Middle Mesial Research Articles

The Middle Mesial Canal: Combined Endodontic and Restorative Treatment Approach - A Case Report

The management of the middle mesial canal (MMC) in mandibular first molars presents considerable challenges during endodontic treatment due to its complex anatomy. Challenges may arise throughout various stages of treatment, including canal location, instrumentation, and obturation. The inability to identify and shape this canal can lead to endodontic failure and post-treatment apical periodontitis. Therefore, understanding this aberrant root canal anatomy and its clinical implications during the various stages of endodontic treatment is essential for successful management, including the selection of the optimal coronal restoration to enhance the efficacy of the obturation’s coronal seal and to ensure the restoration’s maximal longevity. This case report describes the diagnosis and successful endodontic and restorative management of an MMC in a mandibular first molar.

Prevalence of middle mesial canal in mandibular molars: A cross-sectional cone-beam computed tomography study.

The first tooth to erupt is the first mandibular molar, which is the tooth with the highest number of retreatments. Several factors are responsible for the failure of the endodontic success and one of the most important being the particular pulp anatomy of each tooth. To aim was determine the prevalence of the middle mesial (MM) canal in first mandibular molars and to study if there are predisposing factors to the presence of this canal by retrospectively analyzing cone-beam computed tomography (CBCT) images in vivo. CBCT images of 100 patients were selected. A total of 206 first mandibular molars were examined. The CBCTs were analysed using Careastream CS 3D imaging software. Findings of MM canals were recorded along the variables sex and left/right side. Prevalence was compared using the Chi-square test (P< 0.05) and Cramer's V was used to indicate the effect size between the variables. Of the 206 teeth analysed, the prevalence of MM canals was 33.11% (49 teeth). There was no statistically significant difference between sex and prevalence of the MM canal. There was a significant difference between sex and the distance between the mesial canals was found, being the most common range in women was 1-2 mm (35.8%) and 2-3 mm (51%) in men. The most common range of distance between the mesial canals where the MM canal was localized was 3-4 mm (50%), being statistically significant (p<0,05). This cross-sectional study showed a high prevalence of MM canals (33.11%) in first mandibular molars. The prevalence of the MM canal was significantly higher when the distance between mesiobucal and mesiolingual canals was 3-4mm. This knowledge let direct the clinicians in locating MM canal for improving endodontic prognosis. Key words:Cone-beam computed tomography, middle mesial canal, prevalence.

Micro-computed tomographic evaluation of the shaping ability of three nickel-titanium rotary systems in the middle mesial canal of mandibular first molars: an ex vivo study based on 3D printed tooth replicas

BackgroundThe preparation of the middle mesial (MM) canal of mandibular molars represents a challenge because it is often curved, narrow, and close to the root concave. The purpose of this study was to evaluate the ex vivo shaping ability of 3 nickel-titanium (NiTi) rotary systems in the MM canal using 3D printed resin tooth replicas.MethodsA permanent mandibular first molar with a MM canal was acquired from a pool of extracted teeth and reproduced by a 3D printer. The resin tooth replicas (n = 18) were equally assigned to 3 groups for the evaluation of the shaping abilities of 3 NiTi rotary systems (OneShape [OS], Twisted Files [TF], and ProTaper Gold [PTG]) according to the manufacturer’s recommendations. The tooth replicas were scanned by micro-computed tomography (micro-CT) twice before and after instrumentation of the mesiobuccal (MB), mesiolingual (ML), and MM root canals. After 3D reconstruction, the canal straightening, change of root canal volume and surface area, the mesial and distal canal wall thickness and canal transportation at the levels of 1, 2, and 3 mm below furcation were assessed. One-way variance analysis and Turkey’s post hoc test were used for comparisons of the means among different groups, and paired-t test was used to compare the mesial and distal sides of the mesial roots.ResultsAs compared with OS and TF, the use of PTG in preparation of MM canals resulted in significantly more straightening of canal curvature (p < 0.05), greater post-instrumentation canal volume and surface area, and thinner mesial and distal remaining canal wall thickness at 1, 2 and 3 mm below furcation (all p < 0.05). Regarding the root canal transportation in the mesiodistal direction, there was no significant difference among the 3 instruments (all p > 0.05) after the preparation of the MB and ML canals. However, in the MM canal, more pronounced transportation was detected in the PTG group at 2 mm below furcation, and in the TF group at 3 mm below furcation as compared with the other 2 systems (both p < 0.05).Conclusions3D printed tooth replicas have the advantages of consistency and can be an ideal model to evaluate the shaping ability of different instruments in the MM canal. OS and TF files performed similarly and both are appropriate for shaping the MM canal, while PTG may cause excessive and uneven resin removal, especially near the furcation, and may lead to root fragility and procedural errors.

Prevalence and morphology of middle mesial canal in mandibular first molars in an Indian sub-population: A cone-beam computed tomographic analysis

Aim: The aim of this study was to check for the prevalence and morphology of middle mesial (MM) canals in mandibular first molars in an Indian population divided as per the different zones of the country using cone-beam computed tomography (CBCT) scans. Methods: A total of 452 CBCT scans were selected according to the inclusion and exclusion criteria on December 2021. The scans were obtained from five different zones of the country with 80–100 scans selected from each zone. They were checked in an axial view to see for the presence of a MM canal (MMC) and if present, were confirmed in a coronal view. Results: Of the 452 scans viewed, 39 showed the presence of MMCs (8.6%). Bilateral presence was seen in 8 scans (1.8%). Hence, overall, 47 molars out of 904 examined showed the presence of MMCs. Thus, the tooth prevalence rate for the presence of MMC was 5.2%. Seventy percent of teeth presenting with MMCs showed two apical exits. Males showed more prevalence when compared to the female population (10.25% vs. 6.88%, P &lt; 0.05). Furthermore, with increasing age, there was a consistent decrease in the incidence of MMCs (P &lt; 0.05). Conclusion: Overall, the prevalence of MMCs in an Indian sub-population is 8.6%. Although on a lower range compared to other population, careful exploration is necessary to avoid missing the MMC which might lead to failure of treatment. Age and gender are also found as the important factors that influence the presence of a MMC.

Unveiling Hidden Canals: Middle Mesial Canal Prevalence in Mandibular First Molars Using Cone-Beam Computed Tomography Analysis in Central India.

Background The most frequent reason involving failure of root canal treatment in molar teeth is the inability to locate additional canals. While much research has been conducted on the morphology of mandibular molars, little is known about isthmuses and middle mesial (MM) canals in the Indian population. The primary aim of the present research was to determine the prevalence of MM canals and isthmusesof mandibular first molars in the Central India population using cone-beam computed tomography (CBCT) images. Methodology CBCT of 140 mandibular first molar teeth was analyzed from the institutional database images in the coronal, sagittal, and axial planes. Data concerning the number of root canals, the presence of middle mesial canals, and the presence of isthmus were noted. Information collected was transferred into an Excel sheet and analyzed using the Statistical Package for Social Sciences (IBM Corp., Armonk, NY, USA). Results Eight images (5.71%) revealed the presence of middle mesial canals with no statistically significant occurrence. The incidence of isthmi in the mandibular first molar was 84.3%, and the presence of isthmi in the coronal third was about 38.6%. This showed a considerable presence. Conclusion There is incidence of the middle mesial canal, which emphasizes the need to locate extra canals in patients undergoing root canal endodontic treatment. The implementation of CBCT will help identify the extra canal before the treatment. This will help ultimately in providing better patient care.

Follow-up of Non-Surgical Endodontic Treatment of Permanent Mandibular First Molars with Middle Mesial Root Canals –Four Clinical Case Series Report with a Mini Literature Review

Introduction: Root canal treatment’s long-term favorable prognosis is dependent on a good pulpal-periapical diagnosis and periodontium health, clear preoperative radiographs, an adequate understanding of complex root canal anatomy and endodontic pathology, proper treatment protocol that involves careful examination of root anatomy, identifying unusual root canal anatomy, access modification, negotiation of all the canals, complete debridement by shaping and chemical disinfection of all the portals of entry and exit within the root canal system, hermetic three- dimensional obturation of root canal space with an inert filling material followed by a fluid-tight tooth coronal seal. Clinicians are challenged with aberrations in the root canal anatomy of permanent mandibular molars especially when this anatomy is difficult to visualize from radiographs. The presence of a middle mesial root canal in permanent mandibular molars has been reported. Extensive exploration of the groove between mesiobuccal and mesiolingual orifices in mandibular permanent molars may reveal the presence of additional middle mesial canal orifice. Objectives: This clinical case series discusses the Follow-up of non-surgical endodontic management of four mandibular permanent first molars with an additional Middle Mesial (MM) canal in the mesial root. A mini literature review of this anatomical anomaly is also presented. Materials and Methods: The four mandibular molars with middle mesial canal endodontic cases done at Endodontics Clinic, Primary Health Care Corporation (PHCC), Qatar by the author in the year 2021 were reviewed with follow-up in the year 2023, address the endodontic management from identification of additional canals to complete obturation and follow up. Results: Clinical follow-up post endodontic treatment demonstrated that the treated molars with extra canals were asymptomatic with no sensitivity to percussion or palpation, no swelling or tooth mobility, and normal periodontal ....

Prevalence and Morphology of the Middle Mesial Canal in the First and Second Mandibular Molars Using Cone-Beam Computed Tomography

Introduction: Understanding of the normal anatomy of the teeth as well as the anatomical variations of each tooth and between different teeth is a prerequisite for successful endodontic treatment, and errors in this area can lead to treatment failures .The aim of this study was to determine the prevalence and morphology of the middle mesial canal in the first and second mandibular molars using Cone-Beam Computed Tomography (CBCT) in the population of Isfahan City and its relationship with the distance between the orifice canals. Methods: This retrospective descriptive study examined 180 reconstructed CBCT radiographs in modified axial, coronal, and sagittal sections, and evaluated the number, location, and morphology of the canals and the spacing of the orifices. Results: 47.5% of participants had left-side first molars with three canals and 48% had right-side first molars with three canals.46.1% had a second molar on left-side with three canals and 46% had a right-side three canal second molar. 1% of participants had four canals in the left-side first molars and 1% had four canals in the right-side first molars. Conclusion: The middle mesial canal is more likely to be near the mesiobuccal and mesiolingual canals. The highest prevalence is in the right-side first molar of women and the lowest is in the left-side second molar of men. Due to the low probability of the presence of this additional canal, careful examination of the patient's molar teeth before starting endodontic treatment is recommended.

Prevalence of middle mesial canals in mandibular first molars in coastal Andhra population – A Cone beam computed tomography study

Introduction: Recognition of variations in root canal anatomy is an essential prerequisite for successful endodontic diagnosis and treatment. Most of the endodontic failures result from missed canals. The mandibular first molar has the most complex root canal system and a high percentage of treatment failures are due to the impossibility of locating, instrumenting and obturating the middle mesial canal (MM). There are very few studies available regarding the incidence of MM canal in mandibular first molar. The present study evaluated the prevalence of the middle mesial canals in mandibular first molars using cone beam computed tomography (CBCT). Materials and Methodology: CBCT images of mandibular first molars were collected from patients (n= 100) who had undergone CBCT imaging. The images were analyzed and the prevalence of MM canals were calculated. Results: The data were analysed using descriptive statistics. In total of 100 patients, 60 were women and 40 were men, with age range 11-60 years old. 21 MM canals were identified in this study. In this, 11 were female and 10 were male. The prevalence of the MM canal in mandibular first molar MM canals were identified in 21% (21/100). Conclusion: Within the limitations of the study, it can be concluded that though advanced techniques like troughing and magnification help in finding and negotiating MM canals, 3D radiographies like CBCT can be as used as valuable adjunct to the above mentioned methods. When these canals are treated, the success rate of the endodontic treatment would definitely increase. Clinical studies with long-term follow-ups are needed to determine the effect of preparation of MM canals on the outcome of nonsurgical endodontic treatment in mandibular first molars. Keywords: Cone Beam Computed Tomography, Mandibular First Molar, Middle Mesial Canal, Prevalence.

ASSESSMENT OF THE OCCURRENCE OF MIDDLE MESIAL CANAL IN MANDIBULAR MOLARS USING CONE-BEAM COMPUTED TOMOGRAPHY AND DENTAL OPERATING MICROSCOPE: AN IN VITRO STUDY

Introduction: Failures of root canal treatments may be resulted due to missed canals and ignorance of the clinician about the complex anatomy of the root canal system. One such example of anatomic variation is the middle mesial (MM) canal in mandibular molars. Literature on methods for identifying them is limited. Aim: This in vitro study aimed to assess the occurrence of MM canal with cone-beam computed tomography (CBCT) and then under dental operating microscope (DOM) in the mandibular rst and second molars. A total of 40 extract Materials and Method: ed intact human permanent mandibular rst and second molars were selected. These were subjected to CBCT imaging and magnication under DOM for the detection of MM canals. The percentage of incidence in the detection of MMC was compared between these two methods. The incidence of MM canals detected in mandibular molars using CBCT and Results: DOM was 7.50 and 10 % respectively and the comparison between the two methods was statistically not signicant. Since Conclusions: the incidence of MM canals was higher with the use of DOM, it is preferred to use simpler, chairside aids like magnication and ultrasonic troughing. On the other hand, one should be judicious in preoperative CBCT evaluation in nding accessory canals like MM.

Evaluation of Radix Entomolaris and Middle Mesial Canal in Mandibular Permanent First Molars in an Iraqi Subpopulation Using Cone-Beam Computed Tomography.

The aim of this study was to evaluate the radix entomolaris (RE) and middle mesial canal (MMC) in mandibular permanent first molars in an Iraqi subpopulation using cone-beam computed tomography (CBCT). Their prevalence and types were investigated in 201 patients (301 tooth subjects), among which 156 were of the right side, and 145 of the left side mandibular first molars (MFM), using CBCT scans. The effects of gender, age, and unilateral/bilateral on the presence of both RE and MMC were evaluated. Chi-square and Fisher's exact tests were used to determine the level of significance (p ≤ 0.05), and the kappa value was used to check reliability of results of the research. In MFM, the prevalence of right and left RE was 4.5% and 4.1%, respectively, and it was significantly higher in males than females (p = 0.006) based on the Chi-square test. No significant difference was identified in the prevalence of RE in relation to age and tooth position. MMC was found in 14.7% of teeth in the right side and 19.3% in the left side, with no significant differences for age or gender. MMC merged with mesiolingual canal presented with higher prevalence compared to other types of MMC (8.3% right side and 7.6% left side), again with no significant differences for age or gender. Within the limits of this study, no significant association was detected between the prevalence of MMC and RE in MFM.

Radiographic analysis of interorifice distance and canal configuration in mesial roots of mandibular first molars

Introduction: The Middle Mesial Canal (MMC) is an additional root canal that can be present in the mandibular molars of some patients with high chances of being missed. The aim of this study is to determine the inter orifice distance between Messiobuccal (MB) and Mesiolingual (ML) canal orifice and its association with the presence or absence of MMC using CBCT to help the operator clinically in identifying the presence of MMC. Methods: 50 CBCT samples consisting of 100 permanent mandibular first molar teeth were analysed. The distance between the mesiobuccal and mesiolingual orifice was recorded. Statistical Analysis such Independent T test and Pearson correlation were used to determine the association between MB and ML interorifice distance and presence of MMC and variation in the prevalence of MMC among male and female and different age groups. Results: The mean distance between MB and ML canal orifice was 3.19 ± 0.42mm, in the presence and absence of MMC the mean distance was 3.66±0.24mm and 3.07±0.38 mm respectively. The mean inter orifice distance in males was 3.29 ± 0.38 mm and in females was 3.08 ± 0.45 mm.

Middle mesial canal

The occurrence, instrumentation, and obturation of the isthmus between the mesiobuccal and mesiolingual canals in mandibular first molars were studied. The morphology of these middle mesial canals was as follows: eight fins, two confluent canals, and two independent canals. Failures of root canal treatment are mainly due to missed canals and ignorance about the anatomy of the root canal system. The middle mesial (MM) canal is one such type of canal in mandibular molars which is often missed. This case series explain and illustrates three cases with middle mesial canals which is treated successfully.

Retreatment of a Chronically Infected Mandibular Molar with Missed Middle Mesial Canal: A Case Report

Retreatment of a Chronically Infected Mandibular Molar with Missed Middle Mesial Canal: A Case Report

The Effect of Root Canal Preparation Size and Taper of Middle Mesial Canals on Fracture Resistance of the Mandibular Molar Teeth: An In Vitro Study

IntroductionThe aim of the present study was to investigate the influence of root canal preparation size and taper of middle mesial (MM) canals on fracture resistance of mandibular molars. MethodsFifty-five mandibular molar teeth having an MM canal were selected based on the cone-beam computed tomographic analysis. After the decoronation and distal root separation procedure, the lengths of the mesial roots were standardized to 13 mm. The specimens were randomly distributed into 5 groups (n = 11). Mesiobuccal and mesiolingual canals were prepared up to size 30.06 using VDW.ROTATE rotary files (VDW, Munich, Germany). The MM canal was prepared up to size 25.04, 25.06, 30.04, and 30.06, respectively. No preparation was done in the MM canal in the control group. After the irrigation protocol, the canals were obturated with the single-cone technique. A thin layer of silicone-coated specimens was embedded in acrylic resin and subjected to a fracture strength test by a universal testing machine. A vertical force was applied to the roots until they fracture. Statistical analysis was performed with 1-way analysis of variance and post hoc Duncan tests (P = .05). ResultsThere was no significant difference between group 25.04 and the control group, but the fracture strengths of these groups were found to be significantly higher than that of groups 25.06, 30.04, and 30.06 (P < .05). ConclusionsWithin the limitations of this study, we concluded that increasing the apical diameter and taper in the MM canal reduces the fracture strength of mandibular molar teeth. Among the tested instrumentation sizes, fracture strength decreased significantly when greater than 25.04 instrumentation sizes were chosen.

Prevalence and Distribution of the Middle Mesial Canal in Mandibular First Molar Teeth of the Kerman Population: A CBCT Study.

Purpose Missed additional canals are one of the most important reasons for RCT failures in molar teeth. This study aimed to determine the prevalence and distribution of middle mesial canals in mandibular first molars of the Kerman population. Materials and Methods A retrospective study was performed on de-identified cone beam image sets from 3 private radiology centers in Kerman. A total of 100 mandibular first molars from 62 patients (mean age 32 years) were included. Information regarding the patient's age and gender, the location of teeth, and the presence or absence of a MMC and also a second distal canal in MMC cases was recorded in an Excel table. Data were analyzed using SPSS software (IBM-USA). Results The overall prevalence of MMCs in the mandibular first molars was 8.1% (10.0% in females and 6.3% in males). More cases of MMCs were seen on the right side (12.2%) than the left side (3.4%). One case of bilateral MMCs combined with bilateral second distal canals in the mandibular first molars was seen in a 26-year-old female. A further case of bilateral MMCs was found in a 32-year-old male but with single-canal distal roots on both sides. Conclusion The overall prevalence of MMCs in the Kerman population (8.1%) is at the lower end of the reported range of the international literature (0.26% to 53.8%). In the cohort examined in this study, mid mesial canals were more prevalent in females and on the right side. There was no definite relationship between MMCs and second distal canals in the mandibular first molar teeth in the same subject. MMCs may be unilateral or bilateral. Careful exploration of the pulpal floor between canal orifices is essential to prevent missing the MMC, as this would cause undesirable clinical outcomes.

Endodontic management of radix entomolaris with middle mesial canal –A case report

Mandibular molars exhibit variations in its internal anatomy; one among those is the presence of an extra canal in the mesial root called as middle mesial (MM) canal. Variation in the number of roots and canal morphology is not scarce. Presence of an additional root when found disto-lingually called as Radix entomolaris. This case report describes the treatment of chronic apical periodontitis with unusual morphology of mandibular first molars in 34 years old male patient. The treatment strategy included root canal therapy without the aid of any magnification devices.

Middle Mesial Canal Preparation Enhances the Risk of Fracture in Mesial Root of Mandibular Molars

IntroductionThe aim of this investigation was to evaluate the effect of the presence and preparation of middle mesial (MM) canals on the fracture resistance of the mesial root of mandibular molars. MethodsForty intact mesial roots of mandibular first molars having 2 (n = 20) or 3 (n = 20) independent canals from the furcation level for up to at least 5 mm apically were selected based on preoperative micro–computed tomographic scanning. The selected roots were then distributed into 2 experimental (n = 10) and 2 control groups (n = 10) according to the root length, canal configuration (2 or 3 independent canals), and root thickness at the furcation level. In the experimental groups 1 (2 independent canals) and 3 (3 independent canals), root canals were enlarged up to the ProTaper Next X3 rotary instrument (Dentsply Sirona, Ballaigues, Switzerland), whereas in groups 2 (2 independent canals) and 4 (3 independent canals) root canals were not prepared. The specimens were embedded in acrylic resin after their surfaces were coated with a thin layer of silicone and subjected to a fracture strength using a universal testing machine. The types of fracture extension and course were recorded and statistically compared with the chi-square test, whereas fracture strength was analyzed using 1-way analysis of variance and post hoc Tukey tests (α = 5%). ResultsNo statistical difference in fracture strength was observed between nonprepared roots with 2 (group 2, 696.1 ± 186.3 N) or 3 (group 4, 558.4 ± 154.6 N) independent canals (P > .05), whereas the lowest values were obtained in the prepared roots with an MM canal (groups 3, 377.1 ± 77.2 N) (P < .05). The mean fracture strength observed in the prepared roots with 2 canals (group 1, 528.4 ± 134.3 N) showed no statistically significant difference compared with nonprepared roots with 3 canals (group 4, 558.4 ± 154.6 N) (P > .05). The chi-square test revealed no significant differences in fracture extent, types, and courses among groups (P > .05). Fracture extensions in all groups were mostly central and buccal-central types, whereas the highest frequency of fracture course was the curved and zigzag types. ConclusionsThe fracture resistance of the mesial roots of the mandibular molars decreased after the preparation of mesial canals with large-tapered instruments. Preparation of the MM canal further diminished the fracture resistance of the mesial roots. The resultant fracture displayed a distinct pattern in the buccolingual plane.

Cone-beam computed tomography investigation of middle mesial canals and isthmuses in mandibular first molars in a Chinese population

BackgroundWhile there is ample research into the anatomy of mandibular molars, little is known regarding isthmuses and middle mesial (MM) canals in Chinese populations. The goal of this study was to determine the prevalence of MM canals and isthmuses in the mesial root of mandibular first molars using Cone-beam Computed Tomography.MethodsCone-beam Computed Tomography images of 357 mature mandibular first molars were retrospectively analyzed. Presence of isthmuses and MM canals, and the length of isthmuses in the mesial root were recorded. Meanwhile, we also recorded possible correlated factors such as demographics, side of mandible, presence of separated distal-lingual roots.ResultsOf these 357 teeth, 209 showed evidence of either complete or partial communication in the mesial root. Of these, 11(3.1%) exhibited true MM canals while 198(55.5%) exhibited isthmuses. Sex or side of mandible was not correlated with the prevalence of isthmuses (P > 0.05). However, there was a significant association between the presence of a distal-lingual root and the prevalence of such communication (P < 0.001). The average length of isthmuses was 4.3 ± 3.1 mm.ConclusionsWe detected high rate of isthmuses and low rate of MM canals in mesial roots of mandibular first molars, which is important as such areas should be identified and cleaned during root canal treatment.

Prevalence of middle mesial and middle distal canals in mandibular molars in an Egyptian subpopulation using micro-computed tomography.

To study the prevalence of middle mesial and middle distal canals in permanent mandibular molars in Egyptian subpopulation using micro-computed tomography. Two hundred and forty extracted mandibular permanent molars of Egyptian patients were scanned using micro-computed tomography, then the images were reconstructed to allow for the detection of the middle mesial (MM) and middle distal (MD) canals of the molars examined. The path of each extra canal was studied to determine the configuration of each canal. Data were analyzed statistically using the Chi-square test with a level of significance set at P< 0.05. The evaluation of three-dimensional (3D) images of this study showed that no significant difference was found between the percentage of MM (27.5%) and MD canals (22.5%) (P = 0.2064); however, there was a significant difference between the percentage of teeth having both extra canals (10%) and teeth having only one of these canals (P < 0.05). The confluent configuration (71%) was significantly higher than the other configurations (P < 0.05). A higher percentage of MM canal was detected followed by the MD canal. The least significant was both canals occurring within the same molar. The percentage of the confluent configuration was the highest. The apt knowledge of the variations of the root canal system anatomy and the respect of the discrepancies associated with diverse demographic areas will ensure the proper management of each tooth with endodontic involvement and its long-term success.

Evaluation of dentine thickness of middle mesial canals of mandibular molars prepared with rotary instruments: a micro-CT study.

To evaluate, using micro-CT, the remaining dentine thickness after preparation of the mesiobuccal (MB), mesiolingual (ML) and middle mesial (MM) canals of mandibular first molars with the ProTaper Next rotary system. Eleven mesial roots of mandibular first molars having three independent canals from the furcation level up to at least 5mm towards the apical direction were selected. Preparation of MM canals was performed in two steps using ProTaper Next X2 (step 1) and X3 (step 2) instruments, whilst MB and ML canals were prepared in a single step up to X3 instruments. The roots were scanned (pixel size of 10µm) before and after each step, and the dentine volume was calculated. Postoperative models of the roots were coregistered with their preoperative dataset and colour-coded cross-sections of the roots were used to measure the smallest dentine thickness surrounding each canal at 1.0-mm intervals from the furcation level up to 5mm in the apical direction, in both mesial and distal aspects of the roots. Changes in the remaining wall thickness between mesial canals were analysed with repeated-measures anova and post hoc Tukey test. Significance level was set at 5%. Mean percentage reduction of dentine volume after steps 1 and 2 was 4.66% and 5.16%, respectively. Overall, pre- and postoperative dentine thickness of the MM canal walls, in both mesial and distal aspects of the root, were significantly thinner than those of MB and ML canals (P<0.05). No significant difference was observed when comparing dentine thickness in the mesial and distal directions of MM canal after preparation step 1 (0.88±0.18mm and 0.73±0.26mm, respectively) or 2 (0.83±0.17mm and 0.67±0.26mm, respectively) (P >0.05). Dentine thickness values less than 0.5mm were observed mostly towards the distal aspect of the MM canal. Mesial roots were not associated with strip perforations after canal preparation procedures. A significant decrease in the thickness of canal walls at all levels evaluated in the mesial roots of mandibular molars suggests that files with small tapers should be used in preference to instruments with large tapers to prepare mesial canals in mandibular molars.