonstrates the endodontic management of a mandibular first molar featuring four canals within its mesial root.

Timeline

The timeline is shown in Table 1.

Narrative

A 20-year-old male patient presented with pain in the right mandibular first molar, exacerbated during mastication. When taking the patient’s medical history, it was found that he had undergone endodontic treatment on the mandibular first molar approximately two years ago following spontaneous pain.

Diagnostics

Radiographic documentation of endodontic treatment phases (Figure 1).

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Figure 1. Radiographic documentation of endodontic treatment phases. (A) Diagnostic intraoral periapical radiograph prior to any therapeutic intervention. (B) Post-extraction intraoral periapical radiograph of the distal root. (C) Intraoral periapical radiograph demonstrating the four mesial canals. (D) Post-obturation intraoral periapical radiograph of the four canals. (E) A cone beam computed tomography (CBCT) image revealing the four canals. (F) Six-month follow-up CBCT image.

Patient perspective

The patient expressed a strong desire to preserve his remaining teeth, particularly this tooth. Indeed, the outcome was satisfactory for him, as no pain was reported upon mastication after the completion of treatment, and functional efficiency was restored.

Discussion

Root canal therapy maintains its position as the gold standard for treating irreversible pulpitis and periapical periodontitis. The fundamental objectives of endodontic treatment involve complete debridement, precise canal shaping, and three-dimensional obturation of the root canal system. Failure to identify and properly treat all canal spaces may compromise effective disinfection, ultimately leading to treatment failure [1]. Mandibular first molars emerge as the most frequently treated permanent teeth endodontically, owing to their early eruption and marked susceptibility to dental caries. While these molars typically exhibit two canals in the mesial root and one or two canals in the distal root, anatomical variations present significant diagnostic and therapeutic challenges [19].

Current data indicate that the middle mesial canal, situated between the mesiobuccal and mesiolingual canals, demonstrates a prevalence ranging from 1 to 15% [3]. In contrast, the presence of a fourth mesial canal is exceptionally rare, with only isolated cases reported in the endodontic literature (Table 2).

The anatomical configuration of root canal systems exhibits significant ethnic variations, a critical consideration for effective endodontic diagnosis and treatment. This diversity is evidenced by disparate prevalence rates reported across different populations. For instance, Goel et al. [12] documented a 3.3% incidence of a four-canal morphology in the mesial root of mandibular first molars within an Indian population, while Wasti et al. [9] identified a classic Vertucci Type VIII configuration in a single specimen out of 30 teeth studied in Pakistan.

Further underscoring these population-specific variations, large-scale analyses reveal both the variety and frequency of these anatomical complexities. Sert and Bayirli’s [22] examination of 2,800 teeth in a Turkish cohort identified 36 specimens with configurations that deviated entirely from the established Vertucci classification, noting a pronounced propensity for such anomalies in mandibular teeth. In a Burmese population, Gulabivala et al. [11] reported a unique four-canal morphology (designated Type XI), distinguished by the canals merging to exit through two distinct apical foramina. This case report contributes a pivotal data point to this global tapestry of dental morphology by presenting, to our knowledge, the first documented instance and successful management of a mandibular first molar with four mesial canals in a Syrian patient.

Notably, the presentation of these anatomical complexities can also be influenced by factors beyond ethnicity, such as age. Significantly, while existing literature indicates a higher probability of additional canals in patients over 30 years of age, we observed this rare anatomical variation in a much younger patient (20 years old) [20].

The evolution of diagnostic imaging in endodontics, particularly the advent of cone beam computed tomography (CBCT), has fundamentally enhanced our ability to decipher complex root canal anatomies. CBCT offers unparalleled three-dimensional visualization, proving diagnostically superior to conventional radiography in identifying multi-canal systems, developmental anomalies, and pathological conditions [23, 24]. Its judicious application is, however, tempered by considerations of increased radiation exposure and availability. Notably, the successful management of the present case, which involved a rare four-canal mesial configuration, was achieved relying solely on meticulous clinical evaluation—including careful tactile exploration with fine files under high magnification and conventional radiography with multiple angulations. This outcome invites a critical discussion on the role of technology in clinical decision-making. It serves as a crucial reminder that advanced imaging, while powerful, is an adjunct to, rather than a replacement for, fundamental diagnostic acumen. This case demonstrates that when CBCT is unavailable, contraindicated due to radiation concerns (particularly in a young patient), or simply not deemed essential based on initial assessment, exceptional outcomes are still achievable. The cornerstone of success remains a rigorous, pre-operative clinical protocol: a deep understanding of anatomical possibilities, dedicated access cavity refinement, and the strategic use of ultrasonic troughing to uncover occult orifices. Therefore, this report does not diminish the value of CBCT but rather clarifies its role. It underscores that CBCT is best reserved for cases where conventional methods yield ambiguous or conflicting findings, thereby reinforcing the principle of As Low As Reasonably Achievable (ALARA) in radiation exposure while celebrating the enduring efficacy of masterful clinical skill.

Effective chemomechanical preparation constitutes the cornerstone of endodontic success, necessitating a tailored approach that reconciles the principle of optimal shaping with the imperative for complete debridement and disinfection according to specific clinical findings. Although conservative canal preparation remains a well-established tenet in contemporary endodontics [25], clinical judgment is paramount and may dictate modifications based on individualized anatomical and pathological presentations. In the present case, the patient’s youth was associated with relatively wide canals, and the presence of infection accompanied by changes in the canal walls warranted judicious yet sufficient enlargement to ensure thorough debridement and disinfection. This approach is consistent with established literature underscoring that customizing the extent of canal preparation to the specific clinical scenario is a critical determinant of long-term success [14, 26, 27]. However, even with optimal shaping, the complex anatomy of the root canal system, with its intricate web of canals, isthmi, and recesses, presents a significant challenge. Conventional syringe irrigation is often insufficient against these untouched areas. Therefore, passive ultrasonic irrigation (PUI) was employed, as its acoustic microstreaming significantly enhances biofilm disruption and debris removal, thereby complementing the mechanical preparation [28]. Furthermore, the selection of an obturation technique must account for the complexity of the prepared canal system. Bioceramic sealers are capable of flowing into irregularities and accessory canals, facilitating a consistent, homogeneous three-dimensional seal that ensures the complete obturation of intricate anatomical structures. These sealers also exhibit unique bioactive properties, most notably a demonstrated capacity to induce biomineralization. This process is characterized by the formation of mineral tags within the dentinal tubules and at the sealer-dentin interface, which significantly enhances the long-term seal. This approach underscores the importance of selecting materials and techniques that are specifically tailored to the unique anatomical challenges of each clinical case [29].

The long-term prognosis of posterior teeth that have undergone root resection and endodontic retreatment remains a topic of clinical debate, particularly given their exposure to higher occlusal forces compared to anterior teeth. The absence of occlusal force assessment in such cases further limits the accurate estimation of functional load. However, several factors positively contribute to tooth survival, including the preservation of adequate root length and width, the absence of supporting periodontal complications, and full coronal coverage to distribute occlusal forces. Available literature indicates that these teeth can achieve long-term survival when carefully selected. A study by Carnevale et al. [30] reported a 93% ten-year survival rate for molars treated with supportive therapy following root resection, while Falabella et al. [31] documented a 97.6% ten-year survival rate, with no significant influence of restoration type. Although Bühler’s [32] analysis demonstrated a failure rate of approximately 32% after ten years in some hemisection cases, case reports such as that by Ajlan have shown the potential for successful root resection in maxillary molars, with maintained function and structure for up to 14 years [33]. Therefore, ensuring sufficient root dimensions, the absence of periodontal disease, and full coronal coverage to distribute occlusal forces are critical factors in achieving high long-term survival rates for posterior teeth even after hemisection.

Conclusions

This case report adds to the growing yet limited evidence on four-canal mesial roots by presenting a successful short-term outcome. It underscores the importance of meticulous examination and customized treatment planning in endodontic retreatments. Although the six-month follow-up showed favorable results, longer-term observations are necessary to assess the prognosis more comprehensively. The use of magnification, ultrasonic activation, and bioceramic sealers played a key role in addressing this complex anatomical configuration.