Mystery of Middle Mesial Canals in Mandibular Molars
Introduction:
In the world of endodontics, success hinges on a thorough understanding of root canal anatomy. Among the many anatomical variations that challenge general dentists and endodontists, the middle mesial canal (MMC) in mandibular molars stands out as a subject of special interest. First described by Vertucci and Williams in 1974 and further elaborated by Pomeranz et al. in 1981, MMCs have since been a topic of debate regarding their prevalence, clinical significance, and best practices for detection and treatment.
Recent advancements in imaging technology, particularly cone-beam computed tomography (CBCT), have revolutionized our ability to visualize complex root canal systems. However, the reported prevalence of MMCs varies widely in the literature, ranging from as low as 0.95% to as high as 46.2%, depending on the study methodology and population examined. This is a truly wide range, but what does our experience say?
We have recently published a large-scale clinical study focused on the incidence and factors associated with MMCs in both initial root canal treatments (RCTs) and nonsurgical retreatments (NSRetxs). This research, involving over 3,000 mandibular molars, provides valuable insights that can significantly impact our clinical approach. Key findings from this comprehensive study include (You can read the full article at https://www.sciencedirect.com/science/article/abs/pii/S0099239924001596) :
Overall incidence: MMCs were found in 8.8% of all cases, aligning more closely with conservative estimates from previous CBCT studies.
Age factor: Younger patients showed a higher incidence of MMCs, consistent with earlier findings by Nosrat et al. (2015) and Azim et al. (2015).
Tooth type: First molars had a significantly higher incidence compared to second molars, corroborating results from a recent systematic review by Al-Maswary et al. (2023).
Gender association: Male patients showed a higher incidence, particularly in initial RCT cases, a finding that warrants further investigation.
Imaging impact: Preoperative CBCT scans were associated with higher detection rates, especially in retreatment cases, highlighting the value of advanced imaging in complex cases.
These findings underscore the importance of a nuanced approach to mandibular molar treatment. The variability in MMC incidence based on patient demographics and tooth type emphasizes the need for careful preoperative assessment and tailored treatment strategies.
Moreover, the study raises important questions about the long-term implications of MMC treatment. While addressing all canal spaces is a fundamental principle of endodontics, recent research by Keleş et al. (2020) suggests that instrumenting MMCs may increase the risk of vertical root fracture.
This introduces a clinical dilemma: balancing thorough disinfection with preservation of root structure. However, can we still disinfect and clean the whole canal space without aggressively compromising the root structure?
Here, as we will discuss some cases, we'll explore the clinical implications of these results, discuss best practices for MMC detection and management, and consider how this knowledge can inform our daily practice. All these patients presented here were treated by Dr. Omid Dianat, DDS, MS, MDS. By understanding the complexities surrounding MMCs, endodontists can make more informed decisions, potentially improving treatment outcomes and long-term tooth prognosis.
Case Presentations
CASE #1
A 62-year-old male patient presented with a chief complaint of lingering pain in the lower left quadrant. Clinical examination revealed a crewn on tooth #19 with no visible cracks or fractures. Radiographic examination showed a relatively large radiolucent lesion in both mesial and distal roots with widening of the periodontal ligament space. Based on these findings, a diagnosis of necrotic pulp with symptomatic apical periodontitis was made for tooth #19.
Root canal therapy was planned and initiated under local anesthesia. Upon access, four distinct canal orifices were initially located: mesiobuccal (MB), mesiolingual (ML), distobuccal (DB), and distolingual (DL). However, negotiation of the mesial canals proved challenging, with repeated blockages encountered despite careful instrumentation attempts.
Given the difficulty in negotiating the mesial canals, a careful exploration of the isthmus area between the MB and ML canals was undertaken. Using the dental operating microscope at high magnification and ultrasonic tips, a small groove was carefully traced in the developmental groove between the MB and ML canals.
After meticulous exploration, a small orifice was discovered midway between the MB and ML canals. This middle mesial canal was initially tight but negotiable with a #08 K-file. Coronal enlargement was performed with an orifice opener to improve straight-line access, followed by careful instrumentation using nickel-titanium rotary files.
Working length was established using an electronic apex locator and confirmed radiographically. All canals, including the MMC, were thoroughly cleaned and shaped using a crown-down technique. Copious irrigation with 5.25% sodium hypochlorite was performed throughout the procedure, and activated with ultrasonic agitation.
Given the anatomical challenges presented by the calcified canals and the concavity of the mesial root, a conservative approach to instrumentation was adopted. The treatment strategy focused on minimal shaping combined with efficient irrigation protocols to achieve optimal disinfection. Special care was taken not to over-prepare the middle mesial canal due to the anatomical constraints of the root concavity.
Obturation was completed using warm vertical compaction with gutta-percha and Hiflow Bioceramic sealer. The post-operative radiograph clearly demonstrated the presence of the middle mesial canal, with the filling material visible in all three mesial canals. The patient's postoperative course was uneventful, with complete resolution of symptoms at the one-week follow-up. A final radiograph taken at the 6-month recall showed healing of the periapical tissues and no signs of persistent inflammation. Here is the radiograph of the recall appointment:
CASE #2
A 32-year-old male patient presented with a chief complaint of a bump on the gum. Clinical examination of tooth #18 revealed a small crack extending to the cementoenamel junction (CEJ) on the buccal surface. Diagnostic testing confirmed pulp necrosis, and radiographic examination showed internal resorption in the distal canal. Based on these findings and the presence of a sinus tract, a diagnosis of chronic apical abscess was established.
Root canal treatment was initiated under local anesthesia. During access preparation and canal exploration, a middle mesial canal was discovered between the main mesial canals. Special attention was given to addressing the internal resorption defect in the distal canal. The resorptive defect was thoroughly cleaned and sealed as part of the treatment protocol.
All canals, including the middle mesial canal, were carefully instrumented and irrigated following standard protocols. The obturation was completed using appropriate filling materials and techniques. The post-operative evaluation showed complete healing of the sinus tract, indicating a successful treatment outcome.
CASE #3
A 43-year-old patient presented with a crowned tooth #19 and reported intermittent pain. Clinical examination and testing revealed pulp necrosis. The access cavity was prepared through the crown. During careful exploration under high magnification, a middle mesial canal was identified, in addition to the mesial buccal and mesial lingual canals. This additional canal was confirmed using tactile exploration and radiographic verification.
The canals were instrumented and irrigated with sodium hypochlorite and EDTA to facilitate cleaning and removal of debris. Obturation was completed using the warm vertical compaction technique to ensure a three-dimensional seal of the root canal system.
A postoperative radiograph confirmed adequate obturation of all canals. The patient was advised on postoperative care and scheduled for follow-up to assess healing.
Additional Cases Overview
The following four cases will demonstrate various presentations and management approaches of middle mesial canals (MMCs) in mandibular molars. Each case offers unique insights into the detection, negotiation, and treatment of these anatomical variations, further enriching our understanding of complex root canal anatomy.
These cases highlight several key points:
The presence of MMCs is not rare and should be actively sought, particularly in:
Younger patients
Cases with difficult initial canal negotiation
Situations with persistent symptoms
Treatment success requires:
Careful pre-operative assessment
Use of appropriate magnification and illumination
Modified instrumentation approaches based on root anatomy
Thorough irrigation protocols
CASE #4
CASE #5
CASE #6
Case Analysis
The presented cases showcase several important aspects of middle mesial canal management:
Varied Patient Demographics
Age range: 32-62 years
Different presenting symptoms: from lingering pain to asymptomatic lesions
Various pre-existing conditions: crowned teeth, crack lines, resorption
Detection Patterns
Initial challenge in canal negotiation often prompted careful exploration
Use of magnification (dental operating microscope) was crucial
Systematic exploration of developmental grooves between main canals
Important role of advanced imaging in treatment planning
Treatment Considerations
Conservative approach necessary, especially in cases with root concavity
Balance between adequate cleaning and preservation of root structure
Emphasis on irrigation protocols over excessive mechanical preparation
Adaptation of treatment strategy based on individual case factors
Conclusion
The successful management of middle mesial canals requires a thorough understanding of root canal anatomy and careful attention to detail during treatment. These cases demonstrate that while MMCs present technical challenges, they can be predictably treated when proper protocols are followed. The key to success lies in:
Maintaining a high index of suspicion for their presence
Using appropriate technology and magnification
Following conservative preparation principles
Employing enhanced irrigation protocols
The favorable outcomes in these cases, demonstrated by resolution of symptoms and radiographic healing, underscore the importance of identifying and treating middle mesial canals. This anatomical variation should be considered a regular part of mandibular molar anatomy rather than an exception, and clinicians should be prepared to manage these cases as part of their routine endodontic practice.
Interested in more cases?
You can find other cases that Dr. Dianat has previously published by clicking on the following links. You can also visit his Instagram page (https://www.instagram.com/endogram.drd/) and find out ICR cases alongside with other interesting daily cases!
Stay Tuned! We can’t wait to be back with another short clinical article!